Planet Found Orbiting Alpha Centauri

[Drakkith]

From here: http://blogs.discovermagazine.com/badastronomy/2012/10/16/alpha-centauri-has-a-planet/

The planet orbits close into Alpha Cen B, and is technically called Alpha Centauri Bb – planets have lower case letters assigned to them, starting at b. Its mass is only 1.13 times the Earth’s mass, making this one of the lower mass planets yet found! But don’t get your hopes up of visiting it – its period is only 3.24 days, meaning it must be only about 6 million kilometers (less than 4 million miles) from its star. Even though Alpha Cen B is a bit cooler than the Sun, this still means the planet is baking hot, far too hot to sustain any kind of life as we know it, or even liquid water.

 

[marcus]

Good find! The impressive thing was that the wobble speed they were detecting, by Doppler, was only about 1/2 a meter per second. 20 inches per second.

A foot per second is about one billionth of the speed of light----one ten-millionth of a percent.

So they were detecting the regular lengthening and shortening of particular wavelengths in the star's light by on the order of a ten-millionth of a percent.

The ability to do that is a step forward---it means being able to detect significantly lower-mass planets including some farther out from star. Fine accomplishment!

 

[Drakkith]

Wow, that's one hell of a fine measurement! Now if only my little 8 inch scope was able to do that...

 

[SHISHKABOB]

too hot for liquid water?

>puts away his copy of SMAC :(

 

[litup]

So many close in planets have been found, is that the galactic norm? It kind of takes the wind out of our sails for the interstellar science fiction 'just found a nice Earth planet we can get to in 100 years with our new photon drive' set:)

 

[litup]

I will say, however, on the new planet at AC, if and/or when we ever get to do interstellar probes or human travel to the nearby stars, AC would seem to be a natural first try, since besides being the closest, you get a nice 3 for one deal, 3 stars within 1/10th of a light year from one another, 3 for the price of one, great deal for the astronaut set.

 

[Drakkith]

So many close in planets have been found, is that the galactic norm? It kind of takes the wind out of our sails for the interstellar science fiction 'just found a nice Earth planet we can get to in 100 years with our new photon drive' set:)

It is simply a result of planets that are close to their stars being MUCH easier to detect than planets further away. I fully expect to find lots of planets at all kinds of distances from their stars as time passes and our detections methods get more sensitive.

 

[mfb]

Good find! The impressive thing was that the wobble speed they were detecting, by Doppler, was only about 1/2 a meter per second. 20 inches per second.

~4 orders of magnitude below doppler broadening of the spectral lines.
And just a factor of ~5 above an earth-like planet.
The next generation of telescopes will find them.
It is an amazing time to live in.

So many close in planets have been found, is that the galactic norm?

A significant fraction of all stars nearby has known planets - and that includes only planets which can be detected today.

It is simply a result of planets that are close to their stars being MUCH easier to detect than planets further away.

Transits are not so distance-dependent. The other interesting exoplanet this week is 5000 light years away. It orbits a double-star, which is part of a system with 4 stars.

 

[Drakkith]

Transits are not so distance-dependent. The other interesting exoplanet this week is 5000 light years away. It orbits a double-star, which is part of a system with 4 stars.

Sure they are. The closer to the star, the more transits, the easier it is to detect and confirm them. One of the reasons so many hot jupiters were found initially by the Kepler spacecraft was that their transits occurred very rapidly, whereas longer period planets weren't detected until later on and then had to wait much longer for a 2nd transit to verify them.

 

[mfb]

Oh sorry, I misread your post as "planets close to our star".
That distance matters, too, as the overall apparent brightness (and with it, the precision of spectroscopy and relative luminosity measurements) goes down.

You are right, the distance between planets and their corresponding stars is really important.

and then had to wait much longer for a 2nd transit to verify them.

Kepler requires 3 transits for a confirmation - the second transit does not confirm that the signal is periodic.

