Very Small Martians

Martians may want to kill us, perhaps they are huddled deep beneath those supposed ice lakes waiting for the first ride over to the blue planet. But the thing is, they are probably so small that we won't see them coming. You think I'm kidding, but this is exactly the worry, as The Times UK describes it today:

Earth must take precautions to avoid contamination from lifeforms that must now be presumed to exist on Mars, leading scientists gave warning yesterday. Potentially deadly microorganisms could be returned to Earth on a probe which is being planned to collect samples from the Martian surface. The warning comes after a detailed scientific analysis of data sent back by the roving vehicle Opportunity which landed on Mars on January 25. Jeffrey Kargel of the US Geological Survey said that protection of our own planet from alien forms of life requires the assumption that Martian life exists. “Before proceeding with sample returns or human missions to Mars, we must review measures for planetary biological protection.”

[Thanks Art Caplan]