Icebergs on Early Mars

The smooth topography of the Martian Northern Lowlands has been classically equated to an ancient ocean basin. The High-Resolution Imaging Science Experiment (HiRISE) onboard the Mars Reconnaissance Orbiter (MRO) provides images of unprecedented resolution of the Martian surface at scales of 25 to 32 cm per pixel. Our analysis of HiRISE imaging reveals the presence of scour marks over the northern plains and other large basins, along with meter-sized boulders distributed in clusters and mounds. Here we show that the association of scour marks with clusters of boulders and mounds on the northern plains of Mars and the Hellas basin can be related to the dual processes of ice keel scouring and ice rafting of both glacial and non-glacial detritus. These processes are well documented on Earth, where they result in distinctive morphologies and sedimentary patterns recognizable on the ocean floor, comparable to those we identified on Mars. We conclude that the presence of icebergs floating in very cold oceans early in the history of the planet can explain the observed occurrence of scour marks and boulder distribution on the major lowlands of Mars.