 

[cepheid]

Don't get me wrong, I share the optimism that this result produces about our ability to make measurements fine enough to detect Earth-like planets -- eventually. But I wonder if that ability isn't being overstated somewhat. After all, presumably a large reason why this worked (given our current sensitivity and precision) is because we were looking at *the most nearby star* that we could possibly look at, right?

Also, when I mentioned this find to a colleague, their response was, "okay, so why is this exciting?" A valid question. Sure, it's an Earth-size planet orbiting the nearest star. But it's not like the conditions there are anything like Earth, nor is the probability of going to the nearest star (and it not being a one-way trip) in our lifetimes any better than the probability of going to any other star. Not only that, but even if conditions were like Earth, why would that be exciting? Maybe I can understand the public's fascination with that, but not astronomers. It presupposes that the "holy grail" of exoplanet science is to find *a* planet just like Earth that might be capable of supporting life similar to our own. I would dispute that that is of primary importance, *astronomically* speaking. (Besides, even if you hold finding evidence of extraterrestrial life to be of primary importance, which I don't, why the bias towards life similar to what's here? If there's anything life has taught us, it's that it is extremely resilient and adaptable. Who's to say that some other really alien form of life with a totally different biochemistry that isn't immediately recognizable as such doesn't exist? But this is off-topic). Shouldn't exoplanet people be trying to understand more about how the physical process of planet formation works, and about how prevalent (or exceptional) solar systems like our own are? About what kinds and diversities of systems and planets exist? Not to mention how common planets are at all in our Galaxy (and I acknowledge that Kepler is beginning to answer that question)? It really bothers me sometimes what the media gets all worked up about and what they portray as being meaningful and scientifically significant, as compared to what actually is.

 

[Garth]

One reason that this is so exciting is that an Earth sized planet has been discovered in the star system 'next door'. They are therefore probably not rare.

Okay this one is too hot, but cooler 'Earths' (further away from their parent star) will be more difficult to find - give them time...

Garth

 

[cepheid]

If you think my main objection to to the buzz was that this one was too hot, you didn't read my post in its entirety.

Okay, maybe I'm just in a snarky mood today...

 

[sshai45]

Don't get me wrong, I share the optimism that this result produces about our ability to make measurements fine enough to detect Earth-like planets -- eventually. But I wonder if that ability isn't being overstated somewhat. After all, presumably a large reason why this worked (given our current sensitivity and precision) is because we were looking at *the most nearby star* that we could possibly look at, right?

Also, when I mentioned this find to a colleague, their response was, "okay, so why is this exciting?" A valid question. Sure, it's an Earth-size planet orbiting the nearest star. But it's not like the conditions there are anything like Earth, nor is the probability of going to the nearest star (and it not being a one-way trip) in our lifetimes any better than the probability of going to any other star. Not only that, but even if conditions were like Earth, why would that be exciting? Maybe I can understand the public's fascination with that, but not astronomers. It presupposes that the "holy grail" of exoplanet science is to find *a* planet just like Earth that might be capable of supporting life similar to our own. I would dispute that that is of primary importance, *astronomically* speaking. (Besides, even if you hold finding evidence of extraterrestrial life to be of primary importance, which I don't, why the bias towards life similar to what's here? If there's anything life has taught us, it's that it is extremely resilient and adaptable. Who's to say that some other really alien form of life with a totally different biochemistry that isn't immediately recognizable as such doesn't exist? But this is off-topic). Shouldn't exoplanet people be trying to understand more about how the physical process of planet formation works, and about how prevalent (or exceptional) solar systems like our own are? About what kinds and diversities of systems and planets exist? Not to mention how common planets are at all in our Galaxy (and I acknowledge that Kepler is beginning to answer that question)? It really bothers me sometimes what the media gets all worked up about and what they portray as being meaningful and scientifically significant, as compared to what actually is.

I think you just answered why the media would get so excited. Because the general public (i.e. those who are not researchers in the field) and researchers in the field have two very different standards of what constitutes "exciting". The general media is made for the general public, not for researchers, when it comes to these topics. And why should it be anything else? I don't see anything wrong with them getting excited about it, since their target audience is not researchers.

