Berkeley Astronomers: Billions of Earth-Like Planets Just in Milky Way
October 29th, 2010Via: Washington Post:
Nobody has seen them yet, but scientists now think there are tens of billions of planets the general size and bulk of Earth in the Milky Way galaxy alone – a startling conclusion based on four years of viewing a small section of the nighttime sky.
The estimate, made by astronomers Andrew Howard and Geoffrey Marcy of the University of California at Berkeley, flows from the logic that the number of small but detectable exoplanets – planets outside Earth’s solar system – is substantially larger than the number of big exoplanets in distant solar systems.
In a paper released Thursday by the journal Science, the two report that based on this galactic preference for smaller planets, they think that almost one-quarter of the stars similar to our sun have Earth-size planets orbiting them.
“This is the first estimate based on actual measurements of the fraction of stars that have Earth-size planets,” said Marcy, who did his observing with Howard at the Keck Observatory in Hawaii.
Their observations and extrapolations say nothing about whether these Earth-size planets will have the characteristics of Earth: its density, a distance from the sun that is just right for liquid water, the fact that it is a rocky structure rather than a gaseous ball.
But Marcy said that with so many Earth-size planets now expected to be orbiting distant suns – something on the order of 50,000,000,000,000,000,000,000 across the universe – the likelihood is high that many are in “habitable zones” where life can theoretically exist.
“It’s tantalizing, without a doubt, to think some of those Earths are in habitable zones,” Marcy said. “And based on what we know, really, why wouldn’t they be?”