Charon in Enhanced Color NASA’s New Horizons captured this high-resolution enhanced color view of Charon just before closest approach on July 14, 2015. Credits: NASA/JHUAPL/SwRI

NASA’s New Horizons spacecraft has returned the best color and the highest resolution images yet of Pluto’s largest moon, Charon – and these pictures show a surprisingly complex and violent history.

At half the diameter of Pluto, Charon is the largest satellite relative to its planet in the solar system. Many New Horizons scientists expected Charon to be a monotonous, crater-battered world; instead, they’re finding a landscape covered with mountains, canyons, landslides, surface-color variations and more.

“We thought the probability of seeing such interesting features on this satellite of a world at the far edge of our solar system was low,” said Ross Beyer, an affiliate of the New Horizons Geology, Geophysics and Imaging (GGI) team from the SETI Institute and NASA Ames Research Center in Mountain View, California, “but I couldn’t be more delighted with what we see.”

High-resolution images of Charon were taken by the Long Range Reconnaissance Imager on NASA’s New Horizons spacecraft, shortly before closest approach on July 14, 2015, and overlaid with enhanced color from the Ralph/Multispectral Visual Imaging Camera (MVIC). Charon’s cratered uplands at the top are broken by series of canyons, and replaced on the bottom by the rolling plains of the informally named Vulcan Planum. The scene covers Charon’s width of 754 miles (1,214 kilometers) and resolves details as small as 0.5 miles (0.8 kilometers). Credits: NASA/JHUAPL/SwRI

High-resolution images of the Pluto-facing hemisphere of Charon, taken by New Horizons as the spacecraft sped through the Pluto system on July 14 and transmitted to Earth on Sept. 21, reveal details of a belt of fractures and canyons just north of the moon’s equator.  This great canyon system stretches more than 1,000 miles (1,600 kilometers) across the entire face of Charon and likely around onto Charon’s far side. Four times as long as the Grand Canyon, and twice as deep in places, these faults and canyons indicate a titanic geological upheaval in Charon’s past.

“It looks like the entire crust of Charon has been split open,” said John Spencer, deputy lead for GGI at the Southwest Research Institute in Boulder, Colorado. “With respect to its size relative to Charon, this feature is much like the vast Valles Marineris canyon system on Mars.”

The team has also discovered that the plains south of the Charon’s canyon — informally referred to as Vulcan Planum — have fewer large craters than the regions to the north, indicating that they are noticeably younger. The smoothness of the plains, as well as their grooves and faint ridges, are clear signs of wide-scale resurfacing.

This composite of enhanced color images of Pluto (lower right) and Charon (upper left), was taken by NASA’s New Horizons spacecraft as it passed through the Pluto system on July 14, 2015. This image highlights the striking differences between Pluto and Charon. The color and brightness of both Pluto and Charon have been processed identically to allow direct comparison of their surface properties, and to highlight the similarity between Charon’s polar red terrain and Pluto’s equatorial red terrain. Pluto and Charon are shown with approximately correct relative sizes, but their true separation is not to scale. The image combines blue, red and infrared images taken by the spacecraft’s Ralph/Multispectral Visual Imaging Camera (MVIC).
Credits: NASA/JHUAPL/SwRI

One possibility for the smooth surface is a kind of cold volcanic activity, called cryovolcanism. “The team is discussing the possibility that an internal water ocean could have frozen long ago, and the resulting volume change could have led to Charon cracking open, allowing water-based lavas to reach the surface at that time,” said Paul Schenk, a New Horizons team member from the Lunar and Planetary Institute in Houston.

Even higher-resolution Charon images and composition data are still to come as New Horizons transmits data, stored on its digital recorders, over the next year – and as that happens, “I predict Charon’s story will become even more amazing!” said mission Project Scientist Hal Weaver, of the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.

The New Horizons spacecraft is currently 3.1 billion miles (5 billion kilometers) from Earth, with all systems healthy and operating normally.

