Alpha Centauri: Gateway to the Stars

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Meet Alpha Centauri

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Alpha Centauri and its surrounding stars. NASA/DSS

You may have heard that Russian philanthropist Yuri Milner and scientist Stephen Hawking, and others want to send a robotic explorer to the nearest star: Alpha Centauri. In fact, they want to send a fleet of them, a swarm of spacecraft each no bigger than a smartphone. Sped along by light sails, which would accelerate them to a fifth of the speed of light, the probes would eventually get to the nearby star system in about 20 years. Of course, the mission won't leave for a couple of decades yet, but apparently, this is a real plan and would be the first interstellar travel achieved by humanity. As it turns out, there could be a planet for the explorers to visit! 

Alpha Centauri, which is really three stars called Alpha Centauri AB (a binary pair) and Proxima Centauri (Alpha Centauri C), which is actually the closest to the Sun of the three. They all lie at about 4.21 light-years from us. (A light-year is the distance that light travels in a year.) 

The brightest of the three is Alpha Centauri A, also known more familiarly as Rigel Kent. It's the third-brightest star in our night sky after Sirius and Canopus. It is somewhat larger and a bit brighter than the Sun, and its stellar classification type is G2 V. That means it's a lot like the Sun (which is also a G-type star). If you live in an area where you can see this star, it looks quite bright and easy to find.

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Alpha Centauri B

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Alpha Centauri B, with its possible planet (foreground) and Alpha Centauri A in the distance. ESO/L. Calçada/N. Risinger - http://www.eso.org/public/images/eso1241b/

Alpha Centauri A's binary partner, Alpha Centauri B, is a smaller star than the Sun and much less bright. It's an orange-red colored K-type star. Not long ago, astronomers determined that there's a planet about the same mass as the Sun orbiting this star. They named it Alpha Centauri Bb. Unfortunately, this world doesn't orbit in the star's habitable zone, but much closer. It has a 3.2-day-long-year, and astronomers think that its surface is probably quite hot — around 1200 degrees Celsius. That's about three times hotter than the surface of Venus, and is obviously too hot to support liquid water on the surface. Chances are this little world has a molten surface in many places! It doesn't look like a likely spot for future explorers to land when they get to this nearby star system. But, if the planet IS there, it's going to be of scientific interest, at the very least! 

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Proxima Centauri

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A Hubble Space Telescope view of Proxima Centauri. NASA/ESA/STScI

Proxima Centauri lies about 2.2 trillion kilometers away from the main pair of stars in this system. It's an M-type red dwarf star, and much, much dimmer than the Sun. Astronomers have found a planet orbiting this star, making it the nearest planet to our own solar system. It's called Proxima Centauri b and it's a rocky world, just as Earth is.

A planet circling Proxima Centauri would bask in reddish-colored light, but it would also be subject to frequent outbursts of ionizing radiation from its parent star. For that reason, this world might be a risky place for future explorers to plan a landing. Its habitability would depend on a strong magnetic field to ward off the worst of the radiation. It's not clear that such a magnetic field would last long, particularly if the planet's rotation and orbit are affected by its star. If there's life there, it could be quite interesting. The good news ​is, this planet orbits in the star's "habitable zone", meaning it could support liquid water on its surface.

Despite all these issues, it's quite likely that this star system will be humanity's next steppingstone to the galaxy. What future humans learn there will help them as they explore other, more distant stars and planets. 

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Find Alpha Centauri

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A star-chart view of Alpha Centauri, with the Southern Cross for reference. Carolyn Collins Petersen

Of course, right now, traveling to ANY star is quite difficult. If we had a ship that could move at the speed of light, it would take 4.2 years to make the trip TO the system. Factor in a few years of exploration, and then a return trip to Earth, and we're talking about a 12- to 15-year trip! 

The reality is, we are constrained by our technology to travel at fairly slow speeds, not even a tenth of the speed of light. The Voyager 1 spacecraft is among the fastest-moving of our space probes, at about 17 kilometers per second. The speed of light is 299,792,458 meters per second. 

So, unless we come up with some fairly fast new technology to transport humans across interstellar space, a round trip to the Alpha Centauri system would take centuries and involve generations of interstellar travelers on the ship. 

Still, we CAN explore this star system now both using the naked eye and through telescopes. The easiest thing to do, if you live where you can see this star (it's a Southern Hemisphere stargazing object), is step outside when the constellation Centaurus is visible, and look for its brightest star.