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Don Alexander
2012-Oct-16, 10:54 PM
Nancy just upped this on UT:

http://www.universetoday.com/98031/next-door-neighbors-earth-sized-planet-discovered-in-nearest-star-system-to-us

This is INCREDIBLE!!!!:D

I'm so elated!!!

EDIT: Okay, okay, Wunderland is afaik a planet of Alpha Cen A and not B, and of course a 3.2 day orbit is a bit too hot to handle. ;) But everyone will be calling it this (I HOPE).

Also, 51 cm/s precision, that is phenomenal. GO, HARPS!!!!!!

EDIT2: Official ESO Press Release. (http://www.eso.org/public/news/eso1241/)

KaiYeves
2012-Oct-16, 11:08 PM
Wow, incredible!

Noclevername
2012-Oct-16, 11:53 PM
At least we know what direction the Kzin will attack from...

Van Rijn
2012-Oct-17, 12:25 AM
This is INCREDIBLE!!!!:D


Yes, it did hit me after a bit. My first thought was: Oh, okay, another exoplanet. Then my second thought was: Whoa - a planet in the Alpha Centauri system! The fact that exoplanet discoveries are so common now, and that one was found at Alpha Centauri reminds me that we really do live in the future.

Now I wonder what science fiction writer will be the first one to use this in a story?

Rhaedas
2012-Oct-17, 12:27 AM
And where there's one, there could be others.

It's getting to a point where the list might be, which stars don't have something of interest around them.

Swift
2012-Oct-17, 01:54 AM
I just heard about this. I really think this is incredible news. I suspect (and hope) this will get A LOT of public attention. This isn't some star 500 ly away, this is our next door neighbor.

:dance:

By the way, here is part of the press release:


European astronomers have discovered a planet with about the mass of the Earth orbiting a star in the Alpha Centauri system — the nearest to Earth. It is also the lightest exoplanet ever discovered around a star like the Sun. The planet was detected using the HARPS instrument on the 3.6-metre telescope at ESO’s La Silla Observatory in Chile. The results will appear online in the journal Nature on 17 October 2012.

Alpha Centauri is one of the brightest stars in the southern skies and is the nearest stellar system to our Solar System — only 4.3 light-years away. It is actually a triple star — a system consisting of two stars similar to the Sun orbiting close to each other, designated Alpha Centauri A and B, and a more distant and faint red component known as Proxima Centauri [1]. Since the nineteenth century astronomers have speculated about planets orbiting these bodies, the closest possible abodes for life beyond the Solar System, but searches of increasing precision had revealed nothing. Until now.

“Our observations extended over more than four years using the HARPS instrument and have revealed a tiny, but real, signal from a planet orbiting Alpha Centauri B every 3.2 days,” says Xavier Dumusque (Geneva Observatory, Switzerland and Centro de Astrofisica da Universidade do Porto, Portugal), lead author of the paper. “It’s an extraordinary discovery and it has pushed our technique to the limit!”

StupendousMan
2012-Oct-17, 02:39 AM
I don't want to rain on the parade here, but .... uh, I encourage people to read the paper / press release carefully. Look carefully at the illustrations showing just how many effects had to be removed from the radial velocity curve in order to reveal the signal from the planet. Look also at the scatter in the measurements.

It could be real, and I hope it's real. But at this point, I'm not sure I'd bet the farm on it.

chornedsnorkack
2012-Oct-17, 09:08 AM
Is that 1,13 its mass, or just m sin i?

Don Alexander
2012-Oct-17, 09:28 AM
Yeah. :(

Already, a reasonably renowned exoplanet researcher contacted me, telling me they do not believe it's real...

Also, it's m sin i (of course).

Tom Mazanec
2012-Oct-17, 11:00 AM
If it turns out to be real, I assume we will call it Alpha Centauri Bb. Then will one around A be called Alpha Centauri Ab, or Alpha Centauri Ac? And then a circumbinary planet Alpha Centauri ABb, or Alpha Centauri ABd?

