by JOSHUA A. KRISCH
What really lies across the surface of Mars? Rovers have scurried about the red planet for years, drilling, scooping and analyzing for signs of life, past or present. But to really understand the Martian landscape, scientists need to look at the entire surface. What they have needed is a global geologic map.
The red planet is long overdue for a new one. The last major effort in Martian cartography was published in 1987, scraped together from the early Viking probes’ scant images and datasets. Since then, four additional orbiters with superior imaging capabilities have journeyed into Martian orbit, collected data and transmitted their findings back to Earth.
Now, scientists at the United States Geological Survey have used that data to create an updated map of the entire Martian surface. The new map shows that ancient rock — dating back billions of years ago, when Mars’s environmental conditions might have closely resembled Earth’s— exists in many more locations than previously thought. Because the map highlights the location of the oldest rocks on Mars, it could help future missions chart a course for these areas.
“We are disproportionately interested in the early part of Martian history,” said David Beaty, the chief scientist for the Mars Exploration Directorate at the Jet Propulsion Laboratory in Pasadena, Calif., who was not involved in the research. “It was during that period that more water would have been around, which is one of the key aspects of the origin of life.”
The project, funded by NASA, was not simply a compilation of photographs from Martian orbit. Recent probes, such as the Mars Global Surveyor launched in 1996, were outfitted with advanced topographical instruments that helped cartographers pinpoint the subtler features of the Martian landscape.
One important instrument was the laser altimeter, which could fire up to 600 million laser beams at a planet’s surface. By measuring the time it took to bounce a laser beam off the Martian landscape, the researchers estimated the heights of peaks and the depths of valleys. This tool, among others, “greatly improved topographic mapping accuracy of the planet,” said Kenneth L. Tanaka, a scientist at the geological survey and lead author of the map. “It’s based on a lot more data than the previous Mars map.”
Digital mapping technology also played an important role in the research. Dr. Tanaka, who was a junior author on the original 1987 Mars map, recalled trying to chart the Martian surface before the digital age.
“We were drafting maps by hand, using ink,” he said.
The new Mars data is already available through the geologic survey’s website, and Dr. Tanaka says he suspects that scientists around the world will make use of it. But at least one important revelation has already come out of his research.
“We now have a better idea of where really old rocks are and where really young rocks are,” Dr. Beaty said.
Future Mars missions will probably focus on older rocks, because they represent a chapter of Martian history that may have featured water. And if more ambitious plans to send humans to Mars ever pan out, astronauts will want to find safe and scientifically meaningful locations to land and begin their research.
“The map is a fantastic piece of work,” Dr. Beaty said. “It’s a pretty big deal for forward exploration of the planet.”