科学美国人60秒:Faraway Planets May Be Far Better for Life

Earth is the only place where we know for sure that life exists. We have liquid water and a strong magnetic field that shields out harmful cosmic radiation.
 
But what if Earth isn’t the most habitable type of planet? Researchers say they’ve listed the qualities that would make a planet extra-friendly to life, or “superhabitable.” Their paper is in the journal Astrobiology. [René Heller and John Armstrong, Superhabitable Worlds]
 
A “superhabitable” planet should be two or three times the size of Earth. The extra surface area provides more room for species to spread out and evolve. And the stronger gravity of a giant-Earth would flatten the surface, allowing for more lakes and archipelagos—crucibles of life here.
 
Our “superhabitable” planet should also be well-aged. The sun and earth are about five billion years old—middle aged, cosmically speaking. But some stars that are slightly smaller and dimmer than our sun are more than 10 billion years old. That’s a lot of extra time for life to take hold and evolve.
 
Astronomers estimate that our Milky Way galaxy is home to around 100 billion planets. Compared with planets yet to be found, Earth could barely be making a living.

—Michael Moyer