New Horizons is part of NASA’s New Frontiers Program, managed by the agency’s Marshall Space Flight Center in Huntsville, Alabama.  APL designed, built, and operates the New Horizons spacecraft and manages the mission for NASA’s Science Mission Directorate. SwRI leads the science mission, payload operations, and encounter science planning.

The post Pluto’s Big Moon Charon Reveals a Colorful and Violent History appeared first on Astrobiology Magazine.

Yesterday’s post on what we’re learning about Rosetta’s comet (67P/Churyumov–Gerasimenko) briefly touched on the issue of changing the orbit of such bodies for use in resource extraction. Moving the comet Grigg-Skjellerup is part of the plot of Neal Stephenson’s novel Seveneves, where the idea is to support a growing human population in space with the comet’s huge reserves of water. Just how hard it would be to move a comet is made clear by how a proposed near-term mission approaches the question of deflecting a small asteroid.

The mission, discussed at the ongoing European Planetary Science Congress in Nantes, is called AIDA, for Asteroid Impact and Deflection Assessment. A joint mission being developed by the European Space Agency and NASA, AIDA is actually a two-pronged affair. ESA is leading the Asteroid Impact Mission (AIM), while NASA is behind the Double Asteroid Redirection Test (DART). The plan is to rendezvous with the asteroid (65803) Didymos and its tiny satellite (known informally as ‘Didymoon’) for scientific study and a deflection test.

Think about this comparison: Comet Grigg-Skjellerup (studied by the Giotto probe in 1992, though from a considerable distance) is approximately 2.6 kilometers in diameter. Didymos is about 750 meters in diameter, and the Didymoon about 160 meters across. It’s the Didymoon that ESA and NASA plan on deflecting, driving the DART spacecraft into it as AIM observes and analyzes the plume of ejected material. With AIM remaining on the job, further mapping and monitoring will study the impact area and reveal any changes in Didymoon’s orbit.

Image: Arrival of AIM at Didymos and Didymoon. Credit: ESA.

Thus the spread between a near-future science fiction story (the acquisition of Grigg-Skjellerup for resources in Seveneves) and present-day technology — we can assume that Stephenson’s comet-catcher has some powerful propulsive assets compared to what we can deploy today. But the novel explains all this on its own terms and I’ll say no more about it. As to AIDA, the words of Patrick Michel give us the gist. Michel is lead on the AIM Investigation team:

“To protect Earth from potentially hazardous impacts, we need to understand asteroids much better – what they are made of, their structure, origins and how they respond to collisions. AIDA will be the first mission to study an asteroid binary system, as well as the first to test whether we can deflect an asteroid through an impact with a spacecraft. The European part of the mission, AIM, will study the structure of Didymoon and the orbit and rotation of the binary system, providing clues to its origin and evolution. Asteroids represent different stages in the rocky road to planetary formation, so offer fascinating snapshots into the Solar System’s history.”

Image: Impact on Didymoon, as observed by AIM and its deployed CubeSats. Credit: ESA.

AIM would launch in October of 2020, with rendezvous at (65803) Didymos in May of 2022. Didymos rotates rapidly, about once every 2.26 hours, and is considered the most accessible asteroid of its size from Earth. Didymoon orbits Didymos every 11.9 hours at an altitude of 1.1 kilometers — the name Didymos (Greek for ‘twin’) was chosen by astronomer Joe Montani, who discovered the objects, when light-curve analysis revealed the binary nature of the asteroid. While Didymos is thought to be a ‘chondrite’ (stony) asteroid, we know nothing about the mass and density of Didymoon, a lack that AIM and DART would be able to correct in short order.

