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Posted by: vikingmars May 15 2012, 12:37 PM

In 2009, the Planetary Society (TPS) made a grant to Yale University astronomer Debra Fischer. With those funds, Debra and her team developed the FINDS Exo-Earths project to record the light from distant stars with increased precision in the search for Earth-like planets, which they then installed on the telescope at Lick Observatory in California. "I'm betting that there are planets like Earth or Mars or Venus around either or both of the stars of Alpha Centauri, and the only question is whether we'll be able to detect them," said Debra Fischer in 2009.
Well... If the astronomers succeed in detecting small planets orbiting around "Alpha-A" and/or "Alpha-B" stars, no doubt that it will be a scientific bombshell -- and also, it will raise the question of how we might someday send a probe to get a closer look.

Now, Debra Fischer and her team are focusing again on Earth’s nearest neighboring star system, Alpha Centauri, to look for Earth-like planets. And TPS wants everyone interested by this great quest to join the team. The telescope will be in the southern hemisphere to see Alpha Centauri, so Debra and her team need to rent time at the Cerro Tololo Inter-American Observatory in Chile. They need TPS to sponsor at least 20 nights of observation time.
And because Alpha Centauri B shares the system with Alpha Centauri A, we can also begin to understand the question : how do planets develop in a true binary system, pulled by two gravitational bodies?

As a TPS member, but also belonging to Societe Astronomique in France, I'm really thrilled by this new research project which fits exactly within TPS's goals which are: "To inspire and involve the world's public in space exploration through advocacy, projects, and education".
Many thanks to the TPS's team for this idea of great science value
Now you can, please like me, follow the link and make a donation :
http://support.planetary.org/site/Donation2?1640.donation=form1&df_id=1640

Also, I put herebelow some interesting links and science articles abour the "A-B" system, you may like to read to better understand what it is all about.
Enjoy !
http://www.planetary.org/explore/projects/finds/
http://www.planetary.org/blogs/bruce-betts/planets-around-alpha.html

 Davis_1b_xxx.pdf ( 585.56K ) : 807
("One planet can be reliably detected after the first 2 years of observations, and 3 planets can be detected within 4.7 years." !!!)
 AlphaCenApJPaper_2__Part1.pdf ( 291.76K ) : 690

Posted by: vikingmars May 15 2012, 12:39 PM

(Another document...)
 AlphaCenApJPaper_2__Part2.pdf ( 894.7K ) : 773

Posted by: vikingmars May 15 2012, 12:40 PM

(...idem...)
 AlphaCenB_1_xxx.pdf ( 359.86K ) : 1020

Posted by: vikingmars May 15 2012, 01:05 PM

(...and the last document)
 AlphaCen_1_xxx.pdf ( 995.08K ) : 2546

Enjoy

Posted by: IM4 May 16 2012, 03:42 PM

There was a poster at the Extreme Solar Systems II conference last year by Dumusque et al on Alpha Cen. He stated that "No planet larger than 4 Earth mass with a period shorter than 300 days.” Quite the contrary to previous expectations, isn't it?

Posted by: vikingmars May 16 2012, 04:46 PM

Well... For me, it means that they may be planets there, but having masses below 4 Earth mass. When you look to the papers hereabove, all simulations show planets no larger than Earth and even some simulations show the formation of planetary systems with bodies having masses no larger than Mars (for this, please, see page 993 of "Terrestrial Planet Formation in the Alpha Centauri System"). So, there is still an hope

Posted by: IM4 May 16 2012, 05:50 PM

I don't believe in simulations, I love facts. Kepler results suggest that "neptunes" are common in the exoplanetary systems, including binaries. We see no massive planets at Centauri. That's a really bad sign.

Posted by: Hungry4info May 16 2012, 08:00 PM

Not in the slightest. Remember if a perfect copy of the inner solar system were around either of the stars at Alf Cen, we wouldn't have detected them yet.