 

[Drakkith]

Why is this exciting? Why is finding a new moon around Neptune exciting? Because it is! Lol.
Anyways, I thought it was cool and worth posting given that Alpha Centauri is the closest star system to our own and is a triple star system. If that isn't exciting, then I guess you aren't excited about exoplanets like I am.

Of course you are speaking to a guy who has done exoplanet transit light curves and participated in the Planethunters project at Zooniverse.org, so maybe I'm just biased!

 

[cepheid]

I think you just answered why the media would get so excited. Because the general public (i.e. those who are not researchers in the field) and researchers in the field have two very different standards of what constitutes "exciting". The general media is made for the general public, not for researchers, when it comes to these topics. And why should it be anything else? I don't see anything wrong with them getting excited about it, since their target audience is not researchers.

My complaint was not that the public should be interested in different things, but that the media misrepresent the science that is being done, what avenues of inquiry are being pursued, what questions are of interest, and the significance of a given finding in the broader context of the field.

Why is this exciting? Why is finding a new moon around Neptune exciting? Because it is! Lol.
Anyways, I thought it was cool and worth posting given that Alpha Centauri is the closest star system to our own and is a triple star system. If that isn't exciting, then I guess you aren't excited about exoplanets like I am.

Of course you are speaking to a guy who has done exoplanet transit light curves and participated in the Planethunters project at Zooniverse.org, so maybe I'm just biased!

Not only are extrasolar planets the branch of astronomy towards which I'm least inclined, but I think I've also just been oversaturated with exoplanet talks and media hype surrounding "discoveries" that just involve the results of applying the same observational technique over and over again. I don't want to see another light curve, or to hear about one particular object that somehow managed to serve as an excuse for a whole paper.

 

[Drakkith]

Not only are extrasolar planets the branch of astronomy towards which I'm least inclined, but I think I've also just been oversaturated with exoplanet talks and media hype surrounding "discoveries" that just involve the results of applying the same observational technique over and over again. I don't want to see another light curve, or to hear about one particular object that somehow managed to serve as an excuse for a whole paper.

Well, that's disheartening to hear, but to each his own. As for the observational techniques, isn't that what practically all astronomical discoveries involve? Doing the same thing but more accurate, for longer, at different wavelengths, etc? And is the orbital characteristics of a planet in a multiple star system or the analysis of a spectrum of the emitted light from a hot planet not good enough for a paper? I thought that was how all science got done, by doing little things one at a time.

 

[cepheid]

On the contrary, I think observational techniques are ever evolving, as the instrumentation that enables them improves. It's really important to innovate and think of new ways of observing the universe! Observations in previously unobserved frequency bands. Interferometry (even in the optical). Integral field spectroscopy to get spatially resolved spectral information (also with Fourier transform spectroscopy). Things like coronography and differential imaging techniques (that they used for direct imaging of planets). FFT telescopes (sort of) like CHIME. Adaptive Optics, including advanced varieties like multi-conjugate adaptive optics and robotic AO. The nascent field of gravitational wave astronomy (which hasn't seen anything yet).

Dude, the radial velocity method has been around since forever (okay, so has interferometry). It's just the same techniques that used to be applied to binary stars that are now being applied to planets. Transits are starting to seem kind of old hat too. So now you can do really really *really* precise photometry instead of just really really precise photometry. I'm not saying that sort of incremental progress isn't important. I'm just saying that it is boring. EDIT: and I'm also saying that some work in this field could stand to be more astrophysically motivated and smacks of stamp collecting. Like you said, to each his own. I'm not even saying that it's intrinsically boring, but it becomes boring when you are constantly beaten over the head with it. Like I've said, I've just attended a few too many planet talks in too short a span of time and am planeted out. I am sorry if I ruffled a few feathers. I will drop it.

 

[Drakkith]

Understandable. I'm sure if I had been beaten over the head with the same kind of technique over and over it would become boring too.

