# Alpha Centauri B has a roughly Earth-mass planet **URL:** \ **Category:** Miscellaneous and Personal Stuff I Must Share\ **Created:** [October 16, 2012, 11:10pm UTC](https://boards.straightdope.com/t/alpha-centauri-b-has-a-roughly-earth-mass-planet/637938 "2012-10-16T23:10:21Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![wolfstu](https://avatars.discourse-cdn.com/v4/letter/w/d6d6ee/32.png) [@wolfstu](https://boards.straightdope.com/u/wolfstu)\ **Post date:** [October 16, 2012, 11:10pm UTC](https://boards.straightdope.com/t/alpha-centauri-b-has-a-roughly-earth-mass-planet/637938/1 "2012-10-16T23:10:21Z")
The European Southern Observatory [has just announced](http://www.eso.org/public/news/eso1241/) the detection of a planet in orbit of Alpha Centauri B. This is a roughly Sun-like star, and part of the closest star system to Earth (together with Alpha Centauri A and Proxima Centauri). The estimated mass of the planet is slightly higher than that of the Earth, but it orbits too close to the star to be in the habitable zone. Nonetheless, this is suggestive of other planets in the same system. My day just got a lot more exciting 😃 ---
**Author:** ![Der\_Trihs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/der_trihs/32/233_2.png) [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)\ **Post date:** [October 16, 2012, 11:16pm UTC](https://boards.straightdope.com/t/alpha-centauri-b-has-a-roughly-earth-mass-planet/637938/2 "2012-10-16T23:16:55Z")
Very cool discovery. ---
**Author:** ![MEBuckner](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mebuckner/32/2896_2.png) [@MEBuckner](https://boards.straightdope.com/u/MEBuckner)\ **Post date:** [October 16, 2012, 11:30pm UTC](https://boards.straightdope.com/t/alpha-centauri-b-has-a-roughly-earth-mass-planet/637938/3 "2012-10-16T23:30:53Z")
Well, actually, given that it’s got a 3.2 day orbit, it’s a pretty _hot_ discovery. 😃 Man. In my adult lifetime, we’ve gone from exoplanets being pure, 100% speculation, and the province of science fiction, to knowing about _hundreds_ of them, from the closest star beyond our own Sun, all the way out to stars [tens of thousands of light-years away](http://en.wikipedia.org/wiki/OGLE-2005-BLG-390L). ---
**Author:** ![Grey](https://avatars.discourse-cdn.com/v4/letter/g/b782af/32.png) [@Grey](https://boards.straightdope.com/u/Grey)\ **Post date:** [October 17, 2012, 12:43pm UTC](https://boards.straightdope.com/t/alpha-centauri-b-has-a-roughly-earth-mass-planet/637938/4 "2012-10-17T12:43:16Z")
This is pretty awesome. ---
**Author:** ![Quartz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quartz/32/267_2.png) [@Quartz](https://boards.straightdope.com/u/Quartz)\ **Post date:** [October 17, 2012, 1:26pm UTC](https://boards.straightdope.com/t/alpha-centauri-b-has-a-roughly-earth-mass-planet/637938/5 "2012-10-17T13:26:31Z")
This is totally awesome. Hopefully this will spur development of techniques to find Earth-mass planets in habitable zones. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [October 17, 2012, 2:00pm UTC](https://boards.straightdope.com/t/alpha-centauri-b-has-a-roughly-earth-mass-planet/637938/6 "2012-10-17T14:00:47Z")
Do we know of any stars where there _almost certainly are not_ planets now? ---
**Author:** ![Alka\_Seltzer](https://avatars.discourse-cdn.com/v4/letter/a/c89c15/32.png) [@Alka\_Seltzer](https://boards.straightdope.com/u/Alka_Seltzer)\ **Post date:** [October 17, 2012, 2:26pm UTC](https://boards.straightdope.com/t/alpha-centauri-b-has-a-roughly-earth-mass-planet/637938/7 "2012-10-17T14:26:52Z")
With an estimated surface temperature of 1,200 C, you’d better slap on the sunscreen. The good news is, in a system where one planet has formed, it’s likely there are others. They will be much more difficult to detect, being further from the parent star. ---
