In H.G. Wells's "The War of the Worlds," Earth's unwitting defense against the Martian hordes comes in the form of pathogenic bacteria to which the invaders lack immunity.

In reality, earthlings have created an international network whose next great mission is to protect potentially fragile Martian life, should there be any, from earthly contamination.

Catharine "Cassie" Conley, the planetary protection officer at NASA - and possessor of perhaps the coolest title in the federal government - is in charge of that mission for the United States, and as a result is part of a small global team charged with keeping space exploration as clean as possible.

Conley is quick to joke that the coolest title at NASA actually came in the old days when agency divisions had simple names - Sun, Earth, Planets, Universe and so on - and there was a "director, Universe."

But her job is as serious as a NASA post can be. In addition to protecting potential extraterrestrial life and monitoring for contamination on trips back to Earth, the protection office oversees protocols that assure Earth ships are sterile enough on departure that if they do find evidence of anything living, it won't be some Earth-based organism that was missed during the cleaning process and dragged across the solar system.

Also important is logging which pathogens humans might be carrying at launch, so that if someone gets sick on the way back from a theoretical future trip to Mars, NASA can quickly determine whether it's a garden variety human bug or some new kind of Martian flu turning a homeward-bound space vehicle into a "plague ship."

So far, the worries of the planetary protection program have focused mainly on keeping probes and equipment sterile before takeoff, or "forward contamination." NASA does not have manned missions leaving Earth's orbit, and the moon has never been much of a protection worry, having been deemed inhospitable to life in the late 1960s and naturally contaminated by Earth.

The planetary protection officer also works on historic preservation questions, such as protecting the tracks of the first lunar landing from later unmanned touchdowns that could kick up dust.

The golden grail will be a Mars mission that brings back material.

"We have been planning a Mars sample return mission since the 1970s," Conley said.

Indeed, the Planetary Protection Office at NASA was established with an eye toward such a mission, and in response to concerns raised by the first missions there, the Viking orbiters and landers launched in 1975.

Since 1976 the office has overseen the alcohol wipe-downs, high-temperature dry baking and HEPA-filter treatment of equipment set for missions to Mars, such as the recent Mars Exploration Rovers, as well as selected other solar system bodies.

The Obama administration's freshly announced vision for NASA, which would scrap a return to the moon in favor of a manned mission to an asteroid and the eventual trip to Mars, would emphasize the areas of greater concern for Conley's office. "The administration's policy changes have the potential to affect my office predominantly in refocusing the human exploration program towards locations that are of concern for planetary protection - Mars, and some asteroids," she said.

In the next year, the office will be overseeing the Juno mission to Jupiter, the Mars Science Laboratory lander mission (a rover named Curiosity) and the early stages of the MAVEN orbiter mission to Mars that launches in 2013. Conley also will be working closely with the European Space Agency on planning for the joint Mars mission set in 2016 and 2018, with a possible Mars sample return mission sometime early the following decade.

Conley moved into her position in 2006 after more than half a decade at the NASA Ames Research Center and obtaining her doctorate in plant biology from Cornell University in 1994.

In addition to her scientific qualifications, she has firsthand knowledge of just how hardy organisms plummeting to Earth can be. In 2003, she was studying muscle contractions in flat worms as a possible model for humans. Her experiment went up with the payload on the last flight of the space shuttle Columbia. It came back down when the space shuttle broke up during re-entry.

Several months later, she recovered hardware from the debris in East Texas that was found to contain still-living nematodes.

"They had survived not just the flight and the experiment as we had planned, but the disaster and the re-entry," she said.