New Horizons Part 2

- "Arrokoth has the physical features of a body that came together slowly, with ‘local' materials in the solar nebula," said Will Grundy, New Horizons composition theme team lead from Lowell Observatory in Flagstaff, Arizona, and the lead author of a second Science paper. "An object like Arrokoth wouldn't have formed, or look the way it does, in a more chaotic accretion environment."

- The latest Arrokoth reports significantly expand on the May 2019 Science paper, led by Stern. The three new papers are based on 10 times as much data as the first report, and together provide a far more complete picture of Arrokoth's origin.

- "All of the evidence we've found points to particle-cloud collapse models, and all but rule out hierarchical accretion for the formation mode of Arrokoth, and by inference, other planetesimals," Stern said.

- New Horizons continues to carry out new observations of additional Kuiper Belt objects it passes in the distance. New Horizons also continues to map the charged-particle radiation and dust environment in the Kuiper Belt. The new KBOs being observed now are too far away to reveal discoveries like those on Arrokoth, but the team can measure aspects such as each object's surface properties and shape. This summer the mission team will begin using large ground-based telescopes to search for new KBOs to study in this way, and even for another flyby target if fuel allows.

- The New Horizons spacecraft is now 4.4 billion miles (7.1 billion kilometers) from Earth, operating normally and speeding deeper into the Kuiper Belt at nearly 31,300 miles (50,400 kilometers) per hour.

Journal references: 22) 23) (plus Ref. 25)

• February 13, 2020: New observations on the farthest, most primitive object in the Solar System ever to be visited by a spacecraft – a tiny, frozen, bi-lobed world known as Arrokoth – offer a unique glimpse into the early formation of our Solar System and perhaps the planet Earth. 24)

- The new findings expand upon the first published observations of the Kuiper Belt object, announced in a May 2019 issue of Science, which were based on a small amount of data sent from the New Horizons spacecraft shortly after its New Year's Day 2019 encounter.

- Using more than ten times as much data – including the highest-resolution images from the flyby – the New Horizons team describes Arrokoth in unprecedented detail across three reports in the February 14 issue of Science.

- Also known as 2014 MU69 and previously nicknamed Ultima Thule, the Kuiper Belt planetesimal was recently officially named Arrokoth, a Native American term meaning "sky" in the Powhattan/Algonquin language.

- These studies provide a far more complete picture of the composition and origin of Arrokoth and help to resolve a longstanding scientific controversy about how planetesimals – the primordial building blocks of our Solar System's planets – were formed.

- After passing Pluto in 2015, NASA's New Horizons spacecraft continued its mission deeper into the Kuiper Belt – a vast ring of icy bodies spread beyond the orbit of Neptune – to investigate the objects observed slowly orbiting in the outer reaches of the Solar System. Its target: Arrokoth, a peanut-shaped Kuiper Belt object discovered by the Hubble Telescope the previous year. New Horizons flew past the distant bi-lobed world after a journey spanning more than three years and one billion miles.

- Like the asteroids of the well-known asteroid belt between Mars and Jupiter, many of the objects drifting in the Kuiper Belt are remnants left over from the formation of the Solar System. One of the class of bodies called Cold Classical Kuiper Belt Objects, Arrokoth is an ancient relic preserved from the time when the planets first began to form nearly 4.5 billion years ago. Scientists still debate the process by which the dust and gases surrounding the new Sun coalesced to become the eight planets we recognize today.

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Figure 31: Peanut-shaped Arrokoth is the farthest and most primitive object in the Solar System ever to be visited by a spacecraft (image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Roman Tkachenko)

- "To understand planet formation, we have to understand planetesimal formation, since this is a key first step," said Lowell Observatory astronomer William Grundy, lead author of one of the studies. "Arrokoth is a planetesimal – an essential stepping-stone on the way to building planets, starting from dust in a protoplanetary nebula." 25)

- While there are planetesimals closer to Earth in the asteroid belt, according to Grundy, those visited via space probes have all been badly battered by colliding with each other or cooked by the sun, looking far different than when they first formed. However, in the cold, vast and remote Kuiper Belt, primordial planetesimals like Arrokoth remain largely untouched – even by the heat of the Sun – thus avoiding many of the processes that have obscured or erased the earliest histories of other worlds. As a result, Kuiper Belt planetesimals are the best-preserved time capsules of the early stages of planet formation known to exist.

- "For decades, we've been thinking about how planetesimals are made and debating the pros and cons of the various hypothesized mechanisms," said Grundy. "So, it's thrilling to finally be able to see one still pretty much just as it was after its formation."

- New Horizon's visit to Arrokoth was brief – the spacecraft rocketed past the roughly 22-mile-long object at almost 32,000 miles per hour before careening even deeper into the Kuiper Belt. However, the encounter was close and long enough to characterize, map and image the distant object's geological and geophysical features, including its most striking aspect – its unique shape.

- Images from New Horizons show that Arrokoth is what's known as a contact binary. Its shape – something akin to a slightly flattened snowman – is the product of two separate, mutually orbiting planetesimals, which gently merged with one another. According to John Spencer, a planetary scientist at the Southwest Research Institute and lead author of another study in the issue, this is something that could only happen during the early stages of Solar System formation.

- "The gentle merger provides strong support for the idea that planetesimals formed from local clouds of material that collapsed under their own gravity," rather than the longstanding theory of hierarchical accretion, said Spencer.

- The hierarchical accretion hypothesis – whereby colliding dust grains become larger, and so on up through pebbles, cobbles and boulders, colliding ever more forcefully into one another as they gradually grow to become the size of planets – is the currently accepted method of planetesimal formation.

- However, the formation and merging of Arrokoth's lobes bear no signs of such violent processes. Instead, the new evidence from Arrokoth suggest a rapid but gentle process of planetesimal formation – a formally underdog hypothesis known as local cloud collapse – where local concentrations of protoplanetary dust and debris come together under the influence of their own collective gravity.

- "It's hard to communicate about something to the public when we don't even have a good idea of what it looks like," said Grundy. "Just knowing that it plays an important role as a building block of planets isn't enough."

- "Now we finally have that picture and a much clearer idea of how it forms," he said.

- New Horizons is speeding onwards in the outer fringes of the Solar System, already 300 million miles beyond Arrokoth, and its exploration of the Kuiper Belt is ongoing. According to the researchers, distant observations of other Kuiper Belt Objects will help to place Arrokoth's observations in context. And, however unlikely, the team hopes to find another potential target for a close flyby.

- "I entered this field because I was inspired by Carl Sagan's point that only a couple of generations of scientists in all of human history would be the first to send craft to explore the planets of our Solar System," said NASA's Alan Stern, New Horizons' principal investigator. "I have been fortunate to be a part of that scientific revolution."

- "We successfully accomplished the most distant flyby in the history of planetary exploration of a world we didn't know existed five years ago," said Spencer. "Seeing a new world for the first time – there's nothing else like that experience."

• December 2, 2019: Measurements taken by the SWAP (Solar Wind Around Pluto) instrument aboard NASA's New Horizons spacecraft are providing important new insights from some of the farthest reaches of space ever explored. In a paper recently published in the Astrophysical Journal, a team led by Southwest Research Institute shows how the solar wind — the supersonic stream of charged particles blown out by the Sun — evolves at increasing distances from the Sun. 26)

- "Previously, only the Pioneer 10 and 11 and Voyager 1 and 2 missions have explored the outer solar system and outer heliosphere, but now New Horizons is doing that with more modern scientific instruments," said Dr. Heather Elliott, a staff scientist at SwRI, Deputy Principal Investigator of the SWAP instrument and lead author of the paper. "Our Sun's influence on the space environment extends well beyond the outer planets, and SWAP is showing us new aspects of how that environment changes with distance." 27)

- The solar wind fills a bubble-like region of space encompassing our solar system, called the heliosphere. From aboard New Horizons, SWAP collects detailed, daily measurements of the solar wind as well as other key components called "interstellar pickup ions" in the outer heliosphere. These interstellar pickup ions are created when neutral material from interstellar space enters the solar system and becomes ionized by light from the Sun or by charge exchange interactions with solar wind ions.

- As the solar wind moves farther from the Sun, it encounters an increasing amount of material from interstellar space. When interstellar material is ionized, the solar wind picks up the material and, researchers theorized, slows and heats in response. SWAP has now detected and confirmed this predicted effect.

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Figure 32: Solar wind speed diagram. The SWAP instrument aboard NASA's New Horizons spacecraft has confirmed that the solar wind slows as it travels farther from the Sun. This schematic of the heliosphere shows the solar wind begins slowing at approximately 4 AU radial distance from the Sun and continues to slow as it moves toward the outer solar system and picks up interstellar material. Current extrapolations reveal the termination shock may currently be closer than found by the Voyager spacecraft. However, increasing solar activity will soon expand the heliosphere and push the termination shock farther out, possibly to the 84-94 AU range encountered by the Voyager spacecraft (image credit: SwRI, background artist rendering by NASA and Adler Planetarium)

- The SWAP team compared the New Horizons solar wind speed measurements from 21 to 42 astronomical units to the speeds at 1 AU from both the Advanced Composition Explorer (ACE) and Solar TErrestrial RElations Observatory (STEREO) spacecraft. (One AU is equal to the distance between the Sun and Earth.) By 21 AU, it appeared that SWAP could be detecting the slowing of the solar wind in response to picking up interstellar material. However, when New Horizons traveled beyond Pluto, between 33 and 42 AU, the solar wind measured 6-7% slower than at the 1 AU distance, confirming the effect.

- In addition to confirming the slowing of the solar wind at great distances, the change in the solar wind temperature and density could also provide a means to estimate when New Horizons will join the Voyager spacecraft on the other side of the termination shock, the boundary marking where the solar wind slows to less than the sound speed as it approaches the interstellar medium. Voyager 1 crossed the termination shock in 2004 at 94 AU, followed by Voyager 2 in 2007 at 84 AU. Based on current lower levels of solar activity and lower solar wind pressures, the termination shock is expected to have moved closer to the Sun since the Voyager crossings. Extrapolating current trends in the New Horizons measurements also indicates that the termination shock might now be closer than when it was intersected by Voyager. At the earliest, New Horizons will reach the termination shock in the mid-2020s. As the solar cycle activity increases, the increase in pressure will likely expand the heliosphere. This could push the termination shock to the 84-94 AU range found by the Voyager spacecraft before New Horizons has time to reach the termination shock.

- New Horizons' journey through the outer heliosphere contrasts Voyager's in that the current solar cycle is mild compared to the very active solar cycle Voyager experienced in the outer heliosphere. In addition to measuring the solar wind, New Horizons' SWAP is extremely sensitive and simultaneously measures the low fluxes of interstellar pickup ions with unprecedented time resolution and extensive spatial coverage. New Horizons is also the only spacecraft in the solar wind beyond Mars (1.5 AU) and, consequently, the only spacecraft measuring interactions between the solar wind and the interstellar material in the outer heliosphere during the current mild solar cycle. New Horizons is on course to be the first spacecraft to measure both the solar wind and interstellar pickup ions at the termination shock.

- "New Horizons has significantly advanced our knowledge of distant planetary objects, and it's only fitting that it is now also revealing new knowledge about our own Sun and its heliosphere," said New Horizons Principal Investigator Dr. Alan Stern of the SwRI.

