Space Topics: Mars
The Year in Pictures: 2007
Mars Express: Phobos over Mars
Credit: ESA / DLR / FU Berlin (G. Neukum) |
Mars' three active orbiters typically point down at the
surface, peering through the atmosphere to capture photos of rocks, ice,
and soil. Sometimes, the view sideways is more compelling, as in this image
of Mars’ moon Phobos taken
by the High Resolution Stereo Camera on
Mars Express on January 10.
Phobos is the larger and innermost of Mars' two moons; it travels around
Mars' equator once every 7.65 hours. Mars Express is in a polar orbit,
so the spacecraft and the moon were crossing paths when this photo was
taken. Phobos appears crisp and sharp; below it, the edge of Mars' disk
appears fuzzy and striated because of layering in Mars' atmosphere. The
image also demonstrates how dark the charcoal-black Phobos is compared
to Mars' bright dusty surface.
Mars' atmosphere
is thin, however, so even when the planet is viewed from this angle, sighting
along the longest possible path through the atmosphere, surface features
are visible through the haze. You can see a few impact craters below the
moon; they appear as line segments that are bright on the left and dark
on the right in this severely foreshortened view.
Mars Express has been
taking photos of Phobos as opportunities present themselves throughout
its four years at Mars, producing enough data to make major improvements
to our understanding of the moon's shape, rotation, and orbit. After Phoenix has
landed in May 2008, and Mars Express has discharged its obligation to listen
to the lander during its descent (which requires Mars Express to maintain
its current orbit), the orbit of Mars Express will be shifted to permit
it to photograph more of Phobos' anti-Mars hemisphere. Those data will
be invaluable to the planners of the Russian Phobos-Grunt sample return
mission, to be launched in 2009.
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