* Astronomy

Individual mesas stand like islands in an ocean in this false-colour THEMIS image that focuses on Deuteronilus Mensae. This region lies on the border between the rugged southern highlands and the flat northern lowlands and it shows features found in both.


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Credit: NASA/JPL/ASU

Today, a dozen miles or more separate the mesas, but at one time they likely formed a continuous layer. Planetary scientists think that subsurface water escaped through cracks and faults, making the ground collapse. In this manner, the layer began to break apart into isolated pieces, and mesas developed as slopes retreated.
The neutron- and gamma-ray spectrometers on the Mars Odyssey spacecraft found strong evidence for water (as ice) in the ground, both here and elsewhere on Mars. When ice and lots of rocky debris mix, the result is a rock glacier. Like ordinary glaciers, which contain mostly just ice, a rock glacier can flow slowly, given the right temperatures and slopes.
As THEMIS flew over this scene before dawn, it captured heat radiation coming from the surface. The colours in the image (which was taken at infrared wavelengths) tell about the materials in the ground. Bluer colours show colder surface temperatures while yellows and reds indicate warmer ones.
During desert nights on Earth and Mars alike, rocks hold on to daytime heat better than fine-grain materials such as dust. Thus the yellow and red colours map where the surface has more rocks and boulders exposed, while blue colours show what are likely cold, dust-covered areas.