• November 12, 2019: In a fitting tribute to the farthest flyby ever conducted by spacecraft, the Kuiper Belt object 2014 MU69 has been officially named Arrokoth, a Native American term meaning "sky" in the Powhatan/Algonquian language. 28)

- With consent from Powhatan Tribal elders and representatives, NASA's New Horizons team – whose spacecraft performed the record-breaking reconnaissance of Arrokoth four billion miles from Earth – proposed the name to the International Astronomical Union and Minor Planets Center, the international authority for naming Kuiper Belt objects. The name was announced at a ceremony today at NASA Headquarters in Washington, DC.

- "The name ‘Arrokoth' reflects the inspiration of looking to the skies and wondering about the stars and worlds beyond our own," said Alan Stern, New Horizons principal investigator from Southwest Research Institute, Boulder, Colorado. "That desire to learn is at the heart of the New Horizons mission, and we're honored to join with the Powhatan community and people of Maryland in this celebration of discovery."

- New Horizons launched in January 2006; it then zipped past Jupiter for a gravity boost and scientific studies in February 2007 and conducted an historic first flight through the Pluto system on July 14, 2015. The spacecraft continued its unparalleled voyage on New Year's 2019 with the exploration of Arrokoth – which the team had nicknamed "Ultima Thule" — a billion miles beyond Pluto, and the farthest flyby ever conducted.

- Arrokoth is one of the thousands of known small icy worlds in the Kuiper Belt, the vast "third zone" of the solar system beyond the inner terrestrial planets and the outer gas giant planets. It was discovered in 2014 by a New Horizons team – which included Marc Buie, of the Southwest Research Institute – using the powerful Hubble Space Telescope.

- "Data from the newly-named Arrokoth, has given us clues about the formation of planets and our cosmic origins," said Buie. "We believe this ancient body, composed of two distinct lobes that merged into one entity, may harbor answers that contribute to our understanding of the origin of life on Earth."

- In accordance with IAU (International Astronomical Union) naming conventions, the discovery team earned the privilege of selecting a permanent name for the celestial body. The team used this convention to associate the culture of the native peoples who lived in the region where the object was discovered; in this case, both the Hubble Space Telescope (at the Space Telescope Science Institute) and the New Horizons mission (at the Johns Hopkins Applied Physics Laboratory) are operated out of Maryland — a tie to the significance of the Chesapeake Bay region to the Powhatan people.

- "We graciously accept this gift from the Powhatan people," said Lori Glaze, director of NASA's Planetary Science Division. "Bestowing the name Arrokoth signifies the strength and endurance of the indigenous Algonquian people of the Chesapeake region. Their heritage continues to be a guiding light for all who search for meaning and understanding of the origins of the universe and the celestial connection of humanity."

- The Pamunkey Reservation in King William County, Virginia, is the oldest American Indian reservation in the U.S. — formed by a treaty with England in the 1600s and finally receiving federal recognition in July 2015. The Pamunkey tribe and its village were significant in the original Powhatan Confederacy; today, Pamunkey tribal members work collaboratively with other Powhatan tribes in Virginia and also have descendants who are members of the Powhatan-Renape Nation in New Jersey. Many direct descendants still live on the Pamunkey reservation, while others have moved to Northern Virginia, Maryland, D.C., New York and New Jersey.

- The Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, designed, built and operates the New Horizons spacecraft, and manages the mission for NASA's Science Mission Directorate. NASA's Marshall Space Flight Center (MSFC) Planetary Management Office, in Huntsville, Alabama, provides the NASA oversight for the New Horizons. The Southwest Research Institute, based in San Antonio, directs the mission via Principal Investigator Stern, and leads the science team, payload operations and encounter science planning. New Horizons is part of the New Frontiers Program managed by NASA's MSFC.

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Figure 33: New Horizons Path of Exploration through the KBOs (Kuiper Belt Objects), image credit: NASA

• July 8, 2019: Scientists have unlocked clues about the earliest forms of life on Earth by studying fossils found across our planet. Similarly, we're now learning more about the earliest formation of our solar system from a different kind of fossil – a Kuiper Belt Object (KBO) known as 2014 MU69. 29)

Figure 34: Scientists are unlocking clues about the earliest formation of our solar system from a Kuiper Belt Object known as 2014 MU69 (video credit: Science At NASA, Published on 8 July 2019)

- Travel back in time to the solar system's very beginning. There, two objects were formed that eventually came together in a body resembling a flattened bowling pin. When looking at the object from the vicinity of the Earth, which is 4 billion miles (6.4 billion km) away, MU69 looked like a point of light, even when using the powerful Hubble Space Telescope. But thanks to the New Horizons spacecraft, this is what it looked like on New Year's Day, 2019, from approximately 4,100 miles (6,600 km) away, about 7 minutes before the spacecraft's closest approach.

- New Horizons is a grand piano-sized spacecraft that was launched back in 2006, with the undertaking of exploring the Kuiper Belt – that donut-shaped disc of space that begins just beyond the orbit of Neptune. Dwarf planet Pluto and its largest moon Charon reside in the Kuiper Belt, as do over 100,000 KBOs. MU69 was discovered by the New Horizons team, and was found to be located in the neighborhood of New Horizons' trajectory when the spacecraft reached the Kuiper Belt in 2015. Its location led to its selection as a flyby target.

- New Horizons Project Scientist Hal Weaver, of the Johns Hopkins Applied Physics Lab, notes three wondrous impressions about this 22 mile (35 km) long primeval object.

- "First, this is the most primitive object ever encountered by a spacecraft. By that I mean the least changed since the time of the solar system's formation."

- "Second, the shape of MU69's body is giving us new insights into how planets formed. Scientific hypotheses change as New Horizons delivers new data. Until we saw it up close, we didn't know for sure if MU69 was a single object or two distinct pieces. Now we know it's actually composed of two distinct pieces – a large, flat lobe and a smaller, rounder lobe, that have merged into one entity. This fusion gives us clues regarding the initial steps that were taken to form a planet."

- "Third, the flyby showed MU69's red color – redder even than Pluto – and we believe that this may come from organic material – the same material that may have contributed to the origin of life on Earth."

- Fossils of once-living things on Earth convey vital clues about the past. In space, KBOs can also convey fossil-like clues – about 4.5 billion years' worth of solar system history. Scientists are poring over the information they've received so far, and the data transmissions from the MU69 flyby will continue through the late summer of 2020. In the meantime, New Horizons is traveling farther into the Kuiper Belt at about 31,500 miles (51,000 km) per hour. The spacecraft is now observing additional KBOs and exploring the region's concentration of charged particle radiation and dust within the Kuiper Belt.

• May 16, 2019: NASA's New Horizons mission team has published the first profile of the farthest world ever explored, a planetary building block and Kuiper Belt object called 2014 MU69. 30)

- Analyzing just the first sets of data gathered during the New Horizons spacecraft's New Year's 2019 flyby of MU69 (nicknamed Ultima Thule) the mission team quickly discovered an object far more complex than expected. The team publishes the first peer-reviewed scientific results and interpretations – just four months after the flyby – in the May 17 issue of the journal Science. 31)

- In addition to being the farthest exploration of an object in history – four billion miles from Earth – the flyby of Ultima Thule was also the first investigation by any space mission of a well-preserved planetesimal, an ancient relic from the era of planet formation.

- The initial data summarized in Science reveal much about the object's development, geology and composition. It's a contact binary, with two distinctly differently shaped lobes. At about 22 miles (36 kilometers) long, Ultima Thule consists of a large, strangely flat lobe (nicknamed "Ultima") connected to a smaller, somewhat rounder lobe (nicknamed "Thule"), at a juncture nicknamed "the neck." How the two lobes got their unusual shape is an unanticipated mystery that likely relates to how they formed billions of years ago.

- The lobes likely once orbited each other, like many so-called binary worlds in the Kuiper Belt, until some process brought them together in what scientists have shown to be a "gentle" merger. For that to happen, much of the binary's orbital momentum must have dissipated for the objects to come together, but scientists don't yet know whether that was due to aerodynamic forces from gas in the ancient solar nebula, or if Ultima and Thule ejected other lobes that formed with them to dissipate energy and shrink their orbit. The alignment of the axes of Ultima and Thule indicates that before the merger the two lobes must have become tidally locked, meaning that the same sides always faced each other as they orbited around the same point.

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Figure 35: This composite image of the primordial contact binary Kuiper Belt Object 2014 MU69 (nicknamed Ultima Thule) – featured on the cover of the May 17 issue of the journal Science – was compiled from data obtained by NASA's New Horizons spacecraft as it flew by the object on Jan. 1, 2019. The image combines enhanced color data (close to what the human eye would see) with detailed high-resolution panchromatic pictures (image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Roman Tkachenko)

- "We're looking into the well-preserved remnants of the ancient past," said New Horizons Principal Investigator Alan Stern, of the Southwest Research Institute, Boulder, Colorado. "There is no doubt that the discoveries made about Ultima Thule are going to advance theories of solar system formation."

- As the Science paper reports, New Horizons researchers are also investigating a range of surface features on Ultima Thule, such as bright spots and patches, hills and troughs, and craters and pits on Ultima Thule. The largest depression is a 5-mile-wide (8 km wide) feature the team has nicknamed Maryland crater – which likely formed from an impact. Some smaller pits on the Kuiper Belt object, however, may have been created by material falling into underground spaces, or due to exotic ices going from a solid to a gas (called sublimation) and leaving pits in its place.

- In color and composition, Ultima Thule resembles many other objects found in its area of the Kuiper Belt. It's very red – redder even than much larger, 1,500-mile (2,400 km) wide Pluto, which New Horizons explored at the inner edge of the Kuiper Belt in 2015 – and is in fact the reddest outer solar system object ever visited by spacecraft; its reddish hue is believed to be caused by modification of the organic materials on its surface New Horizons scientists found evidence for methanol, water ice, and organic molecules on Ultima Thule's surface – a mixture very different from most icy objects explored previously by spacecraft.

- Data transmission from the flyby continues, and will go on until the late summer 2020. In the meantime, New Horizons continues to carry out new observations of additional Kuiper Belt objects it passes in the distance. These additional KBOs are too distant to reveal discoveries like those on MU69, but the team can measure aspects such as the object's brightness. New Horizons also continues to map the charged-particle radiation and dust environment in the Kuiper Belt.

- The New Horizons spacecraft is now 4.1 billion miles (6.6 billion kilometers) from Earth, operating normally and speeding deeper into the Kuiper Belt at nearly 33,000 miles (53,000 kilometers) per hour.

- The Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, designed, built and operates the New Horizons spacecraft, and manages the mission for NASA's Science Mission Directorate. The MSFC Planetary Management Office provides the NASA oversight for the New Horizons. Southwest Research Institute, based in San Antonio, directs the mission via Principal Investigator Stern, and leads the science team, payload operations and encounter science planning. New Horizons is part of the New Frontiers Program managed by NASA's Marshall Space Flight Center in Huntsville, Alabama.

• March 18, 2019: The farthest object ever explored is slowly revealing its secrets, as scientists piece together the puzzles of Ultima Thule – the Kuiper Belt object NASA's New Horizons spacecraft flew past on New Year's Day, four billion miles from Earth. 32) 33)

- Analyzing the data New Horizons has been sending home since the flyby of Ultima Thule (officially named 2014 MU69), mission scientists are learning more about the development, geology and composition of this ancient relic of solar system formation. The team discussed those findings today at the 50th Lunar and Planetary Science Conference in The Woodlands, Texas.

