Mars HiRise: Ancient Rocks of the Isidis Basin and Libya Montes Exposed and Preserved by Hashir Crater

The focus of this HiRISE observation is the inner portion of the approximately 9-kilometer diameter Hashir Crater.

Hashir is located at 84.56 degrees east, 3.63 degrees north within the transition from the vast Isidis Basin plains (Isidis Planitia) to the great circumferential mountains of Libya Montes (i.e., the ancient and dissected mountains raised-up from the Isidis-forming event).

Hashir is of particular interest to scientists because there are several spectral units that are characteristic of the Isidis Basin/Libya Montes region that are exposed or preserved within it.

Hashir and its surroundings have been spectrally characterized by multiple orbiting spectrometers spanning almost 25 years, including: Phobos 2-ISM, MGS-TES, MO-THEMIS, MEx-OMEGA and most recently by MRO-CRISM.

The results from the analysis of these data indicate the presence of surface materials rich in olivine, pyroxene, clays (Fe/Mg-smectites) and carbonate.

The latter two are of particular interest as they were likely formed by alteration of the ancient basaltic rocks through interactions with water.

The Fe/Mg-phyllosilicates and carbonate are often associated with olivine in CRISM and HiRISE images because these alteration minerals are observed where the olivine-rich lavas have been eroded away.

This 3D perspective image of Hashir Crater was generated by combining color from CRISM with the high-resolution of a gray-scale HiRISE RED image draped over a HiRISE stereo derived digital terrain model (DTM) with a 3x vertical enhancement.

This close-up view from the south (looking north) illustrates the occurrence of the pyroxene-bearing caprock in blue on top of olivine-bearing layered bedrock in green, which in turn overlies a Fe/Mg-smectite-bearing unit in red.

The hilly red unit is interpreted to be the central uplift of Hashir Crater, which are rocks uplifted and exposed by the crater-forming event.

The blue and green units are more recent lava flows or impact melt deposits from Isidis that filled in Hashir after it formed and have been since eroded back by the high winds in the Libya Montes region.

Jupiter's heart is dissolving

Even the mighty can lose heart. New calculations suggest that Jupiter's rocky core is dissolving like an antacid tablet plopped in water.

The work could help explain why its core appears smaller and its atmosphere richer in heavy elements than predicted.

Giant planets like Jupiter and Saturn are thought to have begun their lives as solid bodies of rock and ice. 

When they grew to about 10 times the mass of Earth, their gravity pulled in gas from their birth nebula, giving them thick atmospheres made mainly of hydrogen.

Curiously, some studies have suggested that Jupiter's core may weigh less than 10 Earths, while the core of its smaller sibling Saturn packs a bigger punch at 15 to 30 Earths. Last year, researchers led by Shu Lin Li of Peking University in China offered a grisly explanation – a rocky planet bigger than Earth slammed into Jupiter long ago, vaporising most of the giant planet's core.

That scenario could also explain another mystery – why Jupiter's atmosphere contains a higher fraction of heavy elements than the sun, whose composition is thought to mirror that of the nebula that gave birth to the solar system's planets.

Now Hugh Wilson and Burkhard Militzer of the University of California, Berkeley, suggest a competing – though no less macabre – explanation: Jupiter's core has gradually been dissolving since its formation 4.5 billion years ago.

Read More at Jupiter's heart is dissolving

NASA: Comet Elenin Gone and Should Be Forgotten

Comet Elenin is no more. Latest indications are this relatively small comet has broken into even smaller, even less significant, chunks of dust and ice.

This trail of piffling particles will remain on the same path as the original comet, completing its unexceptional swing through the inner solar system this fall.

"Elenin did as new comets passing close by the sun do about two percent of the time: It broke apart," said Don Yeomans of NASA's Near-Earth Object Program Office in Pasadena, Calif.

"Elenin's remnants will also act as other broken-up comets act. They will trail along in a debris cloud that will follow a well-understood path out of the inner solar system.

After that, we won't see the scraps of comet Elenin around these parts for almost 12 millennia."

Twelve millennia may be a long time to Earthlings, but for those frozen inhabitants of the outer solar system who make this commute, a dozen millennia give or take is a walk in the celestial park.

Comet Elenin came as close as 45 million miles (72 million kilometers) to the sun, but it arrived from the outer solar system's Oort Cloud, which is so far away its outer edge is about a third of the way to the nearest star other than our sun.

For those broken up over the breakup of what was formerly about 1.2 miles (two kilometers) of uninspiring dust and ice, remember what Yeomans said about comets coming close to the sun - they fall apart about two percent of the time.

"Comets are made up of ice, rock, dust and organic compounds and can be several miles in diameter, but they are fragile and loosely held together like dust balls," said Yeomans.

"So it doesn't take much to get a comet to disintegrate, and with comets, once they break up, there is no hope of reconciliation."

