Can the rate of past discoveries be used to predict future ones? We may soon find out. Two researchers have used the pace of past exoplanet finds to predict that the first habitable Earth-like planet could turn up in May 2011.
In 1965, Intel co-founder Gordon Moore observed that the number of transistors that fit on a chip doubles about once every two years – a trend now known as Moore’s law. Samuel Arbesman of Harvard Medical School in Boston wants to see if scientometrics – the statistical study of science itself – can similarly be used to not only study past progress but also to make predictions.
He and Greg Laughlin of the University of California, Santa Cruz, are testing the idea with exoplanets. Over the past 15 years or so, the pace of planet discoveries has been accelerating, with some 490 planets now known. “It is actually somewhat similar to Moore’s law of exponential growth,” Arbesman says.
To predict when astronomers might find the first planet similar in size to Earth that also orbits far enough from its star to boast liquid water, the team scoured the discovery records of 370 exoplanets.
They focused on two basic properties needed for habitability: a planet’s mass and its surface temperature. They used these two factors to assign each planet a ‘habitability metric’ ranging from 0 to 1, where 0 was uninhabitable and 1 is close to Earth’s twin.
A rough estimate of each planet’s habitability was then plotted against the date of its discovery. Using different subsets of the 370 planets, the researchers made curves from the individual points and extrapolated the curves to find when a planet would be found with a habitability of 1. They then analysed the range of discovery dates to determine which would be most probable.
Their calculations suggest there is a 50 per cent chance that the first habitable exo-Earth will be found by May 2011, a 75 per cent chance it will be found by 2020, and a 95 per cent chance it will be found by 2264.