The latest attempt to work out how much alien life is out there suggests there may be a lot more than most people thought.
According to a new statistical analysis based on how quickly life got going on Earth, life will start on at least a third of Earth-like planets within a billion years of them developing suitable conditions. And with recent discoveries that planets are common around Sun-like stars, there’s probably no shortage of prospective homes.
Earlier attempts to estimate the likelihood of life on Earth-like planets floundered because we have only a single data point – the Earth itself. Isotopic and fossil evidence suggest that life originated here 25 to 600 million years after the planet became habitable.
But we cannot be sure whether life is an accident unique to our planet, or is common on similar planets throughout the Universe.
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Winning the lottery
To address this problem, Charles Lineweaver and Tamara Davis of the University of New South Wales in Sydney looked at the implications of the rapid beginning of life on Earth for the probability of it evolving elsewhere.
The chance of life is like winning a lottery, says Lineweaver. “It is having won quickly that lets us estimate probability.” If you know only that a lottery player won on the third try, you can’t be sure of the real odds, but you can say the chance of winning is more likely to be one in three than one in a billion.
From life’s lottery on Earth, Lineweaver says he’s 95 per cent certain that given a billion years, the chance of life starting on a suitable planet is at least one in three.
“It’s an interesting attempt to put some valid statistical analysis into a term that otherwise appears completely unknown,” says Mario Livio of the Space Telescope Science Institute in Baltimore.