Posted by: vikingmars May 19 2012, 04:27 PM

When you look to Kepler's data (please see link : http://kepler.nasa.gov/Mission/discoveries/ ), NO planets having an Earth mass have been (yet) discovered (Earth being 0.00314 Jupiter's mass). As some say, " "neptunes" are common in the exoplanetary systems", it is because "neptunes" are close to the lower limit of Kepler's detectability. Ten years ago we could have say "jupiters" are common... Although we are being close to discover another "earth" (Kepler-20e for example), we will more easily see the ones transiting oftenly in front of their star, which is not the case for Alpha Centauri's A-B system because its orbital inclination (as seen from Earth) is 79.23° : thus, Kepler technique would not work unfortunately for the detection of planets around those two stars. To detect other "earths" orbiting in the life zones of their stars (at 1 AU distance from its star) with Kepler's technique would take some more time. So, I would say : wait a little more for Kepler's stunning results, but do not expect Kepler to detect "earth" planets at 1 AU with great orbital inclinations.
So... Only the techniques funded by TPS could detect planets around the A-B system (with more than 20 nights perhaps..).
=> So be kind to donate, please ! You will be part of the discovery !

Posted by: Drkskywxlt May 20 2012, 02:17 AM

There's been a number of Kepler candidates detected with radii equal to or less than Earth's. Mass is obviously the harder number to determine, but it's certainly very likely that at least some of these candidates have masses less than or equal to Earth's.

http://exoplanetarchive.ipac.caltech.edu/cgi-bin/ExoTables/nph-exotbls?kepler=1

Posted by: vikingmars May 20 2012, 08:07 AM

Thanks a lot for this much interesting link. Unfortunately, the "Planet-Star distance" data in AU shows no figures (yet) with "0.8xxx" or "1.xxx"... Those quasi-"earths" discovered are really too close from their parent stars and thus, much too hot. Well, let's wait more time : maybe, by chance, we will discover an "earth" orbiting at 1 AU in the plane of sight of its parent star (orbital inclination = 0° towards us, i.e. towards the Kepler telescope)...

Posted by: Drkskywxlt May 21 2012, 05:05 PM

Right. Kepler's original stated criteria was 3 orbits for confirmation of a planet, so a true Earth-analog would have taken a minimum of 3 years to show up in Kepler data. Kepler-22b is the closest to an Earth-analog yet, as it has a ~289 day orbit, but has a radii of 2.4 Earth-radii, making it almost certainly not rocky.
http://arxiv.org/abs/1112.1640

What's complicated everything is the surprising amount of stellar activity in the Kepler field stars. That's why the extended mission is so important, since it will probably take more like 5-6 transits to feel confident in a detection of a planet around these active/jittery stars.

Posted by: JRehling May 25 2012, 05:47 PM

Various points:

1) Kepler is reporting almost exclusively (the "Tatooine" discovery withstanding) on single stars. How evolution of double star systems compare is inevitably quite different. Kepler is providing excellent (I would say definitive) evidence that most single stars have planets. Whether or not the same is true of double stars is speculative.

2) The lack of larger planets is not necessarily a bad sign. It may even be a good sign: Large planets at a given orbital distance make it difficult for smaller planets to occupy nearby orbits.

3) Many earth-sized planets have been detected among the candidates from Kepler, and Kepler candidates have a quite low rate of false positives, so many of these are real. But so far, none of those have been confirmed through the radial velocity method. The point is: The transit method is wonderfully sensitive to such planets (and they do exist, in considerable quantity), but the RV method is not.

The great thing about any planetary discovery at Alpha Centauri would be the enhanced opportunity for follow-on science. Any such planet would have 100 times the apparent luminosity of a similar world located 44 light years away. In terms of the proximity of planetary systems, we have to accept the cards the universe has dealt us: rocketry avails us little in terms of getting a better look at objects light years away.

