Almost every month we see news dispatches from Mars, where the nuclear-powered rover Curiosity finds water-bearing minerals in rocks and other circumstantial clues that the Red Planet could have once supported life.
But in terms of finding direct evidence of past or present Martians, the rover barely scratches the surface, says geochemist Jan Amend of the University of Southern California. Amend spoke at the Space Telescope Science Institute in Baltimore, Md., on April 5. (You can watch a video of the research presentation here.)
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Curiosity's drill can, at best, penetrate a few inches into the crust of Mars rock. Amend's guess is that life has buried itself deep into the Martian crust a half-mile or more beneath the withering orange surface. Even if the ancient streams or lakes on Mars evaporated, there could very likely still be substantial reservoirs of water, in either liquid or frozen form, in the subsurface.
Amend's lab at the University of Southern California studies microbial chemistry in ocean hydrothermal vents. Recently, NASA funded his astrobiology team to do experiments searching for life deep underground as a guide to hunting for extraterrestrial life on neighboring planets and moons.
The project also includes collaborating scientists from Caltech, JPL, Japan's Agency for Marine-Earth Science and Technology, and several other U.S. research institutions, including Arizona State University and Rensselaer Polytechnic Institute.
It's estimated that one-third of Earth's carbon biomass is locked away beneath the crust. The team is going far beneath the sedimentation at the bottom of Earth's oceans and into porous rock to look for life. Destinations are the Mid-Atlantic ocean floor - more than two and a half miles below the water's surface. More Mars-like conditions call for borrowing a half mile into deep mine shafts in locations in the continental United States, including, ironically, Death Valley in California.
This region beneath Earth's deserts is just about as alien as Mars - but much more reachable. It is completely unknown how much life or what kinds of new life forms are down there in a pitch-black, rocky, high-pressure, low-nutrient environment. "We are going to biotic fringe to look for new organisms," says Amend.
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The idea of an underground biosphere was popularized in Jules Verne's 1864 novel, "A Journey to the Center of the Earth." Perhaps inspired by Charles Darwin's emerging theory of evolution, Verne describes his geologist explorers finding Earth's interior alive with prehistoric plants and animals. Now, Earth's subsurface frontier will help scientists test ways to look for subterranean life on other worlds.
Over the next five years, Amend will drop eight-foot long torpedo-shaped biology probes, called SEALs (Subsurface Explorer for Assessment of Life), down boreholes and mine shafts. He will try to catch a glimpse of any organisms that dwell thousands of feet below the surface. They've been dubbed "intraterrestrials."
New life detection technologies being developed for the exploration of the deep biosphere could be precursors to what might be dispatched to other planets and moons someday. This includes a miniaturized ultraviolet microscope to detect bioluminescence. The probes will look for microbes, collect data on understanding them, and try to grow them in situ (as was done on the Viking Mars lander experiments in 1976). Other samples will be brought back to labs for analysis. The ultimate goal is to learn more about the range of conditions that support life on our planet.