Evidence of geothermal activity within icy dwarf planets

A team co-led by Southwest Research Institute found evidence for hydrothermal or metamorphic activity within the icy dwarf planets Eris and Makemake, located in the Kuiper Belt. Methane detected on their surfaces has the tell-tale signs of warm or even hot geochemistry in their rocky cores, which is markedly different than the signature of methane from a comet.

"We see some interesting signs of hot times in cool places," said SwRI's Dr. Christopher Glein, an expert in planetary geochemistry and lead author of a paper about this discovery.

The Kuiper Belt is a vast donut-shaped region of icy bodies beyond the orbit of Neptune at the edge of the solar system.

Eris and Makemake are comparable in size to Pluto and its moon Charon.

These bodies likely formed early in the history of our solar system, about 4.5 billion years ago.

Far from the heat of our Sun, KBOs were believed to be cold, dead objects.

Newly published work from JWST studies made the first observations of isotopic molecules on the surfaces of Eris and Makemake.

These so-called isotopologues are molecules that contain atoms having a different number of neutrons.

They provide data that are useful in understanding planetary evolution.

The JWST team measured the composition of the dwarf planets' surfaces, particularly the deuterium (heavy hydrogen, D) to hydrogen (H) ratio in methane.

Deuterium is believed to have formed in the Big Bang, and hydrogen is the most abundant nucleus in the universe.

The D/H ratio on a planetary body yields information about the origin, geologic history and formation pathways of compounds containing hydrogen.

"The moderate D/H ratio we observed with JWST belies the presence of primordial methane on an ancient surface. Primordial methane would have a much higher D/H ratio," Glein said.

"Instead, the D/H ratio points to geochemical origins for methane produced in the deep interior. The D/H ratio is like a window. We can use it in a sense to peer into the subsurface. Our data suggest elevated temperatures in the rocky cores of these worlds so that methane can be cooked up. Molecular nitrogen (N2) could be produced as well, and we see it on Eris. Hot cores could also point to potential sources of liquid water beneath their icy surfaces."

Over the past two decades, scientists have learned that icy worlds can be much more internally evolved than once believed.

Evidence for subsurface oceans has been found at several icy moons such as Saturn's moon Enceladus and Jupiter's moon Europa.

Liquid water is one of the key ingredients in determining potential planetary habitability.

The possibility of water oceans inside Eris and Makemake is something that scientists are going to study in the years ahead.

If either of them is habitable, then it would become the most distant world in the solar system that could possibly support life.

Finding chemical indicators of internally driven processes takes them a step in this direction.

"If Eris and Makemake hosted, or perhaps could still host warm, or even hot, geochemistry in their rocky cores, cryovolcanic processes could then deliver methane to the surfaces of these planets, perhaps in geologically recent times," said Dr. Will Grundy, an astronomer at Lowell Observatory, one of Glein's co-authors and lead author of a companion paper.

"We found a carbon isotope ratio (13C/12C) that suggests relatively recent resurfacing."

This work is part of a paradigm shift in planetary science. It is increasingly being recognized that cold, icy worlds may be warm at heart.

Models developed for this study additionally point to the formation of geothermal gases on Saturn's moon Titan, which also has abundant methane.

Furthermore, the inference of unexpected activity on Eris and Makemake underscores the importance of internal processes in shaping what we see on large KBOs and is consistent with findings at Pluto.

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A new ring system discovered in our Solar System

Scientists have discovered a new ring system around a dwarf planet on the edge of the Solar System. The ring system orbits much further out than is typical for other ring systems, calling into question current theories of how ring systems are formed.

The ring system is around a dwarf planet, named Quaoar, which is approximately half the size of Pluto and orbits the Sun beyond Neptune.

The discovery, published in Nature, was made by an international team of astronomers using HiPERCAM -- an extremely sensitive high-speed camera developed by scientists at the University of Sheffield which is mounted on the world's largest optical telescope, the 10.4 metre diameter Gran Telescopio Canarias (GTC) on La Palma.

The rings are too small and faint to see directly in an image. Instead, the researchers made their discovery by observing an occultation, when the light from a background star was blocked by Quaoar as it orbits the Sun. The event lasted less than a minute, but was unexpectedly preceded and followed by two dips in light, indicative of a ring system around Quaoar.

Ring systems are relatively rare in the Solar System -- as well as the well-known rings around the giant planets Saturn, Jupiter, Uranus and Neptune, only two other minor planets possess rings -- Chariklo and Haumea. All of the previously known ring systems are able to survive because they orbit close to the parent body, so that tidal forces prevent the ring material from accreting and forming moons.

What makes the ring system around Quaoar remarkable is that it lies at a distance of over seven planetary radii -- twice as far out as what was previously thought to be the maximum radius according to the so-called `Roche limit', which is the outer limit of where ring systems were thought to be able to survive. For comparison, the main rings around Saturn lie within three planetary radii. This discovery has therefore forced a rethink on theories of ring formation.

Professor Vik Dhillon, co-author of the study from the University of Sheffield's Department of Physics and Astronomy, said: "It was unexpected to discover this new ring system in our Solar System, and it was doubly unexpected to find the rings so far out from Quaoar, challenging our previous notions of how such rings form. The use of our high-speed camera -- HiPERCAM -- was key to this discovery as the event lasted less than one minute and the rings are too small and faint to see in a direct image.

"Everyone learns about Saturn's magnificent rings when they're a child, so hopefully this new finding will provide further insight into how they came to be."

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Modeling reveals how dwarf planet Ceres powers unexpected geologic activity

For a long time, our view of Ceres was fuzzy, said Scott King, a geoscientist in the Virginia Tech College of Science. A dwarf planet and the largest body found in the asteroid belt -- the region between Jupiter and Mars speckled with hundreds of thousands of asteroids -- Ceres had no distinguishable surface features in existing telescopic observations from Earth.

Then, in 2015, the hazy orb that was Ceres came into view. That view was stunning to scientists such as King. Data and images collected by NASA's Dawn mission gave a clearer picture of the surface, including its composition and structures, which revealed unexpected geologic activity.

Scientists had seen the general size of Ceres in earlier observations. It was so small it was assumed to be inactive. Instead, Dawn discovered a large plateau on one side of Ceres that covered a fraction of the dwarf planet, similar to what a continent might take up on Earth. Surrounding it were fractures in rocks clustered in one location. And there were visible traces of an ocean world: deposits all over the surface where minerals had condensed as water evaporated -- the mark of a freezing ocean.

A professor in the Department of Geosciences, King, who mostly studies larger bodies such as planets, wanted to know how a body as small as Ceres could generate the heat needed to power that kind of geological activity and account for the surface features picked up by Dawn.

Through modeling, he and a team of scientists from multiple universities as well as the United States Geological Survey and the Planetary Science Institute found that the decay of radioactive elements within Ceres's interior could keep it active. Their findings were recently published in American Geophysical Union Advances.

King's study of big planets such as Earth, Venus, and Mars had always shown him that planets start out hot. The collision between objects that form a planet creates that initial heat. Ceres, by contrast, never got big enough to become a planet and generate heat the same way, King said. To learn how it could still generate enough heat to power geologic activity, he used theories and computational tools previously applied to bigger planets to study Ceres's interior, and he looked for evidence that could support his models in data returned by the Dawn mission.

The team's model of the dwarf planet's interior showed a unique sequence: Ceres started out cold and heated up because of the decay of radioactive elements such as uranium and thorium -- which was alone enough to power its activity -- until the interior became unstable.

