LONG BEACH, California – New estimates suggest that roughly 50 percent of sun-like stars could have planets the size of Earth orbiting in a place where liquid water might exist on their surface.
The results also indicate that almost all sun-like stars have a planetary system of some sort.
“If you could randomly travel to a star, it will have planets,” said astronomer Francois Fressin from the Harvard-Smithsonian Center for Astrophysics, during a press conference today here at the American Astronomical Society 2013 meeting.
The finding uses data from NASA’s Kepler space telescope, which is currently scanning 150,000 stars in the constellation Cygnus for evidence of planets. Astronomers analyzed this data using a program called Transiting ExoEarth Robust Reduction Algorithm (TERRA) to try and estimate the percentage of planets that Kepler is missing.
Kepler looks for the very tiny dimming of a star’s light that can be detected when an exoplanet passes in front of it, causing a mini eclipse. The telescope is good at detecting the dimming from a larger Jupiter-sized planet, but a tiny Earth-like planet will cause such a slight change that Kepler might miss it. TERRA found that Kepler had missed about 37 Earth-like planets in its data analysis, which means it’s missing about 25 percent of these worlds.
The findings suggested that smaller extrasolar planets form more frequently than larger ones, a result consistent with previous research. But TERRA found that the trend doesn’t hold true past a certain point. Planets twice the diameter of Earth are about as common as those that are Earth-sized or smaller, a result that astronomers hadn’t previously seen.
The results are heartening for anyone who likes imagining a universe full of life. Previous analysis suggested billions of Earth-like planets could exist in our galaxy, and recently another team announced the discovery of 15 potentially habitable exoplanets.
But the researchers caution that many of the worlds they find are not necessarily habitable. Exoplanets two or three times the size of Earth – nearly the same size as Neptune or Uranus – would likely have a rocky core surrounded by a thick atmosphere of hydrogen and helium. These planets would number roughly the same as Earth-sized planets in the universe but not have conditions that we know to produce living organisms.
Furthermore, about 17 percent of stars have Earth-sized planets in the wrong location. These worlds orbit their host star closer than Mercury orbits our own sun, which would scorch their surfaces and make them difficult places to live. But planets one to two times the size of Earth could, if composed mostly of rock and silicates and located at the right distance to have liquid water, have life on their surface.
Image: ESO/M. Kornmesser
