Mars' First Inhabitants May Be Bacteria Stowaways On Interplanetary Spacecraft
If scientists ever discover life on another planet, one of the first things they'll likely do is try to determine whether the organisms formed there on their own or whether they hitched a ride from Earth on a meteor or spacecraft. Ever since we began sending rockets to Mars, the latter possibility has increasingly concerned astrobiologists.
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As a result, the world's space agencies this week unveiled the results of a suite of science experiments designed to determine which, if any, Earthling microbes could survive the harsh conditions of space and Mars. Their answer, in short, is: many. "To our surprise," said co-author Kasthuri J. Venkateswaran of NASA's Jet Propulsion Laboratory, "some of the spores survived for 18 months."
The research, published in the journal Astrobiology, raises the possibility that bacteria will permanently colonize Mars before humans do and bolsters a theory called "panspermia," which supposes that life could transfer between celestial bodies on the backs of meteors. Some bacteria from "extremely hostile regions on Earth are also partially resistant to the even more hostile environment of outer space, including high vacuum, temperature fluctuation, the full spectrum of extraterrestrial solar electromagnetic radiation, and cosmic ionizing radiation," wrote the authors of one paper.
Currently, NASA has standards for how clean a spacecraft should be, a measure known as the spacecraft's "bioburden." According to a NASA summary of the findings, scientists now believe some bacteria could adapt or evolve better than previously thought, potentially muddying the difference between Earth-grown life forms and true extraterrestrials.
To find out, teams of scientists simply exposed microbes to outer space on the exterior of the International Space Station. Spores of Bacillus pumilus were mounted in a test module and left to sink or swim. After 1.5 years, a portion of the spores were still alive. Researchers discovered the surviving spores to have proteins associated with a greater resistance to the sun's ultraviolet rays. They also simulated Martian conditions on Earth and discovered that this same species could survive 30 minutes on Mars, whereas other microbes last just 30 seconds.
Asteroids frequently crash into the planets and moons of our solar system. Sometimes they strike with such force that pieces of rock and dust fly off into space. Under the theory of panspermia, some astrobiologists believe microbes could survive on these ejected rocks for thousands or millions of years until the rocks collide with some other planet or moon. "The reported experimental period of 1.5 years in space is not comparable with the time spans of thousands or millions of years believed to be required for" panspermia, the authors wrote. But they say their data are the "first evidence" of extremely hardy microbes and offer grounds for further research.
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