 

[mfb]

On the contrary, I think observational techniques are ever evolving, as the instrumentation that enables them improves. It's really important to innovate and think of new ways of observing the universe! Observations in previously unobserved frequency bands. Interferometry (even in the optical). Integral field spectroscopy to get spatially resolved spectral information (also with Fourier transform spectroscopy). Things like coronography and differential imaging techniques (that they used for direct imaging of planets). FFT telescopes (sort of) like CHIME. Adaptive Optics, including advanced varieties like multi-conjugate adaptive optics and robotic AO. The nascent field of gravitational wave astronomy (which hasn't seen anything yet).

It is hard to sell that to the public. "Planet with mass of Earth discovered at the nearest star system" is easier to understand.

Concerning life: We do not know where life can evolve yet - we just have one example: We know that it can evolve on earth-like planets. Naturally, our theories are biased and propose Earth as perfect place for life.

 

[Philosophaie]

Alpha Centauri is a Binary Star with Alpha Centauri B and a Companion Star Alpha Centauri C.

Alpha Centauri A is solar-like yellow main sequence star.

Alpha Centauri B is smaller solar-like yellow main sequence star.

Alpha Centauri C is a small main sequence star (Type V) or sub-dwarf (VI) with emission lines.

All three combine to be the brightest and the closest of all the stars at 4.366 light years or 4.131E+13 km away.

A planet rotating around a Binary Star will be very unstable, at the very least, and would probably not be first on my list to be a habitable planet.

 

[cepheid]

It is hard to sell that to the public. "Planet with mass of Earth discovered at the nearest star system" is easier to understand.

I wasn't *talking* about selling any of that to the public. I was addressing Drakkith's question (post #17) about whether observational astronomy mainly consists of doing the same types of observations repeatedly, with only slight refinements or improvements each time. I was just trying to point out that in fact observational techniques have changed dramatically in the past few decades, with many innovations arising. I know I said I would drop this, but please don't make arguments against points I never made in the first place.

 

[mfb]

Well, I viewed your post in the context of that:

I don't want to see another light curve, or to hear about one particular object that somehow managed to serve as an excuse for a whole paper.

@Philosophaie:

All three combine to be the brightest and the closest of all the stars at 4.366 light years or 4.131E+13 km away.

It is not sure that Proxima Centauri ("Alpha Centauri C") is gravitationally bound. Sirius, Canopus and Arcturus are brighter (and our sun, too, of course).

A planet rotating around a Binary Star will be very unstable, at the very least

There are several known exoplanets around binary stars, and simulations show that they are quite stable.

and would probably not be first on my list to be a habitable planet.

Depends on the orbit, as always.

 

[cepheid]

Well, I viewed your post in the context of that:

That wasn't the right context, but since I didn't quote the part of Drakkith's post that I was responding to, it's understandable that there would be some confusion as to what my point was.

It's supposed to be my job to keep things on topic, but instead I am guilty of veering off topic myself. Regarding planets in binary or multiple systems: what are the stable orbital configurations?

I imagine that if you had a close binary, the planet could perhaps orbit around the centre of mass of the system, only much farther out, so that it would essentially be in orbit around both stars.

On the other hand, given stars with a very wide separation, and a planet very close into one of them, as seems to be the case with Alpha Cen B, then I imagine that the planet would orbit around its parent star, and then the planet + star would orbit around the centre or mass of the system.

Am I at least somewhat close the the mark?

 

[mfb]

I imagine that if you had a close binary, the planet could perhaps orbit around the centre of mass of the system, only much farther out, so that it would essentially be in orbit around both stars.

On the other hand, given stars with a very wide separation, and a planet very close into one of them, as seems to be the case with Alpha Cen B, then I imagine that the planet would orbit around its parent star, and then the planet + star would orbit around the centre or mass of the system.

That two options are the "conventional" stable orbits.

And then there is Kepler 16b.

