Let’s get right down to it: Is there life on Mars? Most scientists say we just don’t know. When will we find out? Some say we’ll have to wait a decade, while others insist that the answer could be available significantly sooner.
The big question about life on Mars has been asked for centuries, but it’s only been in the last few years that researchers have focused on the possibilities for a conclusive answer. Several factors have fueled the controversy.
First, there was the discovery that life is thriving in hostile climes on Earth, such as the ice of Antarctica and volcanic vents at the bottom of the ocean. If life existed in those places, researchers asked, why couldn’t it also exist on Mars?
Indeed, in 1996, a team of scientists said they saw evidence of organic molecules and fossilized microorganisms in a meteorite traced back to Mars.
Then, one year ago, the Mars Pathfinder probe captivated the public’s imagination and provided ample evidence that areas of Mars were once awash in liquid water — a key requirement for life as we know it.
The data from Pathfinder and from the Global Surveyor spacecraft now orbiting the planet are continuing to provide insights into the geology and climate of Mars. But is that enough to hold the public’s attention?
“There’s only one question about Mars: Is there life there? This is the major scientific question facing the world today,” said Gilbert Levin, an environmental engineer who designed a life detection experiment for the Viking spacecraft two decades ago.
Levin isn’t talking about little green men here. Rather, he and other scientists say the most likely suspects for Martian life would be microscopic in scale and shielded from the ultraviolet radiation pounding the planet’s surface.
In 1976, Levin’s experiment turned up hints of biological activity in Martian soil, but most scientists concluded instead that the activity was some sort of chemical reaction. Based on what’s been learned about life in the past few years, Levin now insists that his experiment discovered Martian microorganisms, and other researchers say his findings merit a second look.
“The Viking results showed something, I’m convinced of that,” said Barry diGregorio, who pleads Levin’s case in the book “Mars: The Living Planet.”
But Levin, who now heads the Maryland-based company Biospherics, said he hasn’t gotten a receptive hearing from officials at NASA. “They’ll send an orbiter to look at the Face on Mars, but they’re definitely afraid of looking at these data,” he grumbled.
There are also growing calls to put life detection experiments on future robotic missions to Mars. So far, the space agency is taking a less direct approach — perhaps in part because of the questions raised about the meteorite study.
Any evidence gleaned remotely from Mars “would have to look incontrovertibly biological in order to avoid the controversy we had over that rock,” said Thomas Pike of NASA’s Jet Propulsion Laboratory. “I don’t know what would be the definitive Mars experiment for life.”
That view was seconded by Cornell astronomer Steven Squyres, the principal investigator for the next-generation Mars rover and a member of NASA’s Solar System Exploratory Committee.
“It’s unrealistic for us, given the incredible constraints on equipment you can send to another planet, to expect you’re going to be able to put life or biological instrumentation directly on a spacecraft,” Squyres said.
So how can you answer the big question about Mars?
“The way to address that question is to find the right Martian samples and bring them back,” Squyres answered.
The big mission
Under NASA’s current plan, that won’t happen until the spring of 2008, when a spacecraft returns to Earth with rocks and soil collected during a robotic round trip to Mars. The sample return mission, scheduled for launch in 2005, represents the climax of five sets of missions starting with Mars Pathfinder.
Researchers say that if they can agree by 2008 on the criteria that separate life (living or fossilized) from non-life, the Martian samples should provide an answer to the big question.
“One of the things we have to do in the next eight or nine years ... we have to figure out how we’re really going to tell, without a shadow of a doubt, whether there’s life in those samples,” said NASA planetary scientist David McKay, one of the leaders of the Martian meteorite research team.
Although the big mission is still on the drawing board, the current scenario calls for the samples to come back within a sealed, reinforced container that plummets down into the Utah desert at about 80 mph, said Rob Manning, chief engineer for the Mars robotic exploration program at the Jet Propulsion Laboratory.
“We’re actually looking at welding techniques to keep that sample in there,” Manning said.
Why the dramatic re-entry? Manning said the spacecraft’s weight limitations rule out having enough fuel to put the package into Earth orbit. Packing a parachute is an open question — because of weight as well as the fact that you’d have to have a backup plan anyway in case the chute didn’t open. And for a water landing, you’d have to make sure that the entire spacecraft was watertight and that you could find it after splashdown, Manning said.