Comet Elenin first came to light last December, when sunlight reflecting off the small comet was detected by Russian astronomer Leonid Elenin of Lyubertsy, Russia.

Pluto's rival is tinier but shinier than thought

Pluto may be the king of the dwarfs after all.

New observations confirm that Eris, the dwarf planet whose discovery got Pluto kicked out of the planet club in 2006, is almost exactly the same size as Pluto and may be a bit smaller.

When Eris was discovered in 2005, images from the Hubble Space Telescope suggested that it was 2400 kilometres wide, 5 per cent wider than Pluto, which is only about 2340 kilometres wide.

Later observations with the infrared Spitzer Space Telescope made Pluto's case even worse, finding Eris's diameter to be around 2600 kilometres but both measurements left room for doubt.

Last November, astronomers got a chance to know for sure which rock ruled the outer solar system, when Eris passed directly in front of a distant star and cast a small shadow on the Earth.

Bruno Sicardy of the Paris Observatory and colleagues compared the shadow's size from two different sites in Chile, and found that Eris's diameter is 2326 kilometres, reported Scientific American's Observations blog. That's hardly different from the best values for Pluto's size.

"It could be smaller, it could be larger; basically, it is a twin," Sicardy said at the meeting, according to the Planetary Society Blog. Sicardy presented the results at the Division of Planetary Sciences meeting in Nantes, France, on 4 October, and they will be published in an upcoming issue of Nature.

Eris is still the dwarf planet heavyweight, though. It is much more massive than Pluto, meaning it is substantially denser.

That suggests Eris is mostly composed of rock, with a relatively thin icy mantle. Models of the solar system's composition at various distances suggest it should have had a thicker layer of ice if it formed where it is. If so, much of its original ice may have been "blasted away" in a catastrophic impact.

The new observations also revealed that the dwarf planet is brighter than fresh snow, and possibly the second brightest object in the solar system, after Saturn's icy moon Enceladus.

That hints at a surface layer of nitrogen or methane frost, the remnants of a collapsed atmosphere which goes through a cycle of freezing and thawing as the small world wheels around the sun.

NASA MARS Rover Opportunity: On verge of new discovery

A closeup of the Cape York rim segment of Endeavour Crater with the Opportunity rover's path shown. 

Tisdale, the rock Opportunity sampled earlier, is on the southern tip of Cape York.

Mars rover Opportunity was poised on the rim of the 22,000 meter-wide Endeavour Crater, preparing to sample a novel rock type.

Much older than the sedimentary samples the rover's "tasted" so far, this new sample is flush with the promise of revealing clues to the planet's environment when running rivers coursed the surface.

What was supposed to have been a 90- to 180-day exploration of two distinct regions of the red planet has turned into a saga that has become one of science's most compelling and long-lasting adventures (now into its eighth year), enthralling the public and the science communities alike.

Launched the summer of 2003 and landing in January 2004, the solar-powered Mars Exploration Rovers (MER) Spirit and Opportunity completed their intended basic missions in April 2004.

Raymond E. Arvidson, PhD, the James S. McDonnell Distinguished University Professor in Arts and Sciences at WUSTL, is the MER deputy principal investigator. Each continued roving until March 2010, when Spirit, mired in unexpected but scientifically interesting martian sand and pointed in an unfavorable direction to survive the winter dark, gave up the ghost.

Opportunity, on the other hand, remains active, having reached the rim of Endeavour Crater Aug. 9, 2011, knocking at the door of geology different from any it has explored during its first seven-plus years on Mars.

"Opportunity now is in a brand new mission," Arvidson says. "In late August, we looked at a rock named Tisdale, with a composition unlike any we've seen before. It has an enormous amount of zinc, bromine, phosphorus, chlorine and sulfur, all elements that are mobile in the presence of water.

The ancient rim of Endeavour represents a period when there was probably a lot more water on the surface," Arvidson says. "So, we're trying to get the chemical, mineralogical and geological setting to 'back out' those ancient conditions to reconstruct environmental conditions during this earlier time period."

The conditions that formed the sandstones Opportunity has sampled over the past seven years represent a kind of drying-out period of Mars.

Occasionally wet but usually dry and wind-blown, the sulphur-rich mineral grains formed vast dune fields that were cemented into sandstone over millions of years by occasional seeping groundwater.

But the terrain Opportunity now is sampling - largely buried by lake bed sediments - pops up in places like the Endeavour rim and is much older, going back to the earliest days of the planet.

That's some 3.5 to 4 billion years ago in the last stages of heavy bombardment, when Mars was sweeping up the last planetessimals - cosmic dust grains that collided and stuck to each other to form larger bodies. Endeavour is an impact crater produced during that heavy bombardment period.

