H. G. Wells famously ended The War of the Worlds by having the Martians laid low by terrestrial microorganisms; as the flu season settles around New York, I know how they felt. (By the way, if the Martians' oversight seems dumb for an allegedly superior civilization, remember that Wells published his story in 1898, just 20 years after Pasteur published the Germ Theory of Disease.) But all indications are that Wells had the situation backward. We humans will be the technologically advanced race invading Mars. The special section on human exploration of our reddish neighbor, beginning on page 40, describes how we might do it within the next few decades. Cross-contamination by terrestrial or hypothetical Martian microbes will be one of the concerns for mission planners.
What dangers might Martian germs pose to human colonists or to Earth dwellers if they were accidentally brought back and escaped? The catastrophic line of speculation says that microbes hardened to life on Mars would run amok in Earth's cushy biosphere. But I'll climb out on the opposing limb and suggest that the poor things would get stomped. Our oxygen-rich atmosphere could be highly damaging. More significantly, because terrestrial life has evolved to survive in a competitive milieu, cells used to the quiet, arid emptiness of Mars might not have adequate defenses against our own hungry, territorial biota.
This article was originally published with the title The Second War of the Worlds.