Princeton University researchers are throwing some cold water on the hot notion that astrobiologists and other scientists expect to one day find life on other planets.
Recent discoveries of planets similar to Earth in size and proximity to the planets' respective suns have sparked scientific and public excitement about the possibility of also finding Earth-like life on those worlds, but the expectation that life -- from bacteria to sentient beings -- has or will develop on other planets as on Earth might be based more on optimism than scientific evidence stated Princeton astrophysical sciences professor Edwin Turner and David Spiegel, a former Princeton postdoctoral researcher and now with the Institute for Advanced Study in a paper on the subject.
In fact the current knowledge about life on other planets suggests that it's very possible that Earth is a cosmic aberration where life took shape unusually fast. If so, then the chances of the average terrestrial planet hosting life would be low, Turner and Spiegel state. Finding a single case of life arising independently of our lineage (on Earth, elsewhere in the solar system, or on an extrasolar planet) would provide much stronger evidence that the emergence of life or what the researchers call abiogenesis is not extremely rare in the universe.
According to a release, the researchers used a Bayesian analysis -- which weighs how much of a scientific conclusion stems from actual data and how much comes from the prior assumptions of the scientist -- to determine the probability of extraterrestrial life once the influence of these presumptions is minimized.
"The idea that life has or could arise in an Earth-like environment has only a small amount of supporting evidence, most of it extrapolated from what is known about abiogenesis on early Earth. Instead, their analysis showed that the expectations of life cropping up on exoplanets -- those found outside Earth's solar system -- are largely based on the assumption that it would or will happen under the same conditions that allowed life to flourish on this planet," the researchers said.
"Fossil evidence suggests that life began very early in Earth's history and that has led people to determine that life might be quite common in the universe because it happened so quickly here, but the knowledge about life on Earth simply doesn't reveal much about the actual probability of life on other planets," Turner said. "Information about that probability comes largely from the assumptions scientists have going in, and some of the most optimistic conclusions have been based almost entirely on those assumptions."