"What I would see in the model is, all of a sudden, one part of the interior would start heating up and would be moving upward and then the other part would be moving downward," King said.

That instability could explain some of the surface features that had formed on Ceres, as revealed by the Dawn mission. The large plateau had formed on only one side of Ceres with nothing on the other side, and the fractures were clustered in a single location around it. The concentration of features in one hemisphere signaled to King that instability had occurred and had left a visible impact.

"It turned out that you could show in the model that where one hemisphere had this instability that was rising up, it would cause extension at the surface, and it was consistent with these patterns of fractures," King said.

Based on the team's model, Ceres didn't follow a planet's typical pattern of hot first and cool second, with its own pattern of cool, hot, and cool again. "What we've shown in this paper is that radiogenic heating all on its own is enough to create interesting geology," King said.

He sees similarities to Ceres in the moons of Uranus, which a study commissioned by NASA and the National Science Foundation recently deemed high priority for a major robotic mission. With additional improvements to the model, he looks forward to exploring their interiors as well.

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Dwarf planet Vesta a window to the early solar system

The dwarf planet Vesta is helping scientists better understand the earliest era in the formation of our solar system. Two recent papers involving scientists from the University of California, Davis, use data from meteorites derived from Vesta to resolve the "missing mantle problem" and push back our knowledge of the solar system to just a couple of million years after it began to form. The papers were published in Nature Communications Sept. 14 and Nature Astronomy Sept. 30.

Vesta is the second-largest body in the asteroid belt at 500 kilometers across. It's big enough to have evolved in the same way as rocky, terrestrial bodies like the Earth, moon and Mars. Early on, these were balls of molten rock heated by collisions. Iron and the siderophiles, or 'iron-loving' elements such as rhenium, osmium, iridium, platinum and palladium sank to the center to form a metallic core, leaving the mantle poor in these elements. As the planet cooled, a thin solid crust formed over the mantle. Later, meteorites brought iron and other elements to the crust.

Most of the bulk of a planet like Earth is mantle. But mantle-type rocks are rare among asteroids and meteorites.

"If we look at meteorites, we have core material, we have crust, but we don't see mantle," said Qing-Zhu Yin, professor of earth and planetary sciences in the UC Davis College of Letters and Science. Planetary scientists have called this the "missing mantle problem."

In the recent Nature Communications paper, Yin and UC Davis graduate students Supratim Dey and Audrey Miller worked with first author Zoltan Vaci at the University of New Mexico to describe three recently discovered meteorites that do include mantle rock, called ultramafics that include mineral olivine as a major component. The UC Davis team contributed precise analysis of isotopes, creating a fingerprint that allowed them to identify the meteorites as coming from Vesta or a very similar body.

"This is the first time we've been able to sample the mantle of Vesta," Yin said. NASA's Dawn mission remotely observed rocks from the largest south pole impact crater on Vesta in 2011 but did not find mantle rock.

Probing the early solar system

Because it is so small, Vesta formed a solid crust long before larger bodies like the Earth, moon and Mars. So the siderophile elements that accumulated in its crust and mantle form a record of the very early solar system after core formation. Over time, collisions have broken pieces off Vesta that sometimes fall to Earth as meteorites.

Yin's lab at UC Davis had previously collaborated with an international team looking at elements in lunar crust to probe the early solar system. In the second paper, published in Nature Astronomy, Meng-Hua Zhu at the Macau University of Science and Technology, Yin and colleagues extended this work using Vesta.

"Because Vesta formed very early, it's a good template to look at the entire history of the Solar System," Yin said. "This pushes us back to two million years after the beginning of solar system formation."

It had been thought that Vesta and the larger inner planets could have got much of their material from the asteroid belt. But a key finding from the study was that the inner planets (Mercury, Venus, Earth and moon, Mars and inner dwarf planets) got most of their mass from colliding and merging with other large, molten bodies early in the solar system. The asteroid belt itself represents the leftover material of planet formation, but did not contribute much to the larger worlds.

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ESO telescope reveals what could be the smallest dwarf planet yet in the solar system

A new SPHERE/VLT image of Hygiea, which could be the Solar System's smallest dwarf planet yet. As an object in the main asteroid belt, Hygiea satisfies right away three of the four requirements to be classified as a dwarf planet: it orbits around the Sun, it is not a moon and, unlike a planet, it has not cleared the neighbourhood around its orbit. The final requirement is that it have enough mass that its own gravity pulls it into a roughly spherical shape. This is what VLT observations have now revealed about Hygiea.

Astronomers using ESO's SPHERE instrument at the Very Large Telescope (VLT) have revealed that the asteroid Hygiea could be classified as a dwarf planet. The object is the fourth largest in the asteroid belt after Ceres, Vesta and Pallas. For the first time, astronomers have observed Hygiea in sufficiently high resolution to study its surface and determine its shape and size. They found that Hygiea is spherical, potentially taking the crown from Ceres as the smallest dwarf planet in the Solar System.

As an object in the main asteroid belt, Hygiea satisfies right away three of the four requirements to be classified as a dwarf planet: it orbits around the Sun, it is not a moon and, unlike a planet, it has not cleared the neighbourhood around its orbit. The final requirement is that it has enough mass for its own gravity to pull it into a roughly spherical shape. This is what VLT observations have now revealed about Hygiea.

"Thanks to the unique capability of the SPHERE instrument on the VLT, which is one of the most powerful imaging systems in the world, we could resolve Hygiea's shape, which turns out to be nearly spherical," says lead researcher Pierre Vernazza from the Laboratoire d'Astrophysique de Marseille in France. "Thanks to these images, Hygiea may be reclassified as a dwarf planet, so far the smallest in the Solar System."

The team also used the SPHERE observations to constrain Hygiea's size, putting its diameter at just over 430 km. Pluto, the most famous of dwarf planets, has a diameter close to 2400 km, while Ceres is close to 950 km in size.

Surprisingly, the observations also revealed that Hygiea lacks the very large impact crater that scientists expected to see on its surface, the team report in the study published today in Nature Astronomy. Hygiea is the main member of one of the largest asteroid families, with close to 7000 members that all originated from the same parent body. Astronomers expected the event that led to the formation of this numerous family to have left a large, deep mark on Hygiea.

"This result came as a real surprise as we were expecting the presence of a large impact basin, as is the case on Vesta," says Vernazza. Although the astronomers observed Hygiea's surface with a 95% coverage, they could only identify two unambiguous craters. "Neither of these two craters could have been caused by the impact that originated the Hygiea family of asteroids whose volume is comparable to that of a 100 km-sized object. They are too small," explains study co-author Miroslav Bro? of the Astronomical Institute of Charles University in Prague, Czech Republic.

The team decided to investigate further. Using numerical simulations, they deduced that Hygiea's spherical shape and large family of asteroids are likely the result of a major head-on collision with a large projectile of diameter between 75 and 150 km. Their simulations show this violent impact, thought to have occurred about 2 billion years ago, completely shattered the parent body. Once the left-over pieces reassembled, they gave Hygiea its round shape and thousands of companion asteroids. "Such a collision between two large bodies in the asteroid belt is unique in the last 3-4 billion years," says Pavel Ševe?ek, a PhD student at the Astronomical Institute of Charles University who also participated in the study.

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Giant impact caused difference between Moon's hemispheres

Moon.

The stark difference between the Moon's heavily-cratered farside and the lower-lying open basins of the Earth-facing nearside has puzzled scientists for decades.

Now, new evidence about the Moon's crust suggests the differences were caused by a wayward dwarf planet colliding with the Moon in the early history of the solar system. A report on the new research has been published in AGU's Journal of Geophysical Research: Planets.

