Science Article

Tiny carbon nuggets in meteorites from Mars were formed by cooling magma, not left by ancient alien microbes. That's both good news and bad news for astrobiologists.

The 1996 discovery of carbonate structures in meteorite ALH-84001 – which travelled to Earth from Mars more than 13,000 years ago – was hailed at the time as evidence that alien microbes once lived on the red planet. However, subsequent studies of both the carbonate structures and tiny nuggets of macromolecular carbon (MMC) in the meteorite cast doubt on the claims.

Paradoxically, the find actually boosts prospects for finding signs of ancient life in Martian rocks. The carbon in MMC was originally chemically reduced – meaning it carries extra electrons and is quick to react. Such readily available and reactive carbon could have joined with other elements to create complex chemical molecules, perhaps even life.

NASA and the European Space Agency (ESA) were planning a pair of joint missions to Mars that could have made important strides in the search for past or present life.

The ExoMars Trace Gas Orbiter, which was to launch in 2016, would have followed up on hints of methane discovered in the Martian atmosphere by previous missions. The gas is of particular interest as it is commonly produced by microbes on Earth.

ExoMars ( Mars Rover)

The ExoMars rover, which had been slated for launch in 2018, would have drilled beneath the Martian surface to get samples of pristine material, possibly including complex carbon-based molecules that could have provided clues to past Martian life.

The Mars budget was slashed as a result, with NASA's contribution to the flagship ExoMars mission the main casualty.

NASA still hopes to mount a less costly mission to Mars in 2018, but it might not land on the surface. The agency has not specified exactly where it would go, but orbiters tend to be less expensive than rovers.

The proposed budget also confirms that NASA plans to continue building the James Webb Space Telescope with a launch targeted for 2018, and continue payments to private space companies like SpaceX to help them develop space taxis that could take crew to the International Space Station.

NASA wants $830 million for space taxi development in 2013. It asked for a similar amount in 2012, but Congress cut it by more than half, to about $400 million.