Frosted Gullies in the Northern Summer
Frosted Gullies in the Northern Summer
ESP_019033_2495  Science Theme: Seasonal Processes
Many images show that Martian gullies have formed on impact crater walls in both the Northern and Southern hemispheres. Gullies such as the ones shown here have an alcove at the top of the crater wall and channels leading downhill to debris aprons that run out over the crater floor.

Some of these gullies show activity today with new material appearing on top of the debris aprons. Many scientists believe that these gullies have been carved by liquid water so this present-day activity is of immense interest. Recently however, an alternate theory has been gaining ground.

An analysis of gully activity in craters and on sand dunes shows that activity seems to only occur in the winter at the coldest time of year. The alternate suggestion for gully activity is that accumulations of frost in the gully alcoves starts an avalanche of loose material that does not involve liquid water.

This HiRISE image shows gullies on a crater wall in the North Polar region. Although it was late summer (2010) when we acquired this image, you can see frost within the gully alcoves. These alcoves are on the poleward facing crater wall and so spend much of the time in shadow. This allows the frost to survive. The full-image shows that the opposite (south-facing) wall has similar gullies, but no frost during this season. Scientists are analyzing many images like this in order to try and answer the broader question of whether liquid water is responsible for the these gullies or not.

Written by: Shane Byrne  (22 September 2010)

This is a stereo pair with ESP_018809_2495.
Acquisition date
18 August 2010

Local Mars time

Latitude (centered)

Longitude (East)

Spacecraft altitude
316.2 km (196.5 miles)

Original image scale range
65.4 cm/pixel (with 2 x 2 binning) so objects ~196 cm across are resolved

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50 cm/pixel

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Solar incidence angle
58°, with the Sun about 32° above the horizon

Solar longitude
134.9°, Northern Summer

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North azimuth:  102°
Sub-solar azimuth:  329.4°
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NASA’s Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, Calif., manages the Mars Reconnaissance Orbiter for NASA’s Science Mission Directorate, Washington. The HiRISE camera was built by Ball Aerospace and Technology Corporation and is operated by the University of Arizona.