The mystery of the Moon's two faces began in the Apollo era when the first views of its farside revealed the surprising differences. Measurements made by the Gravity Recovery and Interior Laboratory (GRAIL) mission in 2012 filled in more details about the structure of the Moon -- including how its crust is thicker and includes an extra layer of material on its farside.

There are a number of ideas that have been used to try and explain the Moon's asymmetry. One is that there were once two moons orbiting Earth and they merged in the very early days of the Moon's formation. Another idea is that a large body, perhaps a young dwarf planet, found itself in an orbit around the Sun that put it on a collision course with the Moon. This latter giant impact idea would have happened somewhat later than a merging-moons scenario and after the Moon had formed a solid crust, said Meng Hua Zhu of the Space Science Institute at Macau University of Science and Technology and lead author of the new study. Signs of such an impact should be visible in the structure of the lunar crust today.

"The detailed gravity data obtained by GRAIL has given new insight into the structure of the lunar crust underneath the surface," Zhu said.

The new findings from GRAIL gave Zhu's team of researchers a clearer target to aim for with the computer simulations they used to test different early-Moon impact scenarios. The study's authors ran 360 computer simulations of giant impacts with the Moon to find out whether such an event millions of years ago could reproduce the crust of today's Moon as detected by GRAIL.

They found the best fit for today's asymmetrical Moon is a large body, about 480 miles (780 kilometers) in diameter, smacking into the nearside of the Moon at 14,000 miles per hour (22,500 kilometers per hour). That would be the equivalent of an object a bit smaller than the dwarf planet Ceres moving at a speed about one-quarter as fast as the meteor pebbles and sand grains that burn up as "shooting stars" in Earth's atmosphere. Another good fit for the impact combinations the team modeled is a slightly smaller, 450-mile (720-kilometer) diameter, object hitting at a mildly faster 15,000 miles per hour (24,500 kilometers per hour).

Under both these scenarios, the model shows the impact would have thrown up vast amounts of material that would fall back on the Moon's surface, burying the primordial crust on the farside in 3 to 6 miles (5 to 10 kilometers) of debris. That is the added layer of crust detected on the farside by GRAIL, according to Zhu.

The new study suggests the impactor was not likely an early second moon of Earth's. Whatever the impactor was -- an asteroid or a dwarf planet -- it was probably on its own orbit around the Sun when it encountered the Moon, said Zhu.

The giant impact model also provides a good explanation for the unexplained differences in isotopes of potassium, phosphorus and rare-earth elements like tungsten-182 between the surfaces of the Earth and Moon, the researchers explain. These elements could have come from the giant impact, which would have added that material to the Moon after its formation, according to the study's authors.

"Our model can thus explain this isotope anomaly in the context of the giant impact scenario of the Moon's origin." the researchers write.

The new study not only suggests an answer to ongoing questions about the Moon, but may also provide insight into the structure of other asymmetrical worlds in our solar system like Mars wrote the researchers.

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Pluto should be reclassified as a planet, experts say

Should Pluto be reclassified a planet again? UCF scientist Philip Metzger says yes based on his research.

The reason Pluto lost its planet status is not valid, according to new research from the University of Central Florida in Orlando.

In 2006, the International Astronomical Union, a global group of astronomy experts, established a definition of a planet that required it to "clear" its orbit, or in other words, be the largest gravitational force in its orbit.

Since Neptune's gravity influences its neighboring planet Pluto, and Pluto shares its orbit with frozen gases and objects in the Kuiper belt, that meant Pluto was out of planet status. However, in a new study published online Wednesday in the journal Icarus, UCF planetary scientist Philip Metzger, who is with the university's Florida Space Institute, reported that this standard for classifying planets is not supported in the research literature.

Metzger, who is lead author on the study, reviewed scientific literature from the past 200 years and found only one publication -- from 1802 -- that used the clearing-orbit requirement to classify planets, and it was based on since-disproven reasoning.

He said moons such as Saturn's Titan and Jupiter's Europa have been routinely called planets by planetary scientists since the time of Galileo.

"The IAU definition would say that the fundamental object of planetary science, the planet, is supposed to be a defined on the basis of a concept that nobody uses in their research," Metzger said. "And it would leave out the second-most complex, interesting planet in our solar system." "We now have a list of well over 100 recent examples of planetary scientists using the word planet in a way that violates the IAU definition, but they are doing it because it's functionally useful," he said. "It's a sloppy definition," Metzger said of the IAU's definition. "They didn't say what they meant by clearing their orbit. If you take that literally, then there are no planets, because no planet clears its orbit."

The planetary scientist said that the literature review showed that the real division between planets and other celestial bodies, such as asteroids, occurred in the early 1950s when Gerard Kuiper published a paper that made the distinction based on how they were formed.

However, even this reason is no longer considered a factor that determines if a celestial body is a planet, Metzger said.

Study co-author Kirby Runyon, with Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, said the IAU's definition was erroneous since the literature review showed that clearing orbit is not a standard that is used for distinguishing asteroids from planets, as the IAU claimed when crafting the 2006 definition of planets.

"We showed that this is a false historical claim," Runyon said. "It is therefore fallacious to apply the same reasoning to Pluto," he said. Metzger said that the definition of a planet should be based on its intrinsic properties, rather than ones that can change, such as the dynamics of a planet's orbit. "Dynamics are not constant, they are constantly changing," Metzger said. "So, they are not the fundamental description of a body, they are just the occupation of a body at a current era."

Instead, Metzger recommends classifying a planet based on if it is large enough that its gravity allows it to become spherical in shape.

"And that's not just an arbitrary definition, Metzger said. "It turns out this is an important milestone in the evolution of a planetary body, because apparently when it happens, it initiates active geology in the body."

Pluto, for instance, has an underground ocean, a multilayer atmosphere, organic compounds, evidence of ancient lakes and multiple moons, he said.

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Martian moons model indicates formation following large impact

This composite image compares how big the moons of Mars appear, as seen from the surface of the Red Planet, in relation to the size that our Moon appears from Earth’s surface. While Earth’s Moon is 100 times bigger than the larger Martian moon Phobos, the Martian moons orbit much closer to their planet, making them appear relatively larger in the sky. Deimos, at far left, and Phobos, beside it, are shown together as photographed by NASA’s Mars rover Curiosity on Aug. 1, 2013.

Southwest Research Institute scientists posit a violent birth of the tiny Martian moons Phobos and Deimos, but on a much smaller scale than the giant impact thought to have resulted in the Earth-Moon system. Their work shows that an impact between proto-Mars and a dwarf-planet-sized object likely produced the two moons, as detailed in a paper published today in Science Advances.

The origin of the Red Planet's small moons has been debated for decades. The question is whether the bodies were asteroids captured intact by Mars gravity or whether the tiny satellites formed from an equatorial disk of debris, as is most consistent with their nearly circular and co-planar orbits. The production of a disk by an impact with Mars seemed promising, but prior models of this process were limited by low numerical resolution and overly simplified modeling techniques.

"Ours is the first self-consistent model to identify the type of impact needed to lead to the formation of Mars' two small moons," said lead author Dr. Robin Canup, an associate vice president in the SwRI Space Science and Engineering Division. Canup is one of the leading scientists using large-scale hydrodynamical simulations to model planet-scale collisions, including the prevailing Earth-Moon formation model.

