Explanation:
What are these strange shapes on Mars?
Defrosting sand dunes.
As spring now dawns on the Northern Hemisphere of Mars,
dunes of sand near the pole, as pictured above, are beginning 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.
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