SoMany"Earths"

The Milky Way（银河）contains billions of Earth-sizedplanets that could support life.That's the finding of a new study.It draws ondata that came from NASA's top planet-

hunting telescope.

A mechanical failurerecently put that Kepler space telescope out of service.Kepler had played a bigrole in creating a census of planets orbiting some 170,000 stars.Its data

have been helpingastronomers predict how common planets are in our galaxy.The telescope focusedon hunting planets that might have conditions similar to those on Earth.

The authors of astudy,published in The Proceedings of the National Academy of Sciences,concludethat between 14 and 30 out of every 100 stars,with a mass and

temperature similarto the Sun,may host a planet that could support life as we know it.Such aplanet would have a diameter at least as large as Earth's,but no more thantwice

that big.The planetalso would have to orbit in a star's habitable zone.That's where the surfacetemperature would allow any water to exist as a liquid.

The new estimate ofhow many planets might fit these conditions comes from studying more than42,000 stars and identifying suitable worlds orbiting them.The scientists

used those numbersto extrapolate（推算） to therest of the stars that the telescope could not see.

The estimate isrough,the authors admit.If applied to the solar system,it would define ashabitable a zone starting as close to the Sun as Venus and running to as faraway as

Mars.Neither planetis Earthlike (although either might have been in the distant past).Usingtighter limits,the researchers estimate that between 4 and 8 out of every 100

sunlike stars couldhost an Earth-sized world.These are ones that would take 200 to 400 days tocomplete a yearly orbit.

Four out of every100 sunlike stars doesn't sound like a big number.It would mean,however,thatthe Milky Way could host more than a billion Earth-sized planets with a

chance for life.The estimate ofthe number of planets that could support life is not very accurate.

A.Right

B.Wrong

C.Not mentioned