The European Space Agency’s Mars Express orbiter has found further evidence than an ocean may have covered parts of the red planet billions of years ago.

The spacecraft, which has been orbiting Mars since late 2003, detected sediments on the planet’s northern plains that are reminiscent of an ocean floor in a region that also has been identified previously as the site of ancient Mars shorelines, according to researchers.

“We interpret these as sedimentary deposits, maybe ice-rich,” study leader Jeremie Mouginot of the Institut de Planetologie et d’Astrophysique de Grenoble in France and the University of California, Irvine said in a statement. “It is a strong new indication that there was once an ocean here.”

As part of its mission, Mars Express uses a radar instrument, called Marsis, to probe beneath the martian surface and search for liquid and solid water in the upper portion’s of the planet’s crust.

The researchers analyzed more than two years of Marsis data and found that the northern plains of Mars are covered in low-density material that suggest the region may have been an ancient ocean.