Recent missions to Mars have focused on the search for water, past or present, as a surrogate for life itself. But now a British-led team is working to renew the search for life directly, fueled by doubts about the equipment that prompted NASA to declare Mars a dead world some 26 years ago.
If all goes according to plan, a Soyuz-Fregat booster rocket will lift off from Baikonur cosmodrome next month carrying an extremely compact and sophisticated life detection probe that might finally settle one of the most intriguing questions in science: did Mars once harbor microbial life—and is it still there?
The probe is hitching a ride on the European Space Agency's (ESA's) Mars Express orbiter as part of the agency's first home- grown mission to the Red Planet. Named Beagle 2, in honor of the HMS Beagle in which Charles Darwin made the historic voyage of discovery that led him to the theory of evolution, it was designed by scientists from Britain's University of Leicester and Open University in collaboration with Martin-Baker Aircraft and Matra Marconi Space Systems. Once the orbiter reaches Mars, Beagle 2 will be sent down to dig around on the planet's surface.
But even after it has dropped off its passenger, the Mars Express orbiter will not be idle. It will use a sounding radar called Marsis to search below the surface for water. It will have an ultraviolet and infrared spectrometer called Spicam to study the atmosphere over the course of a Martian year. And it will relay data transmitted from the lander back to Earth.
Did Viking get it wrong?
The first spacecraft with dedicated equipment to look for life on Mars were NASA's twin Viking landers, which touched down on the surface in 1976. Why send another now?
On board both Viking landers were miniature life detection laboratories, and some of the data they returned could indeed be interpreted as evidence for life on Mars. Yet the majority of the project's scientists became convinced that inorganic oxidants in the soil were responsible for the ambiguous data. The next year, NASA publicly announced its conclusion: that Viking had found no life.
Was the U.S. agency jumping to conclusions? In recent years, questions have been raised about the effectiveness of a key instrument—a combined gas chromatograph and mass spectrometer (GCMS)—that swayed most of the Viking scientists into the no-life camp. The GCMS failed to detect any organic molecules on the Martian surface at all, which posed something of a puzzle, as even the barren surface of the moon is host to some organic molecules. To explain the anomaly, scientists postulated a harsh chemical environment that supposedly made the planet self-sterilizing by actively destroying organic matter [see "Why NASA Said No to Life on Mars"].
To find out if this picture is correct, Beagle 2 is designed to search for organic material below, as well as on, the surface of Mars. In addition, it will study the inorganic chemistry and mineralogy of the landing site, says Mark Sims, the Beagle 2 mission manager who is based at Leicester University.
Without question, the Beagle 2 lander manifests an enormous leap of scientific engineering. It costs only US $40 million versus Viking's $1 billion, and weighs in at a mere 60 kg at launch, as opposed to 661 kg for each fully fueled Viking lander. In its set of scientific instruments are the first ever optical microscope to fly to Mars, as well as a gas analysis package (GAP) that will directly challenge or confirm the results of Viking's gas chromatograph-mass spectrometer (GCMS).
Beagle 2's destination on Mars is a region known as Isidis Planitia [see map]. This relatively flat basin may have been formed by sedimentary deposits and was chosen not just for the chances of finding life there but with a view to the safety of the lander as well. A rocket engine will not be used for a soft landing. Instead, like NASA's Mars Pathfinder mission in 1997, it will use parachutes, along with a system of airbags to absorb the shock of landing.
There are differences between the Beagle 2 and Mars Pathfinder approaches, however. "Mars Pathfinder had a series of 24 interconnecting airbag spheres, whereas the Beagle 2 will only have three," says Colin Pillinger, the lander's project scientist at the Open University, headquartered in Milton Keynes, England.
The Beagle 2's primary science mission will last 180 Martian days, or sols (a sol is about 37 minutes longer than an Earth day). The probe will stay put wherever it lands, but will be able to obtain and analyze samples of rock and soil from within a 75-cm radius, thanks to a 2.5-kg robotic arm known as the position-adjustable workbench (PAW). Although some of the Beagle 2's instruments are housed in the lander's body, such as the GAP, several are located on the adjustable workbench itself [see "A Miniature Marvel"].
The PAW is the brainchild of a multidisciplinary science team from the Space Research Center of the University of Leicester led by Mark Sims. The original idea was for the robotic arm to pick up and use different instruments in turn, but "now it carries an entire science instrument module, with six instruments as well as a brush, scoop, and wide-angle mirror," says Derek Pullan, the lander's instrument manager. Discrete electronic interfaces between each instrument and the lander would have been complex to build and heavy as well. So the PAW uses a single interface with a field-programmable gate array that can reconfigure itself to match each instrument's needs.
Stereo cameras built into the PAW will help researchers identify suitable soil and rock samples. They will obtain a number of overlapping stereo images of the landing site, from which a computer back on Earth will construct a three-dimensional representation of the site, called a digital elevation model. Pullan explains that "although the [model] is useful for creating 3-D images of the landing site, it becomes particularly important when...we wish to maneuver the PAW arm. The 3-D model... is used to plan our close-up experiments on rocks and soils."
At 0.75 milliradian per pixel, the stereo cameras have 1.3 times the resolution of those on board Mars Pathfinder, according to Andrew Griffiths, the stereo camera project manager. Normally they focus from 1.2 meters to infinity, but one camera is also equipped with a close-up lens for inspecting objects only 10 cm distant.