Mars Reconnaissance Orbiter examines Mars' 'cryptic terrain'

One type of landscape near Mars' south pole is called "cryptic terrain" because it once defied explanation, but new observations bolster and refine recent interpretations of how springtime outbursts of carbon-dioxide gas there sculpt intricate patterns and paint seasonal splotches.
"A lot of Mars looks like Utah, but this is an area that looks nothing like Planet Earth," said Candice Hansen of NASA's Jet Propulsion Laboratory, Pasadena, Calif., deputy principal investigator for the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter.

In addition to radially branching patterns called "spiders," which had been detected by an earlier Mars orbiter, other intriguing ground textures in the area appear in the new images. "In some places, the channels form patterns more like lace. In others, the texture is reminiscent of lizard skin," Hansen said.

Results from all six instruments on the Mars Reconnaissance Orbiter, which reached Mars last year, are described in dozens of presentations this week by planetary scientists in San Francisco at the fall meeting of the American Geophysical Union.

By taking stereo pictures of a target area from slightly different angles during different orbits, HiRISE can show the surface in three dimensions. Channels found to widen as they run uphill in the cryptic terrain region testify that the channels are cut by a gas, not a liquid.

Earlier evidence for jets of gas active in the region came from fan-shaped blotches appearing seasonally, which scientists interpret as material fallen to the surface downwind of vents where the gas escapes. Some of the fans are dark, others bright. "The dark fans are probably dust, but the exact composition of the brighter fans had remained unknown until now," said Tim Titus of the U.S. Geological Survey's Astrogeology Team, Flagstaff, Ariz.

Image Credit: NASA/JPL-Caltech/ASU

A regional landscape near Mars' south pole is called "cryptic terrain" because it once defied explanation, but new observations bolster and refine interpretations of how springtime outbursts of carbon-dioxide gas there sculpt intricate patterns and paint seasonal splotches. This map indicates locations of three sites that have been examined within the area of cryptic terrain, informally designated "Manhattan," "Giza" and "Ithaca."

The underlying map offers context of brightness measurements from the Thermal Emission Spectrometer instrument draped over a shaded relief map based on data from the Mars Orbiter Laser Altimeter instrument. Cool colors are areas with a low albedo (dark) and warm colors are areas which have high albedo (bright). Both of those instruments flew on NASA's Mars Global Surveyor orbiter.




Image Credit: NASA/JPL/University of Arizona
High resolution image

Dark fans and bright fans on Mars.




Image Credit: NASA/JPL/University of Arizona
High resolution image

This is a perspective view of a scene within Mars' Candor Chasma based on stereo imaging by the High Resolution Imaging Science Experiment (HiRISE) camera aboard NASA's Mars Reconnaissance Orbiter. It shows how the surface would appear to a person standing on top of one of the many hills in the region and facing southeast.

The hills in the foreground are several tens of meters to about 100 meters (tens of yards to about 100 yards) wide and several tens of meters or yards tall. The light-toned layers of rock likely consist of material laid down by the wind or under water. The dark-toned material is a layer of windblown sand on the surface. The orientations of these layers were measured in three dimensions in order to understand the region's geologic history. The particular patterns in which these rocks are oriented to the surrounding Candor Chasma are most consistent with the idea that the layers formed as basin-filling sediment, analogous to the sedimentary rocks of the Paradox Basin in southeastern Utah. This implies that these sediments are younger than the formation of the chasm, providing important constraints on the maximum age of groundwater (about 3.7 billion years) within the region.

The width of the scene at bottom of the image is approximately 500 meters (1,640 feet). There is no vertical exaggeration.

The detailed three-dimensional information of the area comes from a pair of HiRISE observations. Those full observations are available at http://hirise.lpl.arizona.edu/PSP_003474_1735 and http://hirise.lpl.arizona.edu/PSP_003540_1735.

Observations by the new orbiter's Compact Reconnaissance Imaging Spectrometer for Mars suggest that the bright fans are composed of carbon-dioxide frost. See related story. Here's the story researchers now propose: Spring warms the ground under a winter-formed coating of carbon dioxide ice. Thawing at the base of the coating generates carbon-dioxide gas, which carves channels as it pushes its way under the ice to a weak spot where it bursts free. The jet of escaping gas carries dust aloft and also cools so fast from expanding rapidly that a fraction of the carbon dioxide refreezes and falls back to the surface as frost.

The processes creating the cryptic terrain are current events on Mars. Repeated HiRISE observations of the same target area show the downwind fans can form and grow perceptibly in less than five days.

Other new findings from the Mars Reconnaissance Orbiter reveal processes of Martian environments long ago. A team including Chris Okubo of the University of Arizona, Tucson, used stereo HiRISE images to examine layered deposits inside Mars' Candor Chasma, part of Valles Marineris, the largest canyon system in the solar system.

"The high-resolution structural map allowed us to interpret the geological history of the area," Okubo said. "The layers are tilted in a way that tells us they are younger than the canyon." Spectrometer studies of the composition of these deposits had indicated water played a role in their formation, but their age relative to the formation of the canyon had been uncertain. The new findings suggest water was present after the canyon formed.

Source: Jet Propulsion Laboratory
	More on • Mars Reconnaissance Orbiter • HiRISE • Mars