ESA’s Beagle: Sniffing Out Life on Mars

ESA’s Beagle: Sniffing Out Life on Mars

colin_pillinger
Professor Colin Pillinger in January, 2000.
Credit: All Rights Reserved Beagle 2

The European Space Agency’s Beagle 2 Mars lander is small – a mere 30 kg (66 pounds) – and can never move from its landing spot. But at its core sits a miniaturized version of a sophisticated chemical laboratory. The lander’s Gas Analysis Package, or GAP, is central to its mission to discover signs of past or present life on Mars.

"The gas-analysis package is based on the system that we have used for 20 years now to analyze Martian meteorites," says chemist-turned-planetary-scientist Colin Pillinger of The Open University, Milton Keynes, UK.

The only previous life-detection experiments on Mars were carried out by NASA’s Viking 1 and 2 landers in 1976. Viking’s biology experiments did not produce unequivocal evidence for present or past life on Mars. But the results didn’t rule out life either. Nearly thirty years later, astrobiologists continue to disagree about how to interpret Viking’s results.

"Viking did a very noble job," says Pillinger. "They had three experiments which were configured to see whether there were any actively metabolizing organisms on the planet. When [one experiment] got results which could be interpreted as actively metabolizing organisms, they got very concerned, because they had [another] experiment onboard, called the Gas Chromatograph, which couldn’t detect any organic matter. So their interpretation was that the chemistry of Mars was playing them a big confidence trick."

GAP
The Gas Analysis Package awaiting installation.
Credit: All Rights Reserved Beagle 2

Scientists are hopeful that, by using a different life-detection technique than that used by Viking, the GAP, in conjunction with a suite of other instruments aboard Beagle 2, will produce less ambiguous biology results than its predecessors.

"The thing which is crucial is to see whether we can detect any organic matter. And the way in which I plan to detect organic matter is to burn it," says Pillinger.

In its first stage, the GAP works like a well-sealed kitchen oven. The GAP slowly heats a sample, soil or rock, in the presence of pure oxygen. Different carbon compounds in the sample will break down at different temperatures, producing pure carbon dioxide.

"If you burn this sample of rock, or heat it up," Pillinger explains, "you should see any organic matter burning to give you CO2, and at a higher temperature, you should see mineralogical carbonates breaking down to give you CO2 as well."

Carbonates are minerals, such as limestone, that form by precipitating out of water. Finding carbonates in a sample will tell scientists that liquid water was present when the mineral formed. Organics are chemical compounds, such as sugars and amino acids, that, on Earth, typically are produced by living organisms. Finding organics in a sample will provide the first hint of life on Mars.

But the GAP will go beyond merely detecting these compounds. "If you find the two carbon-containing phases, the inorganic and the organic, together, you have to measure the isotopic fractionation between them," says Pillinger. This measurement is the GAP’s second task.

mass_spec_team
Around the table with bits of the mass spectrometer and some of the mass spectrometer team.
Credit: All Rights Reserved Beagle 2

The GAP will shunt the carbon dioxide produced by the burning process into a mass spectrometer, an instrument that can measure the amount of the carbon dioxide released and can also garner important information about individual carbon atoms. This latter capability has never appeared before in a Mars lander. The spectrometer will tell scientists what the ratio is of carbon-12 to carbon-13 for the various compounds contained in a sample.

Carbon atoms come in two stable forms, called isotopes: carbon-12 and carbon-13. The only difference between isotopes is the number of neutrons in the atom’s nucleus.

Measuring the carbon-12:13 ratio of carbonates will give scientists important information about the martian atmosphere. A planet’s atmosphere contains carbon-12 and -13 in a ratio that varies little worldwide. It is this atmospheric CO2 that supplies the carbon that ends up in carbonates. So when the GAP burns carbonates, the CO2 released will tell scientists how much carbon-12 and carbon-13 were present in the martian atmosphere at the time the carbonates formed.

As organisms build organic molecules, however, they use carbon-12 more readily than carbon-13. Compounds that arise from biological processes therefore end up with a distinctive carbon 12:13 ratio different from that of the atmosphere, enriched in carbon-12.

These ratios show up in living or recently dead tissues, but also remain intact in chemical compounds long after the organisms die, preserving a detectable signature showing the past presence of life.

beagle2_surface
Simulation of Beagle 2 on the martian surface.
Credit: All Rights Reserved Beagle 2

If the organic material in one of the samples scooped up by Beagle 2 shows an elevated ratio of carbon-12 to carbon-13, it will provide the most convincing evidence to date that Mars is, or once was, a living world.

Says Pillinger, "On Earth, the organic material that co-exists with the carbonate is always enriched in carbon-12, due to biology, relative to the carbonate. This has been borne out on 10,000 samples on Earth. People have spent their lives working on this stuff, analyzing every sedimentary sample that they can lay their hands on. And it’s always true."

Because its spectrometer analyzes gasses, the GAP can also analyze the present-day Martian atmosphere. Instead of heating the atmosphere, the GAP will first chemically concentrate the atmosphere in tiny reactor vessels. The GAP can detect not only carbon but also nitrogen and methane (swamp gas). Because researchers believe that methane can persist in the Martian atmosphere for less than 300 years, any methane they find can be assumed to arise from recent biological processes, produced, for example, by methane-producing bacteria.

What’s Next?

Pillinger steadfastly refuses to speculate about when the first results from Beagle 2′s GAP will be announced. "The priority is to stabilize the lander and make sure that this is a mission, and not just an image. So when we get some images, the team will sit down and say, well this is what we want to do. This is what we can do, this is what’s feasible, this is the order of priority in which we know we want to work. And we will tell you, the world, the media, on a rolling basis, what we are going to do tomorrow, and we will tell you tomorrow what we did yesterday."

But, he adds, "I’m not making any predictions about when we will analyze a sample and tell you about the results of the GAP experiment. Because if I do that, I could be forever answering the phones, with people saying, ‘Have you done it yet?’"


Related Web Pages

OU Press Release
Astrobiology Magazine ’01 Beagle 2 Article: Europe Heads for Mars
Beagle 2: Seeking the Signatures of Life on Mars, Everett K. Gibson, Jr., et. al. pdf
The Gas Analysis Package on the Beagle 2 Lander, G.H. Morgan pdf
Beagle 2 Site
Viking Biology Experiments
Life Beneath the Surface