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So Many 'Earths'

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

A mechanical failure recently put that Kepler space telescope out of service. Kepler　had played a big role in creating a census of planets orbiting some 170,000 stars. Its data　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 a liquid.

The new estimate of how many planets might fit these conditions comes from　studying more than 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 to the Sun as Venus and running to as far　away as Mars. Neither planet is Earthlike (although either might have been in the distant　past). Using tighter limits, the researchers estimate that 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　change for life.

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

A. Right B. Wrong C. Not mentioned

答案：C

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

答案：A

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

A. Right B. Wrong C. Not mentioned

答案：B

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

A. Right B. Wrong C. Not mentioned

答案：A

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

A. Right B. Wrong C. Not mentioned

答案：B

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

A. Right B. Wrong C. Not mentioned

答案：A

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

A. Right B. Wrong C. Not mentioned

答案：C

（責任編輯：vstara）

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