This brand-new, six-meter-diameter crater was shot by HiRISE on (left) October 18, 2008, and (right) January 14, 2009. The bright material in the left-hand image is water ice exposed at the crater's bottom, which is estimated to be 1.3 meters deep. In the right-hand image, the ice has sublimated away in the northern-hemisphere summer or has been obscured by fresh dust.

...And More Ice on Mars

The poles aren't the only places on Mars with ice. JPL's Mars Reconnaissance Orbiter (MRO) found that several small meteorites had struck Mars in the last year, uncovering bright white water ice in the resulting craters. The fact that there was ice at all was surprising—the icy craters were in latitudes thought to be too low, and therefore too dry, for ice to exist.

The icy craters were between the latitudes of 45 and 55 degrees north—near where Viking 2 landed in 1976. In fact, had Viking dug just 10 centimeters deeper into the ground, it likely would've hit ice. Instead, the discovery had to wait another 33 years.

On August 10, 2008, MRO's Context Camera, which returns images of Mars in 30-kilometer-wide swaths, noticed a meteor crater that hadn't been there just 67 days before. Scientists then took a closer look with the High Resolution Imaging Science Experiment (HiRISE), and they saw brilliant white. The area was too small for MRO's onboard spectrometer to analyze, but the researchers found a larger, newly formed crater nearby and confirmed the suspicious material to indeed be water ice. In total, the team found ice in five small craters, which ranged in depth from a half-meter to 2.5 meters deep. After a few months, much of the whiteness disappeared as the ice sublimated and became mixed in with dust.

The 18 researchers from six institutions reported their findings in the September 25 issue of Science. —MW