"A key result of the new work is the size of the impactor; we find that a large impactor -- similar in size to the largest asteroids Vesta and Ceres -- is needed, rather than a giant impactor," Canup said. "The model also predicts that the two moons are derived primarily from material originating in Mars, so their bulk compositions should be similar to that of Mars for most elements. However, heating of the ejecta and the low escape velocity from Mars suggests that water vapor would have been lost, implying that the moons will be dry if they formed by impact."

The new Mars model invokes a much smaller impactor than considered previously. Our Moon may have formed when a Mars-sized object crashed into the nascent Earth 4.5 billion years ago, and the resulting debris coalesced into the Earth-Moon system. The Earth's diameter is about 8,000 miles, while Mars' diameter is just over 4,200 miles. The Moon is just over 2,100 miles in diameter, about one-fourth the size of Earth.

While they formed in the same timeframe, Deimos and Phobos are very small, with diameters of only 7.5 miles and 14 miles respectively, and orbit very close to Mars. The proposed Phobos-Deimos forming impactor would be between the size of the asteroid Vesta, which has a diameter of 326 miles, and the dwarf planet Ceres, which is 587 miles wide.

"We used state-of-the-art models to show that a Vesta-to-Ceres-sized impactor can produce a disk consistent with the formation of Mars' small moons," said the paper's second author, Dr. Julien Salmon, an SwRI research scientist. "The outer portions of the disk accumulate into Phobos and Deimos, while the inner portions of the disk accumulate into larger moons that eventually spiral inward and are assimilated into Mars. Larger impacts advocated in prior works produce massive disks and more massive inner moons that prevent the survival of tiny moons like Phobos and Deimos."

These findings are important for the Japan Aerospace Exploration Agency (JAXA) Mars Moons eXploration (MMX) mission, which is planned to launch in 2024 and will include a NASA-provided instrument. The MMX spacecraft will visit the two Martian moons, land on the surface of Phobos and collect a surface sample to be returned to Earth in 2029.

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Pluto's hydrocarbon haze keeps dwarf planet colder than expected

Pluto's haze layer is blue in this image taken by the New Horizons Ralph/Multispectral Visible Imaging Camera and computer generated to replicate true color. Haze is produced by sunlight-initiated chemical reactions of nitrogen and methane, leading to small particles that grow and settle toward the surface.

The gas composition of a planet's atmosphere generally determines how much heat gets trapped in the atmosphere. For the dwarf planet Pluto, however, the predicted temperature based on the composition of its atmosphere was much higher than actual measurements taken by NASA's New Horizons spacecraft in 2015.

A new study published November 16 in Nature proposes a novel cooling mechanism controlled by haze particles to account for Pluto's frigid atmosphere.

"It's been a mystery since we first got the temperature data from New Horizons," said first author Xi Zhang, assistant professor of Earth and planetary sciences at UC Santa Cruz. "Pluto is the first planetary body we know of where the atmospheric energy budget is dominated by solid-phase haze particles instead of by gases."

The cooling mechanism involves the absorption of heat by the haze particles, which then emit infrared radiation, cooling the atmosphere by radiating energy into space. The result is an atmospheric temperature of about 70 Kelvin (minus 203 degrees Celsius, or minus 333 degrees Fahrenheit), instead of the predicted 100 Kelvin (minus 173 Celsius, or minus 280 degrees Fahrenheit).

According to Zhang, the excess infrared radiation from haze particles in Pluto's atmosphere should be detectable by the James Webb Space Telescope, allowing confirmation of his team's hypothesis after the telescope's planned launch in 2019.

Extensive layers of atmospheric haze can be seen in images of Pluto taken by New Horizons. The haze results from chemical reactions in the upper atmosphere, where ultraviolet radiation from the sun ionizes nitrogen and methane, which react to form tiny hydrocarbon particles tens of nanometers in diameter. As these tiny particles sink down through the atmosphere, they stick together to form aggregates that grow larger as they descend, eventually settling onto the surface.

"We believe these hydrocarbon particles are related to the reddish and brownish stuff seen in images of Pluto's surface," Zhang said.

The researchers are interested in studying the effects of haze particles on the atmospheric energy balance of other planetary bodies, such as Neptune's moon Triton and Saturn's moon Titan. Their findings may also be relevant to investigations of exoplanets with hazy atmospheres.

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Scientists dig into the origin of organics on dwarf planet Ceres

SwRI scientists are studying the geology associated with the organic-rich areas on Ceres. Dawn spacecraft data show a region around the Ernutet crater where organic concentrations have been discovered (background image). The color coding shows the surface concentration of organics, as inferred from the visible and near infrared spectrometer. The inset shows a higher resolution enhanced color image of the Ernutet crater acquired by Dawn’s framing camera. Regions in red indicate higher concentration of organics.

Since NASA's Dawn spacecraft detected localized organic-rich material on Ceres, Southwest Research Institute (SwRI) has been digging into the data to explore different scenarios for its origin. After considering the viability of comet or asteroid delivery, the preponderance of evidence suggests the organics are most likely native to Ceres.

"The discovery of a locally high concentration of organics close to the Ernutet crater poses an interesting conundrum," said Dr. Simone Marchi, a principal scientist at SwRI. He is discussing his team findings today at a press conference at the American Astronomical Society's 49th Division for Planetary Sciences Meeting in Provo. "Was the organic material delivered to Ceres after its formation? Or was it synthesized and/or concentrated in a specific location on Ceres via internal processes? Both scenarios have shortfalls, so we may be missing a critical piece of the puzzle."

Ceres is believed to have originated about 4.5 billion years ago at the dawn of our solar system. Studying its organics can help explain the origin, evolution, and distribution of organic species across the solar system. The very location of Ceres at the boundary between the inner and outer solar system and its intriguing composition characterized by clays, sodium- and ammonium-carbonates, suggest a very complex chemical evolution. The role of organics in this evolution is not fully understood, but has important astrobiological implications.

"Earlier research that focused on the geology of the organic-rich region on Ceres were inconclusive about their origin," Marchi said. "Recently, we more fully investigated the viability of organics arriving via an asteroid or comet impact."

Scientists explored a range of impact parameters, such as impactor sizes and velocities, using iSALE shock physics code simulations. These models indicated that comet-like projectiles with relatively high impact velocities would lose almost all of their organics due to shock compression. Impacting asteroids, with lower incident velocities, can retain between 20 and 30 percent of their pre-impact organic material during delivery, especially for small impactors at oblique impact angles. However, the localized spatial distribution of organics on Ceres seems difficult to reconcile with delivery from small main belt asteroids.

"These findings indicate that the organics are likely to be native to Ceres," Marchi said.

From Science Daily

Moon orbits third largest dwarf planet in our solar system

These two images, taken a year apart, reveal a moon orbiting the dwarf planet 2007 OR10. Each image, taken by the Hubble Space Telescope's Wide Field Camera 3, shows the companion in a different orbital position around its parent body. 2007 OR10 is the third-largest known dwarf planet, behind Pluto and Eris, and the largest unnamed world in the solar system. The pair is located in the Kuiper Belt, a realm of icy debris left over from the solar system's formation.

The combined power of three space observatories, including NASA's Hubble Space Telescope, has helped astronomers uncover a moon orbiting the third largest dwarf planet, catalogued as 2007 OR10. The pair resides in the frigid outskirts of our solar system called the Kuiper Belt, a realm of icy debris left over from our solar system's formation 4.6 billion years ago.

With this discovery, most of the known dwarf planets in the Kuiper Belt larger than 600 miles across have companions. These bodies provide insight into how moons formed in the young solar system.

