Source(s):
Wayne Nicholson WLN@ufl.edu, 321-861-3487
Andrew Schuerger acschuerger@ifas.ufl.edu, 321-861-3478
KENNEDY SPACE CENTER, Fla.—Wayne Nicholson works with the world’s smallest astronauts.
In April, he launched a sample of the microbe Bacillus subtilis 70 miles into space on the metal skin of a rocket launched from New Mexico’s White Sands Missile Range.
His goal was to discover whether B. subtilis, a hard-to-kill microbe found almost everywhere on Earth, could have hitched a ride on a probe from Earth to Mars — or on a terrestrial rock launched into space by a meteor strike.
“If an organism can survive this process, it could mean that the planets are not isolated islands, but rather part of a sort of interplanetary ecosystem,” said Nicholson, an associate professor of microbiology at the University of Florida’s Institute of Food and Agricultural Sciences. “It could change our theories about the origin of life, and the way we look at the probes we’ve sent to other planets.”
Nicholson is one of several UF researchers associated with the UF’s Center for Space Agricultural and Biotechnology Research and Education, or SABRE, located at the Kennedy Space Center. While most SABRE research is focused on the technologies astronauts will need to grow plants on long-term space missions, Nicholson and fellow UF researcher Andrew Schuerger are taking a close look at organisms that may have already made the journey from planet to planet.
When the first Mars probes revealed a cold, desertlike surface on the Red Planet, long thought the best candidate for extraterrestrial life, hopes for life elsewhere in the solar system plummeted. But in recent years, space scientists have begun to entertain the notion of a universe where microscopic life hangs on in even in the most inhospitable conditions.
That notion is driven by the discovery, in recent decades, of bacteria that can thrive in Earth’s harshest environments. Such organisms, known as extremophiles, have been found on the frozen surface of Antarctica, in rocks more than a mile below the earth’s surface, or in boiling hot water near underwater volcanic vents.
And scientists have long known that some microbes, such as B. subtilis, can form spores that withstand extremes of ultraviolet irradiation, cold, low pressure and lack of water for years on end.
There’s a chance such spores could survive the months-long trip to Mars on the surface of a space probe, and grow once they’ve arrived on the Red Planet. For scientists looking for indigenous life on the planet’s surface, that would pose a serious problem.
“I’d love to see life discovered on the surface of Mars,” said Schuerger, a research assistant professor in plant pathology at UF. “But I don’t want us to find a microbe on the Martian surface only to discover later that we brought it there.”
Since the days of the Viking Mars probes, NASA has carefully sanitized its spacecraft before sending them to other planets. But even with the best sterilization processes currently available, a few individual microbes likely survive the process. And tough, spore-forming organisms like B. subtilis, ubiquitous on Earth, could easily be among those microbes.
“No one knows for sure that we’ve sent organisms to Mars, but we have to assume that we have,” Schuerger said. “The real question is, if life has made it to Mars, what is it doing once it gets there?”
To answer that question, Schuerger tries to grow microbes in his Mars simulation chamber — a barrel-shaped, stainless-steel device where the bugs face the cold temperatures, ultraviolet radiation, and low atmospheric pressure found on the Red Planet.
So far, the news is good. Of several hardy species tested in Schuerger’s lab, not one has been able to grow when exposed to all the rigors of the Martian environment.
“It’s one thing to find an organism that can withstand a single stressor like low temperature,” he said. “It’s another thing to find an organism that can handle the whole suite of extremes that Mars has to offer. So far, we haven’t found an organism that can do that.”
For Nicholson, the main question is not whether life made interplanetary journeys in recent years, but whether it made the trip in the ancient past. Scientists know that major collisions between planets and asteroids can launch some bits of rock from the planet’s surface into deep space. That’s why scientists have been able to find Moon or Mars rocks on Earth.
If a few hardy microbes could survive such an impact, and subsequent journey through space, they could potentially seed life on other planets. In fact, some scientists have theorized that life may have first arrived on Earth aboard a meteorite.
“That would explain an anomaly in the fossil record,” Nicholson said. “We have a record of apparently modern-looking microbes appearing about 3.5 to 4 billion years ago, but no record of any precursors to those microbes. If those early organisms arrived here from somewhere else, that could explain the apparent gap.”
Nicholson’s ongoing experiments with B. subtilis are an attempt to determine whether bacteria could withstand the toughest phases of such a journey. His rocket test was designed to determine whether spores of the microbe could survive the heat that a spacecraft or rock fragment would generate while entering a planet’s atmosphere.
In a related experiment, he fired projectiles — at speed of 3 miles per second — at a rock covered with the bacteria. His goal was to determine whether B. subtilis would survive the kind of high-speed impact that could launch rock fragments into space.
Nicholson said he’s still analyzing samples from both tests, though preliminary results from the rocket test suggest that B. subtilis could survive atmospheric re-entry aboard a man-made space probe at the least.
“Early indications are that some of the organisms survived the rocket ride, but not on the leading edge, where the heat of re-entry is greatest,” he said. “For microbes on a meteor, the ride would probably be rougher. Rocks tend to tumble as they enter the atmosphere, so the entire surface can get the kind of friction you see on the leading edge of a spacecraft.”
There’s still a chance microbes beneath the surface of a meteor could survive re-entry, he said, or a chance that some other species of microbe could weather the ride better than B. subtilis. So far, he said, theories of space-borne life have raised far more questions than answers.
“This field, the search for life in space, is 99 percent conjecture and 1 percent real data,” he said. “The only way to settle the question for sure is to go to the places outside the Earth that might harbor life, and find it there.”
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