What Lies Beneath: Surface Patterns of Glacier-Like Landforms
NASA/JPL/UArizona
What Lies Beneath: Surface Patterns of Glacier-Like Landforms
ESP_046039_2295  Science Theme: Glacial/Periglacial Processes
The rotational axis of Mars is currently tilted by about 25 degrees, very similar to that of the Earth (at 23.4 degrees). However, while Earth’s axial tilt (also known as “obliquity”) tends to change very slightly over time (almost 3 degrees in 40,000 year-cycles), the obliquity of Mars is much more chaotic and varies widely from 0 to almost 60 degrees! The fact that it is currently similar to that of the Earth is merely a coincidence.

Currently, water-ice is stable on the Martian surface only in the polar regions. However, during times of “high obliquity,” that stability shifts towards the equatorial regions. We see evidence for recent periods of high obliquity on Mars in the form of features common in the mid-latitude regions, which planetary scientists call “viscous flow features,” “lobate debris aprons,” or “lineated valley fills.” These are all scientifically conservative ways of describing features on Mars that resemble mountain glaciers on Earth.

We now know from radar observations, particularly using the SHARAD instrument on board the Mars Reconnaissance Orbiter, that these features are really composed of mixtures of pure ice and dust, and as a result, many scientists have started using the term “glacier-like forms” (GLF) to describe some of them. The main reason that these feature are still present for us to observe nowadays—despite the inhospitable conditions for water ice in these latitudes—is that these “glaciers” are covered by thin layers of dust, which protect them from the atmosphere of Mars and prevents, or significantly slows down, the loss of ice through sublimation to the atmosphere.

However, if we were to take a look at this image of a “lobate debris apron,” we will see that some areas show numerous depressions, which suggests that these areas have lost some of the ice creating these “deflation features.” In addition, if we zoom in on one of these depressions, we will see surface polygonal patterns, which are common in cold regions on Earth (such as Alaska, northern Canada, and Siberia) and are indicators of shallow sub-surface water-ice.



Written by: M. Ramy El-Maarry (audio: Tre Gibbs)  (21 September 2016)
 
Acquisition date
22 May 2016

Local Mars time
15:11

Latitude (centered)
49.168°

Longitude (East)
285.532°

Spacecraft altitude
301.9 km (187.6 miles)

Original image scale range
61.1 cm/pixel (with 2 x 2 binning) so objects ~183 cm across are resolved

Map projected scale
50 cm/pixel and North is up

Map projection
Equirectangular

Emission angle
8.1°

Phase angle
48.6°

Solar incidence angle
56°, with the Sun about 34° above the horizon

Solar longitude
156.8°, Northern Summer

For non-map projected images
North azimuth:  96°
Sub-solar azimuth:  337.0°
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POSTSCRIPT
NASA’s Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, Calif., manages the Mars Reconnaissance Orbiter for NASA’s Science Mission Directorate, Washington. The HiRISE camera was built by Ball Aerospace and Technology Corporation and is operated by the University of Arizona.