This cross-section view of underground layers near Mars' south pole is a radargram based on data from the Shallow Subsurface Radar (SHARAD) instrument on NASA's Mars Reconnaissance Orbiter. Researchers interpret the zone that is nearly free of radio-wave reflections (hence dark in the radargram) to be composed of frozen carbon dioxide, or "dry ice."

The newly found deposit of dry ice contains enough carbon dioxide to dramatically increase the total amount of atmosphere on Mars when the frozen carbon dioxide vaporizes, as climate models suggest it does at times when the planet's tilt increases. Mars' current atmosphere is about 95 percent carbon dioxide, and this deposit contains up to about 80 percent as much carbon dioxide as the atmosphere does.

This cross section covers a transect about 330 kilometers (205 miles) long in a region from about 86 degrees to 87 degrees south latitude and 280 degrees to 10 degrees east longitude. The vertical dimension of the graphic is time delay of the radar echoes. The depth of the tallest portion of the cross section corresponds to about 20 microseconds difference in time delay, which can be converted to roughly 1.7 kilometers (about 1 mile).

SHARAD was provided by the Italian Space Agency. Its operations are led by Sapienza University of Rome, and its data are analyzed by a joint U.S.-Italian science team. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter for the NASA Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, built the spacecraft.