One of astronomy’s current goals is to determine the number of sun-like stars that have an earth-like planet. Now, a new guesstimate from the University of California – Berkeley published in Science puts that number at a very high 1-in-4.
To arrive at the 1-in-4 figure, UC Berkeley astronomers Andrew Howard and Geoffrey Marcy chose 166 G and K class stars (G stars are yellow, like our Sun, while K-type stars are slightly smaller and orange-red) within 80 light years of Earth. They then observed these stars with the Keck telescope for five years in order to determine the number, mass and orbital distance of any of the stars’ planets.
The researchers found increasing numbers of smaller planets, down to the smallest size detectable today – planets called super-Earths, about three times the mass of Earth. “Of about 100 typical sun-like stars, one or two have planets the size of Jupiter, roughly six have a planet the size of Neptune, and about 12 have super-Earths between three and 10 Earth masses,” said Howard. “If we extrapolate down to Earth-size planets – between one-half and two times the mass of Earth – we predict that you’d find about 23 for every 100 stars.”
Previous studies have estimated the proportion of Jupiter and Saturn-size exoplanets, but never down to Neptunes and super-Earths, enabling an extrapolation to Earth-size planets. “What this means,” Howard adds, “is that, as NASA develops new techniques over the next decade to find truly Earth-size planets, it won’t have to look too far.”