What is it about beagles and pioneering? It was upon the deck of Her Majesty's Ship Beagle that Charles Darwin began developing his revolutionary idea of evolution by natural selection, and the HMS Beagle you're reading right now has pioneered the genre of the science Webzine. Now comes yet another trailblazing beagle - and this one's going to Mars.

Three years from now, the lander Beagle 2 will travel to the Red Planet as part of the European Space Agency (ESA)'s Mars Express mission, to search for signs of life. Beagle 2, named such in commemoration of Darwin's epic voyage on HMS Beagle, will touch down on Mars at the end of December 2003, just days before two NASA rovers are scheduled to arrive on an independent mission.

The lander is like no other in the history of space exploration. It will detach from the main spacecraft and, upon touching down, will beam a rock song, specifically recorded for the mission by the British band Blur, back to mission control. Following that, Beagle 2 will calibrate its camera settings by focusing on artwork by the controversial modern painter Damien Hirst. And on top of this, Beagle 2's flanks will be plastered with corporate logos.

Such unconventional touches reflect the unusual nature of the mission's design. Rather than being the work of a government space agency, Beagle 2 is the brainchild of astrobiologist Colin Pillinger of the Open University in Milton Keynes, United Kingdom, and is being carried forward by a consortium of scientists and engineers at British and international universities and industries. The team, under Pillinger's direction, is designing a craft compact enough to hitchhike to Mars aboard Mars Express. Such a role necessitates a small size: Beagle 2 will weigh only 60 kilograms, with fully half of that mass being scientific instrumentation.

Beagle 2 will land on the Martian surface with the help of Pathfinder-like air bags and go to work analyzing rocks, soil, atmosphere, and climate - searching for telltale chemical signs of life for up to 180 days.

But let's get two things perfectly clear. One: Nobody's looking for little green men here. Beagle 2, and indeed the whole burgeoning field of astrobiology, is focused on microbes. As the recent book Rare Earth by Peter D. Ward and Donald Brownlee argues, complex and intelligent life is probably extremely rare in the universe, but microbial life may be quite common. Two: Finding something actually alive is not high among anyone's expectations. Most scientists would be ecstatic simply to find evidence that life once existed on another planet at some point in the past.

Why would we even expect Martian life to be a possibility, though? The Viking missions in the 1970s, after all, ran experiments that failed to turn up clear evidence for life. Since that time, however, we've learned a lot. Astrobiologists have come to recognize the ability of many earthly microbes to live in shockingly harsh conditions, and they've analyzed and debated intriguing hints from meteorites originating on Mars.

Although the planet may have been more conducive to life in the past, we know that life on Mars today would face severe challenges. For example, life as we know it requires water, and Mars's surface may not have seen liquid water for many millions or billions of years (although evidence this summer from the Mars Global Surveyor has suggested possible recent water flows). Additionally, the chemistry of Mars's soil and atmosphere indicates thorough oxidization of the planet's surface, which should effectively destroy any living things. Thus, astrobiologists have reasoned that if Martian life exists, it most likely resides beneath the surface.

Beagle 2's instruments, therefore, will focus on collecting samples from within the rock and under the soil. Drilling into rock requires a high-tech grinder and corer (designed, fittingly, by a dentist) to remove the weathered outer rind of rock and get inside. To probe the soil, a robotic "mole" named "Pluto" (planetary undersurface tool), leashed on a five-meter cable, will crawl via a spring mechanism across the surface and burrow into the ground and under boulders.

The rock and soil samples retrieved will be analyzed in situ, employing mass spectrometry to learn their chemical composition. By heating the samples in the presence of oxygen at a series of different temperatures (a technique called "stepped combustion"), Beagle 2 will be able to discriminate between organic and inorganic forms of carbon. It will also analyze isotope ratios to determine if carbon appears to have been involved in biological processes.

Pillinger and his colleagues have used stepped combustion before to analyze Martian meteorites found on Earth; it was this work that motivated Pillinger to propose Beagle 2. "Many of our findings were starting to point toward Mars as a place where life could exist," he explains.

Recall ALH 84001, the meteorite that captured headlines in 1996 when NASA scientists proclaimed that it showed fossil and chemical signs of life. Many scientists begged to differ, but Pillinger's team analyzed the rock and found promising suggestions that organic matter was associated with carbonates.

But another meteorite, EETA 79001, is "more interesting," Pillinger maintains, showing "organic matter associated with carbonates more than any other meteorite we've seen." Portions of the 8-kilogram rock that were low in one were low in the other, and areas high in one were high in the other. Their analysis, he says, provided "clear evidence of the organic matter being indigenous." The carbonate minerals appear to be Martian, he says, and the isotope data, although not conclusive, are consistent with biological processes.

Because extraordinary claims require extraordinary evidence, many scientists are reluctant to accept these findings. "It's very, very tantalizing," Pillinger says. "But since people don't want to believe that, we'll jolly well go to Mars and run the experiments there!"

Running the experiments there may not provide conclusive proof either, however. "To expect unequivocal evidence for life to come out of [experiments on] any one rover, I think, is a little too much to expect," says Cornell University's Steven Squyres, principal investigator for the science package of the NASA rovers.