"The discovery of satellites around all of the known large dwarf planets -- except for Sedna -- means that at the time these bodies formed billions of years ago, collisions must have been more frequent, and that's a constraint on the formation models," said Csaba Kiss of the Konkoly Observatory in Budapest, Hungary. He is the lead author of the science paper announcing the moon's discovery. "If there were frequent collisions, then it was quite easy to form these satellites."

The objects most likely slammed into each other more often because they inhabited a crowded region. "There must have been a fairly high density of objects, and some of them were massive bodies that were perturbing the orbits of smaller bodies," said team member John Stansberry of the Space Telescope Science Institute in Baltimore, Maryland. "This gravitational stirring may have nudged the bodies out of their orbits and increased their relative velocities, which may have resulted in collisions."

But the speed of the colliding objects could not have been too fast or too slow, according to the astronomers. If the impact velocity was too fast, the smash-up would have created lots of debris that could have escaped from the system; too slow and the collision would have produced only an impact crater.

Collisions in the asteroid belt, for example, are destructive because objects are traveling fast when they smash together. The asteroid belt is a region of rocky debris between the orbits of Mars and the gas giant Jupiter. Jupiter's powerful gravity speeds up the orbits of asteroids, generating violent impacts.

The team uncovered the moon in archival images of 2007 OR10 taken by Hubble's Wide Field Camera 3. Observations taken of the dwarf planet by NASA's Kepler Space Telescope first tipped off the astronomers of the possibility of a moon circling it. Kepler revealed that 2007 OR10 has a slow rotation period of 45 hours. "Typical rotation periods for Kuiper Belt Objects are under 24 hours," Kiss said. "We looked in the Hubble archive because the slower rotation period could have been caused by the gravitational tug of a moon. The initial investigator missed the moon in the Hubble images because it is very faint."

The astronomers spotted the moon in two separate Hubble observations spaced a year apart. The images show that the moon is gravitationally bound to 2007 OR10 because it moves with the dwarf planet, as seen against a background of stars. However, the two observations did not provide enough information for the astronomers to determine an orbit.

"Ironically, because we don't know the orbit, the link between the satellite and the slow rotation rate is unclear," Stansberry said.

The astronomers calculated the diameters of both objects based on observations in far-infrared light by the Herschel Space Observatory, which measured the thermal emission of the distant worlds. The dwarf planet is about 950 miles across, and the moon is estimated to be 150 miles to 250 miles in diameter. 2007 OR10, like Pluto, follows an eccentric orbit, but it is currently three times farther than Pluto is from the sun.

Read more at Science Daily

Distant Dwarf Planet DeeDee Stirs Up the Pluto Planethood Debate

Artist concept of the planetary body 2014 UZ224, more informally known as DeeDee. ALMA was able to observe the faint millimeter-wavelength "glow" emitted by the object, confirming it is roughly 635 kilometers across. At this size, DeeDee should have enough mass to be spherical, the criterion necessary for astronomers to consider it a dwarf planet, though it has yet to receive that official designation.

What's a planet? What's a dwarf planet? Should we make a distinction? Should we really care about these definitions in the first place?

As we learn more about the outer solar system, the boundaries begin to blur.

A tiny celestial body called 2014 UZ224 and informally known as DeeDee (for “distant dwarf”) is a distant world about 92 astronomical units, or Earth-sun distances, from our sun. Recent observations from the Atacama Large Millimeter/submillimeter Array (ALMA) revealed that DeeDee is roughly 395 miles (635 kilometers) across, which would give it enough mass to be spherical.

Why does it matter if DeeDee is round? In 2006, a controversial vote by the International Astronomical Union defined three parameters for a planet. Simply speaking, the IAU says a planet must be in orbit around the sun, have enough mass to be round, and have cleared the neighborhood around its orbit — meaning it needs to be gravitationally dominant and hold any nearby bodies within its orbit.

Size comparisons of objects in our solar system, including the recently discovered planetary body "DeeDee."

It's the last part of the definition that most aggravates those who argue that Pluto – redefined as a "dwarf" planet under the IAU – is more planet than not. The argument is that the rocky planets of Earth, Mars, Venus, and Mercury have also not cleared their neighborhoods, as many asteroids co-orbit along with them.

The planetary geologist Kirby Runyon, a Ph.D. student at the Johns Hopkins University Applied Physics Laboratory, wrote a paper this year proposing a geophysical-based definition of a planet that would dispense with the orbital criterion and basically include any round celestial body that isn’t a star. The idea hatched by Runyon and his co-authors — which include Alan Stern, the principal investigator of the New Horizons mission to Pluto — would increase the number of purported planets in our solar system to over 110, including Earth’s moon and DeeDee.

"What it's really showing is the diversity of planets in our solar system,” said Runyon of the DeeDee news, “and giving us a better understanding of planets in the rest of the galaxy.”

"DeeDee is almost certainly made out of ices — water ices, methane, and carbon dioxide — which is similar to what Pluto is made of," he added. "These are very soft materials, compared with rocky silicate. It's more easily pulled into a sphere than rock or metal."

Orbits of objects in our solar system, showing the current location of the planetary body "DeeDee."

Adding more fodder to the debate over the definition, when the New Horizons spacecraft flew by Pluto in 2015, it unveiled a world of surprising complexity, ranging from mountainous areas to vast nitrogen-ice lakes.

"We call Pluto a 'dwarf' planet, but it's just an adjective for 'planet,’” Runyon said. “It's still a planet, and that's where we take umbrage with the IAU.”

"Astronomers aren't experts in planetary science, and they basically passed a bunch of B.S. off on the public back in 2006 with a planet classification so flawed that it rules the Earth out as a planet, too," Stern remarked in 2016. "A week later, hundreds of planetary scientists, more people than at the IAU vote, signed a petition that rejects the new definition. If you go to planetary science meetings and hear technical talks on Pluto, you will hear experts calling it a planet every day."

Read more at Discovery News

Meet 'DeeDee,' a distant, dim member of our solar system

Artist concept of the planetary body 2014 UZ224, more informally known as DeeDee. ALMA was able to observe the faint millimeter-wavelength "glow" emitted by the object, confirming it is roughly 635 kilometers across. At this size, DeeDee should have enough mass to be spherical, the criteria necessary for astronomers to consider it a dwarf planet, though it has yet to receive that official designation.

Using the Atacama Large Millimeter/submillimeter Array (ALMA), astronomers have revealed extraordinary details about a recently discovered far-flung member of our solar system, the planetary body 2014 UZ224, more informally known as DeeDee.

At about three times the current distance of Pluto from the Sun, DeeDee is the second most distant known trans-Neptunian object (TNO) with a confirmed orbit, surpassed only by the dwarf planet Eris. Astronomers estimate that there are tens-of-thousands of these icy bodies in the outer solar system beyond the orbit of Neptune.

The new ALMA data reveal, for the first time, that DeeDee is roughly 635 kilometers across, or about two-thirds the diameter of the dwarf planet Ceres, the largest member of our asteroid belt. At this size, DeeDee should have enough mass to be spherical, the criteria necessary for astronomers to consider it a dwarf planet, though it has yet to receive that official designation.

"Far beyond Pluto is a region surprisingly rich with planetary bodies. Some are quite small but others have sizes to rival Pluto, and could possibly be much larger," said David Gerdes, a scientist with the University of Michigan and lead author on a paper appearing in the Astrophysical Journal Letters. "Because these objects are so distant and dim, it's incredibly difficult to even detect them, let alone study them in any detail. ALMA, however, has unique capabilities that enabled us to learn exciting details about these distant worlds."