**Author:** ![billfish678](https://avatars.discourse-cdn.com/v4/letter/b/7bcc69/32.png) [@billfish678](https://boards.straightdope.com/u/billfish678)\ **Post date:** [October 17, 2012, 2:37pm UTC](https://boards.straightdope.com/t/alpha-centauri-b-has-a-roughly-earth-mass-planet/637938/8 "2012-10-17T14:37:37Z")
Well, at least with that system we have some minor chance of getting there someday. Yeah, 5 light years give or take is no walk in the park but it sure beats hundreds of light years. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [August 8, 2025, 7:12am UTC](https://boards.straightdope.com/t/alpha-centauri-b-has-a-roughly-earth-mass-planet/637938/9 "2025-08-08T07:12:06Z")
Rather than start a new topic, I figure it’d be best to just add to this one: Possible planet discovered at alpha Centauri A: [https://skyandtelescope.org/astronomy-news/alpha-centauri-might-have-a-planet-webb-telescope-finds/](https://skyandtelescope.org/astronomy-news/alpha-centauri-might-have-a-planet-webb-telescope-finds/) ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [August 8, 2025, 9:33am UTC](https://boards.straightdope.com/t/alpha-centauri-b-has-a-roughly-earth-mass-planet/637938/10 "2025-08-08T09:33:02Z")
This one is roughly Saturn sized. Alpha Centauri A only has a very limited region around it which could support stable planetary orbits, because it is so close to Alpha Centauri B; if there is a Saturn-sized planet in that limited volume, then the chance that other planets are present is significantly smaller. ---
**Author:** ![Coriolanus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/coriolanus/32/18769_2.png) [@Coriolanus](https://boards.straightdope.com/u/Coriolanus)\ **Post date:** [August 10, 2025, 11:20pm UTC](https://boards.straightdope.com/t/alpha-centauri-b-has-a-roughly-earth-mass-planet/637938/11 "2025-08-10T23:20:37Z")
(some dinosaur movie) > Life finds a way It would be hard with a dual star system - yet we cannot cross Venus, Jupiter’s moons and Jupiter itself off as lifeless. (ETA: And Saturn, perhaps Titan) The sad thing is Earth may be the only “Class M Planet” ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [August 11, 2025, 1:02am UTC](https://boards.straightdope.com/t/alpha-centauri-b-has-a-roughly-earth-mass-planet/637938/12 "2025-08-11T01:02:52Z")
For now. We’re working on changing that. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [August 11, 2025, 1:36am UTC](https://boards.straightdope.com/t/alpha-centauri-b-has-a-roughly-earth-mass-planet/637938/13 "2025-08-11T01:36:00Z")
> [@Alka\_Seltzer](#): > > With an estimated surface temperature of 1,200 C, you’d better slap on the sunscreen. They are now guessing much cooler- Wiki- ---
**Author:** ![Coriolanus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/coriolanus/32/18769_2.png) [@Coriolanus](https://boards.straightdope.com/u/Coriolanus)\ **Post date:** [August 15, 2025, 4:49pm UTC](https://boards.straightdope.com/t/alpha-centauri-b-has-a-roughly-earth-mass-planet/637938/14 "2025-08-15T16:49:07Z")
Gotta have a star with a 10 billion year life. Be in the Goldilocks zone. Big enough to be round, small enough to not keep every bit of gas. When another planet smashes into proto-earth it settles down to become the Moon - which doesn’t get enough credit. Enough water comes from comets to make deep oceans. And even after multiple asteroid extinction events, life goes on. Even when the most advanced species - just now realizing that planets exist around nearby stars - destroys itself life finds a way. I’m hoping for the bees.