Planet Found Orbiting Alpha Centauri!


by Drakkith
Tags: alpha, centauri, orbiting, planet
Drakkith
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Oct16-12, 09:43 PM
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From here: http://blogs.discovermagazine.com/ba...-has-a-planet/

The planet orbits close in to 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.
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marcus
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Oct16-12, 10:54 PM
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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
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Oct16-12, 11:51 PM
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Wow, that's one hell of a fine measurement! Now if only my little 8 inch scope was able to do that...

SHISHKABOB
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Oct17-12, 10:55 AM
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Planet Found Orbiting Alpha Centauri!


too hot for liquid water?

>puts away his copy of SMAC :(
litup
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Oct17-12, 12:58 PM
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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
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Oct17-12, 01:01 PM
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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
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Oct17-12, 04:36 PM
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Quote Quote by litup View Post
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.
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Oct17-12, 06:56 PM
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Quote Quote by marcus View Post
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.

Quote Quote by litup
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.

Quote Quote by Drakkith
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.
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Oct17-12, 08:09 PM
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Quote Quote by mfb View Post
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.
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Oct18-12, 08:56 AM
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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
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Oct18-12, 10:51 AM
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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
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Oct18-12, 12:57 PM
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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....

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cepheid
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Oct18-12, 01:20 PM
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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
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Oct18-12, 02:41 PM
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Quote Quote by cepheid View Post
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
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Oct18-12, 05:03 PM
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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
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Oct18-12, 07:47 PM
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Quote Quote by sshai45 View Post
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.

Quote Quote by Drakkith View Post
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
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Oct18-12, 09:14 PM
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Quote Quote by cepheid View Post
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
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Oct18-12, 10:18 PM
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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.


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