14 December 2010
At yesterday’s Carl Sagan lecture, titled “Isotope geochemistry and the study of habitability and life on other planets” John Eiler of the California Institute of Technology said that he prepared for the talk by first pulling out his old, dog-eared copy of Sagan’s Cosmos. Apparently, the 13-year-old Eiler was less than thrilled with its musings. though in the intervening years, “Cosmos” grew greatly in his estimation. Noting the plethora of topics in the index–ranging from rockets to Voltaire to Tantric Buddhism–Eiler said Sagan’s intellectual bravery, creativity and willingness to indulge any discussion were qualities that every scientist should emulate.
In that spirit, the question Eiler presented was intriguing and clear: What signatures of life are observable in the rock, ice, and gas records on other planets, and how do we make sense of it?
Eiler focused on Mars, as the red planet has been one of the perennial newsmakers for astrobiologists.
He suggested that life, either past or present, could be detected in the physical evidence we have from Mars, within chunks of rock, chemical examinations of the Martian atmosphere, or observations of ice and water movement on the planet’s dusty surface.
Detecting life’s fingerprints in the geological record of another planet is a challenge. “Everyone should hope that we eventually land on a planetary surface and see something obvious,” Eiler said–like a Europan plesiosaur or a Martian enzyme. But that’s a poor bet, he continued. “We could also imagine discovering things that are related to the chemistry of life in such a distinctive way that they have just as much authority as finding a bone or a tooth or something like that.”
One such discovery could be finding isotopic fingerprints specific to life. But when the NASA’s Mars Science Laboratory, scheduled to launch in 2011, lands on our crimson neighbor, will it contain a way to find such fingerprints? Perhaps, if one of the instruments is a sufficiently sensitive mass spectrometer, which can determine the chemical composition of samples. High-end spectrometers can now discern teensy differences in the average mass of a molecule in a sample–down to a tenth of a mass unit!
Such precision could help determine whether life has specific isotopic signatures. For example: Methane has 10 isotopic variants. What if biologically-produced methane carries a different isotopic signature than methane gas produced from volcanic activity?
Eiler also mentioned that carbon isotope abundance could be used to determine the geological history of Mars. He said they’ve already used this principle to determine that water on Mars is “not the product of systems that resemble the Earth’s oceans,” but instead results from brief, high temperature violent environmental conditions, like impacts.
He concluded by saying that to tease out the full history of Mars–including possible life–scientists need to integrate satellite observations with highly-detailed isotopic analyses of collected samples stored in its rocks, gases and organic compounds.
–Nadia Drake is a science communication graduate student at UC Santa Cruz