Martian Relief

A new topographic map has provided the sharpest views yet of the martian landscape, including the plateaus and lowlands that hint at the processes that shaped the planet. The maps, unveiled in tomorrow's Science, "allow you to settle issues once and for all that have been contested in Mars geology for 25 years," says Jeff Moore, a planetary geologist with the NASA Ames Research Center in Moffett Field, California.

The new map was made by bouncing laser light off the martian surface and using its round-trip time to determine distance. The map reveals a dramatic landscape of higher highs and lower lows, with a total range in elevation of 30 kilometers (km), compared to just 20 km for Earth. "We now have a definitive picture of the shape of the whole planet," says David Smith of the Goddard Space Flight Center in Greenbelt, Maryland, principal investigator of the instrument, called the Mars Orbiter Laser Altimeter (MOLA), that gathered the data from its perch aboard the Mars Global Surveyor spacecraft.

The new view may help explain why Mars is lopsided--thin-crusted, low, and smooth in the north, and thick-crusted, high, and crater-scarred in the south. Although MOLA found no direct evidence of plate tectonics such as mountain belts or earthquake faults, several features suggest an unprecedented amount of past volcanic activity, signaling a hot interior.

MOLA's data also tend to refute the idea of a huge asteroid impact that would have blown apart and thinned the crust in the north. The maps show no sign of a giant northern crater, and the north-south boundary is too irregular to be a circular crater wall. Instead, MOLA's team concludes that the boundary is a mosaic of regional effects, shaped by such factors as erosion, volcanism, and debris flung up from a southern impact.

Experts are impressed with the data, which reveal a host of other details, including the size of the polar ice caps. "We're seeing things that nobody had an inkling existed," adds Bruce Jakosky, a geologist at the University of Colorado, Boulder. "In a sense we're seeing the planet for the first time."