August 1, 2007
Next Stop Mars
Forget all those jokes about little green men. The search for evidence of life beyond Earth is serious business. It's high on the agenda of space agencies in the U.S. and Europe, and it's a front-and-center focus for UC Santa Barbara's Luann Becker.
Becker, a research scientist at UCSB’s Institute for Crustal Studies, has been interested since her grad-student days in the question of how life started. She sees Mars as a place of possible answers, where the record of early living things (if there were any) might be preserved on or just below the cold, dry Martian surface.
Going there in person is not an option for the near future, of course. But Becker is doing the next best thing – sending sophisticated hardware to analyze Martian rock, soil and ice for chemical traces of biologic activity. The Mars Organic Molecule Analyzer (MOMA), being crafted for Becker by engineers at Johns Hopkins University with funding from NASA, has a berth on the European Space Agency’s ExoMars mission, due for launch in 2011 and arrival at Mars in 2013.
As experiments go, scooping up dirt on another planet is a high-cost, high-risk venture. Becker says MOMA will cost some $40 million from initial development to the end of its useful life. With launch still four years away, there will be a long wait for results and plenty of doubt over the prospect of getting any data at all. “You can’t think of a riskier project than to build an instrument, put it on a spacecraft and hope the spacecraft doesn’t crash,” says Becker. But the potential payoff in knowledge is enormous.
MOMA is a suite of instruments designed to analyze samples with a technology known as matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS or LDMS). Its key advantage over earlier sensors sent to Mars is its ability to detect complex organic molecules as large as peptides, the building blocks of proteins. These are less volatile than smaller organic molecules such as amino acids, so they would not have been detected by other mass spectrometers such as the one flown on the Viking mission that landed on Mars in the mid-seventies. Becker notes that MOMA can detect the small organic molecules as well, so that researchers can “interpret the whole spectrum of organics that we should be looking for.” MOMA thus can look not just for specific molecules but also for combinations (such as amino acids with heavier organics) that point to biological activity.
MOMA will have another advantage over earlier Martian probes: access to samples from several feet underground. The ExoMars mission will deploy a Mars rover equipped with a drill that, according to the European Space Agency, can penetrate up to two meters below the surface. Even if its performance in the field is only half that, Becker says it can reach a depth where organic molecules that would have long since vaporized on the surface may be preserved. “The idea is that you can get down far enough below that destructive layer and see some real organics,” she says.
The Meaning of (Martian) Life
If MOMA detects compounds such as those typically produced by organisms on Earth, this would mean Mars could well have harbored life at some point in its history. As for life today, the chances are very slim that living things as we know them could survive in the harsh Martian surface environment, with its thin, bone-dry atmosphere and constant barrage of cosmic rays. But Becker doesn’t rule out the remote possibility that something could survive underground if water is present.
Any evidence of life on Mars, past or present, would have huge implications for both life sciences and astronomy. It would shed light on life’s possible origins on Earth and, of course, shake assumptions that life is unique to this planet. It would also help illuminate the early history of Mars and the Solar System. Like the evidence of flowing water at some point in the Martian past, evidence of life would suggest that Mars once was a far different, and more hospitable, planet than it is now.
That would lead to the obvious question: So what happened? Becker suggests that a cataclysmic event that affected both Earth and Mars just under 4 billion years ago – a heavy bombardment from objects in space – could have blasted away most of Mars’ atmosphere, including its water. The more watery Earth might have provided organisms a deep-sea refuge that enabled them to survive, multiply and evolve into more complex forms.
Testing instruments for the Martian environment is a challenge in itself. No place on or near the Earth’s surface has such an extreme combination of cold, dryness and thin air. Antarctica comes closest, so Becker went there in November 2003 to field-test a pulsed laser device used in the MOMA system to knock off organics from pieces of rock and soil. “We wanted to see how the instrument will work,” she says, “and what will happen to certain minerals when you poke the instrument at them.”
This Antarctic trip was Becker’s second, following a 1998 visit to hunt for meteorites. It also included research on mass extinctions, another topic on which scientists look beyond Earth for answers. Becker and other geologists have done research on the “Great Dying,” a mass extinction of plant and animal species about 250 million years ago that they believe was caused by a massive meteorite impact near Australia. Ancient rocks stay well preserved and largely undisturbed in dry, barren Antarctica, and Becker has found evidence there of meteorite fragments that date from the time of the Great Dying.
Scientists in Antarctica have also picked up meteorites that originated on Mars. One of these extraterrestrial rocks had a deep impact on Becker’s career.
The Rock that Roared?
Labeled ALH84001, it was a magnesium carbonate-rich four-pounder found in the Allan Hills region of Western Antarctica in 1984. Twelve years later, it made headlines when David McKay and other NASA scientists announced that it may contain evidence of microfossils. Becker, then a research scientist at the University of Hawaii, had doubts about the claim. So did her former Ph.D. advisor at UC San Diego’s Scripps Institution of Oceanography, Jeffrey L. Bada.
Temporarily barred from getting samples of ALH840001, Becker and Bada analyzed another Martian meteorite found in Antarctica, EETA79001, and argued that its organics were probably not connected to extraterrestrial life. When they later got a chance to sample ALH840001, they concluded that its organic matter seemed mainly to be from terrestrial sources, with a small portion that fit the profile of organics found in other meteorites and not biological in origin.
The debate was lively, if civil. “This was the first time I had gotten myself into a little tit-for-tat,” Becker says. It also had a dramatic effect on space exploration. Becker says it “revolutionized the way NASA looked at Mars,” reviving efforts – largely abandoned after the Viking landings of the 1970s – to revisit Mars to look for evidence of life and eventually pave the way for manned flights. She says the series of Mars missions planned in coming years by NASA and ESA – along with projects like MOMA – may owe their existence (and funding) to the fuss kicked up by ALH840001.
Were it not for that chunk of space rock, Becker also might not be spending her time in elaborate preparations for a Martian dig six years from now. But the meteorite has done its work, MOMA is moving forward, and Becker sees a niche possibly opening for UCSB as a center of research into exotic new fields such as extraterrestrial geochemistry. Becker says she wants to involve as many students and post-docs as possible in MOMA, since, as she notes, “It’s not everyday you get to do something like this.”