- Ultima Thule is the first unquestionably primordial contact binary ever explored. Approach pictures of Ultima Thule hinted at a strange, snowman-like shape for the binary, but further analysis of images, taken near closest approach – New Horizons came to within just 2,200 miles (3,500 km) – have uncovered just how unusual the KBO's (Kuiper Belt Object) shape really is. At 22 miles (35 km) long, Ultima Thule consists of a large, flat lobe (nicknamed "Ultima") connected to a smaller, rounder lobe (nicknamed "Thule").

- This strange shape is the biggest surprise, so far, of the flyby. "We've never seen anything like this anywhere in the solar system," said New Horizons Principal Investigator Alan Stern, of the Southwest Research Institute, Boulder, Colorado. "It is sending the planetary science community back to the drawing board to understand how planetesimals – the building blocks of the planets – form."

- Because it is so well preserved, Ultima Thule is offering our clearest look back to the era of planetesimal accretion and the earliest stages of planetary formation. Apparently Ultima Thule's two lobes once orbited each other, like many so-called binary worlds in the Kuiper Belt, until something brought them together in a "gentle" merger.

- "This fits with general ideas of the beginning of our solar system," said William McKinnon, a New Horizons co-investigator from Washington University in St. Louis. "Much of the orbital momentum of the Ultima Thule binary must have been drained away for them to come together like this. But we don't know yet what processes were most important in making that happen."

- That merger may have left its mark on the surface. The "neck" connecting Ultima and Thule is reworked, and could indicate shearing as the lobes combined, said Kirby Runyon, a New Horizons science team member from the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland.

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Figure 36: The most distant world we've ever explored, Ultima Thule, keeps getting weirder — but NASA scientists are beginning to unravel its mysteries (image credit: NASA; JHU/APL, SwRI, ESA)

- Runyon and fellow team geologists are describing and trying to understand Ultima Thule's many surface features, from bright spots and patches, to hills and troughs, to craters and pits. The craters, while at first glance look like impact craters, could have other origins. Some may be pit craters, where material drains into underground cracks, or a result of sublimation, where ice went directly from solid to gas and left pits in its place. The largest depression is a 5-mile-wide (8-kilometer-wide) feature the team has nicknamed Maryland crater. It could be an impact crater, or it could have formed in one of the other above-mentioned ways.

- "We have our work cut out to understand Ultima Thule's geology, that is for sure," Runyon said.

- In color and composition, New Horizons data revealed that Ultima Thule resembles many other objects found in its region of the Kuiper Belt. Consistent with pre-flyby observations from the Hubble Telescope, Ultima Thule is very red – redder even than Pluto, which New Horizons flew past on the inner edge of the Kuiper Belt in 2015 – and about the same color as many other so-called "cold classical" KBOs. ("Cold" referring not to temperature but to the circular, uninclined orbits of these objects; "classical" in that their orbits have changed little since forming, and represent a sample of the primordial Kuiper Belt.)

- "This is the first time one of these 'ultra red' objects has been explored, and our observations open all kinds of new questions," said Carly Howett, a New Horizons science team member from SwRI. "The color imaging even reveals subtle differences in coloration across the surface, and we really want to know why."

- New Horizons scientists have also seen evidence for methanol, water ice and organic molecules on the surface. "The spectrum of Ultima Thule is similar to some of the most extreme objects we've seen in the outer solar system," said Silvia Protopapa, a New Horizons co-investigator from SwRI. "So New Horizons is giving us an incredible opportunity to study one of these bodies up close."

- The Ultima Thule data transmission continues, though all of the data from the flyby won't be on the ground until late summer 2020. In the meantime, New Horizons continues to carry out distant observations of additional Kuiper Belt objects and mapping the charged-particle radiation and dust environment in the Kuiper Belt.

- The New Horizons spacecraft is 4.1 billion miles (6.6 billion km) from Earth, operating normally and speeding deeper into the Kuiper Belt at nearly 33,000 miles (53,000 km) per hour.

• February 28, 2019: Using New Horizons data from the Pluto-Charon flyby in 2015, a Southwest Research Institute-led team of scientists have indirectly discovered a distinct and surprising lack of very small objects in the Kuiper Belt. The evidence for the paucity of small Kuiper Belt objects (KBOs) comes from New Horizons imaging that revealed a dearth of small craters on Pluto's largest satellite, Charon, indicating that impactors from 100 meters to 1.6 km in diameter must also be rare. 34)

- The Kuiper Belt is a donut-shaped region of icy bodies beyond the orbit of Neptune. Because small Kuiper Belt objects were some of the "feedstock" from which planets formed, this research provides new insights into how the solar system originated. This research was published in the March 1 issue of the prestigious journal Science.

- "These smaller Kuiper Belt objects are much too small to really see with any telescopes at such a great distance," said SwRI's Dr. Kelsi Singer, the paper's lead author and a co-investigator of NASA's New Horizons mission. "New Horizons flying directly through the Kuiper Belt and collecting data there was key to learning about both large and small bodies of the Belt."

- "This breakthrough discovery by New Horizons has deep implications," added the mission's principal investigator, Dr. Alan Stern, also of SwRI. "Just as New Horizons revealed Pluto, its moons, and more recently, the KBO nicknamed Ultima Thule in exquisite detail, Dr. Singer's team revealed key details about the population of KBOs at scales we cannot come close to directly seeing from Earth."

- Craters on solar system objects record the impacts of smaller bodies, providing hints about the history of the object and its place in the solar system. Because Pluto is so far from Earth, little was known about the dwarf planet's surface until the epic 2015 flyby. Observations of the surfaces of Pluto and Charon revealed a variety of features, including mountains that reach as high as 4 km and vast glaciers of nitrogen ice. Geologic processes on Pluto have erased or altered some of the evidence of its impact history, but Charon's relative geologic stasis has provided a more stable record of impacts.

- "A major part of the mission of New Horizons is to better understand the Kuiper Belt," said Singer, whose research background studying the geology of the icy moons of Saturn and Jupiter positions her to understand the surface processes seen on KBOs. "With the successful flyby of Ultima Thule early this year, we now have three distinct planetary surfaces to study. This paper uses the data from the Pluto-Charon flyby, which indicate fewer small impact craters than expected. And preliminary results from Ultima Thule support this finding."

- Typical planetary models show that 4.6 billion years ago, the solar system formed from the gravitational collapse of a giant molecular cloud. The Sun, the planets and other objects formed as materials within the collapsing cloud clumped together in a process known as accretion. Different models result in different populations and locations of objects in the solar system.

- "This surprising lack of small KBOs changes our view of the Kuiper Belt and shows that either its formation or evolution, or both, were somewhat different than those of the asteroid belt between Mars and Jupiter," said Singer. "Perhaps the asteroid belt has more small bodies than the Kuiper Belt because its population experiences more collisions that break up larger objects into smaller ones."

- The paper published in Science is titled "Impact craters on Pluto and Charon indicate a deficit of small Kuiper Belt objects." The Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, designed, built and operates the New Horizons spacecraft, and manages the mission for NASA's Science Mission Directorate. The MSFC Planetary Management Office provides the NASA oversight for the New Horizons mission. Southwest Research Institute, based in San Antonio, directs the mission via Principal Investigator Stern, and leads the science team, payload operations and encounter science planning. New Horizons is part of the New Frontiers Program managed by NASA's Marshall Space Flight Center in Huntsville, Alabama. 35)

• February 22, 2019: The mission team called it a "stretch goal" – just before closest approach, precisely point the cameras on NASA's New Horizons spacecraft to snap the sharpest possible pics of the Kuiper Belt object nicknamed Ultima Thule, its New Year's flyby target and the farthest object ever explored. 36)

- Now that New Horizons has sent those stored flyby images back to Earth, the team can enthusiastically confirm that its ambitious goal was met.

- These new images of Ultima Thule – obtained by the telephoto Long-Range Reconnaissance Imager (LORRI) just 6½ minutes before New Horizons' closest approach to the object (officially named 2014 MU69) at 12:33 a.m. EST on Jan. 1 – offer a resolution of about 110 feet (33 meters) per pixel. Their combination of high spatial resolution and a favorable viewing angle gives the team an unprecedented opportunity to investigate the surface, as well as the origin and evolution, of Ultima Thule – thought to be the most primitive object ever encountered by a spacecraft.

- "Bullseye!" said New Horizons Principal Investigator Alan Stern, of the Southwest Research Institute (SwRI). "Getting these images required us to know precisely where both tiny Ultima and New Horizons were — moment by moment – as they passed one another at over 32,000 miles per hour in the dim light of the Kuiper Belt, a billion miles beyond Pluto. This was a much tougher observation than anything we had attempted in our 2015 Pluto flyby.

- "These 'stretch goal' observations were risky, because there was a real chance we'd only get part or even none of Ultima in the camera's narrow field of view," he continued. "But the science, operations and navigation teams nailed it, and the result is a field day for our science team! Some of the details we now see on Ultima Thule's surface are unlike any object ever explored before."

- The higher resolution brings out a many surface features that weren't readily apparent in earlier images. Among them are several bright, enigmatic, roughly circular patches of terrain. In addition, many small, dark pits near the terminator (the boundary between the sunlit and dark sides of the body) are better resolved. "Whether these features are craters produced by impactors, sublimation pits, collapse pits, or something entirely different, is being debated in our science team," said John Spencer, deputy project scientist from SwRI.

- Project Scientist Hal Weaver, of the JHU/APL, noted that the latest images have the highest spatial resolution of any New Horizons has taken – or may ever take – during its entire mission. Swooping within just 3,500 km, New Horizons flew approximately three times closer to Ultima than it zipped past its primary mission target, Pluto, in July 2015.

- Ultima Thule is smaller than Pluto, but the Ultima flyby was done with the highest navigation precision ever achieved by any spacecraft. This unprecedented precision was achieved thanks to the ground-based occultation campaigns from 2017 and 2018 conducted in Argentina, Senegal, South Africa and Colombia, as well as the European Space Agency's Gaia mission, which provided the locations of the stars that were used during the occultation campaigns.

- Look for these and other LORRI images on the New Horizons LORRI website this week. Raw images from the camera are posted to the site each Friday.

- Mission operations manager Alice Bowman, of APL, reports that the spacecraft continues to operate flawlessly. New Horizons is nearly 4.13 billion miles (6.64 billion kilometers) from Earth; at that distance, radio signals, traveling at light speed, reach the large antennas of NASA's Deep Space Network six hours and nine minutes after New Horizons sends them. Follow New Horizons on its trek through the Kuiper Belt.

