Today in the New York Times' Arts & Ideas section, I have an article about John Rummel, NASA's "planetary protection officer". He's the guy who makes sure that our space probes are sterilized as much as possible -- so that we don't accidentally send Earth microbes to Mars and seed the red planet with life. "The best way to find life on Mars is to bring it from Florida," as Rummel puts it. But sterilizing a spacecraft is hellaciously difficult. Among other things, it requires baking the component parts in a 233.1-degree-Fahrenheit oven -- which, of course, also requires you build the components so strong that they can endure being baked in an oven. Ever tried putting your Dell in the stove?

The upshot, as I discovered, is that the very concept of planetary protection is somewhat controversial amongst space buffs. Because protection requires such care, it slows down the pace of space exploration considerably. At the nut of it is the following paradox:

At its heart, though, planetary protection is a weirdly philosophical task, simply because there is no proof that life exists anywhere else. What precisely are we protecting against? Mr. Rummel will bend over backward to keep alien life from harm, while cheerfully admitting he is not sure there actually is any. Planetary protection is thus like an Xtreme form of environmentalism. When Galileo finished its mission to explore Jupiter last fall, NASA chose to destroy the probe by flying it into the planet, so it wouldn't accidentally crash on Europa and infect it.

But this caution, Mr. Rummel notes, is not merely about protecting life. It is about protecting science. If a probe were to accidentally seed Mars with Earth microbes, scientists might later mistake them for natives. "The point is to be able to tell" that there is nothing there, he said.