Julie Kalista
Online Editor

The results also provide important clues about the still-mysterious geological history of Mars.

Marsis found evidence that these buried craters - ranging from about 130 to 470 kilometers in diameter - are under much of the northern lowlands' volcanic lava and sediment. With Marsis "it's almost like having X-ray vision," says Thomas R. Watters of the National Air and Space Museum's Center for Earth and Planetary Studies, Washington. "Besides finding previously unknown craters, we've also confirmed that some subtle, roughly circular, topographic depressions in the lowlands are also related to impacts."

Impacts that cause craters can happen anywhere on a planet, so areas with fewer craters are generally interpreted as younger surfaces where geological processes have erased the impact scars, according to ESA. However, the new Marsis data indicate that the underlying crust is extremely old. "The number of buried craters larger than 200 kilometers in diameter tells us that the underlying crust in the northern lowlands must be ancient, dating to the Early Noachian epoch, which lasted from the planet's birth to about four thousand million years ago)," says Jeffrey Plaut, Marsis co-principal investigator.

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