Currently, DeeDee is about 92 astronomical units (AU) from the Sun. An astronomical unit is the average distance from Earth to the Sun, or about 150 million kilometers. At this tremendous distance, it takes DeeDee more than 1,100 years to complete one orbit. Light from DeeDee takes nearly 13 hours to reach Earth.

Gerdes and his team announced the discovery of DeeDee in the fall of 2016. They found it using the 4-meter Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile as part of ongoing observations for the Dark Energy Survey, an optical survey of about 12 percent of the sky that seeks to understand the as-yet mysterious force that is accelerating the expansion of the universe.

The Dark Energy Survey produces vast troves of astronomical images, which give astronomers the opportunity to also search for distant solar system objects. The initial search, which includes nearly 15,000 images, identified more than 1.1 billion candidate objects. The vast majority of these turned out to be background stars and even more distant galaxies. A small fraction, however, were observed to move slowly across the sky over successive observations, the telltale sign of a TNO.

One such object was identified on 12 separate images. The astronomers informally dubbed it DeeDee, which is short for Distant Dwarf.

The optical data from the Blanco telescope enabled the astronomers to measure DeeDee's distance and orbital properties, but they were unable to determine its size or other physical characteristics. It was possible that DeeDee was a relatively small member of our solar system, yet reflective enough to be detected from Earth. Or, it could be uncommonly large and dark, reflecting only a tiny portion of the feeble sunlight that reaches it; both scenarios would produce identical optical data.

Since ALMA observes the cold, dark universe, it is able to detect the heat -- in the form of millimeter-wavelength light -- emitted naturally by cold objects in space. The heat signature from a distant solar system object would be directly proportional to its size.

"We calculated that this object would be incredibly cold, only about 30 degrees Kelvin, just a little above absolute zero," said Gerdes.

While the reflected visible light from DeeDee is only about as bright as a candle seen halfway the distance to the moon, ALMA was able to quickly home in on the planetary body's heat signature and measure its brightness in millimeter-wavelength light.

This allowed astronomers to determine that it reflects only about 13 percent of the sunlight that hits it. That is about the same reflectivity of the dry dirt found on a baseball infield.

By comparing these ALMA observations to the earlier optical data, the astronomers had the information necessary to calculate the object's size. "ALMA picked it up fairly easily," said Gerdes. "We were then able to resolve the ambiguity we had with the optical data alone."

Objects like DeeDee are cosmic leftovers from the formation of the solar system. Their orbits and physical properties reveal important details about the formation of planets, including Earth.

This discovery is also exciting because it shows that it is possible to detect very distant, slowly moving objects in our own solar system. The researchers note that these same techniques could be used to detect the hypothesized "Planet Nine" that may reside far beyond DeeDee and Eris.

Read more at Science Daily

Prickly Pluto Could Reveal Ice Spikes Are Common on Other Worlds

When New Horizons whizzed by Pluto in 2015, images from the spacecraft revealed a geologist's dream. Icy mountains, a nitrogen glacier and a surprisingly youthful surface changed our notions of the distant dwarf planet forever. And even 18 months after the flyby, discoveries continue to pour in as scientists analyze the treasure trove of data.

The latest Pluto finding is evidence of features called "penitentes" — if confirmed this would be the first time these icy formations have been found beyond Earth. On our home planet, we know these icy spikes can grow up to several feet tall. They form in high-altitude environments, where the atmosphere is thinner and melting ice moves directly to vapor without a liquid phase in between. This sublimation (as the process is called) leaves bowl-shaped depressions behind.

But that's not all. John Moores, the lead author of the discovery paper in the journal Nature, says these features may well be in other locations across the solar system. Jupiter's Europa, for example, is a prime suspect given that radar signatures from the Galileo spacecraft suggest they could be there. But he says penitentes may even lurk in more familiar realms — even on Mars.

"We want to investigate other places in the solar system, or perhaps other solar systems, where you expect these features to show up," said Moores, who is with Canada's York University. He pointed out that penitentes may even lurk below the resolution of photos we took at planets and moons in the past. "If they were to be small, they may be in places we feel we already understand."

This is "bladed terrain" on Pluto seen by the New Horizons Ralph/Multispectral Visual Imaging Camera. Images of the dwarf planet appear to show terrain consistent with a feature called penitentes

Regardless of whether penitentes are common — or unique to Earth and Pluto — the find on the dwarf planet shows some remarkable characteristics. Pluto's penitentes are made of methane ice, while on Earth they're composed of water ice. Pluto's are more widely spread apart than what we find on Earth, where Moores says graduate students have trouble clambering among the spikes. On Pluto, by contrast, it appears the features are separated by a couple of miles. So there's plenty of room to set down a lander if we wanted.

What's more, the penitentes suggest that Pluto had calm atmospheric conditions over long periods of time, perhaps tens of millions of years. Regularly spaced and shaped penitentes, like what we see on Pluto, require an atmosphere; irregularly ones could develop where no substantial atmosphere is present, like Europa. Pluto's atmosphere expands and collapses as it gets further and closer from the sun in its nearly 248-year orbit. From numerical models, the team suggests that the penitentes could start growing (and continue developing) given warm enough atmospheric conditions for just a few years at a time.

Read more at Discovery News

Charon Is Pluto's First Line of Defense Against Solar Wind Onslaught

Space weather can be a nightmare for planetary atmospheres, particularly for ones that don't have a magnetic field to protect them — unlike Earth's, which has a powerful magnetosphere acting as a shield. It might therefore be strange to hear that dwarf planet Pluto, which isn't known for its powerful global magnetic field, is able to possess an atmosphere at all. But like other planets in the solar system, the sun erodes Pluto's atmosphere — albeit at a slower rate than expected.

Although astronomical measurements detected the presence of an atmosphere at Pluto long before the NASA New Horizons flyby in July 2015, very little was known about how much was being eroded into space by the continuous stream of solar wind particles. New Horizons measurements, however, proved that the rate of atmospheric loss was 100 times less than expected and, in new research published this week in the journal Icarus, researchers think they know what might be protecting Pluto's tenuous atmospheric gases.

Researchers from Georgia Institute of Technology have shown that when Charon orbits between Pluto and the sun, its presence can modify the dwarf planet's bow shock — a standing shock wave that appears "upstream" of Pluto as the solar wind particles encounter Pluto's thin atmosphere, like the wave that roils in front of a boat's bow when it powers through water — thereby shielding Pluto's atmosphere for a short time. Charon maximizes this protection should it also have an atmosphere, but its protective impact is minimal when it either doesn't have an atmosphere or when it is positioned "downstream" of Pluto.

As Pluto and Charon orbit so close to one another, the pair are believed to share atmospheric gases and when Charon passes behind Pluto particles originating from Pluto are deposited at the moon's poles, appearing as a dark brown deposit in New Horizons observations.

As Pluto is located so far away from the sun in the Kuiper Belt, the impact of the solar wind is much lower than its impact on planets closer to the sun. The space weather impact has been reduced even further with the help of Charon.

"As a result, Pluto still has more of its volatile elements, which have long since been blown off the inner planets by solar wind," said Georgia Tech student John Hale. "Even at its great distance from the sun, Pluto is slowly losing its atmosphere. Knowing the rate at which Pluto's atmosphere is being lost can tell us how much atmosphere it had to begin with, and therefore what it looked like originally. From there, we can get an idea of what the solar system was made of during its formation."