The AIM mission has echoes of Rosetta, for like the latter, it carries a lander. MASCOT-2, built by the German aeronautics and space research center (DLR) will probe the internal structure of Didymoon, emitting low-frequency radar waves that will pass through the object, allowing AIM to chart the deep structure of the asteroid even as it measures Didymoon’s density and maps the surface at visible and infrared wavelengths. DART’s impact with Didymoon is scheduled for October of 2022. I also notice that AIM is scheduled to deploy three CubeSats to assist with impact observations and to test communication links between satellites in deep space.

DART itself is a 300 kg impactor that is designed to carry no scientific payload other than a 20-cm aperture CCD camera to support guidance during the impact approach phase. Launch is currently proposed for July of 2021. The impact at 6.25 kilometers per second is expected to produce a velocity change in the range of 0.4 mm/s, which should change the relative orbit of Didymos and Didymoon but create only a slight change in the binary’s heliocentric orbit.

Related: NASA has funded a concept design study and analysis for a mission called Psyche, which would investigate the interesting asteroid of the same name. Psyche is thought to be the survivor of a collision with another object that stripped off the outer layers of a protoplanet. About 200 kilometers in diameter, it is thought to be the most massive M-type asteroid, with a surface that is 90 percent iron. The Psyche mission, led by Linda Elkins-Tanton (Arizona State) would be an orbiter that would launch in 2020 and arrive in 2026.

Image of the southern polar regions of Comet 67P/C-G taken with Rosetta's OSIRIS imaging system on 29 September 2014, when they were still experiencing the long southern winter. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Since its arrival at Comet 67P/Churyumov-Gerasimenko, Rosetta has been surveying the surface and the environment of this curiously-shaped body. But for a long time, a portion of the nucleus – the dark, cold regions around the comet's south pole – remained inaccessible to almost all instruments on the spacecraft.

Due to a combination of its double-lobed shape and the inclination of its rotation axis, Rosetta's comet has a very peculiar seasonal pattern over its 6.5 year-long orbit. Seasons are distributed very unevenly between the two hemispheres, each of which comprises parts of both comet lobes and of the 'neck'.

For most of the comet’s orbit, the northern hemisphere experiences a very long summer, lasting over 5.5 years, and the southern hemisphere undergoes a long, dark and cold winter. However, a few months before the comet reaches perihelion – the closest point to the Sun along its orbit – the situation changes, and the southern hemisphere transitions to a brief and very hot summer.

When Rosetta arrived at 67P/C-G in August 2014, the comet was still experiencing its long summer in the northern hemisphere and regions on the southern hemisphere received very little sunlight. Moreover, a large part of this hemisphere, close to the comet’s south pole, was in polar night and had been in total darkness for almost five years.

With no direct illumination from the Sun, these regions could not be imaged with Rosetta’s OSIRIS science camera. In addition, their low temperatures – ranging between 25 and 50 degrees above absolute zero – did not allow observations with VIRTIS, the Visible, InfraRed and Thermal Imaging Spectrometer, either.

For the first several months after Rosetta’s arrival at the comet, only one instrument on the spacecraft could observe and characterise the cold southern pole of 67P/C-G: the Microwave Instrument for the Rosetta Orbiter (MIRO).

In a paper accepted for publication in the journal Astronomy and Astrophysics, scientists report on the data collected by MIRO over these regions between August and October 2014.

“We observed the ‘dark side’ of the comet with MIRO on many occasions after Rosetta’s arrival at 67P/C-G, and these unique data are telling us something very intriguing about the material just below its surface,” explains Mathieu Choukroun from NASA's Jet Propulsion Laboratory, lead author of the study.

Subsurface temperature maps of 67P/C-G, showing the southern hemisphere of the comet. The maps are based on observations obtained with MIRO at millimetre (left) and sub-millimetre (right) wavelengths between September and October 2014; the data are projected on a digital shape model of the comet. Credits: ESA/Rosetta/NASA/JPL-Caltech

Observing the comet’s southern polar regions, Choukroun and colleagues found significant differences between the data collected with MIRO’s millimetre and sub-millimetre wavelength channels. These differences might point to the presence of large amounts of ice within the first few tens of centimetres below the surface of these regions.