There are seven single star systems with K or G stars within 10 to 20 light years of us. None closer. Then another eighteen from 20 to 30 light years away. Only one other double-star K/G system (61 Cygni, at 11 LY) is within 16 light years. (Epsilon Indi is a K/M pair.) Those are the cards we're dealt. Alpha Centauri represents a unique opportunity to get that close-up science. If the universe didn't give us planets there, the next closest set around a sunlike star has to be significantly farther.

Posted by: TheAnt May 27 2012, 12:44 PM

Now we know that planetary objects are quite common around many stars, and that no super Earth have been found in the Alpha Centauri system. I feel its a good idea to have another better look again. So I like this proposal.

As JRehling said, if a planet is found there. We would be given a very good opportunity to study that planet if it is cold and icy in one elliptical orbit or hot and Venus like does not really matter. We will have added a new sample to the group of Earth like planets, and it would give us another example to study. There would be a lot of researchers who would jump onto the bandwagon if one were found, so I guess they would eventually be able to coerce at least some spectrograhic data from it.

And in that I agree with JRehling, it is not likely that we will attempt to send anything there for a closer look by "rocketry" or whatever means we can envision in the foreseeable future.

But if a search like this did find something truly extraordinary, like a planet perfectly placed in the habitable zone and hints of an atmosphere that is not to thin, thick or just plain weird by human standards, it might very well trigger one effort to build a space based TPF - which might give us a look not only for that planet but Earth like planets elsewhere.

Posted by: Reed May 28 2012, 02:44 AM

I don't believe this is correct. In http://kepler.nasa.gov/Science/about/ScientificGoals/ #3 is determining the frequency of planets in multi-stellar systems.

Even if this weren't an interesting question in it's own right, I don't think they had much choice. Multiple systems are extremely common, and many would not be identifiable in the surveys used to create the target list. The observations needed to characterize the systems and reject false positives will also identify stellar companions.

An example of this followup work is described here http://arxiv.org/abs/1205.5535. As expected, they find many previously undetected stars, and while they can't directly distinguish between bound and background objects, from statistical arguments it's likely some are bound. These probably aren't Alpha Centauri analogs though, at typical Kepler distances the separation would mostly fall below the 0.1 arcsec limit.

Posted by: JRehling May 29 2012, 06:37 PM

Interesting point, Reed. What I'd noticed is that the Kepler target star list was explicitly seeded with known eclipsing binaries (thus, performing targeted science of such stars) but that number came out to only 600 of the ~200K observed stars. So, as an absolute count, that's a lot of binaries, but as a proportional count, it's less than 1%.

But the citation you name (from last week!) highlights the number of unknown binaries, and indeed, it's an open question as to how many stars are binary. Alpha Centauri is on the short side of separation distance. Where the periods are quite long, we might expect planetary systems that more closely resemble single stars, and greater difficulty determining if the pair of stars is actually bound or not.

Posted by: vikingmars Jun 16 2012, 07:33 AM

I just received from TPS my "Certificate of Mission Participation" and I discovered that my 50 USD offered 15 minutes of observation time to search for exoplanets in the Alpha Centauri system... I'm proud of being member of TPS and now it's time to donate : maybe one of you will offer the minutes when a crucial observation will be made also. Thanks in advance for your support and thanks to TPS to have this mission available to all !

Posted by: JRehling Jun 18 2012, 04:57 PM

Another tidbit about Alpha Centauri which I didn't notice in the papers (though I admit I didn't read them all). Both -A and -B have significantly higher metallicity than the Sun. As has been recorded in the literature, and as I'm seeing more and more in the Kepler data, that is a significant factor in favor of planet formation. Were it not for the relatively close minimum distance, there would be little reason to doubt some planets around one or both stars. I think there's an excellent chance of terrestrial-sized planets in this system. Whether or not we can detect them and do follow-up science is a tougher prospect, but it's definitely an exciting notion.

Posted by: marsophile Jun 23 2012, 03:47 AM

Would it be feasible to observe occultations of more distant stars by planets around Alpha Centauri A or B? Or gravitational lens effects?

Posted by: Hungry4info Jun 23 2012, 04:47 AM

Maybe. The idea has been thought of before for VB 10.