As Pluto and Charon orbit so close, and Charon is roughly half the size of its dwarf planet buddy, the pair orbit a common point in space known as the "barycenter." This orbital oddity added fuel to the debate as to whether Pluto should be called a dwarf planet, or whether Pluto and Charon should be designated a "binary planet." Now, with more findings about the pair's atmospheric interactions, it could be argued that the case for calling Pluto a binary planet is as valid as ever.

From Discovery News

Oddball Ceres Hides Huge Reservoirs of Water Ice

Ceres and Vesta, the two largest bodies in the main asteroid belt, may be contemporaries and neighbors, but the similarities stop there. Ceres, which is about as wide as Texas, is filled with frozen water and hydrated minerals, making it more like an icy moon of Jupiter or Saturn than Vesta, its dry, rocky sibling, new research shows.

Scientists aren't sure why Ceres and Vesta followed such different evolutionary paths, but they expect more answers as analysis of data collected by NASA's Dawn spacecraft continues. Dawn spent 14 months visiting Vesta before firing up its ion engine and settling into orbit around Ceres in March 2015.

Research published in this week's issues of Science and Nature Astronomy confirms a 30-year-old theory that Ceres is an ice-rich world.

"In Ceres' crust today we think we see about 10 percent (by weight) water ice," Dawn scientist Thomas Prettyman, with the Planetary Science Institute in Tucson, Arizona, told Seeker.

But water in the crust is just the beginning of the story. Ceres is replete with minerals and clays that can only form in the presence of water. Extrapolating from measurements made by Dawn, Prettyman estimates that the dwarf planet as a whole is 30 percent water.

Vesta had a different history, one that did not involve much water.

"What happened to Vesta is that it completely melted," Prettyman said.

Once its radioactive elements decayed, Vesta, made mostly of silicates, cooled and formed a basaltic crust, a mantle and an iron-rich core.

"This would have had to happen close to the sun, where you couldn't condense volatiles like water because it was too hot," Prettyman added.

Perhaps because Ceres was bigger than Vesta, or positioned farther from the sun, but it was able to accrete water into its body, setting the stage for a cascade of chemical alterations. Some models show that the separation of water and rock caused Ceres to form a frozen shell over a briny liquid layer that may still exist today.

"The Dawn mission is trying to look back in time to the very earliest stage of the solar system," deputy principal investigator Carol Raymond, with NASA's Jet Propulsion Laboratory in Pasadena, Calif., told reporters at the American Geophysical Union conference in San Francisco.

Of particular interest, she added, is if Ceres' water and rock interacted in such a way that the dwarf planet became chemically suited for life.

Read more at Discovery News

New views of dwarf planet Ceres as Dawn moves higher

Occator Crater, home of Ceres' intriguing brightest areas, is prominently featured in this image from NASA's Dawn spacecraft.

The brightest area on Ceres stands out amid shadowy, cratered terrain in a dramatic new view from NASA's Dawn spacecraft, taken as it looked off to the side of the dwarf planet. Dawn snapped this image on Oct. 16, from its fifth science orbit, in which the angle of the sun was different from that in previous orbits. Dawn was about 920 miles (1,480 kilometers) above Ceres when this image was taken -- an altitude the spacecraft had reached in early October.

Occator Crater, with its central bright region and secondary, less-reflective areas, appears quite prominent near the limb, or edge, of Ceres. At 57 miles (92 kilometers) wide and 2.5 miles (4 kilometers) deep, Occator displays evidence of recent geologic activity. The latest research suggests that the bright material in this crater is composed of salts left behind after a briny liquid emerged from below, froze and then sublimated, meaning it turned from ice into vapor.

The impact that formed the crater millions of years ago unearthed material that blanketed the area outside the crater, and may have triggered the upwelling of salty liquid.

"This image captures the wonder of soaring above this fascinating, unique world that Dawn is the first to explore," said Marc Rayman, Dawn's chief engineer and mission director, based at NASA's Jet Propulsion Laboratory, Pasadena, California.

Dawn scientists also have released an image of Ceres that approximates how the dwarf planet's colors would appear to the human eye. This view, produced by the German Aerospace Center in Berlin, combines images taken from Dawn's first science orbit in 2015, using the framing camera's red, green and blue filters. The color was calculated based on the way Ceres reflects different wavelengths of light.

The spacecraft has gathered tens of thousands of images and other information from Ceres since arriving in orbit on March 6, 2015. After spending more than eight months studying Ceres at an altitude of about 240 miles (385 kilometers), closer than the International Space Station is to Earth, Dawn headed for a higher vantage point in August. In October, while the spacecraft was at its 920-mile altitude, it returned images and other valuable insights about Ceres.

On Nov. 4, Dawn began making its way to a sixth science orbit, which will be over 4,500 miles (7,200 kilometers) from Ceres. While Dawn needed to make several changes in its direction while spiraling between most previous orbits at Ceres, engineers have figured out a way for the spacecraft to arrive at this next orbit while the ion engine thrusts in the same direction that Dawn is already going. This uses less hydrazine and xenon fuel than Dawn's normal spiral maneuvers. Dawn should reach this next orbit in early December.

One goal of Dawn's sixth science orbit is to refine previously collected measurements. The spacecraft's gamma ray and neutron spectrometer, which has been investigating the composition of Ceres' surface, will characterize the radiation from cosmic rays unrelated to Ceres. This will allow scientists to subtract "noise" from measurements of Ceres, making the information more precise.

The spacecraft is healthy as it continues to operate in its extended mission phase, which began in July. During the primary mission, Dawn orbited and accomplished all of its original objectives at Ceres and protoplanet Vesta, which the spacecraft visited from July 2011 to September 2012.

Read more at Science Daily

Cracked, frozen and tipped over: New clues from Pluto's past

In this image of Pluto taken by NASA's New Horizons spacecraft, different colors represent different compositions of surface ices, revealing a surprisingly active body.

Sputnik Planitia, a 1,000-kilometer-wide basin within the iconic heart-shaped region observed on Pluto's surface, could be in its present location because accumulation of ice made the dwarf planet roll over, creating cracks and tensions in the crust that point toward the presence of a subsurface ocean.

Published in the Nov. 17 issue of Nature, these are the conclusions of research by James Keane, a doctoral student at the University of Arizona's Lunar and Planetary Laboratory, and his adviser, assistant professor Isamu Matsuyama. They propose evidence of frozen nitrogen pileup throwing the entire planet off kilter, much like a spinning top with a wad of gum stuck to it, in a process called true polar wander.

"There are two ways to change the spin of a planet," Keane said. "The first -- and the one we're all most familiar with -- is a change in the planet's obliquity, where the spin axis of the planet is reorienting with respect to the rest of the solar system. The second way is through true polar wander, where the spin axis remains fixed with respect to the rest of the solar system, but the planet reorients beneath it."

Planets like to spin in such a way that minimizes energy. In short, this means that planets like to reorient to place any extra mass closer to the equator -- and any mass deficits closer to the pole. For example, if a giant volcano were to grow on Los Angeles, Earth would reorient itself to place L.A. on the equator.

To understand polar wander on Pluto, one first has to realize that unlike Earth, whose spin axis is only slightly tilted so that the regions around the equator receive the most sunlight, Pluto is like a spinning top lying on its side. Therefore, the planet's poles get the most sunlight. Depending on the season, it's either one or the other, while Pluto's equatorial regions are extremely cold, all the time.

Because Pluto is almost 40 times farther from the sun than we are, it takes the little ball of rock and ice 248 Earth-years to complete one of its own years. At Pluto's lower latitudes near the equator, temperatures are almost as cold as minus 400 degrees Fahrenheit -- cold enough to turn nitrogen into a frozen solid.

