Status Report

Mars Odyssey THEMIS Image: Hephaestus Fossae

By SpaceRef Editor

July 3, 2002

Filed under Daily Themis Pictures, Mars Odyssey THEMIS, US

Image Context:

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

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Off the western flank of Elysium are the Hephaestus Fossae, including
linear arrangements of small, round pits. These features are commonly
called ‘pit chains’ and most likely represent the collapse of lava
tubes. Lava tubes allow molten rock to move long distances underground.
When the lava drains out it leaves unsupported tunnels, which can
collapse and form pits. These particular pit chains are unusual because
they change direction abruptly. In the lower portion of the image, pits
have collapsed at the bends and allow us to observe the sharp, nearly
right angle corners. These direction changes are most likely due to some
sort of structural control during the emplacement of the lava tubes.

There is an extraordinarily high concentration of small, degraded
craters on the plains surface. The size range of these craters is fairly
consistent and they all appear to be of similar age. It is unlikely that
these were caused by primary impacts (impacts of meteors onto the
surface) because both the size and timing distributions of primary
impactors vary tremendously. However, the craters in the image could
have been created from secondary impacts. Secondaries are impacts of
material that is excavated during a large cratering event nearby or from
the disintegration of a primary meteor in the atmosphere into many
smaller parts that rain onto the surface.

In contrast to these older, small craters, there is a relatively young
crater in the center of the image. A hummocky ejecta blanket is visible
around the crater and has covered some of the smaller craters on the
plain around it. The edges of the crater are sharp, formed by rocky
material in the crater rim. This material is visible as the layer of
rough, grooved material at the top of the inside walls. Small dust
avalanches have left dark streaks down the inside walls of the crater.

[Source: ASU THEMIS Science Team]

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