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ESA’s Mars Express radar gives strong evidence for former Mars ocean

ESA’s Mars Express has returned strong evidence for an ocean once covering part of Mars. Scientists analysed more than two years of data retreived by the MARSIS radar and found that the northern plains of Mars are covered in low-density material reminiscent of an ocean floor, possibly ice-rich sedimentary deposits.

The existence of oceans on ancient Mars has been suspected before and features reminiscent of shorelines have been tentatively identified in images from various spacecraft. But it remains a controversial issue.

Two oceans have been proposed: 4 billion years ago, when warmer conditions prevailed, and also 3 billion years ago when subsurface ice melted following a large impact, creating outflow channels that drained the water into areas of low elevation.

This later ocean would however have been temporary. Within a million years or less, the water would have either frozen back in place and been preserved underground again, or turned into vapour and lifted gradually into the atmosphere. »