Searching for Planets During Predicted Mesolensing Events: I. Theory, and the Case of VB 10
http://arxiv.org/abs/1202.5316

Searching for Planets During Predicted Mesolensing Events: II. PLAN-IT: An Observing Program and its Application to VB 10
http://arxiv.org/abs/1202.5314

Posted by: JRehling Jun 26 2012, 06:34 PM

The first sentence of Cassan, et al, 2012 is "Gravitational microlensing is very rare: fewer than one star per million undergoes a microlensing effect at any time." So, that's very bleak. Success depends upon observing a massive number of targets and finding a few successes. The papers just mentioned involve a cherry-picked star which is known to be favorable. Picking a desired star and hoping for microlensing is almost certainly a lost cause.

The transiting method is also blind to most planets, but it's not that bleak. Detecting a planet at 1 AU out works out, geometrically, more than 0.1% of the time. However, we can see perfectly well that the Alpha Centauri stars are not aligned favorably, so we have zero probability of a transit for any planet whose plane is near that which contains the stars' mutual orbit.

The radial velocity / Doppler method, on the other hand, is least affected by geometrical luck, but is also less favorable for small planets. (Ie, Mars has only 1/3000th Jupiter's mass, which determines its detectibility by the RV method, but 1/400th its cross section, which is relevant for the transiting method.)

So the RV method is our best bet for Alpha Centauri. But if we had systems for observing close-in planets directly by their reflected light, Alpha Centauri would be a highly favorable target given its proximity. So far, only distant planets (much further than the Alpha Centauri inter-star distance) have been imaged directly. Giants have been observed by their reflected light in Kepler light curves, but such planets are also good targets for RV.

Posted by: ngunn Jun 26 2012, 09:03 PM

And not by reflected starlight, only by their thermal IR. The one object imaged by reflected starlight is much brighter than any planet could be. It's postulated to be a satellite-forming disc on the scale of Jupiter's gallilean system. So directly imaging smallish, cool, non-transiting planets remains a very distant prospect. I don't think next generation telescopes will do it. We have to work with how these worlds influence the light we receive from their parent star.

Posted by: JRehling Oct 17 2012, 04:33 AM

We have a report of Alpha Centauri Bb, with publication by the HARPS team in Nature tomorrow. Earth-sized, but orbiting with a 3.2 day period.

Obviously a fantastic discovery, if it stands. This would mean that whenever we have the means for follow-up science we'll have at least one planet that is much closer than we are likely to find around any other star.

Posted by: Explorer1 Oct 17 2012, 05:55 AM

Yep, I was pretty much ecstatic when I read it this morning. It looks pretty clear that anywhere a planet can form, it will. It also puts in perspective how much observation work will be needed to find something at a less broiling orbit.

Posted by: Seryddwr Oct 17 2012, 08:12 AM

In 1989, Astronomy magazine ran a feature on the possibility of life in the Alpha Centauri system, with diagrams showing the 'Goldilocks zone' etc. - a thought that fuelled my young mind! Pity the discovered planet's so close to the star, but at least it validates the computer modelling done back then, which showed (IIRC) that orbits stable over cosmic timescales were possible. Kudos to all involved

Posted by: belleraphon1 Oct 17 2012, 11:02 AM

I’ve known there are several teams searching Alpha Centauri and have been waiting for such an announcement!!!!

Wo Hooo!!!!

An Earth-mass planet orbiting α Centauri B
Xavier Dumusque,1, 2 Francesco Pepe,1 Christophe Lovis,1 Damien Ségransan,1 Johannes Sahlmann,1 Willy Benz,3 François Bouchy,1, 4 Michel Mayor,1 Didier Queloz,1 Nuno Santos2, 5 & Stéphane Udry1
I am so excited I can barely type...

Wo Hooo!!!!

