Life-forms common on Earth could survive the brutal conditions of space for long enough to travel between worlds, new research suggests, but only as part of a colony. While most voyagers would die in the passage, a few might boldly go where no microbe has gone before, colonizing worlds they land on.
The hypothesis that microorganisms could have traveled between planets is one of the most debated ideas about life's origins. Known as “panspermia”, the concept proposes life emerging in one location before being transported to other planets to flourish anew. The most adventurous form of the panspermia idea would allow the entire galaxy to be seeded from a single planet, allowing life to be common, even if the processes required to start it are exceptionally improbable. A more restricted version sees multiple worlds seeded in this way within the one-star system, while acknowledging the space between the stars might be too wide for such a journey.
Panspermia would explain how life began on Earth so soon after the planet cooled to the point of habitability. However, there remains plenty of doubt as to how likely it would be for anything to survive the journey between the worlds without a spacecraft. Professor Akihiko Yamagishi of Tokyo University of Pharmacy and Life Sciences thinks the chances are higher than many scientists have acknowledged.
If any Earth life can make such a voyage, it's probably the bacterium Deinococcus, known as possibly the planet's most radiation-resistant genus. Yamagishi's past sampling of the upper atmosphere found Deinococcus 12 kilometers (7 miles) above the surface, and they are known to form substantial aggregations.
Now Yamagishi and colleagues report in Frontiers of Microbiology what happened when astronauts placed collections of dried Deinococcus on the outside of the International Space Station and left them there for 1 to 3 years. Bacteria directly exposed to radiation died, but when the sample was more than half a millimeter (0.02 inches) thick, those located closer to the station survived, protected by the bodies of other members of their species. Even the most protected bacteria suffered DNA damage, but nothing so serious they could not revive when exposed to water and nutrients.
"The results suggest that radioresistant Deinococcus could survive during the travel from Earth to Mars and vice versa, which is several months or years in the shortest orbit," Yamagishi said in a statement. The authors calculate a 1-millimeter diameter ball of Deinococcus would preserve the bacteria at the center for eight years in space.
The discovery places extra pressure on space missions to Mars to thoroughly sterilize everything, lest the planet becomes contaminated on arrival.
It doesn't yet prove microbial life could make its way between worlds without assistance. Rocks blasted off the surface of one planet during a large asteroid strike roam the inner Solar System for thousands or millions of years before reaching their new home, and there is still lift-off and re-entry to survive.
Nevertheless, the study shows the idea of a long voyage by a bacterial colony is not as far-fetched as previously believed. The implications are particularly significant for systems like TRAPPIST-1 with multiple planets comfortably inside the “habitable zone” where liquid water can exist. If life as hardy as Deinococcus evolved on one at a time when large asteroid strikes were still common, the chances of some making it to the other planets intact would be good, creating new variations based on the same original biology.
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