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Hank: Maybe you've heard the rumors that have been going around for the past few weeks: people were saying that there might be a new Earth-like, possibly habitable exoplanet out there and that it was orbiting the star Proxima Centauri, our closest neighbor. Well, today astronomers made an official announcement in a study published in the journal Nature. It's true.

The planet's called Proxima b, it has about 1.3 times the mass of Earth which means it's probably a rocky world, and it's just 4.24 light-years away. Proxima Centauri is a red dwarf which means that it's a small, dim star, it only has about 12% of the sun's mass. But Proxima b still gets plenty of light and warmth because it orbits just 7.5 million kilometers from its parent star. Compare that to Earth's 150 million kilometer orbit around the sun. In fact, Proxima b might be warm enough to have liquid water on its surface.

Researchers first discovered evidence of a planet orbiting Alpha Centauri in 2009. They analyzed observations from the star from 2000 to 2008 and found that Alpha Centauri had what's known as a Doppler shift, meaning the spectrum of its light was changing in a consistent way. And those changes matched what would happen if a planet's gravitational pull was tugging on the star, essentially making it wobble as the planet orbited.

Since Proxima Centauri is so small, and the planet, if it existed would be orbiting so close to it, the planet's gravity would influence the star enough that we would detect it with telescopes we have today. But the researchers couldn't actually be sure it was a planet. Star spots for example, which are like sunspots but on other stars, can also change the spectrum of the star's light as it rotates, so the team kept working.

They used data from 2000 to 2014 plus two month's worth of measurements from the beginning of 2016. With all these extra observations of the star's Doppler shift, they were able to confirm the planet's existence and even pin down some of the qualities. They also eliminated the possibility of starspots causing the shift. for one thing, the pattern of the shift didn't quite fit the star's 83 say rotation, which it would if starspots were causing a change in the light.

So there really is an Earth-sized planet orbiting our closest neighboring star. But there's a lot we still don't know about Proxima b, especially when it comes to the planet's habitability. We don't know for sure that it's warm enough for liquid water and we don't know what the atmosphere is like. We don't know if it has an atmosphere to protect it from all of the radiation coming from its very nearby parent star, and even if Proxima b does have all of those things and it turns out to be a perfect environment for Earth-like life, we don't know if life ever actually evolved on the planet. But we definitely want to find out.

The problem is, 4.24 light-years is still very very far, we're talking 40 trillion kilometers. Even our fastest current space probe would take more than 18,000 years to get there. So for now, we have to observe Proxima b from afar.

One of the main goals of future research is to learn more about the planet's atmosphere since that plays a huge role in whether it can support life. With the telescopes we're using now it's possible to detect some of the qualities of a planet's atmosphere if it passes in front of its host star, that is, if the planet blocks out some of the star's light as its orbit takes it between the star and Earth. We don't know if Proxima b passes in front of its star though, and there's only a 1.5% chance that it does. But we might be able to learn more about its atmosphere anyway with the help of NASA's TEST space telescope, which is set to launch in December 2017.

TEST will look for exoplanets orbiting nearby red dwarf stars, specifically planets that pass in front of their host stars. And we'll be able to study the atmospheres of those exoplanets using the James Webb telescope in 2018. Learning more about the atmospheres of other planets orbiting close to red dwarfs means we might be able to predict what Proxima b's atmosphere might be like. So we now know Proxima b isn't just a rumor, in a couple of years we'll hopefully learn a lot more about whether it's habitable, and eventually maybe we'll find out if life actually does exist there. It's the best chance that we've got, it's really close by. This is crazy cool!

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