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.

2025 July 6
A computer construction of what the north pole of Mars looks like. The picture was constructed from measured altitude data. A spiral landscape is seen that is coloured red but is mostly covered with white ice. Please see the explanation for more detailed information.

The Spiral North Pole of Mars
Image Credit: ESA/DLR/FU Berlin; NASA MGS MOLA Science Team

Explanation: Why is there a spiral around the North Pole of Mars? Each winter this pole develops a new outer layer about one metre thick composed of carbon dioxide frozen out of the thin Martian atmosphere. This fresh layer is deposited on a water-ice layer that exists year round. Strong winds blow down from above the cap's centre and swirl due to the spin of the red planet -- contributing to Planum Boreum's spiral structure. The featured image is a perspective mosaic generated in 2017 from numerous images taken by ESA's Mars Express and elevations extracted from the laser altimeter aboard NASA's Mars Global Surveyor mission.

Tomorrow's picture: alien comet

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