今天看到报纸介绍说NASA的天文学家已经发现了迄今为止最适宜人类居住的外星球。

Astronomers have discovered what they say is the most Earth-like planet yet detected a distant, rocky world that's similar in size to our planet and exists in the Goldilocks zone where it's not too hot and not too cold for life.

"This is the best case for a habitable planet yet found. The results are absolutely rock solid," University of California, Berkeley astronomer Geoff Marcy, who had no role in the discovery, said in an email.

The planet was detected by Nasa's orbiting Kepler telescope, which examines the heavens for subtle changes in brightness that indicate an orbiting planet is crossing in front of a star. From those changes, scientists can calculate a planet's size and make certain inferences about its makeup.

The newfound object, dubbed Kepler-186f, circles a red dwarf star 500 light-years from Earth in the constellation Cygnus. A light-year is almost 6 trillion miles.

The planet is about 10 per cent larger than Earth and may very well have liquid water a key ingredient for life on its surface, scientists said. That is because it resides at the outer edge of the habitable temperature zone around its star the sweet spot where lakes, rivers or oceans may exist without freezing solid or boiling away.

The planet probably basks in an orange-red glow from its star and is most likely cooler than Earth, with an average temperature slightly above freezing, "similar to dawn or dusk on a spring day," Marcy said.

The discovery was detailed in Friday's issue of the journal Science.

Astronomers may never know for certain whether Kepler-186f can sustain life. The planet is too far away even for next-generation space telescopes like Nasa's overbudget James Webb, set for launch in 2018, to study in detail.

Kepler completed its prime mission and was in overtime when one of the wheels that keep its gaze steady failed last year. Nasa has not yet decided whether to keep using the telescope to hunt for planets on a scaled-back basis.