/ 7 November 2013

Galaxy gives life a sporting chance

Galaxy Gives Life A Sporting Chance

Twenty years ago, we thought Earth – and even our solar system – was unique: a blue-green sanctuary of life in a freezing universe that was sporadically populated with exploding stars.

The first confirmed observation of an exosolar planet – a planet outside of our solar system – was in the early 1990s. But as scientific techniques become more sensitive and advanced, scientists have observed a glut of planets; and now habitable planets, which have liquid water and could support life as we know it, have become the focus of their scrutiny.

This week astronomers from the universities of California Berkeley and Hawaii estimated there are more than two-billion habitable planets in our galaxy alone. Their findings are the result of a statistical analysis of data from Nasa’s now-defunct planet-hunting spacecraft, Kepler. The research was published in Proceedings of the National Academy of Sciences.

The reason that Earth has liquid water – considered a prerequisite for carbon-based life – is that it is the perfect distance from the Sun, in what scientists call the "Goldilocks" zone because it is neither too hot nor too cold. If Earth were closer to the Sun, its water would evaporate and become water vapour; if it were further away, it would freeze.

"When you look up at the thousands of stars in the night sky, the nearest Sun-like star with an Earth-sized planet in its habitable zone is probably only 12 light years away and can be seen with the naked eyes," Berkeley graduate student Erik Petigura, who led the analysis of the Kepler data, said on Monday.

Andrew Howard, who is with the Institute for Astronomy at the University of Hawaii, said: "It’s been nearly 20 years since the discovery of the first extrasolar planet around a normal star. Since then, we have learned that most stars have planets of some size and that Earth-sized planets are relatively common in close-in orbits that are too hot for life.

"With this result … [we are] showing that planets like our Earth are relatively common through the Milky Way galaxy."

There are between 100-billion and 400-billion stars in the Milky Way, and about 10% of these are yellow dwarf stars, like our Sun. If one in five of these yellow dwarfs has

planets in the Goldilocks Zone, there are more than two-billion habitable planets.

However, the researchers caution that these planets may not be hospitable to life just because they are in the habitable zone.

"Some may have thick atmospheres, making it so hot at the surface that DNA-like molecules would not survive," UC Berkeley astronomy professor Geoffrey Marcy said. "Others may have rocky surfaces that could harbour liquid water suitable for living organisms. We don’t know what range of planet types and their environments are suitable for life."

Howard said that this research could help inform future planet-hunting spacecraft: "For Nasa, this number – that every fifth star has a planet somewhat like Earth – is really important because successor missions to Kepler will try to take an actual picture of a planet, and the size of the telescope they have to build [on the spacecraft] depends on how close the nearest Earth-sized planets are."

"[We are] showing that planets like our Earth are relatively common through the Milky Way"