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.

2015 February 9
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Layered Rocks near Mount Sharp on Mars
Image Credit: NASA, JPL-Caltech, MSSS

Explanation: What caused these Martian rocks to be layered? The leading hypothesis is an ancient Martian lake that kept evaporating and refilling over 10 million years -- but has now remained dry and empty of water for billions of years. The featured image, taken last November by the robotic Curiosity rover, shows one-meter wide Whale Rock which is part of the Pahrump Hills outcrop at the base of Mount Sharp. Also evident in the image is cross-bedding -- rock with angled layers -- which were likely facilitated by waves of sand. Curiosity continues to find many layered rocks like this as it continues to roll around and up 5.5-km high Mount Sharp.

Tomorrow's picture: a long sun

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