A planet at Alpha Centauri B

Lazarus wrote:

Sweet.

I was sort of hoping for a longer-period innermost planet though. Less evidence of migration.

Because there isn't all that much room beyond the habitable zone for planets to migrate inwards into the HZ.

[/pessimism]

No really this is a fantastic discovery.

1992 - PSR B1257+12
2012 - Alpha Centauri B

Impressive what has been achieved in 20 years.

Well there could be further planets. But a stepping stone is good enough on its own.

Planet Found in Nearest Star System to Earth

http://www.eso.org/public/news/eso1241/

http://www.eso.org/public/news/eso1241/

« …“This is the first planet with a mass similar to Earth ever found around a star like the Sun. Its orbit is very close to its star and it must be much too hot for life as we know it,” adds Stéphane Udry (Geneva Observatory), a co-author of the paper and member of the team, “but it may well be just one planet in a system of several. Our other HARPS results, and new findings from Kepler, both show clearly that the majority of low-mass planets are found in such systems...”

Great discovery! And since Harps and Kepler teach us that small planets love company, this could be just the first step in the characterization of the Alpha Centauri systems.

Lazarus wrote:

Interesting... "a remarkable exoplanet" - sounds like it's not one of the large planet batches then.

Sunchaser wrote:

Must be major news if there's an embargo...hopefully those lucky dogs who get to hear the news first won't overhype it.

My guess is something Earthlike, around a nearby solar-type star. The announcement of an announcement to me seems to be one big tease, though.

-M-

Sirius_Alpha wrote:

Nature has lifted the embargo. Earth-mass planet around Alpha Centauri B.

http://abitmoredetail.wordpress.com/2012/10/16/brief-note-alpha-centauri-bb-found/
http://www.centauri-dreams.org/?p=25109

Led_Zep wrote:

http://www.eso.org/public/news/eso1241/

« …“This is the first planet with a mass similar to Earth ever found around a star like the Sun. Its orbit is very close to its star and it must be much too hot for life as we know it,” adds Stéphane Udry (Geneva Observatory), a co-author of the paper and member of the team, “but it may well be just one planet in a system of several. Our other HARPS results, and new findings from Kepler, both show clearly that the majority of low-mass planets are found in such systems...”

Yep. One big overhyped tease.

Other than the host star's proximity, bit of a disappointment, tbh; at least for me.

Gotta start somewhere though.

Greg Laughlin has a post up about Systemic on this: mainly focussing on disentangling the stellar activity.

http://oklo.org/2012/10/16/alpha-centauri-b-b/

Certainly it is interesting to see that close binaries can produce these low-mass planets. The pessimistic prediction was that such systems could only form giant planets via instability (Gamma Cephei Ab etc.) rather than the accretion process that is thought to produce lower-mass worlds.

Dynamics of Cats has a take on it.

If Alf Cen Bb was moved to where it is by planet-planet scattering the HZ could contain a highly-eccentric planet.

To-do list

Haha! The nearest star unveiled

Now there is Tau Ceti left (they'll never find my lair)

YAY! got one in the bag , now , to the other star in the pair.
Great news, but the best news in this is that its just the beginning.

This is incredibly exciting news. I remember reading an article about 20 years back (although the article itself may have been older) about planets around Alpha Centauri. The focus was primarily on A, but B seemed a strong contender as well. C was discounted completely (although Kepler certainly has put red dwarfs in race for habitable worlds.)

This is probably the first of several worlds discovered...can't wait to see what else may be out there!

-M-

Now on EPE.
http://exoplanet.eu/catalog/alf_cen_b_b/

Comments to the Systemic article discuss how Debra Fischer's Alpha Centauri campaign may help...

Quote :

In the most recent season, Debra’s campaign is accumulating data at a very good rate, but HARPS has a substantially longer base line of high-cadence observations. I’m hopeful that Debra will be able to make a confirmation statement relatively soon, but my sense is that there may not be quite enough data yet to be completely definitive.

Hopefully we will get a dedicated observation program regarding Alpha Centauri system. Maybe one of the smaller space telescopes that were recently proposed by Sara Seager which would observe only one star?

How can HARPS with precision of 1 m/s find planet with K = 0,5 m/s?

If you read the paper, you'll see the instrumental sensitivity is < 1 m/s. But the major thing to remember is that the sensitivity of the signal you can detect scales with the square root of the total number of observations, and isn't firmly limited by your measurement precision. If you can detect a 12 m/s signal with the dataset you have, then you can detect a 6 m/s signal if you gather four times as many observations. If you increase your dataset sixteen-fold, you can detect a 3 m/s signal. That's why it's so important to gather a huge amount of radial velocity measurements to detect planets so small.

