Status Report

Mars Odyssey THEMIS Image: Northern Arabia Etched Terrain

By SpaceRef Editor

May 23, 2002

Filed under Daily Themis Pictures, Mars Odyssey THEMIS, US

Image Context:

Context image credit: NASA/Mars Orbiter Laser Altimeter (MOLA) Team

The Science

The Story

Many places on Mars display scabby, eroded landscapes that commonly are
referred to as etched terrain. These places have a ragged, tortured
look that reveals a geologic history of intense deposition and erosion.
This THEMIS image shows such a place. Here a 10 km diameter crater is
superposed on the floor of a 40 km diameter crater, most of which is
outside of the image but apparent in the MOLA context image. The rugged
crater rim material intermingles with low, flat-topped mesas and layers
with irregular outlines along with dune-like ridges on many of the flat
surfaces. The horizontal layers that occur throughout the scene at
different elevations are evidence of repeated episodes of deposition.
The apparent ease with which these deposits have been eroded, most
likely by wind, suggests that they are composed of poorly consolidated
material. Air-fall sediments are the likely candidate for this material
rather than lava flows. The dune-like ridges are probably inactive
granule ripples produced from the interaction of wind and erosional
debris. The large interior crater displays features that are the result
of deposition and subsequent erosion. Its raised rim is barely
discernable due to burial while piles and blocks of slumped material
along the interior circumference attest to the action of erosion. Some
of the blocks retain the same texture as the surrounding undisrupted
surface. It appears as if the crater had been buried long enough for
the overlying material to be eroded into the texture seen today. Then
at some point this overburden foundered and collapsed into the crater.
Continuing erosion has caused the upper layer to retreat back from what
was probably the original rim of the crater, producing the noncircular
appearance seen today. The length of time represented by this sequence
of events as well as the conditions necessary to produce them are
unknown.

[Source: ASU THEMIS Science Team]

Have you ever seen an ink etching, where the artistic cross-hatching of lines creates the image of a town or a landscape? Click on the large THEMIS image above, and you’ll see why this scabby, eroded landscape is known as etched terrain. Etched terrain is found in lots of areas of Mars. These places have a ragged, tortured look that reveals a geologic history where material has been deposited and eroded away with great intensity over time.

Much of the terrain looks like peeling, layered-on paint. In a sense, that’s what it’s all about. Deposits of dust and dirt settled down from the air in layer after uneven layer, while the wind kept eroding it away. Dune-like ridges also mark the surface in tiny ripples. Unlike the loose sand dunes we’re familiar with on Earth, these ridges are probably harder and more stationary, They are produced by long-term interactions between the sculpting, knife-like action of the Martian wind and the deposited materials of dust and “dirt” on the surface.

What we can also see in this image is a six-mile-wide crater. If you look at the context image to the right, you can see that it is actually a crater within a crater. The larger crater is about 24 miles wide in diameter. (Students! How many times bigger is the larger crater than the one that lies inside of it? If you look at the context image, you can get a really good sense of what “four times bigger” really means.)

What’s interesting about this crater is that it doesn’t have typical features known to many craters: it isn’t nice-and-neatly round and its raised rim is barely noticeable. That’s because there’s been a whole lot of depositing and eroding going on here too. After the impact crater formed, it was probably entirely buried by deposits over time. In fact, it was probably buried long enough for the overlying material to be eroded into the texture seen today. At some point, the load on top foundered and collapsed into the crater.

Around the inside circumference of the crater, you can see piles of slumped material (material that has slid downslope). Some of these blocks of material have the same texture as surrounding terrain that hasn’t been disrupted. That’s because of continuing erosion acting on all of these features. In the upper layers, continuing erosion has also caused a retreat from the original rim of the crater, producing the noncircular shape seen today.

[Questions? Email marsoutreach@jpl.nasa.gov]

[Source: NASA/JPL Mars Outreach]

Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

NASA’s Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA’s Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

Image Credit: NASA/JPL/Arizona State University