Kepler 22b， a planet more like Earth than any yet discovered， has been identified as a potential future home for mankind．
Kepler 22b contains both land and water and has temperatures which average around 22℃． It also contains the right atmosphere to potentially support life．
It is， however， 600 light years from Earth． The planet， where a year lasts 290days， was first spotted two years ago．
However， NASA scientists using the agency's Kepler space telescope have now concluded that it offers the best hope yet for future human habitation outside the Solar System．
One of the key standards for a planet to be habitable is that it remains roughly the right distance from its main star to be neither too cold nor too hot．
This range of ideal temperatures is known to scientists as the "Goldilocks" zone， as the temperature is "just right" for life．
Bill Borucki， Kepler principal investigator at NASA Ames Research Centre， said： "We have now got good planet confirmation with Kepler 22b． We are certain that it is in the habitable zone and if it has a surface it ought to have a nice temperature．"
There are now three planets outside the system， known as exoplanets， which experts believe could potentially be colonised （建殖民地） by future generations．
In May， French astronomers identified Gliese 581d， which is far closer at around 20 light years away． It is about six times the mass （质量） of Earth and is one of a family of at least six planets．
In August， a team from Switzerland reported that another planet called HD 85512b and 36 light years away seemed to be habitable．
The planet is in the constellation of Vela， measuring around 3.6 times the Earth's mass．
According to an online catalogue that indexes bodies outside our solar system， a total of 47 exoplanets and exomoons are potential habitable candidates but not enough research has been done to be sure．



Whether a planet is suitable for mankind to live on doesn't depend on ______ ．

A. whether it is close enough to Earth
B. whether there are proper temperatures
C. whether there is atmosphere around it
D. whether there is land and water on it

In what way is Kepler 22b like Earth？ ______

A. Its mass．
B. Its size．
C. Its shape．
D. Its conditions．

It can be learnt from the passage that ______ ．

A. Kepler 22b is closer to Earth than Gliese 581d
B. Kepler 22b's mass is greater than HD 85512b's
C. Kepler 22b's year lasts longer than the earth's
D. Kepler 22b is most likely to be habitable of all

We can infer from the passage that ______ ．

A. the farther a planet is away from the earth， the more likely it is to be habitable
B. the longer a year of a planet lasts， the farther it is away from the Solar System
C. the more potential habitable exoplanets are found， the more research we should do
D. the smaller mass a planet has than the earth， the less possibly there is water on it