Inset
The High Resolution Imaging Science Experiment (HiRISE) camera on NASA's
Mars Reconnaissance Orbiter took two images of the larger of Mars' two
moons, Phobos, within 10 minutes of each other on March 23, 2008. This is
the first, taken from a distance of about 6,800 kilometers (about 4,200
miles). It is presented in color by combining data from the camera's
blue-green, red, and near-infrared channels.
The illuminated part of Phobos seen in the images is about 21 kilometers
(13 miles) across. The most prominent feature in the images is the large
crater Stickney in the lower right. With a diameter of 9 kilometers (5.6
miles), it is the largest feature on Phobos.
The color data accentuate details not apparent in black-and-white images.
For example, materials near the rim of Stickney appear bluer than the rest
of Phobos. Based on analogy with materials on our own moon, this could
mean this surface is fresher, and therefore younger, than other parts of
Phobos.
A series of troughs and crater chains is obvious on other parts of the
moon. Although many appear radial to Stickney in this image, recent
studies from the European Space Agency's Mars Express orbiter indicate
that they are not related to Stickney. Instead, they may have formed when
material ejected from impacts on Mars later collided with Phobos. The
lineated textures on the walls of Stickney and other large craters are
landslides formed from materials falling into the crater interiors in the
weak Phobos gravity (less than one one-thousandth of the gravity on
Earth).
In the full-resolution version of this image, a pixel encompasses 6.8
meters (22 feet), providing a resolution (smallest visible feature) of
about 20 meters (about 65 feet). The image is in the HiRISE catalog as
PSP_007769_9010.
NASA's Jet Propulsion Laboratory, a division of the California Institute
of Technology in Pasadena, manages the Mars Reconnaissance Orbiter for
NASA's Science Mission Directorate, Washington. Lockheed Martin Space
Systems, Denver, is the prime contractor for the project and built the
spacecraft. The High Resolution Imaging Science Experiment is operated by
the University of Arizona, Tucson, and the instrument was built by Ball
Aerospace & Technologies Corp., Boulder, Colo.