There are lots of reasons why living things will generally die in outer space: lack of air, sizzling radiation and extreme temperatures, just to name a few.
This is why it's notable that some little blue-green bacteria hitching a ride on the exterior of the International Space Station came out of it alive -- after a record-setting 553 days. That's a year and a half in a near-vacuum.
These hardy star-trekkers were a type of cyanobacteria from the cliffs of the British fishing village Beer. They were sent up by geomicrobiologists Karen Olssen-Francis and Charles Cockell from the Open University at Milton Keynes, England, in an experiment to identify useful microbes for future space colonies.
"We weren't sure they could survive that long, but we thought potentially they could," Olssen-Francis told Discovery News.
It turned out they could. When the little rock chips containing the bacteria were brought back to Earth and placed in a liquid solution, the bacteria were rejuvenated and filled the glass tubes with blue-green blooms.
These bugs are used to living in tough environments. Clinging to the limestone cliffs of Beer, they have to withstand salt water, radiation and dry spells.
Cyanobacteria have also colonized many other hostile places, including Antarctica, the African soda lakes and the boiling hot springs of Yellowstone National Park.
Several factors help make cyanobacteria tenacious, says Igor Brown, an astrobiologist who has researched this type of photosynthesizing bacteria for NASA.
When these bacteria are faced with an adverse environment, say outer space, they exude a gel-like covering -- a biopolymer -- that protects them from drying out. All their biological processes slow down, until they are barely, just barely alive, Brown says.
Cyanobacteria are also specially equipped to rid themselves of dangerous compounds, called reactive oxygen species, that are produced when the cells are exposed to UV radiation. They probably developed this ability, Brown says, because they are the only type of bacteria to produce oxygen.
The blue-green cells are now back in a cozy lab in England, where Olssen-Francis says the next step is figuring out exactly how they were able to survive their space trip.
With their incredible survival abilities, these bacteria are sure to pique the interest of those who think that life might be able to travel from planet-to-planet on meteoroids, a hypothesis called panspermia. A space trip on a meteoroid, after all, isn't that far off from a ride on a limestone chunk.
According to this hypothesis, life-bearing meteoroids could explain how life spreads throughout the universe. It could even explain how life started on Earth.
Unfortunately for panspermists, Olssen-Francis says this is an unlikely scenario for cyanobacteria.
While cyanobacteria could theoretically survive a meteoroid ride through space, they would probably burn up while entering a planet's atmosphere.
That's because they photosynthesize, so they'd need to be on the surface of a meteoroid where they can reach sunlight. Anything on a meteoroid's surface, Olssen-Francis says, would likely burn up as it falls through the atmosphere.
Meteoroids aside, cyanobacteria could help spread life through space in a totally different way. Olssen-Francis says the power of cyanobacteria could be harnessed by humans for efforts to colonize the moon or Mars.
"The cyanobacteria would basically be used to harvest energy from the sun," she said. "They would produce food and water for the astronauts, so you wouldn't have to keep coming back to Earth."
Sci-fi sounding, of course. But it wouldn't be the first time these bugs have colonized a bare, harsh planet. Fossilized cyanobacteria found on Earth have been dated to 2.8 billion years old.
Scientists say humans partly have cyanobacteria to thank for the Earth's oxygen-rich atmosphere today. And some are hoping these cells can make other worlds more hospitable to humans, too.