Data received from the Mars Express space probe contain what are regarded as evidence that there was an ocean on Mars. In the past, certain areas had already been identified as shores of an ancient sea, now sediments have been identified suggesting that it was the bed of an ocean within those shores.

One of the instruments of the space probe Mars Express is the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding), a radar developed by NASA and the Italian Space Agency. The MARSIS radar sends a medium frequency pulse – between 1.5 and 5.5 MHz – to Mars, a part of the pulse is reflected by the surface but another part penetrates into the underground and is reflected by the elements that compose it. The analysis of the reflected pulses allows to determine the composition of the underground.

In November 2005, an underground frozen lake was discovered on Mars near Chryse Planitia thanks to the MARSIS and in 2007 this instrument was used to estimate the amount of ice in Mars’ south pole.

In the case of the search of the ocean, the MARSIS was used to make scans that reached 60-80 meters deep underground. In those layers scans found evidence of the presence of low density sedimentary granular materials resulting from the erosion of water but they also found the presence of ice.

The analysis of data collected by the Mars Express space probe for over two years has led to propose the possibility that an ocean existed in two separate periods. The discoveries made in recent years lead us to think that about 4 billion years ago the Mars climate was more similar to Earth so there could’ve been liquid water to form an ocean. Another possibility is that about 3 billion years ago following a big impact there was a warming that led to the melting of underground ice so for a while there may have been an ocean.

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Should any form of life have been born in one of the oceans of Mars it’s more likely that it happened in the most ancient one because if an ocean existed 3 billion years ago probably it lasted too shortly before the water got frozen again. The possibility that Mars has ever hosted life forms remains an open question.

This research carried out by the Mars Express space probe adds more information about the history of Mars, the question that remains is: if there was an ocean what happened to its water? The search goes on.