Comparing sonar maps and satellite images of Antarctica with images of Mars, a geologist has bolstered a long-held belief that some Martian channels may have been carved by ice, rather than catastrophic floods of liquid water. Terrestrial ice streams, which snake slowly beneath the frozen surface of Antarctica, were long invisible to normal satellite imaging until radar imaging made them visible in the late 1990s. And now, ship-based sonar missions map the area where these ice flows merged with the surrounding seafloor during the last Ice Age, carving telltale patterns.