Defrosting in Inca City
Defrosting in Inca City
ESP_011544_0985  Science Theme: Polar Geology
This image shows a region known as “Inca City” near the South Pole, so named because its rectilinear grid of ridges is reminiscent of the ruins of an ancient city.

Of course, these ridges are not tumble-down stone walls, but their origin is not known for certain. The ridges most likely have been exhumed by aeolian stripping of overlying material and are not related in origin to the nearby south polar ice deposits.

One possible formation scenario is the filling of cracks (perhaps produced on the floor of an impact crater) by erosionally-resistant material, such as volcanic rock. Now, the ridges are muted by overlying material, most likely dust. In this image, taken in southern spring, the ridges are also covered by seasonal carbon dioxide ice. The dark spots are areas where the ice is translucent enough to see the darker material beneath it and/or where darker material beneath the ice has escaped to the surface and is blown by near-surface winds, creating long, dark streaks.

This image is one in a series of images positioned near this location for the purpose of monitoring these dark spots and streaks throughout southern spring and early summer to ascertain how they form and change as the seasonal ice disappears.

Written by: Kate Fishbaugh  (15 July 2009)
Acquisition date
12 January 2009

Local Mars time

Latitude (centered)

Longitude (East)

Spacecraft altitude
246.7 km (153.3 miles)

Original image scale range
49.5 cm/pixel (with 2 x 2 binning) so objects ~148 cm across are resolved

Map projected scale
50 cm/pixel

Map projection

Emission angle

Phase angle

Solar incidence angle
84°, with the Sun about 6° above the horizon

Solar longitude
189.9°, Northern Autumn

For non-map projected images
North azimuth:  112°
Sub-solar azimuth:  31.9°
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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.