Evidence from the Mars Express High Resolution Stereo Camera for a frozen sea close to Mars’ equator

The Cerberus Fossae fissures on Mars are the source of both lava and water floods 2-10 million years old. Evidence for resulting lava plains has been identified in eastern Elysium, but seas and lakes from these fissures and previous flooding events were presumed to have evaporated and sublimed away. HRSC images from the ESA Mars Express spacecraft indicate that they may still be there. We present evidence consistent with a presently-existing frozen body of water, with surface pack-ice, around +5º latitude and 150º east longitude in southern Elysium. It measures about 800 km x 900 km and averages up to 45 metres deep: similar in size and depth to the North Sea. Its age from crater counts is 5 ±2 Ma. If our interpretation is confirmed, this is one place that might preserve evidence of primitive life, if it has ever developed on Mars