Edasich wrote:

Now there is Tau Ceti left (they'll never find my lair)

Isn't Tau Ceti viewed pole-on?

If so we'd need an astrometry mission to find anything there. (Or else rely on there being a system which had strong planet-planet scattering leaving everything on high-inclination orbits...)

zorro83 wrote:

How can HARPS with precision of 1 m/s find planet with K = 0,5 m/s?

The brightness of the star allows a better Signal-To-Noise ratio and hence higher RV precision than possible for other similar but more distant stars.

There is also a statistical argument - pointed out by Sirius Alpha - sensitivity grows with the square roots of the number of observations taken - and with more than 450 data points the dataset for Alpha Centauri B is one of the richest dataset available for a star, and probably the most sensitive available so far.

In addition, HARPS underwent improvements since commissioning in 2003 - when the original 1 m/s precision was set.
Just take a look on the ESO Annual Report 2011, page 36-37:

http://www.eso.org/public/archives/annualreports/pdf/ann-report2011.pdf

Quote :

During the year the three parts of the HARPS upgrade project initiated in 2008 were delivered: the new polarimeter unit for the HARPS spectrograph was suc­cessfully completed by Uppsala Universi­ty (Sweden) and has been available to the scientific community since Period 86.
This new mode transforms HARPS into the most powerful high ­resolution spec­tro­polarimeter in the southern hemi­sphere. Observatoire de l’Université de Genève (Switzerland) delivered the new Fabry­Perot (FP) calibration system that provides a reference spectrum with numerous equidistant spectral lines of equal intensity and achieves a photon­ noise­limited radial velocity accuracy of about 2 cm/s with long­term drifts that are of the order of only few centimetres per second per hour. The new calibration device is fully supported by the HARPS data reduction pipeline and has been available to the community since Peri­od 88. Finally, this year ESO delivered the secondary (tip­tilt) guiding unit for the ESO 3.6­metre telescope to correct for high­frequency tracking errors of the tele­scope which further stabilises the light injected into the HARPS spectrograph at the fibre entrance. The combined effect of the last two upgrades results in supe­rior radial velocity accuracy down to some 50 cm/s and contributes to main­taining HARPS’s world leading position as the most successful planet hunter

Or it could just be noise.

Radial Velocity Detection of Earth-mass Planets in the Presence of Activity Noise: The Case of Alpha Centauri Bb
http://arxiv.org/abs/1305.4960

Quote :

...It may be premature to attribute the 3.24 day RV variations to an Earth-mass planet. A better understanding of the noise characteristics in the RV data as well as more measurements with better sampling will be needed to confirm this exoplanet.

From the paper:

Quote :

The detected "planet" seemed to be highly sensitive to the details in how the activity variations are removed. Alpha Cen Bb should have been detected by all methods that were employed and at the same level of signicance. A possible explanation for the planet signal found by D2012 Cen Bb is that it is a noise peak in the data whose statistical power has been boosted by a combination of the frequency characteristics of the noise, the under-sampling of the activity signal, and the filtering process

Ouch... hopefully this won't end up like the Gliese 581 "g" saga...

http://www.skyandtelescope.com/news/home/Exoplanet-in-Alpha-Centauri-remains-unconfirmed-208860591.html

"...The Alpha Centauri system is a binary, and the two stars’ orbital motions are bringing them into closer alignment from Earth’s viewpoint. As soon as the end of 2013 they will be too close for measurements of Alpha Centauri B’s radial velocity without contamination by light from brighter Alpha Centauri A, and astronomers will have to wait several years before they separate..."

But more important, they are NOW getting new data

"When I reached Dumusque, he returned my email late at night. The reason: he was in Chile at La Silla Observatory on a week-long observing run, collecting more data with HARPS on Alpha Centauri B."

...and of course there are at least 2 other observing programs dedicated to Alpha Centauri: Debra Fischer's program at CTIO and the Mt John Alpha Centauri Project (warning: Comic Sans). Wonder how they're getting on.

Other ways to confirm the planet may be possible...

Prospects of detecting the polarimetric signature of the Earth-mass planet alpha Centauri B b with SPHERE / ZIMPOL
http://arxiv.org/abs/1306.1006

Easier to do if it is not terrestrial though.

So it is to hope Alf Cen Bb has nearly face-on orbit, with i < 3° and m > 25 M_E.