Looking Beneath Mars’ Skin

Scientists are finding an older, craggier face of Mars buried beneath the surface, thanks to pioneering sounding radar co-sponsored by NASA aboard the European Space Agency’s Mars Express spacecraft.

A radargram presenting data collected by the Mars Advanced Radar for Subsurface and Ionospheric Sounding during the 1,886th orbit of the European Space Agency’s Mars Express orbiter. It shows parabolic-shaped echoes from the rim walls of a buried impact basin.
Credit: NASA

Observations by the first project to explore a planet by sounding radar strongly suggest that ancient impact craters lie buried beneath the smooth, low plains of Mars’ northern hemisphere. The technique uses echoes of waves that have penetrated below the surface.

"It’s almost like having X-ray vision," said Dr. Thomas R. Watters of the National Air and Space Museum’s Center for Earth and Planetary Studies, Washington. "Besides finding previously unknown impact basins, we’ve also confirmed that some of the subtle topographic depressions mapped previously in the lowlands are related to impact features."

Studies of how Mars evolved aid understanding of early Earth. Some signs of the forces at work a few billion years ago are more evident on Mars because, on Earth, many of them have been obliterated during Earth’s more active resurfacing by tectonic activity. Studying the geological history of Mars can also help scientists determine whether or not the Martian environment was ever capable of supporting life as we know it.

Watters and nine co-authors reported the findings in the Dec. 14, 2006 issue of the journal Nature.

The researchers used the orbiter’s Mars Advanced Radar for Subsurface and Ionospheric Sounding, which was provided to the European Mars mission by NASA and the Italian Space Agency. The instrument transmits radio waves that pass through the Martian surface and bounce off features in the subsurface with electrical properties that contrast with those of materials that buried them.

Composite of northern springtime images by the Mars Global Surveyor

The findings bring planetary scientists closer to understanding one of the most enduring mysteries about the geologic evolution of the planet. In contrast to Earth, Mars shows a striking difference between its northern and southern hemispheres. Almost the entire southern hemisphere has rough, heavily cratered highlands, while most of the northern hemisphere is smoother and lower in elevation.

Since the impacts that cause craters can happen anywhere on a planet, the areas with fewer craters are generally interpreted as younger surfaces where geological processes have erased the impact scars. The abundance of buried craters that the radar has detected beneath Mars’ smooth northern plains means the underlying crust of the northern hemisphere is extremely old, "perhaps as ancient as the heavily cratered highland crust in the southern hemisphere."

Learning about the ancient lowland crust has been challenging because that crust was buried first by vast amounts of volcanic lava and then by sediments carried by episodic flood waters and wind.

Related Web Pages

Smithsonian National Air & Space Center for Earth and Planetary Studies
A Flood of Mars Photos
Mars Advanced Radar for Subsurface and Ionosphere Sounding
Looking Down on Opportunity
Dr. Thomas R. Watters, Senior Scientist/Geologist