Sixty-five years ago today, on “mischief night,” Orson Welles spooked millions of radio listeners with his legendary “War of the Worlds” broadcast. Many who did not hear the “only fiction” disclaimers fled their homes to avoid imminent gas attack by marauding Martians who had landed in Grovers Mill, N.J., creating traffic jams and sending dozens to the hospital for shock and hysteria.

Could this happen today? In an age of multiple media, radio has lost some of its punch, but a well-executed Internet hoax of an alien invasion might set some hearts racing. Public fascination with the possibility of extraterrestrial life shows no sign of abating, and the scientific search for it has gained respectability in recent years with the formation and growth of NASA’s Astrobiology Institute.

The threat of invasion by intelligent, high-tech aliens is not one to lose sleep over. Why would aliens even want our Earth? One of the few things we have learned about planets is that they are complex individuals—no two will be exactly alike. Aliens will surely be better adapted to their own planets, and it is highly unlikely that they will be able to breathe our air or infect us, let alone eat us—at least not without some expensive and messy food processing. As entertaining as “War of the Worlds” was for those who did not need treatment for shock or hysteria afterwards, Welles’ scenario is not a likely one.

But there is another threat that deserves immediate attention: the remote but scary possibility of accidental microbial contamination from space. In H.G. Wells’ original “War of the Worlds” (1897), the superior Martian invaders were defeated in the end by “the humblest thing that God in His wisdom put upon this Earth”—by microbes, who caused the defenseless Martians to catch colds and die.

You may not know it, but NASA is guarding you against this danger through the “Office of Planetary Protection,” which is charged with preventing the inadvertent spreading of life between worlds during space exploration. Our efforts to prevent “back contamination”—the accidental return to Earth of dangerous alien microbes from other worlds—are the subject of a new NASA report that details how we might test for living organisms in returned samples. NASA intends to return a sample from Mars within the next decade or two.

NASA is also making concerted efforts to prevent “forward contamination,” in which we would be the evil alien invaders who seed other planets with Earth bugs. NASA crashed the Galileo spacecraft into Jupiter last month in an effort to avoid the remote possibility that the spacecraft would one day smash into Europa and cause an unforgivable planetary pandemic on that watery moon. Three new spacecraft are headed for landings on Mars in the next couple of months, and their missions are all focused on the search for current life, past life and conditions conducive to life. These craft have all been carefully sterilized so that we will not return to Mars one day to find Earthly life forms that we accidentally deposited in an earlier voyage.

Although issues of interplanetary contamination may seem fantastic, they force us to confront the limits of our knowledge about life and where it might thrive. Some prominent scientists have criticized “planetary protection” as based on dubious science, but there is humility and wisdom in this approach. It is true that if our current concepts of biology are correct, then there is virtually no possibility that an alien organism, not adapted for this world, could dangerously out-compete the locals who are marvelously fit to survive here.

“Planetary protection” contains an implicit acknowledgement that scientific knowledge is never final or complete. We have been wrong before in the history of space exploration, and we should not wager our planet’s safety on the assumption that we need not worry about extraterrestrial life accidentally brought back to Earth. All of our ideas about life elsewhere are based on extrapolation from one example—Earth life—and science is not at its best when basing sweeping conclusions on a sample size of one. Although common sense strongly suggests that the threats are minimal, we are wise not to ignore them.

Let’s face it, human intelligence puts us at greater risk than the possibility that malevolent aliens may someday wander through our corner of the galaxy. The fact that we take planetary protection seriously, though, hints that we may have the tools to tame the beast within and use our brains wisely in the service of life. Through the “safe exploring” embodied in planetary protection, we take the best in our nature with us as we take our first steps beyond the Earth.

There is no way to stay 100 percent safe from scary monsters that might lurk in the cosmos, but it would be paranoid and self-defeating to avoid exploration out of vague fears of the unknown. With planetary protection, we strive to insure that, through the marvelous tricks of space exploration, we do not give or receive any unwelcome and dangerous planetary treats.

David H. Grinspoon is a planetary scientist at the Southwest Research Institute in Boulder Colorado. His book Lonely Planets: The Natural Philosophy of Alien Life will be published next week.