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Figure 37: The most detailed images of Ultima Thule — obtained just minutes before the spacecraft's closest approach at 12:33 a.m. EST on Jan. 1 — have a resolution of about 33 m/pixel. Their combination of higher spatial resolution and a favorable viewing geometry offer an unprecedented opportunity to investigate the surface of Ultima Thule, believed to be the most primitive object ever encountered by a spacecraft. — This processed, composite picture combines nine individual images taken with the Long Range Reconnaissance Imager (LORRI), each with an exposure time of 0.025 seconds, just 6 ½ minutes before the spacecraft's closest approach to Ultima Thule (officially named 2014 MU69). The image was taken at 5:26 UT (12:26 a.m. EST) on Jan. 1, 2019, when the spacecraft was 6,628 km from Ultima Thule and 6.6 billion km from Earth. The angle between the spacecraft, Ultima Thule and the Sun – known as the "phase angle" – was 33 degrees (image credit: NASA, JHU/APL, SwRI, National Optical Astronomy Observatory)

• February 15, 2019: Scientists who study the solar system tend to ask big questions: How was our solar system formed? Where did the building blocks of life come from? What hazards from above threaten life on our planet? To find answers, they're looking more and more at small worlds. 37)

Figure 38: Small Worlds hold keys to questions about our solar system and the origin of life on Earth (video credit: Science@NASA, published on 15 February 2019)

- What are small worlds? Asteroids for sure. Comets too. Also the many small satellites or moons that orbit large planets as well as the icy worlds at the distance of Pluto and beyond. Some have combined, only to be broken apart later by collisions and tidal forces. Others have gone largely untouched since the dawn of the solar system. Some carry water and organic compounds, others are almost entirely composed of metal. And all hold keys to questions about our solar system and the origin of life on Earth.

- Dr. Adriana Ocampo, Program Executive for NASA's New Horizons mission, says "Water is key to life as we know it. Learning where water is found in our solar system provides pieces to the puzzle of understanding the origins of life. New Horizons recently surprised us by discovering a large abundance of water ice at Pluto." More surprises are in store, as New Horizons transmits the data from its January 1, 2019 flyby of the Kuiper Belt object 2014 MU69 back to Earth!

- Small worlds can be found in a wide range of locations across the solar system, from the inner solar system all the way out to the Kuiper Belt. When they are studied together, these remnants of the early solar system can help tell the story of solar system formation.

- Dawn recently completed a mission to the Main Asteroid Belt, visiting the dwarf planet Ceres and the Belt's largest asteroid, Vesta. OSIRIS-REx has arrived at Bennu, a near-Earth asteroid about 500 m across, and will return to Earth in 2023 with a sample so scientists can begin to understand Bennu's origin and history. The Lucy mission will be traveling to six Trojan asteroids, trapped in the orbit of Jupiter. These objects are the only remaining unexplored population of small worlds in the solar system. The Psyche mission will be visiting a metal object in the Main Asteroid Belt that could be the remnant core of a protoplanet similar in size to Vesta!

- While those missions travel to their individual targets, NEOWISE, a repurposed space telescope in low-Earth orbit, has made infrared measurements of hundreds of near-Earth objects and tens of thousands of other small worlds in the solar system. These diverse worlds offer insights into how our solar system formed and evolved.

- Dr. Tom Statler, Planetary Science Program Scientist at NASA Headquarters notes, "This is not your grandparent's solar system, and things are not as orderly as we once believed."

- "The data we've gleaned from these objects so far have changed the way we think about the origin of the planets. For example, the small worlds in the Kuiper Belt are leading us to think that Uranus and Neptune formed much closer to the Sun than where they reside now, then gradually moved to their current orbits."

- The biggest misperception about small worlds? Their distance to each other. Statler explains, "In the movies, they always show an asteroid belt with millions of rocks almost touching each other, whereas in reality there is much more empty space. You have to travel hundreds of thousands of miles to get from one asteroid to another."

- Yet scientists are also looking closer to home. Determining the orbits and physical characteristics of objects that might impact Earth is critical to understanding the consequences of any such impact; and responding to an actual impact threat, if one is ever discovered. NASA knows of no asteroid or comet currently on a collision course with Earth. But, to prepare for that scenario NASA is developing the DART (Double Asteroid Redirection Test) mission as the first demonstration of the kinetic impact technique that could be used to change the motion of a hazardous asteroid away from Earth.

• February 8, 2019: An evocative new image sequence from NASA's New Horizons spacecraft offers a departing view of the Kuiper Belt object (KBO) nicknamed Ultima Thule—the target of its New Year's 2019 flyby and the most distant world ever explored. 38)

- These aren't the last Ultima Thule images New Horizons will send back to Earth – in fact, many more are to come — but they are the final views New Horizons captured of the KBO (officially named 2014 MU69) as it raced away at over 31,000 miles/hour (50,000 km/hour) on January 1. The images were taken nearly 10 minutes after New Horizons crossed its closest approach point.

- "This really is an incredible image sequence, taken by a spacecraft exploring a small world four billion miles away from Earth," said mission Principal Investigator Alan Stern, of Southwest Research Institute. "Nothing quite like this has ever been captured in imagery."

- The newly released images also contain important scientific information about the shape of Ultima Thule, which is turning out to be one of the major discoveries from the flyby.

- The first close-up images of Ultima Thule – with its two distinct and, apparently, spherical segments – had observers calling it a "snowman." However, more analysis of approach images and these new departure images have changed that view, in part by revealing an outline of the portion of the KBO that was not illuminated by the Sun, but could be "traced out" as it blocked the view to background stars.

- Stringing 14 of these images into a short departure movie, New Horizons scientists can confirm that the two sections (or "lobes") of Ultima Thule are not spherical. The larger lobe, nicknamed "Ultima," more closely resembles a giant pancake and the smaller lobe, nicknamed "Thule," is shaped like a dented walnut.

- "We had an impression of Ultima Thule based on the limited number of images returned in the days around the flyby, but seeing more data has significantly changed our view," Stern said. "It would be closer to reality to say Ultima Thule's shape is flatter, like a pancake. But more importantly, the new images are creating scientific puzzles about how such an object could even be formed. We've never seen something like this orbiting the Sun."

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Figure 39: The Crescent View: New Horizons took this image of the Kuiper Belt object 2014 MU69 (nicknamed Ultima Thule) on Jan. 1, 2019, when the NASA spacecraft was 5,494 miles (8,862 km) beyond it. The image to the left is an "average" of ten images taken by the Long Range Reconnaissance Imager (LORRI); the crescent is blurred in the raw frames because a relatively long exposure time was used during this rapid scan to boost the camera's signal level. Mission scientists have been able to process the image, removing the motion blur to produce a sharper, brighter view of Ultima Thule's thin crescent (image credit: NASA/Johns Hopkins Applied Physics Laboratory/Southwest Research Institute/National Optical Astronomy Observatory)

- The departure images were taken from a different angle than the approach photos and reveal complementary information on Ultima Thule's shape. The central frame of the sequence was taken on Jan. 1 at 05:42:42 UT (12:42 a.m. EST), when New Horizons was 5,494 miles (8,862 km) beyond Ultima Thule, and 4.1 billion miles (6.6 billion km) from Earth. The object's illuminated crescent is blurred in the individual frames because a relatively long exposure time was used during this rapid scan to boost the camera's signal level – but the science team combined and processed the images to remove the blurring and sharpen the thin crescent.

- Many background stars are also seen in the individual images; watching which stars "blinked out" as the object passed in front them allowed scientists to outline the shape of both lobes, which could then be compared to a model assembled from analyzing pre-flyby images and ground-based telescope observations. "The shape model we have derived from all of the existing Ultima Thule imagery is remarkably consistent with what we have learned from the new crescent images," says Simon Porter, a New Horizons co-investigator from the Southwest Research Institute, who leads the shape-modeling effort.

- "While the very nature of a fast flyby in some ways limits how well we can determine the true shape of Ultima Thule, the new results clearly show that Ultima and Thule are much flatter than originally believed, and much flatter than expected," added Hal Weaver, New Horizons project scientist from the Johns Hopkins Applied Physics Laboratory. "This will undoubtedly motivate new theories of planetesimal formation in the early solar system."

- The images in this sequence will be available on the New Horizons LORRI website this week. Raw images from the camera are posted to the site each Friday.

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Figure 40: Scientists' understanding of Ultima Thule has changed as they review additional data. The "old view" in this illustration is based on images taken within a day of New Horizons' closest approach to the Kuiper Belt object on Jan. 1, 2019, suggesting that both of "Ultima" (the larger section, or lobe) and "Thule" (the smaller) were nearly perfect spheres just barely touching each other. - But as more data were analyzed, including several highly evocative crescent images taken nearly 10 minutes after closest approach, a "new view" of the object's shape emerged. Ultima more closely resembles a "pancake," and Thule a "dented walnut."The bottom view is the team's current best shape model for Ultima Thule, but still carries some uncertainty as an entire region was essentially hidden from view, and not illuminated by the Sun, during the New Horizons flyby. The dashed blue lines span the uncertainty in that hemisphere, which shows that Ultima Thule could be either flatter than, or not as flat as, depicted in this figure (image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)

Figure 41: This animation depicts a shape model of Ultima Thule created by the New Horizons science team based on its analysis of all the pre-flyby images sent to Earth so far. The first half of the movie mimics the view from the New Horizons spacecraft as it approached Ultima Thule and has the "snowman" shape that was so frequently mentioned in the days surrounding the New Year's 2019 flyby. - The movie then rotates to a side-view that illustrates what New Horizons might have seen had its cameras been pointing toward Ultima Thule only a few minutes after closest approach. While that wasn't the case, mission scientists have been able to piece together a model of this side-view, which has been at least partially confirmed by a set of crescent images of Ultima Thule (link). There is still considerable uncertainty in the sizes of "Ultima" (the larger section, or lobe) and "Thule" (the smaller) in the vertical dimension, but it's now clear that Ultima looks more like a pancake than a sphere, and that Thule is also very non-spherical. - The rotation in this animation is not the object's actual rotation, but is used purely to illustrate its shape (video credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)

• January 24, 2018: The wonders – and mysteries – of Kuiper Belt object 2014 MU69 continue to multiply as NASA's New Horizons spacecraft beams home new images of its New Year's Day 2019 flyby target. 39)

- Obtained with the wide-angle MVIC (Multicolor Visible Imaging Camera) component of New Horizons' Ralph instrument, this image was taken when the KBO was 4,200 miles (6,700 km) from the spacecraft, at 05:26 UT (12:26 a.m. EST) on Jan. 1 – just seven minutes before closest approach. With an original resolution of 135 m/pixel, the image was stored in the spacecraft's data memory and transmitted to Earth on Jan. 18-19. Scientists then sharpened the image to enhance fine detail. (This process – known as deconvolution – also amplifies the graininess of the image when viewed at high contrast.)

- The oblique lighting of this image reveals new topographic details along the day/night boundary, or terminator, near the top. These details include numerous small pits up to about 0.4 miles (0.7 km) in diameter. The large circular feature, about 4 miles (7 km) across, on the smaller of the two lobes, also appears to be a deep depression. Not clear is whether these pits are impact craters or features resulting from other processes, such as "collapse pits" or the ancient venting of volatile materials.

- Both lobes also show many intriguing light and dark patterns of unknown origin, which may reveal clues about how this body was assembled during the formation of the solar system 4.5 billion years ago. One of the most striking of these is the bright "collar" separating the two lobes.

- "This new image is starting to reveal differences in the geologic character of the two lobes of Ultima Thule, and is presenting us with new mysteries as well," said Principal Investigator Alan Stern, of the Southwest Research Institute in Boulder, Colorado. "Over the next month there will be better color and better resolution images that we hope will help unravel the many mysteries of Ultima Thule."

- New Horizons is approximately 4.13 billion miles (6.64 billion km) from Earth, operating normally and speeding away from the Sun (and Ultima Thule) at more than 31,500 miles/h (50,700 km/h). At that distance, a radio signal reaches Earth six hours and nine minutes after leaving the spacecraft.

