An Unearthly Landscape, yet Somewhat Familiar

The allure of life on the planet next door has tugged at Earth’s imagination for centuries. And yet, admits Donna Shirley, manager of NASA’s Mars program, “we know very little about Mars.”

Earthlike in some ways but truly otherworldly in others, Mars is small, with less than half the gravitational attraction of Earth. It has no atmospheric blanket to trap the heat, so the surface gets icy cold. It has no ozone umbrella to block ultraviolet solar energy.

The Viking spacecraft, which visited Mars in 1976, discovered no signs of life but did find a highly reactive soil chemistry that chews up organic molecules before they have a chance to stick together. The planet’s surface is more sterile than many Earth laboratories. If there is life anywhere, it would have to be hiding deep beneath the surface. Every trace of carbon appears to be locked in the atmosphere.

In other ways, however, the pink landscape looks a lot like home, with rolling sand dunes embellished with fine ripples, boulder-strewn fields reminiscent of the Wild West, and 50,000-foot-high volcanic peaks. The soil is the same heft as good farming soil on Earth.

The planet has two polar caps of frozen carbon dioxide and water, and possibly Marsquakes similar to earthquakes, though not as frequent. The ground is scarred by parallel fractures that look a lot like Earth’s fault lines.

One major difference is that Mars appears to be bone dry--despite clear evidence that water once flowed freely on its surface. Finding out what happened to the water will be the highest priority in this and future missions, because only water has the remarkable chemical and physical properties that make life as we know it possible.