“Surprisingly, the thermal and electrical properties around the comet’s south pole are quite different to what is found elsewhere on the nucleus. It appears that either the surface material or the material that lies down to a few tens of centimetres below it is extremely transparent at the MIRO wavelengths of 0.5 and 1.6 mm, and could consist mostly of water ice or carbon-dioxide ice,” he adds.

This graph shows the antenna temperatures measured by MIRO during two consecutive scans of Comet 67P/C-G's southern polar regions, performed on 23 October 2014, at millimetre (red) and sub-millimetre (blue) wavelengths. The series of images on the top, obtained from the digital shape model of the comet, show the various portions of the nucleus that were surveyed in these scans. The grey shaded area in the graph indicates a calibration interruption of the data. From M. Choukroun et al., Astronomy & Astrophysics, 2015.

The difference between the surface and sub-surface composition of this part of the nucleus and that found elsewhere might originate in the comet’s peculiar cycle of seasons. One of the possible explanations is that water and other gases that were released during the comet’s previous perihelion, when the southern hemisphere was the most illuminated portion of the nucleus, condensed again and precipitated on the surface after the season changed and the southern hemisphere plunged again into its long and cold winter.

These are, however, preliminary results, because the analysis depends on the detailed shape of the nucleus, and at the time the measurements were made the shape of the dark, southern polar region was not known to great accuracy.

“We plan to revisit the MIRO data using an updated version of the digital shape model, to verify these early results and refine the interpretation of the measurements,” adds Choukroun.

Besides, Rosetta scientists will be testing these and other possible scenarios using data that were collected in the subsequent months, leading to the comet's perihelion, which took place on 13 August 2015, and beyond.

In May 2015, the seasons changed on 67P/C-G and the brief, hot southern summer, which will last until early 2016, began. As the formerly dark southern polar regions started to receive more sunlight, it has been possible to observe them with other instruments on Rosetta, and the combination of all data might eventually disclose the origin of their curious composition.

“In the past few months, Rosetta has flown over the southern polar regions on several occasions, starting to collect data from this part of the comet after summer began there,” explains Matt Taylor, ESA Rosetta project scientist.

The southern hemisphere of Comet 67P/C-G, in a NAVCAM image taken on 26 August 2015. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

“At the beginning of the southern summer, we had a paucity of observations in these regions as Rosetta's trajectory focussed on the northern hemisphere due to ongoing communication with the lander, Philae. However, closer to perihelion we were able to begin observing the south.

“Rosetta is currently on an excursion out to 1500 km from the nucleus to study the comet's environment at large, but it will soon come closer to the comet, focussing on full orbits to compare the northern and southern hemispheres, as well as some slower passes in the south to maximise our observations there. In addition, as activity will start to wane later this year, we hope to get closer to the nucleus and gain higher resolution observations of the surface.”

Mark Hofstadter, MIRO Principal Investigator at NASA's Jet Propulsion Laboratory, describes the result as “a great example of how the scientific process unfolds as Rosetta is studying the evolution of this comet up close.”

“First, we observed these dark regions with MIRO, the only instrument able to do so at the time, and we tried to interpret these unique data. Now, as these regions became warmer and brighter around perihelion, we can observe them with other instruments, too,” he adds.

“We hope that, by combining data from all these instruments, we will be able to confirm whether or not the south pole had a different composition and whether or not it is changing seasonally.”

This blog post is based on the paper “The "Dark Side" of 67P/Churyumov-Gerasimenko in Aug-Oct 2014 – MIRO/Rosetta continuum observations of polar night in the Southern regions,” by M. Choukroun et al, which is accepted for publication in Astronomy and Astrophysics.

Science results from MIRO and other instruments on Rosetta are being presented this week at the European Planetary Science Congress in Nantes, France.