MESSENGER images have revealed intriguing albedo and color variations on
Mercury, providing insight into the compositional differences in the rocks
found on Mercury's surface and the processes that have acted on them. The
term albedo simply refers to the fraction of light reflected by a
material. For example, charcoal has a very low albedo while snow has a
very high albedo. This figure, recently published in Science magazine,
highlights some of these variations.
A: The bright rays of Basho crater (diameter about 80 kilometers, 50 miles)
likely are made of immature material, while the darker material near the
rim is thought also to be immature material but of a different
composition. Surface materials on Mercury are believed to change color and
albedo over time as a result of bombardment by micrometeoroids and
energetic particles from the solar wind. They eventually reach an
unchanging, "mature" state. If the surface is disturbed, for instance by a
cratering impact, underlying material is freshly exposed on the surface.
It is termed "immature" if the disturbance was sufficiently recent that
there hasn't yet been time for the exposed material to gain maturity.
B: Two craters within PIA10383 Caloris basin have dark crater
walls, and the crater at upper right, PIA10603 Sander (diameter about 50
kilometers, 30 miles), has bright patches on its floor. Unlike the rays of
Basho crater, the bright areas are not believed to be immature but are
inherently bright.
C: PIA10607 Mozart crater (diameter about 220 kilometers, 140 miles)
shows linear dark streamers (unlabeled arrows), which are thought to be
material excavated from depth during the crater-forming impact. Similarly
colored dark patches can also be seen in the crater wall (arrows labeled
W) and in the central peak (arrow labeled P) and may be derived from the
same underground layer.
D: The smooth plains (labeled SP) interior to Tolstoj basin are
superimposed on the darker areas shown with unlabeled arrows. Materials
with these two color and albedo characteristics are common on Mercury's
surface. This image is 825 kilometers (513 miles) wide.
E: This image was generated by comparing and contrasting WAC images
taken in 11 different color filters and choosing a color scheme to
highlight differences on Mercury's surface. The image shows the dark
streamers of Mozart crater (white arrows) and a young impact crater with
fresh, immature rays (black arrow). The image is about 800 kilometers (500
miles) wide.
F: Using a similar color scheme, this image of a segment of the
edge and rim of Caloris basin (white arrows) clearly shows that the rocks
present on the basin's floor differ from those exterior to the basin. This
image is about 600 kilometers (370 miles) wide.
Date Acquired: January 14, 2008
Image Mission Elapsed Time (MET): A: 108828233. B: 108826687. C:
108827022. D: 108828337, 108828342. E, F: 108829678-108829728.
Instrument: (A-D) Narrow Angle Camera (NAC) and (E-F) Wide Angle
Camera (WAC) of the Mercury Dual Imaging System (MDIS)
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.