THE MARS BUG: As this article in the Times notes, life on Mars may not be a blessing:

The search for life on Mars, now more than a century old, is still not finally resolved. But the odds that life existed there and may still exist are shortening, according to planetary experts, Dr Kargel said.

Nobody any longer expects Martian life forms to be anything like those on Earth. But there remains a possibility that bacteria or other microscopic organisms may survive in regions where there is still water. On Earth, almost every imaginable habitat, including deep underground, has specialised bacteria — called extremophiles — living and thriving.

The risks are twofold: probes sent from Earth may contaminate Mars with terrestrial bacteria, wrecking future studies of Martian life; or, more important, bacteria brought back from Mars may contaminate the Earth with unpredictable effects.

Here’s a column on the subject that I wrote a while back.