ALMOST everywhere you go on Earth, you encounter alien species that were introduced - often inadvertently - by humans. Now it seems possible that we have done the same to Mars. Despite stringent rules designed to prevent contamination, Earth microbes may have reached the Red Planet.That might look like a blow for efforts to detect Martian life. But, ironically, it may end up being the opposite. Some planetary scientists argue that if contamination is already likely, we should now throw caution to the wind (see "Overprotection may be hampering hunt for Mars life"). The strict rules actually hamper the search for life by adding unnecessary costs to missions, they say.Is there a case for relaxing the rules? Perhaps. If Mars has its own life, it should be different enough from Earth life for us to recognise it. If it doesn't, any bugs we find will be recognisably terrestrial. In either case, Earth life will struggle to colonise Mars. Recent arrivals are unlikely to thrive in the harsh conditions, and the possibility of them outcompeting any natives is about as likely as parrots colonising Antarctica and ousting the penguins.However, many life-detecting experiments rely on picking up whiffs of gas or traces of chemicals rather than finding life itself. Any relaxation of the laws must rule out the chances of earthly contamination leading to infuriating false positives.There's another factor too. While governments of most spacefaring nations have agreed to abide by the rules, the law is unclear on private companies such as SpaceX and Mars One, who are hoping to beat national agencies to Mars. Mars One has declared that it will play by the rules if it ever succeeds in starting the first human colony on Mars. But others may not follow suit.Elsewhere in the solar system, though, sterilisation rules remain vital - especially for icy moons such as Jupiter's Europa and Saturn's Titan, which are the best hopes for finding an independent origin of life.If a spacecraft crashed or melted through Europa's shell into the ocean beneath, it could have fatal consequences for everything living there. The only thing worse than not finding life - if it is there - would be finding it after we've destroyed it.
"This article appeared in print under the headline "Is there Earth life on Mars?"
