NASA Mars MRO HiRISE Image: Formation of a new gully channel on a crater-wall slope

This pair of before (left) and after (right) images from the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter (MRO) documents the formation of a substantial new channel on a Martian slope between Nov. 5, 2010, and May 25, 2013. 

Credit: NASA /JPL-Caltech /Univ. of Arizona 

A comparison of images taken by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter (MRO) in November 2010 and May 2013 reveal the formation of a new gully channel on a crater-wall slope in the southern highlands of Mars.

Gully or ravine landforms are common on Mars, particularly in the southern highlands.

This pair of images shows that material flowing down from an alcove at the head of a gully broke out of an older route and eroded a new channel.

The dates of the images are more than a full Martian year apart, so the observations did not pin down the Martian season of the activity at this site.

Before-and-after HiRISE pairs of similar activity at other sites demonstrate that this type of activity generally occurs in winter, at temperatures so cold that carbon dioxide, rather than water, is likely to play the key role.

The location is on the inner wall of a crater at 37.45 degrees south latitude, 222.95 degrees east longitude, in the Terra Sirenum region.

Gully or ravine landforms are commonly found in the mid-latitudes on Mars, particularly in the southern highlands.

These features typically have an alcove at the upper end, feeding into a channel and an apron of debris that has been carried from above.

Researchers using HiRISE have discovered many examples of gully activity likely driven by seasonal carbon-dioxide frost (dry ice).

The changes visible by comparing the 2010 and 2013 observations at this site formed when material flowing down from the alcove broke out of an older route, eroded a new channel and formed a deposit on the apron.

Although this pair of observations does not pin down the season of the event, locations HiRISE has imaged more often demonstrate that this sort of event generally occurs in winter, when liquid water is very unlikely.

Despite their resemblance to water-formed ravines on Earth, carbon dioxide may play a key role in the formation of many Martian gullies.

NASA Grail: Twin Probes to Crash into Moon Next Week

Artist's concept of NASA's Grail mission. Grail's twin spacecraft are flying in tandem orbits around the moon to measure its gravity field in unprecedented detail. 

CREDIT: NASA/JPL

NASA's twin Grail spacecraft will crash into the lunar surface intentionally next week, bringing their gravity-mapping mission to a spectacular end.

The probes, known as Ebb and Flow, will be commanded to slam into the moon on Dec. 17, NASA officials said.

The agency will host a press conference to discuss the impact and the events leading up to it.

The $496 million Grail mission (Gravity Recovery and Interior Laboratory) launched in September 2011 to map the moon's gravity field in unprecedented detail.

Ebb and Flow arrived in orbit around the moon about one year ago — on New Year's Eve and New Year's Day, respectively.

The washing-machine-size spacecraft were originally tasked with 90-day science missions, which ran from March to May. but NASA extended Grail, allowing the two probes to gather a trove of additional data.

Ebb and Flow have been flying in formation around the moon, detecting the tiny changes in the distance between them caused by lunar mountains, craters and subsurface mass concentrations.

Scientists used these ultra-precise measurements to construct an incredibly accurate map of the lunar gravity field.

This map, unveiled last week at the fall meeting of the American Geophysical Union (AGU) in San Francisco, reveals that the moon's crust is almost completely pulverized.

The surprising find suggests that the moon and other rocky bodies in the inner solar system were pounded by long-ago impacts far more violently than previously believed, researchers said.

The new map was based on data gathered during Grail's original science mission; scientists expect to upgrade it based on measurements the spacecraft made during their extended mission, which brought them even closer to the lunar surface — an average altitude of 14 miles (23 km) as opposed to 34 miles (55 km).

Ebb and Flow are now running low on fuel as expected, NASA officials said, so the end is near for the probes. Mission managers will ensure that they go out in style on Dec. 17.

In Liquid and Air, Scientists Find Order Among the Chaos - NYTimes.com

In Liquid and Air, Scientists Find Order Among the Chaos - NYTimes.com

Assisted by instruments that can track in fine detail how parcels of fluid move, and by low-cost computers that can crunch vast amounts of data quickly, researchers have found hidden structures beyond Monterey Bay, structures that explain why aircraft meet unexpected turbulence, why the air flow around a car causes drag and how blood pumps from the heart's ventricles. In December, the journal Chaos will highlight the research under way to track the moving skeletons embedded in complex flows, known as Lagrangian coherent structures.

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