One of the
best close-ups ever taken of the Martian moon Phobos reveals fresh details of
the strange object.
The impact
crater named Stickney is the largest feature on Phobos with a diameter of
almost 6 miles (9 km). The crater wall textures come from landslides that
formed as materials fell in the weak gravity of the moon.
A series of
grooves appear to radiate outwards from the crater, although studies have shown
the cracks did not come from the crater. Some scientists believe the grooves
are still related to the origin of Stickney, but others speculate that they
originated with leftover space debris from Martian impacts that later pelted Phobos.
Just 13.5
miles (22 km) wide, Phobos appears as a lumpy,
imperfect moon because its weak gravity could not compact it into a sphere.
Both Phobos and its sister moon Deimos seem very similar to some asteroids,
which could suggest their origin as space rocks captured by Martian gravity.
Other
origin theories for the Martian moons include coming from a larger
moon that broke up, forming with Mars in the early solar system, or being
composed of material blasted from the Martian surface by impacts.
The Mars
Reconnaissance Orbiter (MRO) angled in as close as 3,600 miles (5,800
kilometers) to eye Phobos in detail. Two similar images taken from different
distances were combined to give the perception
of a 3-D view.
Spacecraft such as Mars Global Surveyor have taken closer images of Phobos, but
MRO's HiRISE camera provides some of the best quality data to date for the
Martian moon.
Although no
spacecraft have landed on Phobos, the Russians announced plans in 2005 to
develop a Phobos-Grunt
mission to collect soil samples.
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