The Narrow Angle Camera of the Mercury Dual Imaging System (MDIS) on the
MESSENGER spacecraft obtained high-resolution images of the floor of the
Caloris basin on January 14, 2008. Near the center of the basin, an area
unseen by Mariner 10, this remarkable feature—nicknamed "the spider"
by the science team—was revealed. A set of troughs radiates outward
in a geometry unlike anything seen by Mariner 10. The radial troughs are
interpreted to be the result of extension (breaking apart) of the floor
materials that filled the Caloris basin after its formation. Other troughs
near the center form a polygonal pattern. This type of polygonal pattern
of troughs is also seen along the interior margin of the Caloris basin. An
impact crater about 40 km (~25 miles) in diameter appears to be centered
on "the spider." The straight-line segments of the crater walls may have
been influenced by preexisting extensional troughs, but some of the
troughs may have formed at the time that the crater was excavated.
These images are from MESSENGER, a NASA Discovery mission to conduct the
first orbital study of the innermost planet, Mercury. For information
regarding the use of images, see the MESSENGER image use policy.
