Earth 'may be one-off fluke '

The idea that ‘billions’ of other planets in our own Milky Way galaxy are teeming with alien life forms may just be wishful thinking, a new study has claimed.

Two Princeton scientists used what’s known as “Bayesian analysis” - a technique that “boils down” ideas to the actual data, as opposed to scientists’ own ideas about what ''should'' be true.

They suggest that it’s very possible Earth is a one-off aberration where life took hold unusually fast - and on the average extraterrestrial planet, the chances of life are very low indeed.

“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,” the Daily Mail quoted Edwin Turner and David Spiegel as saying.

“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.

“If scientists start out assuming that the chances of life existing on another planet as it does on Earth are large, then their results will be presented in a way that supports that likelihood.

“Our work is not a judgment, but an analysis of existing data that suggests the debate about the existence of life on other planets is framed largely by the prior assumptions of the participants,” they said.

Deep-space satellites and telescope projects have recently identified various planets that resemble Earth in their size and composition, and are within their star''s habitable zone, the optimal distance for having liquid water.

Of particular excitement have been the discoveries of NASA’s Kepler Space Telescope, a satellite built to find Earth-like planets around other stars.

While these observations tend to stoke the expectation of finding Earth-like life, they do not actually provide evidence that it does or does not exist, Spiegel explained. Instead, these planets have our knowledge of life on Earth projected onto them, he said.

Yet, when what is known about life on Earth is taken away, there is no accurate sense of how probable abiogenesis is on any given planet, Spiegel said. It was this ‘prior ignorance,’ or lack of expectations, that he and Turner wanted to account for in their analysis, he said.

“When we use a mathematical prior that truly represents prior ignorance, the data of early life on Earth becomes ambiguous,” Spiegel said.