Microbes on Mars pose risk to Earth

Earth's defences may need to be boosted against the risk of potentially deadly microbes returning on board space probes sent to study Mars, according to leading scientists.

The warning follows a detailed scientific analysis of data sent back by the roving vehicle Opportunity, which landed on the Martian surface on 25 January this year.

Jeffrey Kargel of the United States Geological Survey said: "Before proceeding with sample returns or human missions to Mars, we must review measures for planetary biological protection."

The search for evidence of life on Mars - which has been going on for more than a century - has still not been resolved.

However, according to Dr Kargel, the odds that life existed there and may still exist are shortening.

The latest findings, published in Science magazine, reveal a series of risks faced by those examining the Red Planet.

Researchers claim that probes sent from Earth may contaminate Mars with terrestrial bacteria, wrecking future studies of Martian life.

More importantly, bacteria brought back from Mars may contaminate the Earth with unpredictable effects.