An Earth-mass planet orbiting α Centauri B
Xavier Dumusque,1, 2 Francesco Pepe,1 Christophe Lovis,1 Damien Ségransan,1 Johannes Sahlmann,1 Willy Benz,3 François Bouchy,1, 4 Michel Mayor,1 Didier Queloz,1 Nuno Santos2, 5 & Stéphane Udry1

“Exoplanets down to the size of Earth have been found, but not in the habitable zone—that is, at a distance from the parent star at which water, if present, would be liquid. There are planets in the habitable zone of stars cooler than our Sun, but for reasons such as tidal locking and strong stellar activity, they are unlikely to harbour water–carbon life as we know it. The detection of a habitable Earth-mass planet orbiting a star similar to our Sun is extremely difficult, because such a signal is overwhelmed by stellar perturbations. Here we report the detection of an Earth-mass planet orbiting our neighbour star α Centauri B, a member of the closest stellar system to the Sun. The planet has an orbital period of 3.236 days and is about 0.04 astronomical units from the star (one astronomical unit is the Earth–Sun distance).”

Alpha Centauri system holds the closest stars to Earth… just 4.4 light years away.

http://www.nature.com/news/the-exoplanet-next-door-1.11605

http://www.sciencenews.org/view/generic/id/345756/description/The_alien_next_door

http://www.centauri-dreams.org/?p=25109

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

Posted by: belleraphon1 Oct 17 2012, 11:19 AM

News release and journal paper...

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

http://www.eso.org/public/archives/releases/sciencepapers/eso1241/eso1241a.pdf

Posted by: Holder of the Two Leashes Oct 17 2012, 03:04 PM

From the "Exoplanet next door" article at the Nature site:

" Ralph McNutt, a planetary scientist at Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, has received NASA study funding to design an ‘innovative interstellar explorer’. Even when launched by one of the most powerful rockets on Earth, boosted by a gravitational slingshot around Jupiter, and further accelerated by a radioisotope thruster, that probe would take about 28,000 years to reach α Centauri."

Doesn't say whether they are taking the star system's own motion into account, which most people don't. The Toliman (Alpha Centauri) system will be at its closest to us at just about that time, 3.0 light years away.

Plus, it won't be in the constellation Centaurus anymore as viewed from Earth, so we'll be needing a new designation (Alpha Hydrae?).

Posted by: JRehling Oct 17 2012, 05:08 PM

Well, planets don't end up everywhere they can, because our solar system has no planet interior to Mercury, whereas a lot of stars (and now we know, Alpha Centauri do.

Alpha Centauri's mutual approach of 18 AU obviously doesn't preclude the existence of planets. I might guess that it impaired formation of solid bodies in the ice belt which would go on to be the seeds of gas giants. The fact that an earth-sized planet was discovered and not a jovian first or concurrently suggests that at least there are no jovians in the inner system, and maybe no jovians at all.

Given that some systems have planets in very short periods (<20d) and others don't, it's intriguing to consider whether there is a negative relationship, that inner planets are a sign that planets will not be found at longer periods (~50-500d). For jovians, we could get some data on this. For terrestrial planets, we're still waiting to find any at longer periods, so obviously we'll have to wait longer to find out about the relationship between occurrence at different periods. But the specific query here is: Does Alpha Centauri Bb mean that the star is more or less likely also to have planets in the habitable zone?

Posted by: Hungry4info Oct 17 2012, 06:00 PM

We also knew from RV data that there were no Jovian planets around either star to begin with. In the paper, they state that they have enough data to detect a 4 Earth-mass planet in the habitable zone of Alf Cen B if it were there. Since the habitable zone is about as far as you can get from the star and remain in a stable orbit, I take this to mean there are no planets with an m sin i > 4 M_E around the star (obviously you can rule out lighter and lighter planets as you get closer to the star).

Posted by: ngunn Oct 17 2012, 09:06 PM

I've just looked through the known multiple planet systems (3+planets) and way over half of them have planets with both under 20d and over 50d periods. It's anecdotal, I suppose, but my impression is that the correlation is positive.

