Daytime and nighttime infrared views of White Rock

Daytime and nighttime infrared views of White Rock
Daytime and nighttime infrared views of White Rock These two views of White Rock were captured by Mars Odyssey's thermal infrared camera during the afternoon (left) and toward the end of the night (right). In the late afternoon, sun-facing walls and rims of craters tend to be warmer (brighter) than shadowed walls and rims, which are darker. White Rock shows up as an anomalously dark (cool) area because of its relatively high albedo; it reflects away a higher proportion of the sunlight that hits it, so it does not warm as much during the day as the much darker floor of the crater in which it sits. At night, the temperature of Mars' surface is controlled more by the composition of the surface. Rocks have higher thermal inertia than dust, and tend to stay warmer for longer. So bedrock tends to show up as bright in nighttime images, while sandy and dusty areas tend to be dark. Crater rims, which likely contain bedrock, do show up as bright in this image, but White Rock itself is relatively dark -- indicating that it is not particularly dense, and is thus not as "rocky" as bedrock. NASA / JPL-Caltech / ASU

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