The High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter captured winter images of NASA's Phoenix Mars Lander surrounded by dry-ice frost on Mars.

As the sun began to reappear on the horizon following the deepest, darkest days of north polar winter on Mars, the HiRISE camera imaged the Phoenix landing site on July 30, 2009, (left image) and in Aug. 22, 2009 (right).

The sun was only 1 degree above the horizon when the July image was taken at approximately 2 p.m. local Martian time. In the August image the sun was six degrees above the horizon when the image was taken at about 1:44 p.m., Martian time.

By matching up the images with the known location of the Lander, the HiRISE team identified the hardware, disguised by frost, despite the fact that the views were hindered by poor lighting and atmospheric haze, which often obscures the Martian surface at this location and season.

Carbon dioxide frost completely blankets the surface in both images. The amount of brightness doesn't necessarily indicate the amount of frost seen in the image because of the way the images are processed to produce optical contrast. Each of these images is stretched differently for optimal contrast, so "bright" and "dark" can't be compared directly between images without doing complex calibrations. In fact, if you stretched all of them exactly the same, the darker areas in the frost covered images are still brighter than typical soil, like that surrounding the Lander in the frost-free image.

Other factors affect the relative brightness, such as the size of individual grains of carbon dioxide ice, the amount of dust mixed in with the ice, the amount of sunlight hitting the surface, and different lighting angles and slopes. The winds are also changing direction and strength, moving loose frost and dust around over time.

Studying these changes will help scientists understand the nature of the seasonal frost and winter weather patterns in this area of Mars.

The amount of carbon dioxide frost is increasing as late winter transitions to early spring, so the layer of frost is getting thicker in each image, slowly encasing the Lander. The maximum thickness was expected to be on the order of tens of centimeters, which would have reached its peak in September 2009. The thickness has not been confirmed yet because the MRO spacecraft suspended taking images when it entered safe mode on August 26. Oct. 26 marked the first day of spring in the northern hemisphere of Mars.

The Planetary Society has put together an animation comparing the hardware at different times. http://www.planetary.org/blog/article/00002182/.

The Phoenix Mars Lander ceased communications last November, after successfully completing its mission and returning unprecedented science data to Earth. Launched Aug. 4, 2007, Phoenix safely touched down on Mars on May 25, 2008, at a site farther north than where any previous spacecraft had landed. During the first quarter of 2010, teams at JPL will listen to see if Phoenix is still able to communicate with Earth. Springtime thaw images may also be available.

These views are a portion of a HiRISE image which is available in full-frame at http://hirise.lpl.arizona.edu/ESP_014393_2485.