Posted by: Reed Oct 18 2012, 06:16 AM

I don't think this is quite what they said. I assume you are referring to:

The way I read that, they are only saying HARPS has the sensitivity to detect such a planet. The current detection is based on observing many orbits to identify a periodic signal, and for a habitable zone (200 day) planet they would have far fewer.

Posted by: Bill Dec 8 2012, 04:36 PM

I don't know if this is the right thread, but it seems that nobody talked about this future mission selected by ESA which could study Alpha Centauri, among other things.

CHEOPS on http://www.esa.int/esaCP/SEMXFG4S18H_index_0.html
http://cheops.unibe.ch/index.php/executive-summary

Posted by: K-P Dec 19 2012, 03:11 PM

It seems we have even more interesting planet system available in our "galactic neighborhood" now.

Science team led by Finnish astronomer Mikko Tuomi found 5 (!) planets around Tau Ceti.

It's getting crowded in this corner of our spiral arm...

http://www.space.com/18967-nearby-habitable-alien-planet-tau-ceti.html

Posted by: ngunn Dec 19 2012, 03:34 PM

Link to the paper (from BBC News): http://star-www.herts.ac.uk/~hraj/tauceti/paper.pdf
Orbital data are on page 16.

Posted by: 0101Morpheus Dec 20 2012, 12:05 AM

I've heard about this system last night while lurking on another forum. It's more hard line than this forum though, so I recommend if you want to make an account there you should have a general knowledge about exoplanet mechanics.

http://solar-flux.forumandco.com/

Now I am going to be the skeptic here. While I am not surprised that Tau Ceti could have planets, the inclination of the system is very unknown. Previous studies have given inclinations ranging from near edge on to face on. Now the star is known to have a dust disk and that would normally constrain things, given that low mass systems tend to be coplanar, but there are just as many models of the inclination of the disk as there are the star!

http://adsabs.harvard.edu/abs/2004MNRAS.351L..54G

The RV method only gives minimum masses, if there is a high inclination then these are neptune sized worlds, not super-earths. There are to many to many assumptions right now, and the team used the assumptions that favored their model. There is a better case for Alpha Centauri Bb then these planets found by an experimental method that has yet to be verified.

If I were in charge a followup, I would look for planet b and work my way up. HARPS is in the best position to do this since Tau Ceti is visible in both the North and Southern hemisphere.

Posted by: TheAnt Jan 5 2013, 06:46 PM

A bit late perhaps but I happened upon what I think is the original press release for the Tau Ceti system findings.
Nothing new not covered in the other sources you others already have linked though.

http://www.herts.ac.uk/news-and-events/latest-news/New-Neighbours-Closest-Single-Star-Like-Our-Sun-May-Have-Habitable-Planet.cfm

The study is part of the European http://star.herts.ac.uk/RoPACS/ where the same University of Hertfordshire are coordinating the work.

Posted by: Paolo Mar 27 2015, 09:25 PM

I bring this old topic back to life for this interesting paper: http://arxiv.org/abs/1503.07528. Hubble has observed Alpha Centauri and the results are amazing:

Posted by: algorimancer Apr 1 2015, 05:39 PM

"Wow" seems a bit inadequate. I look forward to a replication. Looks very plausibly like an Earth-size planet, but the inferred short orbital period (15 days) suggests Mercury-like temperatures, even given the lower luminosity of Alpha Centauri B (intuitively; I didn't do the math). Anyone know what "MCMC" refers to in this context? In my world, it's "Markov Chain Monte Carlo", but that doesn't make sense to me in this context [EDIT: Checked the reference... turns-out is is indeed a Markov Chain Monte Carlo... interesting].

Posted by: TheAnt Apr 2 2015, 09:54 AM

@algorimancer: Mercury temperature yes, in that ballpark.
I had a look, and hum, they publish on one observation only. So could you tell how you think they apply the Monte Carlo probability distribution on a sample of one? Because I don't get it either.
(If I did a study of mine with just a sample of one, I'd be hanged upside down from the nearest flagpole as an example of ridicule. Astronomers must live in a relatively protected world compared to some of us others. )

Posted by: centsworth_II Apr 2 2015, 10:52 AM

The information age! Giving "outsiders" a look at the process of science, not just the final product. (An optimistic interpretation.)

