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Oct 18 2012

Earth-sized planet found lurking in data around … Alpha Centauri

We are living in the greatest age of planetary discovery since Galileo looked at Jupiter, and that age may be on the verge of delivering one of the most exciting discoveries imaginable: earth-like planet[s] around Alpha Centauri, AKA Rigel Kent or ACen. Just the name Centauri brings on dreamy eyes in the sci-fi and space exploration community alike. At 4.37 light-years away, the three stars making up the Centauri system are by far our closest stellar neighbors. Via reader/writer “F,” planet hunters pouring over data from the most famous star system outside of ours have found strong hints of an earth-sized world, and there could be more:

The Planetary Society– [A]stronomers 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.

“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.”

KABOOM! I can honestly say, a shiver went down my spine when I followed the link left by F and read the post.

Alpha Centauri is a classic binary star system. Two twin suns, A and B, orbit each other every 80 years in an elegant, joint elliptical orbit with major and minor axis varying between the distance of Neptune and Saturn are from our sun at farthest and cloest approaches respectively. Astronomers speculate the system could be full of debris, vast braided rings that would make Saturn envious, asteroid belts on top of asteroid belts, or it could have long since been cleaned up spic and span compared to our solar system through accelerated ancient collisions and accretion. A red dwarf star, dubbed Promixa as it is technically the closest to us, is thought to be associated with ACen and lingers on the edge of interstellar space a quarter light year from the binary.

Reaching any of these stars would take more efficient and far more powerful propulsion systems than anything we have now. With existing chemical rocket engines, we’re still talking about something on the order of ten thousand years in best case scenarios. But a next-next generation ion drive, or a combo of futuristic light sails or fusion drive, etc, might actually get us there in something like a couple of thousand years. If we can get to just two or three percent of the speed of light, we’re there in a couple of hundred years and five to ten percent of the speed of light means the probe reaches the system within a single human lifetime!

Missions of that duration present engineering challenges beyond mere propulsion, it would mean significant jumps in onboard power requirements and component reliability to say the least. But thanks to the proximity of ACen, it’s tantalizing close to our xurrent technological grasp and near term future vision. We can actually begin to think about mounting such a mission within the lifetime of humans beings living now.

They call us non believers, and that’s saying mildly in some cases. But I do have beliefs, for lack of a better word, I believe near term machine descendents of the clunky rockets and computers in our technological inventory will make it to the stars. The very first alien star and exoplanet[s] we will visit by proxy and in whatever passes for a person at the end of this millennium will be Alpha Centauri.

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  1. 1
    Rutee Katreya

    So how long until Sid Meier’s Alpha Centauri happens?

  2. 2
    heddle

    Probably scientists have always said this but… It is so damn cool to be living through the advances we are making at the moment. To see astronomy (and cosmology) become precision sciences has been nothing short of astounding.

  3. 3
    machintelligence

    We are truly living in a golden age of science and technology. Let’s hope it lasts.

  4. 4
    Raging Bee

    Back in the 1980s, I wrote a science-fiction story about human interactions (read: diplomacy and war) with a species I labelled Beta-Centaurians. And now we’ve found a near-Earth-size planet orbiting Alpha Centauri B. You may all bow to my awesome predictive genius…

  5. 5
    johnbrown

    We probably all read scifi stories about trips to Alpha Centauri as kids. I particularly remember one by Robert Forward, Flight of the (something). [Damn getting older is a bitch.]

    I remember that my thirties were hard for me because I recognized that all the cool things I had read about in my youth weren’t happening in my lifetime. Hope my grandsons can vacation on Titan or stroll the shores of an ocean on Alpha Centauri C!

    Sorry to lower the tone of a great comment thread.

  6. 6
    michaelbusch

    I hate to rain on the parade, but:

    Alpha Cen Bb orbits Alpha Cen B with a 3.236 day period, just 4% as far from B as Earth is from the Sun. For comparison, Mercury never gets closer to the Sun than 30% of the Earth-Sun distance.

    Alpha Cen B is a somewhat fainter star than the Sun is. But subject to uncertainties in Bb’s albedo (how much light it reflects to space) and the thickness of its atmosphere, its surface temperature is at least 1500 Kelvin (1200 Celsius). The planet is made out of lava.

    There could be planets further from either Alpha Cen A or Alpha Cen B, out to about 1 Earth-Sun distance from either star (further out from either star and the perturbations from the other star will scatter the planet out of the system). That includes the region around Alpha Cen B where liquid water could be stable. Right now, all the HARPS team can say is that there are no planets larger than Neptune in that zone.

    Certainly we should look for more planets around both Alpha Cen A and Alpha Cen B. But it will take a lot of precision engineering to build an instrument that can do that.

    In the meantime:

    Celebrate Dumusque and company’s skill and success, and read the paper: http://www.eso.org/public/archives/releases/sciencepapers/eso1241/eso1241a.pdf

    And also, consider this: what should we call Alpha Cen Bb?

    Yesterday, I saw another astronomer wearing an “AC Bb” t-shirt. But I have trouble taking that seriously.

