Earth-Size Planet Closest to Our Solar System: By The Numbers

Alpha Centauri and Surroundings
This wide-field view of the sky around the bright star Alpha Centauri was created from photographic images forming part of the Digitized Sky Survey 2. The star appears so big just because of the scattering of light by the telescope's optics as well as in the photographic emulsion. Alpha Centauri is the closest star system to the Solar System. Image released Oct. 17, 2012. (Image credit: ESO/Digitized Sky Survey 2)

An alien planet discovered around a star in the Alpha Centauri system, the nearest to our own sun, has astronomers buzzing, and not just because it's the closest exoplanet to Earth ever seen.

The newfound extrasolar planet Alpha Centauri Bb, it turns out, is not only the nearest alien world to Earth, it's also extremely Earthlike in size and mass. The planet is much too hot and too close to its parent star to support life, but its existence suggests the tantalizing possibility that there may be more planets waiting to be found in our neighboring star system.

European researchers have detected a planet – just slightly more massive than Earth – orbiting very close to Alpha Centauri B, a sun-like star only 4.3 light-years from our Sun. (Image credit: ESA)

Here's a look at the numbers behind the newfound alien planet Alpha Centauri Bb:

25 trillion: The number of miles Alpha Centauri Bb is from Earth. That's about 40 trillion kilometers. Sound far? It's still the closest star system to our sun.

3.6 million: The distance, in miles, at which the planet orbits its parent star Alpha Centauri B. This is much closer to the star than Mercury is to our sun. Earth is 93 million miles (150 million km) from the sun.

40,000: The approximate number of years it would take an unmanned spacecraft like NASA's Voyager 1 probe now leaving our solar system to reach Alpha Centauri Bb. You'd need a lot of snacks for that trip.

2,240: The likely surface temperature in Fahrenheit (it's 1,227 degrees Celsius) for planet Alpha Centauri Bb. The planet is so hot, its surface is likely melted into a molten slag, making it a truly hellish "lava world." Bring your sunscreen.

800: The lower limit for confirmed alien planets scientists have discovered since the mid-1990s. There are thousands more awaiting confirmation.

4.3: The number of light-years Alpha Centauri Bb is from Earth. The star system is visible only from the Southern Hemisphere of our planet. (Sorry, northern stargazers!)

2: The number of sunlike stars in the Alpha Centauri system. The stars Alpha Centauri A and B are both similar to our sun and. Proxima Centauri is much fainter than Earth.

1.13: The mass of alien planet Alpha Centauri Bb as compared to that of Earth. It is the first Earth-mass planet around a sunlike star ever found, scientists say.

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Tariq Malik

Tariq is the Editor-in-Chief of and joined the team in 2001, first as an intern and staff writer, and later as an editor. He covers human spaceflight, exploration and space science, as well as skywatching and entertainment. He became's Managing Editor in 2009 and Editor-in-Chief in 2019. Before joining, Tariq was a staff reporter for The Los Angeles Times covering education and city beats in La Habra, Fullerton and Huntington Beach. In October 2022, Tariq received the Harry Kolcum Award for excellence in space reporting from the National Space Club Florida Committee. He is also an Eagle Scout (yes, he has the Space Exploration merit badge) and went to Space Camp four times as a kid and a fifth time as an adult. He has journalism degrees from the University of Southern California and New York University. You can find Tariq at and as the co-host to the This Week In Space podcast with space historian Rod Pyle on the TWiT network. To see his latest project, you can follow Tariq on Twitter @tariqjmalik.