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Figure 42: This image, taken during the historic Jan. 1 flyby of what's informally known as Ultima Thule, is the clearest view yet of this remarkable, ancient object in the far reaches of the solar system – and the first small KBO (Kuiper Belt Object) ever explored by a spacecraft (image credit: NASA, JHU/APL, SwRI)

• January 2, 2019: Scientists from NASA's New Horizons mission released the first detailed images of the most distant object ever explored — the Kuiper Belt object nicknamed Ultima Thule. Its remarkable appearance, unlike anything we've seen before, illuminates the processes that built the planets four and a half billion years ago. 40)

- "This flyby is a historic achievement," said New Horizons Principal Investigator Alan Stern of the Southwest Research Institute in Boulder, Colorado. "Never before has any spacecraft team tracked down such a small body at such high speed so far away in the abyss of space. New Horizons has set a new bar for state-of-the-art spacecraft navigation."

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Figure 43: This image, taken by LORRI (Long-Range Reconnaissance Imager), is the most detailed of Ultima Thule returned so far by the New Horizons spacecraft. It was taken at 5:01 UTC on January 1, 2019, just 30 minutes before closest approach from a range of 28,000 km, with an original scale of 140 m/pixel (image credit: NASA, JHU/APL, SwRI)

- The new images — taken from as close as 27,000 km on approach — revealed Ultima Thule as a "contact binary," consisting of two connected spheres. End to end, the world measures 31 km in length. The team has dubbed the larger sphere "Ultima" (19 km across) and the smaller sphere "Thule" (14 km across).

- The team says that the two spheres likely joined as early as 99 percent of the way back to the formation of the solar system, colliding no faster than two cars in a fender-bender.

- "New Horizons is like a time machine, taking us back to the birth of the solar system. We are seeing a physical representation of the beginning of planetary formation, frozen in time," said Jeff Moore, New Horizons Geology and Geophysics team lead. "Studying Ultima Thule is helping us understand how planets form — both those in our own solar system and those orbiting other stars in our galaxy."

- Data from the New Year's Day flyby will continue to arrive over the next weeks and months, with much higher resolution images yet to come.

- "In the coming months, New Horizons will transmit dozens of data sets to Earth, and we'll write new chapters in the story of Ultima Thule — and the solar system," said Helene Winters, New Horizons Project Manager.

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Figure 44: The first color image of Ultima Thule, taken at a distance of 137,000 km at 4:08 UTC January 1, 2019 (and published on 2 January 2019), highlights its reddish surface. At left is an enhanced color image taken by the Multispectral Visible Imaging Camera (MVIC), produced by combining the near infrared, red and blue channels. The center image taken by the Long-Range Reconnaissance Imager (LORRI) has a higher spatial resolution than MVIC by approximately a factor of five. At right, the color has been overlaid onto the LORRI image to show the color uniformity of the Ultima and Thule lobes. Note the reduced red coloring at the neck of the object (image credit: NASA, JHU/APL, SwRI)

• January 1, 2019: NASA's New Horizons spacecraft flew past Ultima Thule in the early hours of New Year's Day, ushering in the era of exploration from the enigmatic Kuiper Belt, a region of primordial objects that holds keys to understanding the origins of the solar system. 41)

- "Congratulations to NASA's New Horizons team, Johns Hopkins Applied Physics Laboratory and the Southwest Research Institute for making history yet again. In addition to being the first to explore Pluto, today New Horizons flew by the most distant object ever visited by a spacecraft and became the first to directly explore an object that holds remnants from the birth of our solar system," said NASA Administrator Jim Bridenstine. "This is what leadership in space exploration is all about."

- Signals confirming the spacecraft is healthy and had filled its digital recorders with science data on Ultima Thule reached the mission operations center at the Johns Hopkins Applied Physics Laboratory (APL) today at 10:29 a.m. EST, almost exactly 10 hours after New Horizons' closest approach to the object.

- "New Horizons performed as planned today, conducting the farthest exploration of any world in history — 4 billion miles from the Sun," said Principal Investigator Alan Stern, of the Southwest Research Institute in Boulder, Colorado. "The data we have look fantastic and we're already learning about Ultima from up close. From here out the data will just get better and better!"

- Images taken during the spacecraft's approach — which brought New Horizons to within just 2,200 miles (3,500 km) of Ultima at 12:33 a.m. EST — revealed that the Kuiper Belt object may have a shape similar to a bowling pin, spinning end over end, with dimensions of approximately 32 by 16 km. Another possibility is Ultima could be two objects orbiting each other. Flyby data have already solved one of Ultima's mysteries, showing that the Kuiper Belt object is spinning like a propeller with the axis pointing approximately toward New Horizons. This explains why, in earlier images taken before Ultima was resolved, its brightness didn't appear to vary as it rotated. The team has still not determined the rotation period.

- As the science data began its initial return to Earth, mission team members and leadership reveled in the excitement of the first exploration of this distant region of space.

- "New Horizons holds a dear place in our hearts as an intrepid and persistent little explorer, as well as a great photographer," said Johns Hopkins Applied Physics Laboratory Director Ralph Semmel. "This flyby marks a first for all of us — APL, NASA, the nation and the world — and it is a great credit to the bold team of scientists and engineers who brought us to this point."

- "Reaching Ultima Thule from 4 billion miles away is an incredible achievement. This is exploration at its finest," said Adam L. Hamilton, president and CEO of the Southwest Research Institute in San Antonio. "Kudos to the science team and mission partners for starting the textbooks on Pluto and the Kuiper Belt. We're looking forward to seeing the next chapter."

- The New Horizons spacecraft will continue downloading images and other data in the days and months ahead, completing the return of all science data over the next 20 months. When New Horizons launched in January 2006, George W. Bush was in the White House, Twitter had just been launched and Time Magazine's Person of the Year was "you — all the worldwide web users." Nine years into its journey, the spacecraft began its exploration of the Kuiper Belt with a flyby of Pluto and its moons. Almost 13 years after the launch, the spacecraft will continue its exploration of the Kuiper Belt until at least 2021. Team members plan to propose more Kuiper Belt exploration.

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Figure 45: At left is a composite of two images taken by New Horizons' high-resolution Long-Range Reconnaissance Imager (LORRI), which provides the best indication of Ultima Thule's size and shape so far. Preliminary measurements of this Kuiper Belt object suggest it is approximately 20 miles long by 10 miles wide (32 kilometers by 16 kilometers). An artist's impression at right illustrates one possible appearance of Ultima Thule, based on the actual image at left. The direction of Ultima's spin axis is indicated by the arrows (image credit: NASA, JHU/APL, SwRI; sketch courtesy of James Tuttle Keane)

- New Horizons acquired gigabytes of photos and other observations during the pass. It will now send these home over the coming months. The radio message from the robotic craft was picked up by one of Nasa's big antennas, in Madrid, Spain. It had taken fully six hours and eight minutes to traverse the great expanse of space between Ultima and Earth.

NASA's New Horizons spacecraft is on track to perform the farthest flyby in history, when it zips past a Kuiper Belt object nicknamed Ultima Thule – more than four billion miles (~6.5 billion km) from Earth – at 12:33 a.m. EST (05:33 UTC) on 1 January 2019. 42)

• December 30, 2018: The Hubble Space Telescope Paved the Way for the New Horizons Mission to Pluto and Ultima Thule. Years before a team of researchers proposed a mission called New Horizons to explore the dwarf planet Pluto, NASA's Hubble Space Telescope had already made initial observations of the world at the dim outer fringes of our celestial neighborhood. Over many years, Hubble's pioneering observations repeatedly accomplished what ground-based telescopes could not — imaging features on Pluto's surface, finding new Plutonian moons, and tracking down a destination to visit after Pluto — an even tinier, icy object in a vast region of small worlds beyond the orbit of Neptune called the Kuiper Belt. 43)

- Thus began a decades-long relationship between Hubble and NASA's New Horizons mission: A legendary space-based telescope and a pioneering space probe hurtling through space at about 32,000 miles/hour (51,500 km/hour).

- In 1990, Hubble produced the first image that illuminated Pluto and its large moon Charon. After Hubble's optical repair in 1993, scientists captured even sharper images. New Horizons Principal Investigator Alan Stern of the Southwest Research Institute in Boulder, Colorado, led the imaging projects while co-investigator Marc Buie, now at SwRI Boulder but then at Lowell Observatory where Pluto was discovered, led the data analysis.

- "We got eight pixels of Pluto in 1994. Each pixel represented more than 150 square miles of Pluto's surface. Fast forward to 2002 and we got even fewer pixels per image. We had to wring every bit of information from each pixel possible," Buie said. "It was a time- and computer-intensive process, but we were able to create the first maps of Pluto's surface, and they were truly spectacular for their time."

- Those crude but valuable maps provided the best evidence that Pluto was not simply a homogenous ball of ices, but has a complex, variegated surface — a promising aspect for close-up inspection by a visiting spacecraft. Hubble's cameras revealed nearly a dozen distinctive bright features, none of which had ever been seen before, including a "ragged" northern polar cap bisected by a dark strip, a puzzling high-contrast bright spot seen rotating with the planet, a cluster of dark spots, and a bright linear marking. That bright spot feature, unusually rich in carbon monoxide frost, became the prime target for New Horizons to examine up close after NASA funded the mission in 2002.

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Figure 46: Full trajectory: side view: This image shows New Horizons' current position along its full planned trajectory. The green segment of the line shows where New Horizons has traveled since launch; the red indicates the spacecraft's future path. Positions of stars with magnitude 12 or brighter are shown from this perspective, which is slightly above the orbital plane of the planets (image credit: JHU/APL, NASA, SwRI) 44)

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Figure 47: Full trajectory: overhead view: This image shows New Horizons' current position along its full planned trajectory. The green segment of the line shows where New Horizons has traveled since launch; the red indicates the spacecraft's future path. Positions of stars with magnitude 12 or brighter are shown from this perspective, which is above the Sun and "north" of Earth's orbit (image credit: JHU/APL, NASA, SwRI)

- Although Charon was discovered in 1978 using ground-based telescopes, Hubble detected all four of Pluto's other moons: Nix and Hydra in 2005, Kerberos in 2011, and Styx in 2012. These moons were spotted in the Hubble images by New Horizons team members, most notably Project Scientist Hal Weaver of the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, and co-investigator Mark Showalter of the SETI Institute in Mountain View, California. By the time the latter two moons were discovered, New Horizons was in the final years of its almost decade-long, 3-billion-mile sprint from Earth to Pluto.

- The discovery of these four small satellites was critical to overall Pluto flyby planning by identifying potential hazards, verifying the optimal spacecraft trajectory, and establishing the need for time to include observations of them as part of the flyby observing sequence. Without Hubble, New Horizons would have discovered these moons only a few months before the encounter — too late to effectively plan for their detailed study. To examine the possibility for an extended mission into the Kuiper Belt, the New Horizons team used Hubble in 2014 to conduct a needle-in-a-haystack search for a suitable Kuiper Belt Object that New Horizons could visit after passing Pluto. Hubble's sensitive telescope allowed it to look for fainter KBOs than ground-based telescopes can see. Hubble took deep exposures on 20 areas of the sky and found three suitable KBO targets about one billion miles beyond Pluto. Following NASA approval for a mission extension in 2016, Stern selected 2014 MU69, since nicknamed Ultima Thule, as the target for its January 2019 flyby. In the years since, Hubble has measured the target's red color and refined its orbit with dozens of additional observations.