  7. 7
    leftwingfox

    it would mean significant jumps in onboard power requirements and component reliability to say the least

    Not to mention shielding. Micro-meteors hitting a probe at .1C would probably be VERY BAD.

  8. 8
    Shawn Smith

    … You may all bow to my awesome predictive genius…

    Somehow, I don’t suspect anything capable of surviving at 1500 K / 1200 C would have much of anything to do with us.

    And as for interstellar travel, there was the study put out in 1988 from people at the Naval Academy and NASA called Project Longshot, which proposed near-future technologies which would get an unmanned probe to α-Centauri B in about 100 years.

  9. 9
    lpetrich

    It’s a rather small effect – a velocity amplitude of only 51 cm/s, comparable to a baby’s crawl of 30 cm/s.

    It’s also much smaller than the noise, which extends to about 200 cm/s. But they took data over about 5 years, and they claim good statistical significance.

    It’s a pity that Carl Sagan could not live to see this epoch of discovery. :( He would have *loved* the discoveries, complete with describing them in his mellifluous voice.

  10. 10
    Stephen "DarkSyde" Andrew

    I think of Sagan every time I learn of something like this. Brian Cox reminds me of him a little.

  11. 11
    Anthony K

    Probably scientists have always said this but… It is so damn cool to be living through the advances we are making at the moment.

    They probably always have, but I know we’re both old enough to remember when exo-planets were simply theorised to exist. Now we’re practically stepping across them like Lego pieces in the carpet.

  12. 12
    Anthony K

    Whoops, lost a paragraph somewhere there. Too lazy to rewrite, so I’m just summarise:

    So yes, it is damn cool.

  13. 13
    michaelbusch

    @myself @7:

    Beg pardon:

    With a longer-term monitoring program, HARPS may be able to push the sensitivity limit for planets in the habitable zone (where liquid water could be stable) around Alpha Cen B down to about 4 times as massive as Earth. So, quite a bit smaller than Neptune, but still inconveniently bulky.

    There is also a ~10% chance that Bb transits (passes in front of) B as seen from here, which would give a measurement of the planet’s size as well as a better constraint on its mass. Bb is very small, so Hubble would be required to detect the fraction of B’s light that it would block if everything is lined up. I am not on the Hubble time allocation committee, but I think they would approve a few hours of observing time to see if this does happen.

    If Bb does not transit B, it will require new instruments to learn anything more about the place.

  14. 14
    F [i'm not here, i'm gone]

    Hopefully, JWST will fly in 2018, but I really wish the TPF was an active project. Using even the current generation of instruments and techniques to observe from outside near space would be fantastic when looking for smaller planets. (No offense to Kepler or the amazing work being done by ground-based teams.)

  15. 15
    typecaster

    If we can get to just two or three percent of the speed of light, we’re there in a couple of hundred years and five to ten percent of the speed of light means the probe reaches the system within a single human lifetime!

    It would be nice if time dilation could cut this down further for the travelers. Sadly, at ten percent of lightspeed, the contraction is only around 0.5% Even cutting travel time in half requires speeds over 90% of lightspeed. Of course, at that speed you get there in just under 4 and a half years anyway.

    Let’s not even start to consider the energy expenditure required to do this, however.

  16. 16
    cyberCMDR

    I hear Mitt has already called dibs on this planet. He’s supposed to get one when he dies….

  17. 17
    Stephen "DarkSyde" Andrew

    B-1 is hellish by any standard. It’s therefore likely Mitt has already struck a binding cost plus terra-reform deal at ten percent over net-net plus an incentive production bonus with the current owners …

  18. 18
    birgerjohansson

    Since Alpha Centauri is a binary star stable orbits only extend up to ca. 1 AU from either star.
    This planet has likely spiralled in like many other hot planets, meaning other planets near Alpha Cen B also will have spiralled in. With a starting point little more than 1 AU out, it seems highly unlikely that any of them remains in the habitable zone.
    .
    But all is not lost. The planets will be tidally locked, with permanent* night zones where metal will be superconducting.

    The first travellers to Alpha Cen wil be robots with strong AI. For those, the nightsides of the planets will be the best real estate possible (not counting planets around chilly brown dwarfs).

    *Provided the orbits are not highly eccentric, but at that close distance stellar tides may circularise the orbits.

  19. 19
    blbt5

    Michaelbusch’s astute comments are a reminder of how critical so many factors are in producing the Goldilocks environment of our own planet!

  20. 20
    jakc

    I’ve been waiting for Darksyde to start this thread ever since I saw the article. It’s incredibly exciting to think we’ve discovered Mercury (essentially) orbiting around Alpha Centauri B. Move it out 3/4 of an AU and it could be Earth.

    Speaking of that @birgerjohansson: I was under the impression that the planets around either AC star could have stable orbits up to 3 AU out. I’m not an expert in orbital mechanics, so I’m not arguing the point, but I’m curious as to why you write that the orbits are only going to be stable to 1 AU and that this planet is likely to have spiraled in.