The best way to test for signs of life, according to NASA's Chris McKay, astrobiology authority at the NASA/Ames Research Center at Moffett Field in California, will be to bring samples back to Earth for extensive analysis. McKay says we don't understand enough about the fundamentals of Martian chemistry and geology to be in a good position to find persuasive evidence of life quite yet. So the NASA rovers that set down on Mars shortly after Beagle's arrival will analyze geochemistry, determine the potential for water, and try to learn about past Martian climate - and will leave attempts to detect life directly to later missions.

Nonetheless, McKay is optimistic about the Beagle mission and calls it "an important step in doing further investigation."

Some others aren't so sanguine. They point to the relative inexperience of Pillinger's group in space travel, their low level of governmental support, and their unconventional and untested entrepreneurial approach. Clearly, Beagle will have to prove itself in the eyes of many old space hands.

But Beagle 2 project manager Mark Sims of the University of Leicester says the mission's unorthodox approach has advantages: it's "an integrated jigsaw." Rather than throwing together a lot of ideas and equipment created independently by different people and institutions in loose contact, Beagle's team is smaller, more interactive, and more coordinated, with "a lot of lateral thinking involved." From the original four main partners - the Open University, the University of Leicester, Astrium (formed by a merger between Matra Marconi Space and the space divisions of DaimlerChrysler Aerospace), and Martin-Baker Aircraft Company – there are now about 30 to 35 institutions and companies on board.

The partner companies are helping to defray the costs of the mission, which is expected to come in around a low-budget $50 million, according to Sims. In addition, Beagle has government funding via the British National Space Centre, and the costs of the launch vehicle and the data relay come under part of the ESA's Mars Express budget.

The Beagle team expects corporate sponsors will cover any remaining expenses. Pillinger says he's actually putting off selling advertising space on the craft until closer to launch, as he expects public, and thus corporate, interest to build. "We are prepared to take money from [corporations] that want to show they're adventurous in high-tech programs," he says, "so we will accept the best offers then."

Indeed, if NASA's Pathfinder mission was any indication, there will be huge public interest. And Sims hopes touches like pop music and avant-garde art will draw in even more people. "It's a great shame that very few people in the U.K. know what the U.K. does in space," he says. "We want to show that the U.K. does have a space program, and that [it] can have other appeal, and not just be a technical feat."

It may be especially interesting to have the Beagle and NASA missions independently traipsing around the Martian surface simultaneously. The two missions, with their complementary objectives (both sides insist there is no sense of competition) may teach us quite a bit about the fourth planet, in quite a short time.

Both Beagle 2 and the NASA rovers will choose their landing sites carefully, aiming for a spot that likely held water recently on or near the surface. This summer's discovery of terrain indicating geologically recent water flows, however, will have no influence on the landing sites of either mission because the areas photographed by Global Surveyor were located near the poles. The 2003 missions must land within five to 15 degrees of the equator so as to assure enough sunlight to power their batteries by solar energy. A good landing site must also be at an especially low altitude, so as to allow the parachutes maximal time to slow down the crafts' fall.

Sims says other Beagle missions may follow. NASA certainly intends to keep pushing ahead with its Mars program. Although the program was set back by recent failures, NASA last month unveiled its revised slate of upcoming missions. Following the twin rovers (which will travel several hundred meters over the Martian surface), NASA will send large orbiters with high-quality cameras and radar in 2005 and 2009, and a sophisticated lander in 2007, possibly accompanied by a low-altitude explorer such as an airplane or balloon. And starting in 2011, we may well see the first Martian rocks and soil returned to Earth for testing.

Which of course raises the issue of protecting our planet from any extraterrestrial killer microbes we might accidentally bring back, a scenario that's quite plausible, given the very real historical epidemics that have swept through society when pathogens have reached populations without evolved immunity (like smallpox in the Americas, and now HIV). NASA and international space agencies have planned adequately for this, McKay holds, and current guidelines for "planetary protection" are exceedingly strict.

McKay thinks chances are good that life exists somewhere on Mars, and that if we can search extensively with ideal technology we can find it. This would mean digging down deep - the deeper the better. "Mars gets more interesting the deeper down you go," he says.

Looking for water, looking for carbon, measuring the chemicals and isotopic patterns associated with earthbound life - these are all good strategies. But what if life on other planets has evolved independently and is fundamentally different from life on Earth? What if it's not based on DNA or carbon? What if it has features we haven't even imagined? Would we be able to detect it?

The answer seems to be (not surprisingly) "it depends." While Beagle is focusing on water- and carbon-based life, broader analyses might potentially be able to detect whether certain objects or areas are out of equilibrium with surrounding rock chemistry, indicating biological processes.

Conventional wisdom among astrobiologists today holds that extraterrestrial life would probably be carbon-based, almost certainly water-based, but not necessarily DNA-based. And Mars's early climate is hypothesized to have been similar enough to Earth's that we shouldn't expect anything too radically different. However, scientists allow that our imagination may be limited by the fact that we have only one data point to guide our thinking. "We've got to be prepared to be surprised," McKay says.

Indeed, not only is our search image for life necessarily Earth-centric, but the very definition of life is problematic. Various definitions have been proposed over the years, based on such features as metabolism, chemistry, or structural complexity. Evolutionary biologist Lin Chao of the University of California at San Diego has recently suggested this definition: "If it evolves, it's life." If Chao's approach is best, then maybe Beagle 2 is even more aptly named than its creators realize.