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First Planet Discovered in Alpha Centauri System

Information on the Discovery, and also Insights from Debra Fischer

Posted by Bruce Betts

17-10-2012 19:22 CDT

Topics: Planetary Society Projects, astronomy, extrasolar planets, Alpha Centauri Planet Search

Using more than four years of data, astronomers using the HARPS instrument on the 3.6-meter telescope at ESO’s (European Southern Observatory) La Silla Observatory in Chile have reported the discovery of a slightly larger than Earth-mass planet orbiting the star Alpha Centauri B. This is the first discovery of a planet in our closest neighbor system of stars, and the least massive exoplanet ever discovered around a star like the Sun. I wanted to share with you some thoughts and insights by Yale astronomer Debra Fischer who leads another Alpha Centauri planet search that is partially supported by The Planetary Society. But first, here is a little more on the discovery (and if you are looking for a primer on exoplanet hunting, check out our online astronomy course lecture on the subject).

First planet discovered orbiting Alpha Centauri B (artist's concept)

ESO/L. Calçada/N. Risinger (

First planet discovered orbiting Alpha Centauri B (artist's concept)
Artist’s impression of the first planet discovered orbiting the star Alpha Centauri B, a member of the triple star system that is the closest to Earth. The planet was found in 2012 with the HARPS spectrograph on the 3.6-m telescope at ESO’s La Silla Observatory in Chile.

The planet would be crispy, toasty hot (not a technical term), at least on the side facing its parent star, since it orbits only 6 million kilometers from its parent star in a 3.2 day orbit. For comparison, the closest point to the Sun in Mercury’s elliptical orbit is 46 million kilometers, and Mercury has an 88 day orbit.

The European discovery team’s research was published today in the journal Nature. The lead author is Xavier Dumusque (Observatoire de Genève, Switzerland; Centro de Astrofisica da Universidade do Porto, Portugal).

The Alpha Centauri system, a little over 4 light years away, consists of three stars labeled A, B, and C from brightest to dimmest. The two brightest are roughly Sun-like, whereas the third, also known as Proxima Centauri because it is the closest to Earth, is a red dwarf much farther out in the system. The planet discovery was around Alpha Centauri B (AlphaCenB, or aCenB or Scooter [not really]), which is somewhat smaller and less bright than the Sun.

The Planetary Society is supporting another Alpha Centauri exoplanet search, led by Debra Fischer at Yale University (read about it here and/or listen to Debra on Planetary Radio here). Debra shared with me her thoughts and some insights on the Alpha Cen planet discovery, as well as how it relates to their search:

“The HARPS team called me a week ago to let me know about their result and we've been analyzing our data and running simulations to test the detectability of this tiny signal. Our best data set for aCenB begins in June 2012, when we completed some stability upgrades to the new spectrograph (CHIRON) that we built for the 1.5-m CTIO telescope (with NSF MRI funding). Our precision since the upgrade matches the HARPS precision, but yields a 5-month string of data compared to the 5-year time baseline of data from HARPS.

There is not a more exciting result for an individual star, even with the long line of spectacular results from the last 2 decades. The indication that our nearest neighbor has rocky planets is incredible. Furthermore, statistical results from the NASA Kepler mission suggest that where there is one, there are usually several rocky planets. This leaves open the possibility of a terrestrial planet in the habitable zone - in fact, I think this strengthens the speculative possibility of a habitable world in the alpha Cen system.

The Geneva team has done something very difficult, but it's an approach that I've advocated for the past few years: they are digging into their data to remove signals that arise from the surface of the star, leaving behind the whiff of a residual signal - a mere 0.5 m/s - induced by a prospective planet. The team is extremely careful and no one wants to be wrong about such a high profile result. I have no doubt that they have carried out every reasonable test of their data before making this announcement. Nevertheless, because these corrections essentially constitute a new approach, confirmation is critical. We are in an excellent position to follow-up, but that will likely require an intensive search over the prospective orbital period of 3.24d when the star rises again in January 2013.”

The first discovery of another world, much less an Earth-sized world around a star in the closest star system to Earth is a profound one, and one that is all the more exciting because, it may portend future discoveries there of planets that are even more Earth-like. Even around our nearest neighbors, the search is not easy, but the results may yield planets we can study in more depth because of their “closeness.” Someday, Alpha Centauri planets could be the first extra-solar system destination for advanced future robotic and, maybe someday, human emissaries.

See other posts from October 2012


Or read more blog entries about: Planetary Society Projects, astronomy, extrasolar planets, Alpha Centauri Planet Search


