Ooops! Mars Robots may have destroyed vital evidence of life

Mars landers and Rovers have been destroying signs of life, instead of identifying chemicals that could point to life. NASA's robot explorers may have been toasting them by mistake.

In 1976, many people's hopes of finding life on Mars collapsed when the twin Viking landers failed to detect even minute quantities of organic compounds - the complex, carbon-containing molecules that are central to life as we know it. "It contributed, in my opinion, to the fact that there were no additional [US lander] missions to Mars for 20 years," says Jeff Moore of NASA's Ames Research Center in Moffett Field, California.

The result also created a puzzle. Even if Mars has never had life, comets and asteroids that have struck the planet should have scattered at least some organic molecules - though not produced by life - over its surface.

Some have suggested that organics were cleansed from the surface by naturally occurring, highly reactive chemicals such as hydrogen peroxide. Then last year, NASA's Phoenix lander, which also failed to detect organics on Mars, stumbled on something in the Martian soil that may have, in effect, been hiding the organics: a class of chemicals called perchlorates.

At low temperatures, perchlorates are relatively harmless. But when heated to hundreds of degrees Celsius they release a lot of oxygen, which tends to cause any nearby combustible material to burn. For that very reason, perchlorates are used in rocket propulsion.