An Alluvial Fan in a Low-Latitude Crater
An Alluvial Fan in a Low-Latitude Crater
ESP_028799_1565  Science Theme: Fluvial Processes
On Earth, alluvial fans form in desert regions when heavy but sporadic rainfall washes debris from upslope and deposits it in a wedge-shaped fan on the lower slopes below.

On Mars, alluvial fans are sometimes visible in impact crater basins, as material from the steep rims is transported radially inward to the relatively flat floor. Because this is a water-driven process on Earth, and therefore might work the same way on Mars, scientists study Martian alluvial fans order to try to better understand the climate history and possible warmer, wetter past of Mars.

This image, along with its stereo companion, displays an alluvial fan on the floor of a large, 60-kilometer (38 mile) diameter equatorial crater. It is one of several present in the crater (see ESP_017340_1565). This one looks particularly nice in the anaglyph, as there are well-delineated ridges in the fan that stand above the crater floor. These ridges are inverted channels, which form when the floor of a channel is more resistant to erosion than the surrounding surface. This can happen if the floor of the channel is cemented by minerals deposited from water, filled by lava, or simply covered by larger rocks which are hard for the wind to sweep away.

Written by: HiRISE Targeting Specialists (narration: Tre Gibbs)  (4 June 2014)

This is a stereo pair with ESP_029221_1565.
Acquisition date
17 September 2012

Local Mars time

Latitude (centered)

Longitude (East)

Spacecraft altitude
257.7 km (160.2 miles)

Original image scale range
52.1 cm/pixel (with 2 x 2 binning) so objects ~156 cm across are resolved

Map projected scale
50 cm/pixel and North is up

Map projection

Emission angle

Phase angle

Solar incidence angle
59°, with the Sun about 31° above the horizon

Solar longitude
173.2°, Northern Summer

For non-map projected images
North azimuth:  97°
Sub-solar azimuth:  24.8°
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IRB color
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Black and white
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non-map           (115MB)

IRB color
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non-map           (132MB)

Merged IRB
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Merged RGB
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RGB color
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Map-projected, reduced-resolution
Full resolution JP2 download
Anaglyph details page

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IRB: infrared-red-blue
RGB: red-green-blue
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Black & white is 5 km across; enhanced color about 1 km
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All of the images produced by HiRISE and accessible on this site are within the public domain: there are no restrictions on their usage by anyone in the public, including news or science organizations. We do ask for a credit line where possible:

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.