Once the package landed, the samples would be removed and studied under the types of conditions that would be used in dealing with a strain of the Ebola virus. There are two reasons for that: to make sure life detection experiments aren’t ruined by contamination from earthly sources, and to keep any potential Martian life forms from getting out of the laboratory.
“This planetary protection part of the job is probably the biggest challenge we have,” Manning said.
The big concerns
NASA headquarters is closely monitoring the planning process, Manning said. “We are being challenged, rightly so, by NASA: ‘Is this the right way to do it? Are you sure you can do it? Are there easier, cheaper ways to do it?’ ” he said.
Levin, meanwhile, questions whether the mission as currently conceived should be done at all.
“No way should that be done,” Levin said. In his mind, the risk of a biohazard is just too great, particularly without any advance experiments in life detection.
DiGregorio said the issue “ought to be put to a vote in front of the United Nations, because it’s not a matter involving just one country, it involves the Earth.”
Indeed, mission planners acknowledge that returning a Martian sample to Earth will require environmental impact assessments and international consultations because of the potential risk.
Colin Pillinger, a planetary scientist at the Open University in England, has his own concerns about bringing back a piece of Mars without running some preliminary life detection tests.
“I think that’s a premature move, to bring samples back from Mars somewhere,” Pillinger said. “Let’s just say that you bring them back to Earth, and you suddenly expose them to the terrestrial environment, which is jam-packed with terrestrial biology. Then you run a big risk of contaminating the sample and confusing the issue.”
Pillinger disputes the claim that Mars landers aren’t big enough to help answer the big question. In fact, he’s the lead scientist for a British project to put life detection experiments aboard the European Space Agency’s 2003 mission to Mars, known as Mars Express.
The 130-pound Beagle 2 lander — named after the ship made famous by naturalist Charles Darwin — would include a drill to delve into Martian rocks as well as a cylindrical, foot-long “mole” that could crawl along the surface and bring samples back to the lander.
The samples would be analyzed by a mass spectrometric gas analysis system that could look for clues to biological activity. Pillinger said the possible signs of life would include an imbalance of methane in the atmosphere or a particular distribution of carbon isotopes in surface samples.
“If biology is involved, there would be a shift toward lighter isotopes” of carbon, he said.
Mars Express is scheduled for launch in 2003, but Beagle 2 is by no means a sure thing. In fact, the biggest challenge for Pillinger’s team is to raise the $40 million required to fund the lander.
Levin has his own ideas for future experiments. He said a minor modification in an experiment aboard the Mars Polar Lander could determine whether chemical processes on Mars favored “left-handed” or “right-handed” compounds.
“All forms of life that we know use only one-handed organic compounds,” he explained. “All Earth life uses and makes only left-handed amino acids, and conversely only the right-handed carbohydrates or sugars.”
If the Polar Lander’s thermal and evolved gas analyzer, known as TEGA, determined that chemical processes on Mars favored one type of organic compound over the other, that would indicate that biological processes were at work, Levin said.
Levin has probably run out of time to make his case, however. TEGA is due to be installed on the Polar Lander on July 6 in preparation for a January 1999 liftoff.
Yet another experimental package, scheduled for the Surveyor 2001 mission, could shed some light on the big question. JPL’s Pike is in charge of instrument development for the 2001 mission’s Mars environmental compatibility assessment package, known as MECA.
The main purpose of MECA is to determine whether there’s anything in Martian soil that might be harmful to eventual human explorers — such as toxic chemicals or asbestos-like particles. But MECA’s wet chemistry lab will be able to atomic-force microscope can also look for the kind of wormlike structures that were seen in the Martian meteorite.
“We will be able to see structures down to the scale of the nanofossils, which are indeed on Earth the earliest life,” Pike said.
But the microscope can’t look within the soil or within rocks and crevices, which are the best bets for finding life. Indeed, it would take an incredible stroke of luck for MECA to happen upon nanofossils in loose soil samples, Pike acknowledged.
Nevertheless, Levin thinks enough evidence will emerge in the next few years — from Antarctica, from meteorites and Mars — to cause NASA to rethink its whole approach to the big question.
“I predict that long before 2003, or 2005 ... the concept of life throughout the universe will be accepted, and either the proof or the high suspicion that we detected life on Mars will become evident,” he said. “And they’re not going to bring that sample back.”