- "Without Hubble there would be no flyby of Ultima Thule," said Stern. "And without Hubble, New Horizons would not have been as productive studying Pluto's small moons. In fact, without Hubble's early images revealing how interesting Pluto's surface markings are, there might have never been a mission to explore this fascinating dwarf planet."

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Figure 48: NASA's Hubble Space Telescope discovered the next target for the New Horizons spacecraft — 2014 MU69, nicknamed Ultima Thule — in June 2014. Seen in these five overlaid images, the object resides more than one billion miles beyond Pluto in the frigid outer reaches of the Kuiper Belt. New Horizons will reach Ultima Thule on New Year's Day 2019 (image credit: NASA, STScI, JHU/APL, SwRI)

 

New Horizons just over 100 days from Ultima Thule (19 September 2018)

NASA's New Horizons spacecraft is just over 100 days away from a high-risk, high-reward flyby of an ancient world on the outskirts of the solar system. 45)

On New Year's Day 2019, the spacecraft will come within 3,500 km of 2014 MU69, an estimated 37 km-wide object the mission team has nicknamed Ultima Thule. The encounter will take place 6.6 billion km from Earth, where it takes more than 6 hours for radio signals traveling at the speed of light to reach NASA's Deep Space Network.

There will only be one chance for New Horizons to perfectly aim its cameras and science instruments at Ultima Thule as it zips past at 14 km/s and there may be unforeseen hazards in the spacecraft's path. Nevertheless, Jim Green, the director of NASA's planetary science division, is looking forward to the drama. "Are there debris in the way? Will the spacecraft make it? I mean, you know, you can't get any better than that," he said Wednesday, during a "science chat" broadcast from the Johns Hopkins University Applied Physics Laboratory in Maryland. "And, we'll get spectacular images on top of that. What's not to like?"

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Figure 49: Artist's impression of New Horizons encountering 2014 MU69 (Ultima Thule), image credit: NASA, JHU/APL, SwRI, Steve Gribben

Scientists think Ultima Thule is a building block of larger objects in the Kuiper Belt, a band of frigid worlds that orbit the Sun beyond Neptune. Objects in the belt serve as time capsules from the dawn of the solar system, when a cloud of dust and gas collapsed to form the Sun, planets, and other small bodies. The temperature on Ultima Thule is expected to be just 40 or 50 degrees above absolute zero, said Alan Stern, the principal investigator of the New Horizons mission. "It's a big deal because we're going 4 billion years into the past," he said. "Nothing that we've ever explored in the entire history of space exploration has been kept in this kind of deep freeze the way Ultima has."

New Horizons made worldwide headlines when it flew past Pluto in 2015, revealing a complex world with icy mountains and frozen plains. The big reveal of Ultima Thule probably won't garner as much publicity — but that hardly means it's going to be a cakewalk. "Everything about this flyby is tougher," said Stern.

For the Pluto encounter, the team knew exactly where to aim, thanks to decades of telescopic observations that refined our understanding of its orbit. That won't be the case with Ultima Thule, which was only discovered in 2014 by the Hubble Space Telescope. The New Horizons team must continually track the object using optical navigation cameras, and make the appropriate course corrections.

"The orbit is not very well characterized," said Alice Bowman, the mission operations manager for New Horizons. "That's why we're doing optical navigation measurements, continuously looking to make sure we know the point in space we want to target."

That's a tricky task because Ultima Thule is dark and reddish, and only reflects about as much light as potting soil, Stern said. The object is also set against a particularly crowded region of space that is flush with background stars.

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Figure 50: New Horizons Ultima Thule encounter timeline (image credit: NASA)

The central objective of the New Horizons prime mission was to make the first exploration of Pluto and its system of moons. Following that, New Horizons has been approved for its first extended mission, which has the objectives of extensively studying the Kuiper Belt environment, observing numerous Kuiper Belt Objects (KBOs) and Centaurs in unique ways, and making the first close flyby of the KBO 486958 2014 MU69. This review summarizes the objectives and plans for this approved mission extension, and briefly looks forward to potential objectives for subsequent extended missions by New Horizons. 46)

 

Pluto Features Given First Official Names (7 September 2017)

It's official: Pluto's "heart" now bears the name of pioneering American astronomer Clyde Tombaugh, who discovered Pluto in 1930. And a crater on Pluto is now officially named after Venetia Burney, the British schoolgirl who in 1930 suggested the name "Pluto," Roman god of the underworld, for Tombaugh's newly-discovered planet. 47)

Tombaugh Regio and Burney crater are among the first set of official Pluto feature names approved by the International Astronomical Union (IAU), the internationally recognized authority for naming celestial bodies and their surface features.

These and other names were proposed by NASA's New Horizons team following the first reconnaissance of Pluto and its moons by the New Horizons spacecraft in 2015. The New Horizons science team had been using these and other place names informally to describe the many regions, mountain ranges, plains, valleys and craters discovered during the first close-up look at the surfaces of Pluto and its largest moon, Charon.

A total of 14 Pluto place names have now been made official by the IAU; many more will soon be proposed to the IAU, both on Pluto and on its moons. "The approved designations honor many people and space missions who paved the way for the historic exploration of Pluto and the Kuiper Belt, the farthest worlds ever explored," said Alan Stern, New Horizons principal investigator from Southwest Research Institute, Boulder, Colorado.

"We're very excited to approve names recognizing people of significance to Pluto and the pursuit of exploration as well as the mythology of the underworld. These names highlight the importance of pushing to the frontiers of discovery," said Rita Schulz, chair of the IAU Working Group for Planetary System Nomenclature. "We appreciate the contribution of the general public in the form of their naming suggestions and the New Horizons team for proposing these names to us."

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Figure 51: Pluto's first official surface-feature names are marked on this map, compiled from images and data gathered by NASA's New Horizons spacecraft during its flight through the Pluto system in 2015 (image credit: NASA, JHU/APL, SwRI, Ross Beyer)

Stern applauded the work of the New Horizons Nomenclature Working Group, which along with Stern included science team members Mark Showalter — the group's chairman and liaison to the IAU — Ross Beyer, Will Grundy, William McKinnon, Jeff Moore, Cathy Olkin, Paul Schenk and Amanda Zangari.

The team gathered many ideas during the "Our Pluto" online naming campaign in 2015. Following on Venetia Burney's original suggestion, several place names on Pluto come from underworld mythology. "I'm delighted that most of the approved names were originally recommended by members of the public," said Showalter, of the SETI Institute, Mountain View, California.

The approved Pluto surface feature names are listed in Table 1. The names pay homage to the underworld mythology, pioneering space missions, historic pioneers who crossed new horizons in exploration, and scientists and engineers associated with Pluto and the Kuiper Belt.

Tombaugh Regio honors Clyde Tombaugh (1906–1997), the U.S. astronomer who discovered Pluto in 1930 from the Lowell Observatory in Arizona.

Burney crater honors Venetia Burney (1918-2009), who as an 11-year-old schoolgirl suggested the name "Pluto" for Clyde Tombaugh's newly discovered planet. Later in life she taught mathematics and economics.

Sputnik Planitia is a large plain named for Sputnik 1, the first space satellite, launched by the Soviet Union in 1957.

Tenzing Montes and Hillary Montes are mountain ranges honoring Tenzing Norgay (1914–1986) and Sir Edmund Hillary (1919–2008), the Indian/Nepali Sherpa and New Zealand mountaineer were the first to reach the summit of Mount Everest and return safely.

Al-Idrisi Montes honors Ash-Sharif al-Idrisi (1100–1165/66), a noted Arab mapmaker and geographer whose landmark work of medieval geography is sometimes translated as "The Pleasure of Him Who Longs to Cross the Horizons."

Djanggawul Fossae defines a network of long, narrow depressions named for the Djanggawuls, three ancestral beings in indigenous Australian mythology who traveled between the island of the dead and Australia, creating the landscape and filling it with vegetation.

Sleipnir Fossae is named for the powerful, eight-legged horse of Norse mythology that carried the god Odin into the underworld.

Virgil Fossae honors Virgil, one of the greatest Roman poets and Dante's fictional guide through hell and purgatory in the Divine Comedy.

Adlivun Cavus is a deep depression named for Adlivun, the underworld in Inuit mythology.

Hayabusa Terra is a large land mass saluting the Japanese spacecraft and mission (2003-2010) that performed the first asteroid sample return.

Voyager Terra honors the pair of NASA spacecraft, launched in 1977, that performed the first "grand tour" of all four giant planets. The Voyager spacecraft are now probing the boundary between the Sun and interstellar space.

Tartarus Dorsa is a ridge named for Tartarus, the deepest, darkest pit of the underworld in Greek mythology.

Elliot crater recognizes James Elliot (1943-2011), an MIT researcher who pioneered the use of stellar occultations to study the solar system – leading to discoveries such as the rings of Uranus and the first detection of Pluto's thin atmosphere.

Table 1: Overview of approved Pluto surface names

The New Horizons spacecraft – built and operated at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, with a payload and science investigation led by SwRI — is speeding toward its next flyby, this one with the ancient Kuiper Belt object 2014 MU69, about 1.6 billion kilometers beyond Pluto, on 1 January 2019.

 

NASA Video Soars over Pluto's Majestic Mountains and Icy Plains (14 July 2017)

In July 2015, NASA's New Horizons spacecraft sent home the first close-up pictures of Pluto and its moons – amazing imagery that inspired many to wonder what a flight over the distant worlds' icy terrain might be like. 48)

Wonder no more. Using actual New Horizons data and digital elevation models of Pluto and its largest moon Charon, mission scientists have created flyover movies that offer spectacular new perspectives of the many unusual features that were discovered and which have reshaped our views of the Pluto system – from a vantage point even closer than the spacecraft itself.

Figure 52: New Horizons flyover of Pluto. Using actual New Horizons data and digital elevation models of Pluto and its largest moon Charon, mission scientists have created flyover movies that offer spectacular new perspectives of the many unusual features that were discovered and which have reshaped (video credit: NASA, JHU/APL, SwRI, Paul Schenk and John Blackwell, Lunar and Planetary Institute)

This dramatic Pluto flyover begins over the highlands to the southwest of the great expanse of nitrogen ice plain informally named Sputnik Planitia. The viewer first passes over the western margin of Sputnik, where it borders the dark, cratered terrain of Cthulhu Macula, with the blocky mountain ranges located within the plains seen on the right. The tour moves north past the rugged and fractured highlands of Voyager Terra and then turns southward over Pioneer Terra — which exhibits deep and wide pits — before concluding over the bladed terrain of Tartarus Dorsa in the far east of the encounter hemisphere.

Figure 53: New Horizons Flyover of Charon (video credit: NASA, JHU/APL, SwRI, Paul Schenk and John Blackwell, Lunar and Planetary Institute)

The equally exciting flight over Charon begins high over the hemisphere New Horizons saw on its closest approach, then descends over the deep, wide canyon of Serenity Chasma. The view moves north, passing over Dorothy Gale crater and the dark polar hood of Mordor Macula. The flight then turns south, covering the northern terrain of Oz Terra before ending over the relatively flat equatorial plains of Vulcan Planum and the "moated mountains" of Clarke Montes.

