Spring in Inca City I
NASA/JPL/University of Arizona
Spring in Inca City I
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Every winter a layer of carbon dioxide ice—or, dry ice—condenses in the Southern polar region, forming a seasonal polar cap less than 1 meter deep. Early in the spring the ice layer begins to sublimate (going directly from a solid to gas) from the top and bottom of the ice layer. Under the ice gas pressure builds up until a weak spot in the ice layer ruptures. The gas rushes out and as it escapes it erodes a bit of the surface.

Fine particles are carried by the gas to the top of the ice and then fall out in fan-shaped deposits. The direction of the fan shows the direction either of the wind or down the slope. If the wind is not blowing a dark blotch settles around the spot the gas escaped.

This region is known informally as Inca City, and it has a series of distinctive ridges. On the floor between the ridges are radially organized channels, known colloquially as spiders, more formally called "araneiforms." The channels have been carved in the surface over many years by the escaping pressurized gas. Every spring they widen just a bit.

This was the first image to be acquired after the sun rose on Inca City, marking the end to polar night. A few fans are visible emerging from the araneiforms.

Written by: Candy Hansen  (13 November 2014)
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Acquisition date
06 August 2014

Local Mars time:
16:23

Latitude (centered)
-81.447°

Longitude (East)
295.885°

Range to target site
257.8 km (161.1 miles)

Original image scale range
51.6 cm/pixel (with 2 x 2 binning) so objects ~155 cm across are resolved

Map projected scale
50 cm/pixel

Map projection
Polarstereographic

Emission angle:
17.8°

Phase angle:
103.8°

Solar incidence angle
89°, with the Sun about 1° above the horizon

Solar longitude
173.7°, Northern Summer

For non-map projected images
North azimuth:  100°
Sub-solar azimuth:  35.4°
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HiView

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IRB: infrared-red-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/JPL/University of Arizona

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.