Olaf Stapledon’s Last and First Men (1930), amongst other wonders, pictures our descendants millions of years hence moving from world to world as they attempt to save the species. The Moon approaches the Earth, an imminent peril the ‘Fifth Men’ escape by terraforming Venus, unfortunately destroying indigenous life forms there. Later, the Fifth Men move on to Neptune, and when their existence there is endangered, they make an attempt to save themselves as a species by seeding their cells among the stars. Interestingly enough, Francis Crick (famed as a co-discoverer of the structure of DNA) suggested in 1973 that life could have been intentionally sent from elsewhere in the universe with the express purpose of finding a new home, an idea that made the later work of Fred Hoyle and Chandra Wickramasinghe seem positively tame.

We’re talking panspermia, the idea that life can survive long journeys through space to seed other planets (a notion Hoyle addressed in 1982’s Evolution from Space). The apotheosis of the concept is in the realms between the stars, as Stapledon and Hoyle both assumed. We already know that materials, though not necessarily life, can move between planets in our own Solar System, as shown by compelling evidence for Martian meteorites. But interstellar journeys are of another order, the distances so vast that the question of survival dominates the debate.

Panspermia among the stars

Yet comets could be interesting places for microbes to thrive, and it’s not beyond the bounds of possibility that an ejected comet might make its way between the stars, finally encountering another stellar companion and making a spectacular arrival upon a warm, rocky planet. There is no way at this juncture to prove whether or not life began on Earth this way, but it’s a concept that demands study. One way to investigate it is to work with microbes in near-Earth orbit, as a Japanese team now proposes to do aboard the International Space Station in an experiment called Tanpopo.

Image: Is panspermia a viable option for moving life not only between planets but also between the stars? Credit: Jess Johnson/UC Santa Cruz.

The discovery of microbes in space would hardly prove the concept of panspermia, for any materials at these altitudes could well have come from Earth. But a positive result could tell us more about how life manages to persist in the most hostile environments. The Tanpopo (‘dandelion’) experiment will examine tiny particles captured onto an aerogel, returning them to Earth for study of their makeup and possible microbes. Survival at ISS altitudes would definitely give panspermia advocates a boost while forcing us to contemplate the possibility that life began elsewhere.

After all, infalling material reaching Earth’s surface from space amounts to tens of thousands of tons on a yearly basis. Tanpopo is unlikely to show us any extraterrestrial microbes, but the researchers do plan, as a second part of the experiment, to expose Earth microbes to space on metal plates placed outside the ISS, as this story in New Scientist explains. The microbes will remain outside the station for periods of one to five years. some protected by clay minerals, some openly exposed to the rigors of the vacuum.

The experiment is slated to begin in 2011, offering a useful follow-up to work performed in 2002 by an ESA team using the Russian Foton satellite. Those remote controlled experiments exposed 50 million unprotected spores of the bacterium Bacillus subtilis to space, mixing another set of 50 million with particles of clay, red sandstone and other materials. The unprotected spores died quickly, but the protected ones produced numerous survivors, particularly those in the red sandstone mix. An exchange of biological materials between planets could not be ruled out by this experiment.

So we’ll see what Tanpopo comes up with as it goes to work on a highly resistant microbe called Deinococcus radiodurans, known to fend off ultraviolet and gamma radiation and to survive extreme dryness and vacuum. The project, which was presented at the recent Astrobiology Science Conference in Santa Clara CA, may offer yet more proof of life’s survival in hostile environments, but it will surely leave the question of the origin of that life open to further debate. Backing out to the big picture, it may be a long time before we identify microbes within a comet, but finding such evidence would keep interstellar panspermia in the picture, with obvious repercussions for life’s chances around other stars.