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.
2019 September 24
Image Credit & License: ESA, Roscosmos, CaSSIS
Explanation: What are these strange shapes on Mars? Defrosting sand dunes. As spring dawned on the Northern Hemisphere of Mars, dunes of sand near the pole, as pictured here in late May by ESA's ExoMars Trace Gas Orbiter, began to thaw. The carbon dioxide and water ice actually sublime in the thin atmosphere directly to gas. Thinner regions of ice typically defrost first revealing sand whose darkness soaks in sunlight and accelerates the thaw. The process might even involve sandy jets exploding through the thinning ice. By summer, spots will expand to encompass the entire dunes. The Martian North Pole is ringed by many similar fields of barchan sand dunes, whose strange, smooth arcs are shaped by persistent Martian winds.
Tomorrow's picture: really big bird
Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
NASA Official: Phillip Newman Specific rights apply.
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