There are even weirder solutions (which might or might not be stable at the timescale of 10^9 years), but I would not expect to see them frequently ;)
Figure-8
Orbits in binary systems

 

[cepheid]

That two options are the "conventional" stable orbits.

And then there is Kepler 16b.

There are even weirder solutions (which might or might not be stable at the timescale of 10^9 years), but I would not expect to see them frequently ;)
Figure-8
Orbits in binary systems

These applets are pretty neat! I would not have expected such solutions. I like the Figure 8 ones that end up looking like spirographs.

 

[EBENEZR]

I guess it would become tedious to someone exposed to the reality of observation techniques time and time again, but I think it's exciting for the sake of being a discovery relatively close.

 

[sshai45]

My complaint was not that the public should be interested in different things, but that the media misrepresent the science that is being done, what avenues of inquiry are being pursued, what questions are of interest, and the significance of a given finding in the broader context of the field.

But is it possible to simultaneously take into account the differing interests of the general public and also not misrepresent the science, etc.? To not misrepresent "what questions are of interest" while also not missing the general public's interest (i.e. what do you do since the two differ and contrast)?

 

[stargazer3]

Dropping by to point out that there is a calculated 10% probabitity that the planet detectable via transit method with transit depth about 10^-4. If we're that lucky, we'll find more about the structure of the planet for sure.

 

[AlaskanGlitch]

That wasn't the right context, but since I didn't quote the part of Drakkith's post that I was responding to, it's understandable that there would be some confusion as to what my point was.

It's supposed to be my job to keep things on topic, but instead I am guilty of veering off topic myself. Regarding planets in binary or multiple systems: what are the stable orbital configurations?

I imagine that if you had a close binary, the planet could perhaps orbit around the centre of mass of the system, only much farther out, so that it would essentially be in orbit around both stars.

On the other hand, given stars with a very wide separation, and a planet very close into one of them, as seems to be the case with Alpha Cen B, then I imagine that the planet would orbit around its parent star, and then the planet + star would orbit around the centre or mass of the system.

Am I at least somewhat close the the mark?

The interesting thing is that since the amount of separation at their closest approach is around 10 AU, there could be a solar system around each star, as long as the planets were not more than 5 AU distant from their own star. This would also seem to eliminate any possibility of a gas giant in either solar system.

Furthermore, both stars are close enough where their solar winds would impact right around the "snow line" which should create gas, dust, and ice particulates. We have observed this in other binary systems, such as R Scuti and WR-104.

With a higher mellicity than Sol, the odds are high that more than one rocky planet will be found around both Alpha Centauri A & B. The optimal distance around Alpha Centauri B would be about 65 million miles since it is 10% smaller, 50% dimmer, and about 10% cooler than Sol. Whereas the optimal distance around Alpha Centauri A would be about 128 million miles since it is 10% bigger, 50% brighter, and about 2% hotter than Sol.

If there are any planets (besides the one found) around either Alpha Centauri A and/or B, every 80 years they would be pelted with meteors and comets, as the stars make their closest approach. Alpha Centauri A would be visible during the day around any planet in the Alpha Centauri B solar system.

 

[mfb]

With a distance of 1/2 of the star separation, you don't get stable orbits around a single star. I think I read something about of 1/7 of the star separation for stable (and nearly circular) orbits.

Gas giant with close orbits should be possible due to orbital mechanics, but I think they would have been visible in the radial velocity measurements (did not check the numbers).

 

[sophiecentaur]

My complaint was not that the public should be interested in different things, but that the media misrepresent the science that is being done, what avenues of inquiry are being pursued, what questions are of interest, and the significance of a given finding in the broader context of the field.

Not only are extrasolar planets the branch of astronomy towards which I'm least inclined, but I think I've also just been oversaturated with exoplanet talks and media hype surrounding "discoveries" that just involve the results of applying the same observational technique over and over again. I don't want to see another light curve, or to hear about one particular object that somehow managed to serve as an excuse for a whole paper.

Man. You really can't be too surprised about that! Science and the Media is the serious. on-going scandal of our times.