Over the course of a Pluto year, nitrogen and other exotic gases condense on the permanently shadowed regions, and eventually, as Pluto goes around the sun, those frozen gases heat up, become gaseous again and re-condense on the other side of the planet, resulting in seasonal "snowfall" on Sputnik Planitia.

"Each time Pluto goes around the sun, a bit of nitrogen accumulates in the heart," Keane said. "And once enough ice has piled up, maybe a hundred meters thick, it starts to overwhelm the planet's shape, which dictates the planet's orientation. And if you have an excess of mass in one spot on the planet, it wants to go to the equator. Eventually, over millions of years, it will drag the whole planet over."

In a sense, Pluto is a (dwarf) planet whose shape and position in space are controlled by its weather.

"I think this idea of a whole planet being dragged around by the cycling of volatiles is not something many people had really thought about before," Keane said.

The two researchers used observations made during New Horizons' flyby and combined them with computer models that allowed them to take a surface feature such as Sputnik Planitia, shift it around on the planet's surface and see what that does to the planet's spin axis. And sure enough, in the models, the geographic location of Sputnik Planitia ended up suspiciously close to where one would expect it to be.

If Sputnik Planitia were a large positive mass anomaly -- perhaps due to loading of nitrogen ice -- it would naturally migrate to Pluto's tidal axis with regard to Charon, Pluto's largest moon, as it approaches a minimum energy state, according to Keane and Matsuyama. In other words, the massive accumulation of ice would end up where it causes the least wobble in Pluto's spin axis.

This phenomenon of polar wander is something that was discovered with Earth's moon and with Mars, as well, but in those cases it happened in the distant past, billions of years ago.

"On Pluto, those processes are currently active," Keane said. "Its entire geology -- glaciers, mountains, valleys -- seems to be linked to volatile processes. That's different from most other planets and moons in our solar system."

And not only that, the simulations and calculations also predicted that the accumulation of frozen volatiles in Pluto's heart would cause cracks and faults in the planet's surface in the exact same locations where New Horizons saw them.

The presence of tectonic faults on Pluto hint at the existence of a subsurface ocean at some point in Pluto's history, Keane explained.

"It's like freezing ice cubes," he said. "As the water turns to ice, it expands. On a planetary scale, this process breaks the surface around the planet and creates the faults we see today."

The paper is published alongside a report by Francis Nimmo of the University of California, Santa Cruz, and colleagues, who also consider the implications for Pluto's apparent reorientation. The authors of that paper agree with the idea that tidal forces could explain the current location of Sputnik Planitia, but in order for their model to work, a subsurface ocean would have to be present on Pluto today.

Read more at Science Daily

New Horizons Spies Distant Dwarf Planet Quaoar

NASA's New Horizons spacecraft has photographed a distant dwarf planet cruising through the dark depths of the outer solar system.

New Horizons captured images of the mysterious, 690-mile-wide (1,110 kilometers) Quaoar at four different times on July 13 and July 14 — exactly one year after the probe's historic July 14, 2015, flyby of Pluto.

New Horizons was 1.3 billion miles (2.1 billion km) from Quaoar when it took the photos with its Long Range Reconnaissance Imager (LORRI) camera, so the dwarf planet is not sharply resolved. But even such fuzzy views have scientific value, NASA officials said.

"With the oblique view available from New Horizons, LORRI sees only a portion of Quaoar's illuminated surface, which is very different from the nearly fully illuminated view of the dwarf planet from Earth," NASA officials wrote in an image description today (Aug. 31). "Comparing Quaoar from the two very different perspectives gives mission scientists a valuable opportunity to study the light-scattering properties of Quaoar's surface."

Quaoar (pronounced kwa-whar) was discovered in 2002 and has not officially been designated a dwarf planet, but it almost certainly qualifies, researchers have said. Dwarf planets need to be massive enough to be shaped into a sphere by their own gravity; with a diameter of 690 miles, Quaoar is larger than the officially recognized dwarf planet Ceres.

Quaoar lies an average of 43 astronomical units (AU) from the sun and completes one lap around the star every 286 Earth years. (One AU is the average distance from Earth to the sun — about 93 million miles, or 150 million km.) The object has one known moon.

The newly released images also show a number of background stars and two galaxies, known as IC 1048 and UGC 09485, both of which are about 370 billion times farther from New Horizons than Quaoar is, agency officials added.

As the Quaoar observations show, New Horizons' work did not end with the Pluto encounter. On Jan. 1, 2019, the probe will fly by an object called 2014 MU69, which lies about 1 billion miles (1.6 billion km) beyond Pluto.

Read more at Discovery News

Puzzling paucity of large craters on dwarf planet Ceres

The top of this false-color image includes a grazing view of Kerwan, Ceres' largest impact crater. This well-preserved crater is 280 km (175 miles) wide and is well defined with red-yellow high-elevation rims and a deep central depression shown in blue. Kerwan gradually degrades as one moves toward the center of the image into an 800-km (500-mile) wide, 4-km (2.5-mile) deep depression (in green) called Vendimia Planitia. This depression is possibly what's left of one of the largest craters from Ceres' earliest collisional history.

A team of scientists led by Southwest Research Institute (SwRI) made a puzzling observation while studying the size and distribution of craters on the dwarf planet Ceres.

Ceres is the largest object in the tumultuous Main Asteroid Belt between Mars and Jupiter. Collision models predicted Ceres should have accumulated up to 10 to 15 craters larger than 400 kilometers (250 miles) wide, and at least 40 craters larger than 100 km (62 miles) wide. Instead, NASA's Dawn spacecraft found only 16 craters larger than 100 km, and none larger than the 280 km (175 miles) across.

Crater size and distribution offer planetary scientists important clues to the age, makeup, and geologic history of planets and asteroids. Ceres is believed to have originated about 4.5 billion years ago at the dawn of our solar system. It grew in size through a history of accretionary collisions of smaller bodies. Some of its largest siblings were subsequently incorporated into larger objects, such as planets. Today, Ceres and Main Belt asteroids remain as the leftovers of the planet-building process.

Although Ceres endured the most violent phase of the solar system's collision-prone past, images of its surface taken by the Dawn spacecraft showed plenty of small impact craters, but the largest well-defined crater is only about 280-km in diameter. This defied most models of crater size and distribution and is at odds with what is known from previously imaged asteroids. For example, Dawn images of the asteroid Vesta, only about half the size of Ceres, revealed huge craters, including one 500 kilometers (300 miles) in diameter, covering almost an entire side of that asteroid.

"We concluded that a significant population of large craters on Ceres has been obliterated beyond recognition over geological time scales, likely the result of Ceres' peculiar composition and internal evolution," said lead investigator Dr. Simone Marchi, a senior research scientist in SwRI's Space Science and Engineering Division.

A closer look at Ceres' topography revealed subtle clues to a possible solution. Up to three roughly circular, shallow basins as much as 800 km (500 miles) wide may lie hidden beneath a surface subsequently marked with small craters.

"These depressions -- or planitiae -- may be 'relict' impact basins, left over from large collisions that took place early in Ceres' history," Marchi said. This implies that the predicted enormous craters may have indeed once marked the surface of Ceres. "It is as though Ceres cures its own large impact scars and regenerates new surfaces, over and over."

The scientists think Ceres' missing large craters may have been erased over time as a deep subsurface ice-rich layer or low viscous material caused the crater rims and bowls to relax, or that cryolava may have flowed across the surface. This process, however, may have not operated as efficiently for the largest, deepest impact features.

Read more at Science Daily