Scientists have made a new planetary discovery--a discovery that brings us one step closer to finding a planet capable of sustaining life. This exoplanet (meaning it orbits a star outside our own solar system) is only about 1.13 times Earth's mass, and it's close. Very, very close on a cosmic scale: a mere 4.3 light years! 25 trillion miles might sound like a long road trip, but that's still half the distance to the next-closest known exoplanet. Here's the incredible part: We know this planet orbits Alpha Centauri B, but we haven't actually seen it. And it will likely be years until we do.
Alpha Centauri actually hosts two stars, A and B, and our favorite new exoplanet has been christened Alpha Centauri Bb because it orbits the second of the binary system's two stars. While Alpha Centauri A is a bit denser and 50 percent brighter than our sun, Alpha Centauri B has about 10 percent less mass and is 50 percent dimmer than our sun. Exoplanet Bb has a 3.24 day orbit around the cooler star, meaning it's only about six million kilometers from AC B.
Sadly, the exoplanet's surface temperature is a none-too-comfy 1000+ degrees Celsius. But, as science journalist Lee Billings writes, that's okay. This is still an incredible discovery for three reasons. Where there is one planet, there are often others. Some scientists believed planets couldn't form in binary systems like Alpha Centauri, but we now know they can--and the Milky Way contains more multi-star systems than single-star systems like ours.
Finally, the method used to detect Alpha Centauri Bb is amazing: We measured its gravitational effect on its star. By monitoring AC B for about four years, a team of scientists picked up a 50 centimeter Doppler shift in the star--a miniscule change in the star's emitted light.
Unfortunately, seeing the exoplanet will be an entirely different challenge. Billings writes that our sun emits about 10 billion times more visible light than the Earth, meaning we're damn hard to spot from another star system. Though Alpha Centauri B isn't as bright as the sun, the exoplanet orbits much, much closer. We need a way to suppress the starlight to see the planet. That technology actually exists, but implementing it won't be cheap. We'll need to spend billions on a new space telescope or spend almost a billion modifying NASA's in-progress James Webb Space Telescope, which won't be completed until 2018.
This discovery brings us a big step closer to what now seems like an inevitability: Finding a planet of just the right size, with just the right orbit, to contain liquid water and the atmosphere to support life. It might be orbiting Alpha Centuari even now--we just can't see it yet.