Pit Crater near Elysium Mons
Pit Crater near Elysium Mons
ESP_043222_2035  Science Theme: Tectonic Processes
This image was taken of an area on the lower southeastern flank of the volcano Elysium Mons. In the center is a small, dark pristine-appearing pit approximately 130 meters in diameter, which is clearly visible among the numerous small impact craters that are heavily covered by dust and sediment. These pit craters are usually appear in the younger Tharsis volcanic region, but this is one of the first seen in the older Elysium volcanic region.

Garden variety craters are excavated by impacts and are characterized by raised rims, sloped walls and surrounded by ejecta blankets, but pit craters are simply sink holes in the ground with near vertical walls and floors that are only visible when the sun is high in the sky. They are deep holes that may lead to underground caves in volcanic terrain. This isolated pit crater is located in a lava field that is crisscrossed by long, linear troughs.

A commonly invoked hypothesis to explain these troughs is that they are collapsed lava tubes, essentially tunnels formed by underground rivers of lava. Lava tube collapse may begin with the buckling of its roof at one location where the roof is thinnest. At this point, light enters into the permanent darkness of the cave from above, forming a skylight. Pits or skylights are distinct from impact craters: they appear as dark, roughly circular shadowed holes because of their steep walls, while the shadows cast by impact craters generally shade only a portion of the crater floor, because the slopes of the walls are shallower. When this picture was taken, sunlight directly lit part of the floor of this pit crater, illuminating the large boulders (see close up image) on its southeastern slope.

The first skylights were discovered in 2007 on Mars, and in 2009 on the Moon. The famous Devil’s Throat is Hawaii is a good Earth-example: it’s 50 meters wide and accessible by foot. Pit craters provide a window into the subsurface structure of Mars, and prior to collapse, might have also provided potential habitats where organisms could be protected from the harsh, sterilizing UV radiation experienced at the surface.

Written by: Henrik Hargitai and Ginny Gulick (audio: Tre Gibbs)  (27 January 2016)
Acquisition date
16 October 2015

Local Mars time

Latitude (centered)

Longitude (East)

Spacecraft altitude
282.6 km (175.6 miles)

Original image scale range
28.6 cm/pixel (with 1 x 1 binning) so objects ~86 cm across are resolved

Map projected scale
25 cm/pixel and North is up

Map projection

Emission angle

Phase angle

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

Solar longitude
55.5°, Northern Spring

For non-map projected images
North azimuth:  97°
Sub-solar azimuth:  10.3°
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Black & white is 5 km across; enhanced color about 1 km
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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.