Image: Mars Viking 21i093

Description: This false color photo of the surface of Mars was taken by Viking Lander 2 at its Utopia Planitia landing site on May 18, 1979, and relayed to Earth by Orbiter 1 on June 7. It shows a thin coating of water ice on the rocks and soil. The time the frost appeared corresponds almost exactly with the buildup of frost one Martian year (23 Earth months) ago. Then it remained on the surface for about 100 days. Scientists believe dust particles in the atmosphere pick up bits of solid water. That combination is not heavy enough to settle to the ground. But carbon dioxide, which makes up 95 percent of the Martian atmosphere, freezes and adheres to the particles and they become heavy enough to sink. Warmed by the Sun, the surface evaporates the carbon dioxide and returns it to the atmosphere, leaving behind the water and dust. The ice seen in this picture, like that which formed one Martian year ago, is extremely thin, perhaps no more than one-thousandth of an centimeter thick. The view is looking towards the south southeast, the long boulder to the right is roughly one meter across.
Title: Mars Viking 21i093
Credit: Own work based on images in the NASA Viking image archive See accurate colors at: PIA00571: Ice on Mars Utopia Planitia Again
Author: "Roel van der Hoorn (Van der Hoorn)"
Permission: I used the original 21i093.blu, 21i093.grn and 21i093.red images from the NASA Viking image archive, converted them to .png, manually removed the noise and finally merged them into one image (almost matching true color; see here for the channel mixing process). Except for the conversion, this was all done in Adobe Photoshop CS2 and Adobe Photoshop CS4. The original files by NASA are in the public domain, and so is this new one.
Usage Terms: Public domain
License: Public domain
Attribution Required?: No