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.

June 18, 1999

Tharsis Volcanos
Credit: Malin Space Science Systems, MGS, JPL, NASA

Explanation: Ice crystal clouds float above the immense Tharsis volcanos of Mars in this recently released picture from NASA's Mars Global Surveyor spacecraft. Olympus Mons at the upper left is 340 miles across and almost 15 miles high - the largest volcano in the solar system. In this sunny afternoon scene, the clouds are formed as warm martian air containing water vapour rises up the volcanic slopes. The water vapour cools and condenses into ice crystals. These reflective clouds are common in the Tharsis region, together creating a bright feature visible in earth-bound telescopes.

Tomorrow's picture: Venus on the Horizon

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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
NASA Technical Rep.: Jay Norris. Specific rights apply.
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& Michigan Tech. U.