Rafting Rocks
NASA/JPL/University of Arizona
Rafting Rocks
ESP_023314_1440  Science Theme: 
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This image shows some interesting features where smoother, dark areas with straight sides are separated by narrow channels of higher material.

This is especially clear in the southern portion of the image (rotated so north is at approximately 11 o'clock, 3.2 kilometers or 2 miles across). It looks as if a flat solid surface broke up, and then the individual pieces were rafted apart.

In other areas of Mars, similar features formed when a layer of lava solidified on top of still-molten rock. The solid layer at the surface broke apart either when it contracted as it cooled, or when the liquid below it flowed and dragged along the bottom of the top layer of solid rock.

However, this area of the Hellas basin is not expected to have any volcanic activity. Hellas is a huge, old impact crater, filled with sediments and heavily eroded. In addition, there are subtle differences in the textures here that make this look different from the plate-like lava we find in other areas of Mars. Instead, perhaps something similar happened, but with a mixture of ice and rock instead of lava.

It's possible that a freezing mudflow was pulled apart here, with a frozen upper layer breaking and rafting apart on top of slushy material. When the underlying slushy ice later froze, it would have expanded and been squeezed up between the plates, creating the raised ridges between them.

Written by: Ingrid Daubar  (25 October 2011)
 
Acquisition date
18 July 2011

Local Mars time
14:16

Latitude (centered)
-35.926°

Longitude (East)
58.569°

Spacecraft altitude
259.4 km (161.2 miles)

Original image scale range
52.2 cm/pixel (with 2 x 2 binning) so objects ~157 cm across are resolved

Map projected scale
50 cm/pixel and North is up

Map projection
Equirectangular

Emission angle
6.0°

Phase angle
34.3°

Solar incidence angle
39°, with the Sun about 51° above the horizon

Solar longitude
329.9°, Northern Winter

For non-map projected images
North azimuth:  97°
Sub-solar azimuth:  35.3°
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POSTSCRIPT
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.