The buzz about the Viking landers continues. Yesterday at the American Astronomical Society’s meeting in Seattle, two scientists argued that we can reinterpret the data from the Vikings’ 30-year old mission in the light of recent findings regarding life in extreme conditions on Earth. Doing so leads to an intriguing possibility: Viking may have found microbes that use water and hydrogen peroxide to survive in the cold, dry Martian climate.
The researchers are Dirk Schulze-Makuch (Washington State) and Joop Houtkooper (Justus-Liebig-University, Germany). Here’s a link to an early article on this work that explains the beauties of hydrogen peroxide in this scenario. For one thing, its freezing point is low, but even better is the fact that when its temperature drops, it doesn’t form the kind of crystals that can destroy cell structures, as water by itself would.
But how do you protect a cell from the corrosive effects of hydrogen peroxide? From the article:
Schulze-Makuch said that despite hydrogen peroxide’s reputation as a powerful disinfectant, the fluid is also compatible with biological processes if it is accompanied by stabilizing compounds that protect cells from its harmful effects. It performs useful functions inside cells of many terrestrial organisms, including mammals. Some soil microbes tolerate high levels of H2O2 in their surroundings, and the species Acetobacter peroxidans uses hydrogen peroxide in its metabolism.
Microbes built around hydrogen peroxide, so the argument goes, are compatible with all the Viking findings. Of particular interest is the Labeled Release experiment, where samples of Martian soil were exposed to water and nutrients, producing an initial burst of carbon dioxide that later tapered off. Did the result show the presence of organisms that died off as they were exposed to liquid water? It’s a possibility, and not inconsistent with the Pyrolytic Release experiment on the same mission.
CNN handles the story here. For more, see Houtkooper and Schulze-Makuch, “A Possible Biogenic Origin for Hydrogen Peroxide on Mars: The Viking Results Reinterpreted,” available online (PDF warning). It’s also interesting in this context to re-examine Gilbert Levin’s 1997 paper “The Viking Labeled Release Experiment and Life on Mars,” SPIE Proceedings of “Instruments, Methods, and Missions for the Investigation of Extraterrestrial Microorganisms,” (29 July-1 August 1997), available here.