So its detection will indicate a source that is continually replenished. Inside Beagle II, the mass spectrometer, which can identify compounds by measuring how far magnetic fields deflect their masses, will examine the Martian atmosphere for methane. It consists of one carbon and four hydrogen atoms, giving it a fairly unique signature.
The British lander's methods of looking for life are quite different from those of Viking, which were more direct but nonetheless proved to be frustratingly ambiguous.
For instance, a Viking experiment added water and nutrients to Martian soil. If the soil held micro-organisms, the thinking went, they would consume the nutrients and emit gases. The test quickly produced oxygen. But most analysts concluded that the results were best explained by oxidants in the moistened soil, not life.
"Viking didn't succeed, so we're trying a different technique," said Pillinger, Beagle II's lead scientist. "We'll decide if it's better when we get the results. It's more universal. It detects all atoms of carbon in all their forms."
The absence of evidence, Pillinger said, quoting an adage, is not evidence of absence. So if Beagle II fails to find life, that in no way will mean that the planet is uninhabited.
"We'd want to keep trying," Pillinger said. "No scientist is going to tell you it's the end of the line."
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