The topographic relief is exaggerated by a factor of two to three times in these movies to emphasize topography; the surface colors of Pluto and Charon also have been enhanced to bring out detail.

 

New Horizons' Top 10 Discoveries at Pluto (14 July 2016)

Five billion kilometers from Earth, NASA's New Horizons spacecraft, moving at speeds that would get it from New York to Los Angeles in about four minutes, was pointing cameras, spectrometers, and other sensors at Pluto and its moons – distant worlds that humankind had never seen up close – recording hundreds of pictures and other data that would forever change our view of the outer solar system. 49)

"New Horizons not only completed the era of first reconnaissance of the planets, the mission has intrigued and inspired. Who knew that Pluto would have a heart?" said NASA's Director of Planetary Science Jim Green. "Even today, New Horizons captures our imagination, rekindles our curiosity, and reminds us of what's possible."

To say that New Horizons shook the foundation of planetary science is an understatement—discoveries already culled from the pictures and compositional and space environment readings have not only introduced us to the Pluto system, but hint at what awaits as scientists examine other worlds in the Kuiper Belt. New Horizons Principal Investigator Alan Stern of the Southwest Research Institute, Boulder, Colorado, lists the mission's most surprising and amazing findings from Pluto (so far):

- The complexity of Pluto and its satellites is far beyond what we expected.

- The degree of current activity on Pluto's surface and the youth of some surfaces on Pluto are simply astounding.

- Pluto's atmospheric hazes and lower-than-predicted atmospheric escape rate upended all of the pre-flyby models.

- Charon's enormous equatorial extensional tectonic belt hints at the freezing of a former water ice ocean inside Charon in the distant past. Other evidence found by New Horizons indicates Pluto could well have an internal water-ice ocean today.

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Figure 54: NASA's New Horizons spacecraft captured this high-resolution enhanced color view of Pluto's moon Charon just before closest approach on July 14, 2015. Charon's striking reddish north polar region is informally named Mordor Macula (image credits: NASA, JHU/APL, SwRI)

- All of Pluto's moons that can be age-dated by surface craters have the same, ancient age—adding weight to the theory that they were formed together in a single collision between Pluto and another planet in the Kuiper Belt long ago.

- Charon's dark, red polar cap is unprecedented in the solar system and may be the result of atmospheric gases that escaped Pluto and then accreted on Charon's surface.

- Pluto's vast 1,000-kilometer-wide heart-shaped nitrogen glacier (informally called Sputnik Planum) that New Horizons discovered is the largest known glacier in the solar system.

- Pluto shows evidence of vast changes in atmospheric pressure and, possibly, past presence of running or standing liquid volatiles on its surface – something only seen elsewhere on Earth, Mars and Saturn's moon Titan in our solar system.

- The lack of additional Pluto satellites beyond what was discovered before New Horizons was unexpected.

- Pluto's atmosphere is blue. Who knew?

"It's strange to think that only a year ago, we still had no real idea of what the Pluto system was like," said Hal Weaver, New Horizons project scientist from the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. "But it didn't take long for us to realize Pluto was something special, and like nothing we ever could have expected. We've been astounded by the beauty and complexity of Pluto and its moons and we're excited about the discoveries still to come."

New Horizons is now nearly 500 million km beyond Pluto, speeding to its next destination deeper into the Kuiper Belt, following NASA approval of an extended mission. About 80 percent of the data stored on the spacecraft's recorders has been sent to Earth; transmission of the remainder will be complete by October.

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Figure 55: Illustration of Pluto and its next science target, 2014 MU69, with the trajectory of New Horizons in yellow (image credit: Alex Parker)

"Our entire team is proud to have accomplished the first exploration of Pluto and the Kuiper Belt—something many of us had worked to achieve since the 1990s," said Stern. "The data that New Horizons sent back about Pluto and its system of moons has revolutionized planetary science and inspired people of all ages across the world about space exploration. It's been a real privilege to be able to do that, for which I'll be forever indebted to our team and our nation."

 

Pluto Flyby in 2015

The 15 July 2015 flyby of Pluto was the culmination of a decades-long quest to see and understand the Solar System's most distant planet. But it turned out to be a new beginning, revealing for the first time the potential complexity of small (or dwarf) planet systems in the Kuiper belt. New Horizons' seven instruments took over 50 Gb of data at Pluto — on approach, passing through the system, and on departure. Pluto was revealed to be a geologically and meteorologically active world. Its size and density were accurately determined; the former turned out to be at the upper range of previous Earth-based estimates. Pluto remains, for now, the physically largest world in the Kuiper belt. Made largely of rock, about 2/3 by mass, but with substantial ice and carbonaceous (organic) material, Pluto appears to have differentiated, possessing a rock core and predominantly water ice mantle. Surface layers and deposits of volatile ices such as nitrogen (N2), methane (CH4), and carbon monoxide (CO), along with dark, reddish, organic matter often referred to as tholins, complete the picture (Ref. 52).

Pluto's volatile ices can sublimate and condense under the influence of even the feeble sunlight at Pluto's distance, and N2-ice in particular is soft enough to flow across Pluto's incredibly cold surface (about 40 K as measured by New Horizons). And flow it does, from high standing water-ice-rich terrains, through gaps in the mountains, and down to a vast, frozen nitrogen-ice sea called Sputnik Planitia (SP for short). This icy plain is actually a giant ice sheet, filling to a depth of several kilometers a great impact basin over 1000 km across, itself the product of the collision of a large (roughly 200-km wide) Kuiper belt object with Pluto over 4 billion years ago. Overall, Pluto's topography is rugged, with some water-ice mountain blocks reaching heights of 5 km. The density of impact craters on Pluto varies widely, from heavily cratered terrains in Cthulhu Regio that must date from the earliest days of the Solar System, to Sputnik Planitia itself, which betrays no impact craters at all in New Horizons' highest resolution images (about 70 m/pixel). The solid nitrogen ice in SP is organized into giant convection cells, slowly churning on a several 100,000 year time scale, transporting Pluto's modest interior heat outward. The position of SP on Pluto's tidal axis (the imaginary line that runs through the centers of Pluto and Charon) may not be coincidence; rather, it could be evidence of the slip, or polar wander, of Pluto's surface to a preferred orientation. Such a slip is circumstantial evidence that under Pluto's water ice mantle, perhaps at a depth of close to 150 km, lies an inner ocean of water.

Pluto's atmosphere was measured by New Horizons UV solar and radio occultations. At present it is quite thin, about 11.5 µbar at the surface, and dominated by N2 gas in vapor-pressure equilibrium with surface N2 ice. Methane is the next most abundant gas and several simple hydrocarbons were discovered as well. The temperature in the atmosphere rises over the first 25 km or so of altitude, peaking at around 115 K, and gradually falling with increasing altitude thereafter. The temperature at Pluto's exobase, 100s of km above the surface, was much lower than previously thought, which means that Pluto's atmosphere is not escaping as fast as previously believed. Even more interesting, the dominant gas escaping is the lighter component, CH4, not N2. As thin as Pluto's atmosphere is, it is capable of transporting sublimed ices from one part of Pluto's surface to another, and downslope wind speeds are great enough to form methane particle "sand dunes" at the edge of SP. But the best surprise was saved for last. Turning New Horizons' imaging telescopes to look back at Pluto on departure, multiple haze layers were discovered wrapping completely around the planet, extending over several 100 km in height above the surface.

Pluto's satellites did not disappoint as well. Charon, the large moon, has a surface dominated by water ice and no atmosphere. New Horizons' LEISA spectrometer confirmed the presence of some form of ammonia ice across much of the surface, along with concentrations associated with specific impact craters. Charon's poles are apparently stained red from CH4 escaping from Pluto but cold trapped and radiation processed there. Charon is not geologically active today, and has sufficient impact craters on its surface the New Horizons science team members estimate its overall surface age to approach 4 billion years. But that does not mean its geological past was anything but spectacular. Much of Charon's northern hemisphere visible to New Horizons at closest approach is broken into great crustal blocks and canyons many kilometers deep. In contrast, the southern hemisphere is slightly younger plains, informally named Vulcan Planitia (VP), and appears to have been resurfaced by a series of thick, icy — or cryovolcanic — flows. The totally of Charon's geological history suggests that it too is differentiated and possessed an internal ocean, but owing to the moon's smaller size relative to Pluto, it cooled and its ocean froze, causing it surface to expand and rupture, which in turn facilitated the cryovolcanic eruptions we see in VP.

Rounding out the tour of the Pluto system were studies of the 4 small moons, Styx, Nix, Kerberos, and Hydra. These moons, discovered after the New Horizons mission started, were imaged on a best effort basis. They are irregular, on the order of 10 to 50 km across, and highly reflective. Infrared spectra indicate surfaces of almost pure water ice. These moons orbit in the same plane as Pluto and Charon but at sufficiently great distances from the two that tides have not slowed any of the small moons to the synchronous spin state common among regular satellites elsewhere in the solar system. In fact, some of spin states are bizarre: all four highly elongated objects rotate much faster than synchronous, with their rotational poles highly inclined relative to those of Pluto and Charon (which are aligned). The relativities and surface compositions of Pluto's small moons are quite different from most Kuiper belt objects in their size class, which are much darker and spectrally featureless, but are consistent with being debris from the giant impact that created the Pluto-Charon binary at the beginning of solar system history.

Figure 56: Pluto's intriguing moons. We talk a lot about Charon, Pluto's largest moon that's about half the size of its host planet. But what about Pluto's other moons? They're strange, to say the least. Pluto's four smaller moons - Styx, Nix, Kerberos and Hydra - are differently fascinating than Charon (video credit: NASA)

 

New Horizons Captures Two of Pluto's Smaller Moons (21 July 2015)

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Figure 57: Pluto's moon Nix (left), shown here in enhanced color as imaged by the New Horizons Ralph instrument, has a reddish spot that has attracted the interest of mission scientists. The data were obtained on the morning of July 14, 2015, and received on the ground on July 18. At the time the observations were taken New Horizons was about 165,000 km from Nix. The image shows features as small as approximately 3 km across on Nix, which is estimated to be 42 km long and 36 km wide (image credit: NASA, JHU/APL, SWRI) 50)

Pluto's small, irregularly shaped moon Hydra (right) is revealed in this black and white image taken from New Horizons' LORRI instrument on July 14, 2015, from a distance of about 231,000 km. Features as small as1.2 km are visible on Hydra, which measures 55 km in length.

While Pluto's largest moon Charon has grabbed most of the lunar spotlight so far, these two smaller and lesser-known satellites are now getting some attention. Nix and Hydra – the second and third moons to be discovered – are approximately the same size, but their similarity ends there.

New Horizons' first color image of Pluto's moon Nix, in which colors have been enhanced, reveals an intriguing region on the jelly bean-shaped satellite, which is estimated to be 42 km long and 36 km wide.

Although the overall surface color of Nix is neutral grey in the image, the newfound region has a distinct red tint. Hints of a bull's-eye pattern lead scientists to speculate that the reddish region is a crater. "Additional compositional data has already been taken of Nix, but is not yet downlinked. It will tell us why this region is redder than its surroundings," said mission scientist Carly Howett, Southwest Research Institute, Boulder, Colorado. She added, "This observation is so tantalizing, I'm finding it hard to be patient for more Nix data to be downlinked."