Posted by: algorimancer Apr 2 2015, 01:55 PM

My best guess is that they use MCMC to model the light curves, with standard errors, and demonstrate that the "detection" curve differs significantly from the background curve, after accounting for other variables which affect the outcome. Frankly, I'm aware of MCMC methods, but don't use them personally. My loose understanding at the moment is that they are a handy way of estimating and putting error bounds on predictor variables, but I haven't taken the time to study how they're used in the current context. I'm not a Bayesian, so for similar problems I'd draw from a different bag of tricks.

The authors don't seem to be over-emphasizing the detection, and the light curve of the detection event is visually persuasive (which doesn't mean it is real). The comparison of two continuously sampled light curves, a linear reference versus the event curve, is arguably rather more robust than comparing a single event point to a reference point, so perhaps we can allow a little leeway on the sample-of-one thing, in an exploratory context. Of course, nobody will believe it until it has been reliably replicated.

Posted by: algorimancer Apr 2 2015, 02:57 PM

Expanding on my earlier thoughts regarding the MCMC method used in the paper ... a component of MCMC is the Markov chain (MCMC: Markov Chain Monte Carlo). A Markov chain is essentially a means of describing the probabilities of changing states among 2 or more states, which in this case might model changing from the neutral state with no eclipse (no planet blocking the star) to the detection state of an eclipse (planet blocking the star), and back again, so a Markov chain is clearly applicable in this case. The Monte Carlo component would involve simulation of a process with an underlying randomization based upon the known underlying variability; the authors invested quite a bit of effort in quantifying the variability of their observations after factoring-out the non-random components, so this would feed into the process. So, the combination of components in an MCMC might simply be used to put error bars on the transition probabilities associated with the Markov chain as a basis for demonstrating that a state change (detection) occurred. On the other hand, the combination of tools encompassed in an MCMC is used for other purposes, like summing a multidimensional integral or finding estimates of predictor variables in a model, which is why I'm a bit unclear on how it was actually used here.

I can envision several other means of testing for the presence of an eclipse. The simplest would be to partition the samples of the light curve over small intervals, and do something like a t-test comparing the mean intensity (or frequency) prior-to versus during a candidate event. Another would expand on that notion, modeling each partition with a non-linear model, and test for differences between the curves. Yet another would be to to do a running regression of the intensity to a mathematical model of eclipse light curves (I like this approach). I'm not sure there is a single best method for quantifying a detection, but I'd guess that the people who do this for a living have given it rather a lot of thought

Posted by: TheAnt Apr 3 2015, 08:58 AM

Thank you algorimancer for your long reply, I finally get it.
Though I had a vague notion that they might have treated the ingress and egress separately. There's nothing in my world like a synthetic set of data to compare with, where the astronomers certainly know what a planet transit should look like.
But yes a second detection is required, and if that's done by one other team we finally have gotten a start on revealing what's hidden in the Alpha Centauri system. =)

Posted by: Aldebaran Apr 10 2015, 11:40 PM

From the Cheops website:

"These key parameters will help scientists to understand the formation of planets from a few times the mass of the Earth – ‘super-Earths’ – up to Neptune-sized worlds."

It seems to be a mix of parameters and makes the statement vaguer than it ought to be. One moment, we're talking mass, and then we're talking "size". Size is quite vague, but not normally applied to mass. In terms of radius, Neptune is about 3.9 times the size of the Earth. In terms of volume, it's 58 times the size of the Earth.

(and in terms of surface gravity, Neptune is about the same as the Earth. )

It all comes down to communication with the general public.

Posted by: alan Oct 20 2015, 07:01 PM

Alpha Centauri planet may not exist:

http://arxiv.org/abs/1510.05598