wavettore: 10/18/2012 02:12 CDT

Contrary to what science still believes, at the time of the Big Bang there were no atoms but only waves carrying energy through the infinite Void. If we could view the Universe from outside, It would look like an egg-shaped cloud with winds running in perpetual motion inside of It. The energy is like those winds running at maximum speed and pushing out the borders of the Universe. The Universe continues to expand as the waves that travel at the border of the Universe have never encountered, nor will ever encounter, any interference from the Void. These waves will forever expand the Space of the Universe they create and leave behind. Wave-behavior relates to the medium in which the waves travel. Thus, wave-behavior at the border of the Universe is different than wave-behavior within the Universe. Inside the Universe, waves change their frequencies by colliding with other energy during their travel. These waves, because of the encountered interference, continue to transform part of their original energy in other forms. Waves travel gradually releasing heat, or amounts of energy, and their original short wavelengths, in time become longer and longer as they carry less and less energy than they did when they first started to travel. These waves lose energy releasing it in form of other waves with wavelengths longer than their own. For example, the gamma rays, over time, diminish their energy level (and their frequency) to become X rays, from X rays they will become ultraviolet and so on. The original quantum is not lost but distributed into other forms of energy through "spontaneous symmetry breaking". Once reached an almost flat longitude (and lower critical energy level) these waves solidify into hydrogen atoms breaking up their energy in opposite elements, like the split ends of a broken hair. When the hydrogen atoms are reached by the heat of other incoming waves they fuse together to create more complex forms of energy.

Björn W: 10/18/2012 04:42 CDT

A landmark astronomical discovery! Looking forward to further confirmation and perhaps more A. Centauri planets as discussed by Debra Fischer. PS. Must the website/comments editor really accept lenghty totally irrelevant comments like the one by "wavettore" ?

bware: 10/19/2012 10:31 CDT

Great article! I'm glad to see we did a great piece on it! Well written. The only aggravating point is that we have to wait until Jan '13. Well I always say astronauts of all disciplines needs to be in space so we can move the Interplanetary Cruiser or Starship to where we need to be. ESPS (Extra Solar Planetary Science) needs to be done from space, not from planets. Until then we have no choice but to wait... orbital mech's are not always our friend with the technology limitations we have. The confirmation, if the planet is real and not an optical/noise ghost, will be worth the wait. Good luck on the confirmation work to all on that team!

dougforworldsexplr: 10/22/2012 03:23 CDT

Hi Bware and everyone; I was very inspired by the discovery of a planet around Alpha Centauri as well partly because one of the first thing people I talk to say when extrasolar planets are found is how far away and hard to get to they are. Anyway in looking in my books about astronomy for Alpha Centauri I found an interesting quote. I would be interested to hear what other Planetary Society members think about it: "The nearest star for which this gravitational perturbation method can be applied is Barnard's Star, the nearest single star. The complex interactions of the three stars in the Alpha Centauri system would make the search for a low-mass companion there very difficult." Cosmos page 176 Carl Sagan 1980

Zorbonian: 10/23/2012 03:03 CDT

Yeah, it's great - from a scientific viewpoint. From a viewpoint of "probably not such a great place to visit", just so-so. That's what I'm waiting for: the place that has lots of flora and fauna (that would probably look at us as more food). LOL

Emily: 10/23/2012 04:43 CDT

Bjorn, comments like that are the price you pay for being able to get your comments published instantly. Otherwise you'd have to wait for moderation, which (given our very small staff) would take a long time and stifle any conversation. As long as they don't take over the conversation, and as long as they aren't objectionable, I think they're useful insight into what the rest of us are up against. I get emails like these several times a week.

eyelessgame: 10/23/2012 06:38 CDT

What's the theoretical maximum distance for a planet around α Cen B not to be perturbed out of its orbit by the larger companion (since they get as close as, what, 10 AU)? I assume it depends somewhat on the relative inclination of the planet's orbit versus the orbital plane of the two stars...

bware: 10/26/2012 12:25 CDT

Hi D4 & Z - Yeah it's pretty cool to know there is a planetary mass about our size. Maybe elsewhere in the the same plane, different orbit, they'll find another in the HZ. Barnard's the last I heard is still planetless and probably will prove out to be so. The science behind it is great. As for socially, well I'd be happier if they find a HX Terra class planet and ecstatic if they found one like Terra.

hemanth: 12/09/2012 07:52 CST

Did anyone notice the band of stars and the black and red dust clouds in the distance. It is the same band that we see from earth on a clear sky at night that we call the milky way.

Gagarin Miljkovich: 12/20/2012 12:06 CST

Bjorn & Emily, don't you remember about mankind's history? Have you already forgotten the story about Giordano Bruno and Galileo Galilei? At their time they was ridiculed in the same manner both of you are ridiculing the commentator "wavettore". Nearly all of our great scientist has been ridiculed at some time in mankind history. The Wright brothers was ridiculed in New York Times for their idea to build heavier-than-air airplane... If we humans have hard time to accept ideas of others, then we stagnate. To go forward we humans must be open minded and not the opposite. It's not interesant to only read comments by politically correct commentators.

Emily Lakdawalla: 01/09/2013 02:39 CST

Sorry, "Being ridiculed" is not equivalent to "being a genius." I will listen to people who have paid attention to the work of others enough to anticipate the objections that other people will have. It's useful when evaluating outsider claims to employ the Crackpot Index at

Jorge Taramona: 04/17/2013 11:48 CDT

Recently, I have read this article, it is very interesting to know that now we are capable to detect planets Earth-like, so this open the possibility to find exoplanets like this in the appropiated distance to its host star. Regarding the above comments, about wavettore is very interesting but it is does not relation with the issue, is not a discussion of cosmology, it is just a discussion of a Exoplanet finding and that is it.

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