So Many "Earths"

　　The Milky Way (银行) contains billions of Earth-sized planets that could support life. That's the finding of new study. It draws on data that came from NASA's top planet-hunting telescope.

　　A mechanical failure recently put that Kepter space telescope out of service. Kepler had played a big role in creating a census of planets orbiting some 170,000 stars. Its date have been helping astronomers predict how common planets are in our galaxy. The telescope focused on hunting planets that might have conditions similar to those on Earth.

　　The authors of a study published in The Proceedings of the National Academy of Sciences conclude that between 14 and 30 out of every 100 stars with a mass and temperature similar to the Sun may host a planet that could support life as we know it. Such a planet would have a diameter at least as large as Earth's but no more than twice that big. The planet also would have to orbit in a star's habitable zone. That's where the surface temperature would allow any water to exist as liquid.

　　The new estimate of how many planets might fit these conditions comes from studying more that 42,000 stars and identifying suitable worlds orbiting them. The scientists used those numbers to extrapolate (推算) to the rest of the stars that the telescope could not see.

　　The estimate is rough, the authors admit. If applied to the solar system, it would define as habitable a zone starting as close ot the Sun as Venus and running to as far away as Mars. Neither planet is Earthlike (although either might have been in the distant pase). Using tighter limits the researchers estimate the between 4 and 8 out of every 100 sunlike stars could host an Earth-sized world. These are ones that would take 200 to 400 days to complete a yearly orbit.

　　Four out of every 100 sunlike stars doesn't sound like a big number. It would mean however that the Milky Way could host more than a billion Earth-sized planets with a chance for life.

　　16. The Kepler space telescope has been in service for 15 years.

　　A. Right

　　B. Wrong

　　C. Not mentioned

　　17. The main task of the Kepler space telescope is to find out planets with similar conditions to Earth's.

　　A. Right

　　B. Wrong

　　C. Not mentioned

　　18. The planet that could support life might be a little bit smaller than Earth.

　　A. Right

　　B. Wrong

　　C. Not mentioned

　　19. The Earth is a planet orbiting in the Sun's habitable zone.

　　A. Right

　　B. Wrong

　　C. Not mentioned

　　20. The new finding is based on a thorough study of 170,000 stars on the Milky Way.

　　A. Right

　　B. Wrong

　　C. Not mentioned

　　21. The estimate of the number of planets that could support life is not very accurate.

　　A. Right

　　B. Wrong

　　C. Not mentioned

　　22. This is the first research finding about the planets with a chance for life.

　　A. Right

　　B. Wrong

　　C. Not mentioned