  21. 21
    silomowbray, sans frottage pour la douche

    Stephen @ 18:

    B-1 is hellish by any standard. It’s therefore likely Mitt has already struck a binding cost plus terra-reform deal at ten percent over net-net plus an incentive production bonus with the current owners …

    “We build those, you know.”

  22. 22
    Aliasalpha

    Damn planets, they lurk in the data for hours, you turn your back on them for a second and they steal your pickernick baskets…

  23. 23
    StevoR : Free West Papua, free Tibet, let the Chagossians return!

    @7. michaelbusch :

    I hate to rain on the parade, but : Alpha Cen Bb orbits Alpha Cen B with a 3.236 day period, just 4% as far from B as Earth is from the Sun. For comparison, Mercury never gets closer to the Sun than 30% of the Earth-Sun distance. Alpha Cen B is a somewhat fainter star than the Sun is. But subject to uncertainties in Bb’s albedo (how much light it reflects to space) and the thickness of its atmosphere, its surface temperature is at least 1500 Kelvin (1200 Celsius). The planet is made out of lava.

    Or possibly diamond (well carbon of various varieties) like 55 cancris e?

    Great news and write up Stephen “DarkSyde” Andrew, thanks.

    @17.cyberCMDR :

    I hear Mitt has already called dibs on this planet. He’s supposed to get one when he dies….

    Given the conditions there, that seems strangely .. apt!

    @4. Raging Bee :

    Back in the 1980s, I wrote a science-fiction story about human interactions (read: diplomacy and war) with a species I labelled Beta-Centaurians.

    You may already know this but Beta Centauri is another very different and more distant type of star.

    Also called Hadar or Agena it like Alpha is one of the two bright pointers to the Southern Cross but where Alpha Centauri is 4 ly off Hadar is 360 or so -massively brighter and a bbinary of B type giants.

  24. 24
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  26. 26
    Amphiox

    Provided the orbits are not highly eccentric, but at that close distance stellar tides may circularise the orbits.

    It seems unlikely to me that the orbits any of existing planets around AlphaCenB would be highly eccentric, because such orbits would put the planets in them out far enough on the long end for AlphaCenA’s gravitational influence to disrupt their orbital stability.

  27. 27
    Amphiox

    From the point of view of astrobiology, of course, a habitable zone planet in Alpha Centauri would indeed by very interesting (an earth analogy habitable world in the next freakin star system away from us would mean earth analog worlds would have to be as common as dirt!)

    And one should keep in mind that the Alpha Centauri system is older than Sol by several billion years, so any hypothetical ecosystem on a habitable world in that system would have billions of years longer to evolve. On the other hand, the older age of the system could mean that previously habitable worlds have already died as increasing stellar luminosity with stellar age moved them out of the habitable zone and cooked them, as has already happened with Venus in our solar system and will happen to earth some point a billion years or so in the future.

    Of course, Alpha Centauri B being a smaller star than the sun will also have a longer life span and probably a slower stellar evolution along the main sequence.

    But Alpha Centauri A being a larger star than the sun will likewise have a shorter main sequence lifespan (and with the system already being older than Sol, that means it doesn’t have all that much time left*). One wonders what Alpha Centauri A going red giant would do any planetary system around Alpha Centauri B. Would it just be a fantastic light show, or would there be more direct effects?

    However, from the point of view of humans going there one day, the existence of a habitable zone planet is really irrelevant. Even at 10% c, a trip there would take four or five decades. That means you absolutely have to have long term sustainable life support technology, ie Biosphere II that actually works, to even contemplate attempting the trip. And if you have that kind of technology, habitable planets are an afterthought. You don’t need habitable planets, you just need raw materials, manufacturing capacity, and energy. And the existence of any planet anywhere in the star system = a planetary system = plenty of resources.

    * still billions of years, of course

  28. 28
    StevoR : Free West Papua, free Tibet, let the Chagossians return!

    Wikipedia now has a page on Alpha Centauri B’s exoplanet here :

    http://en.wikipedia.org/wiki/Alpha_Centauri_Bb

    FWIW.

    There’s also a note of caution stated by exoplanet hunter Artie Hatzes who ..

    .. praised the team’s technical achievements and admitted he observed a planetlike signal amongst the data, but called it a “a weak signal in the presence of a larger, more complicated signal.” He stressed the need for further empirical confirmation, and opined that the existence of the planet was “still open to debate.” (Hatzes had previously expressed scepticism about unproven methods of data analysis during the dispute over unconfirmed planet Gliese 581 g.

    Sorry to be a wet blanket but think that’s worth bearing in mind.

    Still awesome news just hope its confirmed and even more so hope there are other more habitable worlds out there orbiting Rigil Kentauros / Toliman / Bungula / Alpha Cen Bb (planets King & Gun maybe? Nah, I’d rather we used the alternate star names as planet ones actually.)

  1. 29
    Around FtB | Pharyngula

    [...] Steven Andrew reports the discovery of an earth-sized planet orbiting Alpha Centauri. My retirement plans might be firming up. [...]

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