NASA MARS Rover Opportunity: 'Ridout' Rock on Rim of Odyssey Crater

NASA's Mars Exploration Rover Opportunity looked across a small crater on the rim of a much larger crater to capture this raw image from its panoramic camera during the rover's 2,685th Martian day, or sol, of work on Mars (Aug. 13, 2011).

Opportunity had arrived at the western rim of 13-mile-diameter (21-kilometer-diameter) Endeavour crater four days earlier.

A portion of the northeastern rim of Endeavour forms the distant horizon in this view.

A crater about 66 feet (20 meters) in diameter is on the Endeavour rim near Opportunity's arrival point. From a position south of Odyssey, this view is dominated by a rock informally named "Ridout" on the northeastern rim of Odyssey. The rock is roughly the same size as the rover, which is 4.9 feet (1.5 meters) long.

Image Credit: NASA/JPL-Caltech/Cornell/ASU

NASA - 'Ridout' Rock on Rim of Odyssey Crater

NASA Mars Rover Opportunity: Alligator tail rock

A rock that looks like an alligator's tail is seen on the surface of Mars in this Navcam panorama image from the red planet.

The picture showing many interestingly shaped rocks and the edge of the Santa Maria crater was taken by the Mars rover Opportunity on December 15.

Picture: NASA / BARCROFT MEDIA

NASA Martian sheen: Life on the rocks

WHEN NASA's Viking landers touched down on Mars, they were looking for signs of life. Instead, all their cameras showed was a dry, dusty - and entirely barren - landscape.

Or so it seemed. But what the 1976 Viking mission, and every subsequent one, saw was a scene littered with rocks coated with a dark, highly reflective sheen. That coating looks a lot like a substance known on Earth as "rock varnish", found in arid regions similar to those on Mars. The latest evidence hints that rock varnish is formed by bacteria. Could there be microbes on Mars making such material too?

Rock varnish has long been something of a mystery. It is typically just 1 to 2 micrometres thick, but can take a thousand years or more to grow, making it very hard to discover whether biological or purely chemical processes are responsible. If it is biological, though, the race will be on to discover whether the same thing has happened on Mars - and whether microbes still live there today.

If you go to Death Valley in California, you can find rock varnish covering entire desert pavements. Also known as desert varnish, it forms in many places around the globe, and despite its glacial growth rates, can cover vast areas.

The smooth, high sheen, dark brown-to-black coating is mainly made up of clay particles, which bind the iron and manganese oxides that give the coating its mirror-like reflectivity.

In the Khumbu region of Nepal, not far from Mount Everest, it has turned the boulders black. Halfway around the world, it enabled ancient peoples to create the Nazca Lines in the Peruvian desert.

These giant, elaborate images - some over 200 metres across and created over 1000 years ago - were made by simply removing rows of varnished stones to exposing the lighter stones or soil beneath.

George Merrill coined the phrase desert varnish in 1898, while working for the US Geological Survey (USGS). No one really studied it, though, until 1954, when Charles Hunt showed that the veneer forms on many different rock types - meaning that it wasn't simply a chemical production from a certain kind of rock and prompting the first questions about where it might come from (Science, vol 120, p 183). Hunt went on to find rock varnish in humid regions, tropical rainforests and at high altitudes in the Alps and the Rocky mountains.

Theories on how rock varnish forms weren't long in coming - and, initially at least, biology didn't get a look-in. In 1958 Celeste Engel of the USGS and Robert Sharp from the California Institute of Technology explained it as a chemical weathering phenomenon similar to iron oxide stains - red/orange coatings arising when iron particles from the air collect on the surface of rocks and bind together when made wet by dew (Geological Society of America Bulletin, vol 69, p 487).

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Comets Scarred the Face of Lady Moon

A new study suggests comets gouged out the vast majority of craters on the moon (Image: NASA)

Icy comets and not rocky asteroids, launched a dramatic assault on the Earth and moon around 3.85 billion years ago, a new study of ancient rocks in Greenland suggests. The work suggests much of Earth's water could have been brought to the planet by comets.

"We can see craters on the moon's surface with the naked eye, but nobody actually knew what caused them – was it rocks, was it iron, was it ice?" says Uffe Gråe Jørgensen, an astronomer at the Niels Bohr Institute in Copenhagen, Denmark. "It's exciting to find signs that it was actually ice."

Evidence suggests that the Earth and moon had both formed around 4.5 billion years ago. But almost all the craters on the moon date to a later period, the "Late Heavy Bombardment" 3.8 to 3.9 billion years ago, when around 100 million billion tonnes of rock or ice crashed onto the lunar surface. The Earth would have been pummelled by debris at the same time, although plate tectonics on our restless planet have since erased the scars.

To find out whether asteroids or comets were the main culprits for the bombardment, Jørgensen decided to measure levels of the element iridium in ancient terrestrial rocks. Iridium is rare on the Earth's surface because almost all of it bound to iron and sank into the Earth's core soon after the planet had formed. But iridium is relatively common in comets and meteorites.