Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2008 April 7
See Explanation.  Clicking on the picture will download
 the highest resolution version available.

Mysterious White Rock Fingers on Mars
Credit: G. Neukum (FU Berlin) et al., Mars Express, DLR Mars Express

Explanation: What caused this unusual white rock formation on Mars? Intrigued by the possibility that they could be salt deposits left over as an ancient lakebed dried-up, detailed studies of these fingers now indicate that this is not correct. The light material appears to have eroded away from the surrounding area, indicating a very low-density composition, possibly consistent with volcanic ash or windblown dust. The stark contrast between the rocks and the surrounding sand is compounded by the sand's unusual darkness. This picture was taken from the Mars Express spacecraft currently orbiting Mars. Planetary scientist Emily Lakdawalla, among others, has followed her curiosity about this unusual Martian landform into a fascinating investigation that is eloquently described in the Planetary Society Weblog. The mysterious white rock spans about 15 kilometers across inside a larger crater that spans about 100 kilometers.

Tomorrow's picture: witch belt

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