French astronomers studying a "warm and wet" planet 20 light years away say it may be the first outside our solar system that could sustain life. Scientists at the Institute Pierre Simon Laplace in Paris who used a new computer model to simulate the planet's climate concluded that it could resemble Earth's. Here, a brief guide:

What is this planet?
It's called Gliese 581d, and it orbits a red dwarf star about 20 light years away. The planet is twice the size of Earth, with six times the mass. Gliese 581d was originally thought to be too cold to be habitable, but the new report, to be published in Astrophysical Journal Letters, suggests otherwise.

So what makes Gliese 581d so hospitable?
It "has the potential to be warm and wet enough" for life to survive, according to AFP. Its atmosphere, sufficiently rich in carbon dioxide to retain heat, might also allow for water (oceans, clouds, and rainfall). But astronomers admit that their simulations could be faulty. "Gliese 581d could have a thick layer of hydrogen and helium in its atmosphere, which would lead to a much less-hospitable climate," says Hamish Johnston in Physics World.

Would humans be able to live there?
Probably not. Light would have trouble penetrating its dense air and thick clouds, resulting "in a perpetual murky red twilight." It's also possible that one side of Gliese 581d always faces the sun, while the other remains in darkness, and, with gravity that's roughly twice as strong as on Earth, says Evan Ackerman at DVICE, "it's not exactly a vacation spot." Even if it were more attractive, getting there would take 3,000 lifetimes, says Daniel Honan at Big Think. "So if you're tempted to buy real estate on Gliese 581d, consider it a long-term investment."

So what kinds of life could exist there?
Possibilities include "extraterrestrial plant life," says Ackerman at DVICE, and any animal that could survive in a "high gravity, low light, low oxygen environment. So think small and low to the ground with big eyes. And of course, there's lots of potential for animal life in warm oceans, too."

Haven't other planets been hyped as life-sustaining before?
Yes. In fact, Gliese 581d's neighbor, known as Gliese 581g, had once been touted as a potential "Goldilocks planet" that could support life. But "the existence of that planet has since been called into question," says Kristy Lang at BBC News.

Sources: Agence France Presse, BBC News, Big Think, DVICE, Physics World