Meanwhile, the sharpest image yet received from New Horizons of Pluto's satellite Hydra shows that its irregular shape resembles the state of Michigan. The new image was made by the LORRI (Long Range Reconnaissance Imager) on 14 July 2015 from a distance of 231,000 km, and shows features as small as 1.2 km across. There appear to be at least two large craters, one of which is mostly in shadow. The upper portion looks darker than the rest of Hydra, suggesting a possible difference in surface composition. From this image, mission scientists have estimated that Hydra is 55 km long and 40 km wide. Commented mission science collaborator Ted Stryk of Roane State Community College in Tennessee, "Before last week, Hydra was just a faint point of light, so it's a surreal experience to see it become an actual place, as we see its shape and spot recognizable features on its surface for the first time."

Images of Pluto's most recently discovered moons, Styx and Kerberos, are expected to be transmitted to Earth no later than mid-October.

Nix and Hydra were both discovered in 2005 using Hubble Space Telescope data by a research team led by New Horizons project scientist Hal Weaver, JHU/APL (Johns Hopkins University /Applied Physics Laboratory), Laurel, Maryland. New Horizons' findings on the surface characteristics and other properties of Nix and Hydra will help scientists understand the origins and subsequent history of Pluto and its moons.

 

New Horizons Spacecraft Displays Pluto's Big Heart (14 July 2015)

Five billion kilometers away, Pluto has sent a "love note" back to Earth, via NASA's New Horizons spacecraft. 51)

At about 4 p.m. EDT on July 13 - about 16 hours before closest approach - New Horizons captured this stunning image of one of Pluto's most dominant features (Figure 58). The "heart," estimated to be 1,000 miles (1,600 km) across at its widest point rests just above the equator (the angle of view displays mostly the northern hemisphere). The heart's diameter is about the same distance as from Denver to Chicago, in America's heartland.

"Wow!" said New Horizons principal investigator Alan Stern, Southwest Research Institute, Boulder, Colorado, as the image was unveiled before the New Horizons science team at JHU/APL (Johns Hopkins University /Applied Physics Laboratory) in Laurel, Maryland. "My prediction was that we would find something wonderful, and we did. This is proof that good things really do come in small packages."

The newest image from the Long Range Reconnaissance Imager (LORRI) shows an almost perfectly shaped left half of a bright, heart-shaped feature centered just above Pluto's equator, while the right side of the heart appears to be less defined.

The image shows for the first time that some surfaces on Pluto are peppered with impact craters and are therefore relatively ancient, perhaps several billion years old. Other regions, such as the interior of the heart, show no obvious craters and thus are probably younger, indicating that Pluto has experienced a long and complex geological history. Some craters appear partially destroyed, perhaps by erosion. There are also hints that parts of Pluto's crust have been fractured, as indicated by the series of linear features to the left of the heart.

Below the heart are dark terrains along Pluto's equator, including, on the left, the large dark feature informally known as the "whale." Craters pockmark part of the whale's head; areas that appear smooth and featureless may be a result of image compression.

New Horizons traveled nearly a decade to receive its summer valentine, launching on January 19, 2006.

This is just the latest in a series of the New Horizons Pluto "picture show." On Wednesday July 15, more images of surface close-ups will make the more than four-hour journey to Earth at the speed of light to give Pluto fans details as small as New York's Central Park.

"Our data tomorrow (Wednesday, July 15) will have ten times the resolution of what we see today and it will knock your socks off," said Stern.

Curt Niebur, New Horizons program scientist with NASA Headquarters in Washington notes, "The science is amazing, but the team's excitement reminds me of why we really do this."

At 7:49 a.m. EDT on Tuesday, July 14 New Horizons sped past Pluto at 30,800 miles/hr (49,600 km/hr), with a suite of seven science instruments. As planned, New Horizons went incommunicado as it hurtled through the Pluto-Charon system busily gathering data. The New Horizons team will breathe a sigh of relief when New Horizons "phones home" at approximately 9:02 p.m. EDT on July 14. The mission to the icy dwarf planet completes the initial reconnaissance of the solar system.

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Figure 58: Pluto nearly fills the frame in this image from the LORRI (Long Range Reconnaissance Imager) aboard NASA's New Horizons spacecraft, taken on July 13, 2015 when the spacecraft was 768,000 km from the surface. This is the last and most detailed image sent to Earth before the spacecraft's closest approach to Pluto on July 14. The color image has been combined with lower-resolution color information from the Ralph instrument that was acquired earlier on July 13. This view is dominated by the large, bright feature informally named the "heart," which measures approximately 1,600 km across. The heart borders darker equatorial terrains, and the mottled terrain to its east (right) are complex. However, even at this resolution, much of the heart's interior appears remarkably featureless—possibly a sign of ongoing geologic processes (image credit: NASA ,APL, SwRI)

Figure 59: New Horizons is the first mission to the Kuiper Belt, a gigantic zone of icy bodies and mysterious small objects orbiting beyond Neptune. This region also is known as the "third" zone of our solar system, beyond the inner rocky planets and outer gas giants (video credit: NASA, published in 12 June 2015)

 

Jupiter Encounter in 2007

The voyage of NASA's Pluto-bound New Horizons spacecraft through the Jupiter system provided a bird's-eye view of a dynamic planet that had changed since previous close-up looks by NASA spacecraft. 52) 53)

New Horizons passed Jupiter on 28 February 2007, riding the planet's gravity to boost its speed and shave three years off its trip to Pluto. It was the eighth spacecraft to visit Jupiter – but a combination of trajectory, timing and technology allowed it to explore details no probe had seen before, such as lightning near the planet's poles, the life cycle of fresh ammonia clouds, boulder-size clumps speeding through the planet's faint rings, the structure inside volcanic eruptions on its moon Io, and the path of charged particles traversing the previously unexplored length of the planet's long magnetic tail.

"The Jupiter encounter was successful beyond our wildest dreams," says New Horizons Principal Investigator Alan Stern. "Not only did it prove out our spacecraft and put it on course to reach Pluto in 2015, it was a chance for us to take sophisticated instruments to places in the Jovian system where other spacecraft couldn't go, and to return important data that adds tremendously to our understanding of the solar system's largest planet and its moons, rings and atmosphere."

From January through June 2007, New Horizons' seven science instruments made more than 700 separate observations of the Jovian system – twice the activity planned at Pluto – with most of them coming in the eight days around closest approach to Jupiter. "We carefully selected observations that complemented previous missions, so that we could focus on outstanding scientific issues that needed further investigation," says New Horizons Jupiter Science Team Leader Jeff Moore, of NASA Ames Research Center, Moffett Field, Calif. "The Jupiter system is constantly changing and New Horizons was in the right place at the right time to see some exciting developments."

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Figure 60: Jupiter encounter of New Horizons (image credit: NASA)

Jovian weather was high on the list, as New Horizons' visible light, infrared and ultraviolet remote-sensing instruments probed Jupiter's atmosphere for data on cloud structure and composition. They saw clouds form from ammonia welling up from the lower atmosphere and heat-induced lightning strikes in the polar regions – the first polar lightning ever observed beyond Earth, demonstrating that heat moves through water clouds at virtually all latitudes across Jupiter. They made the most detailed size and speed measurements yet of "waves" that run the width of planet and indicate violent storm activity below. Additionally, New Horizons snapped the first close-up images of the Little Red Spot, a nascent storm about half the size of Jupiter's larger Great Red Spot and about 70 percent of Earth's diameter, gathering new information on storm dynamics.

Under a range of lightning and viewing angles, New Horizons also captured the clearest images ever of the tenuous Jovian ring system. In them, scientists spotted clumps of debris that may indicate a recent impact inside the rings, or some more exotic phenomenon; movies made from New Horizons images also offer an unprecedented look at ring dynamics, with the tiny inner moons Metis and Adrastea shepherding the materials around the rings. A search for smaller moons inside the rings – and possible new sources of the dusty material – found no bodies wider than a kilometer.

The mission's investigations of Jupiter's four largest moons focused on Io, the closest to Jupiter and whose active volcanoes blast tons of material into the Jovian magnetosphere (and beyond). New Horizons spied 11 different volcanic plumes of varying size, three of which were seen for the first time and one – a spectacular 200-mile-high eruption rising above the volcano Tvashtar – that offered an unprecedented opportunity to trace the structure and motion of the plume as it condensed at high altitude and fell back to the moon's surface. In addition, New Horizons spotted the infrared glow from at least 36 Io volcanoes, and measured lava temperatures up to 1,900 degrees Fahrenheit (1040ºC), similar to many terrestrial volcanoes.

New Horizons' global map of Io's surface backs the moon's status as the solar system's most active body, showing more than 20 geological changes since the Galileo Jupiter orbiter provided the last close-up look in 2001. The remote imagers also kept watch on Io in the darkness of Jupiter's shadow, noting mysterious glowing gas clouds above dozens of volcanoes. Scientists suspect that this gas helps to resupply Io's atmosphere.

New Horizons' flight down Jupiter's magnetotail gave it an unprecedented look at the vast region dominated by the planet's strong magnetic field. Looking specifically at the fluxes of charged particles that flow hundreds of millions of miles beyond the giant planet, the New Horizons particle detectors saw evidence that tons of material from Io's volcanoes move down the tail in large, dense, slow-moving blobs. By analyzing the observed variations in particle fluxes over a wide range of energies and scales, New Horizons scientists are exploring how the volcanic gases from Io are ionized, trapped and energized by Jupiter's magnetic field, then ultimately ejected from the system.

The Jupiter encounter of the New Horizons mission is documented in a special issue of Science: Science 12 October 2007, Vol. 318, Issue 5848, pp. 215 , DOI: 10.1126/science.318.5848.215 54) 55)

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Figure 61: Jupiter flyby science of New Horizons (image credit: NASA)

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Figure 62: And surprises in Jupiter's magnetotail (image credit: NASA)

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Figure 63: Other observations of New Horizons at Jupiter (image credit: NASA)

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Figure 64: This is a montage of New Horizons images of Jupiter and its volcanic moon Io, taken during the spacecraft's Jupiter flyby in early 2007. The Jupiter image is an infrared color composite taken by the spacecraft's near-infrared imaging spectrometer, the Linear Etalon Imaging Spectral Array (LEISA) at 1:40 UTC on 28 February, 2007 (image credit: NASA, JHU/APL)

Legend to Figure 64: The infrared wavelengths used (red: 1.59 µm, green: 1.94 µm, blue: 1.85 µm) highlight variations in the altitude of the Jovian cloud tops, with blue denoting high-altitude clouds and hazes, and red indicating deeper clouds. The prominent bluish-white oval is the Great Red Spot. The observation was made at a solar phase angle of 75 degrees but has been projected onto a crescent to remove distortion caused by Jupiter's rotation during the scan. The Io image, taken at 00:25 UT on 1 March 2007, is an approximately true-color composite taken by the panchromatic Long-Range Reconnaissance Imager (LORRI), with color information provided by the 0.5 µm ("blue") and 0.9 µm ("methane") channels of the Multispectral Visible Imaging Camera (MVIC). The image shows a major eruption in progress on Io's night side, at the northern volcano Tvashtar. Incandescent lava glows red beneath a 330-kilometer high volcanic plume, whose uppermost portions are illuminated by sunlight. The plume appears blue due to scattering of light by small particles in the plume.

 


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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (herb.kramer@gmx.net).

 

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