Don Alexander
2012-Oct-17, 11:18 AM
If we find one around Alpha Cen A, it will be Ab, not Ac - pretty sure of that.

Also, pretty sure there can't be any circumbinary planets, unless they had orbits lasting thousands of years.

chornedsnorkack
2012-Oct-17, 11:35 AM
Also, pretty sure there can't be any circumbinary planets, unless they had orbits lasting thousands of years.

I am not.

Kepler 16 has circumbinary planet whose period, at 229 days, is just 5,6 times the period of the binary at 41 days.

Thus Toliman AB, period 80 years, might have quite viable circumbinary planets at just 500 years orbit.

What is the semimajor axis of Toliman Bb?

Period 3,236 days
primary mass 0,934 solar
hm... About 1/24 AU?

geonuc
2012-Oct-17, 07:00 PM
Already, a reasonably renowned exoplanet researcher contacted me, telling me they do not believe it's real...




I haven't seen anything (except here) suggesting it is not a valid discovery.

Don Alexander
2012-Oct-17, 08:43 PM
Please have a look to the link at the bottom of my opening post...

chornedsnorkack
2012-Oct-17, 09:03 PM
Please have a look to the link at the bottom of my opening post...

Who?

Don Alexander
2012-Oct-17, 10:12 PM
That was obviously addressed to the person posting right above me.

Romanus
2012-Oct-18, 12:26 AM
This news really, truly made my day. Like another poster, my first reaction was, "What's so special about this exoplanet?" Then...bam.


The fact that exoplanet discoveries are so common now, and that one was found at Alpha Centauri reminds me that we really do live in the future.


QFT.

It may not be a pleasant place to live, but even something like this has been on astronomers' bucket list long before the first exoplanet was discovered. Tremendously exciting; who knows what we'll find next in this system?

glappkaeft
2012-Oct-18, 12:38 AM
That was obviously addressed to the person posting right above me.

You're obviously using a definition of the word "obviously" that I was previously unaware of. ;)

While I finaly understood you I had to check and double check to be reasonably sure. My experience is that it almost always useful to use the "quote" function.

Don Alexander
2012-Oct-18, 02:25 AM
I'm used to reading fora sequentially and am moderator in a place where we actually remove quotes if the just quote the post exactly above one's own. :P

So I'll just say it again:

This is based on a paper accepted by the journal Nature, now published online, and was already presented a day earlier as an official ESO press release (link see OP).

The detection MAY be bogus, but for now, it IS a result in a peer-reviewed high-impact journal and should be treated as such.

George
2012-Oct-18, 03:27 AM
Given the fast ~ 3 day period, will we see a fairly quick confirmation?

geonuc
2012-Oct-18, 08:21 AM
I'm used to reading fora sequentially and am moderator in a place where we actually remove quotes if the just quote the post exactly above one's own. :P

So I'll just say it again:

This is based on a paper accepted by the journal Nature, now published online, and was already presented a day earlier as an official ESO press release (link see OP).

The detection MAY be bogus, but for now, it IS a result in a peer-reviewed high-impact journal and should be treated as such.

Wasn't obvious to me, either.

Your previous post, which I quoted in part, mentioned that you had been contacted by a 'renowned' researcher who did not believe this discovery was real. That was what I was questioning. I've read the ESO page (or I did yesterday), both before and after you suggested I do so. They seem to be ecstatic and give no hint of reservation about the findings. Perhaps you misread my first post.

lpetrich
2012-Oct-18, 09:54 AM
The amplitude of its induced velocity is *very* tiny: about 51 cm/s. That seems to me to be good reason to be skeptical -- it could be some statistical fluke.

kzb
2012-Oct-18, 11:55 AM
The amplitude of its induced velocity is *very* tiny: about 51 cm/s. That seems to me to be good reason to be skeptical -- it could be some statistical fluke.

This link goes straight to the Nature article (it appears to be open access). All I can say is, the authors seem very sure it is real.

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

Here is an interesting clip from this paper:

...the observed radialvelocity
semi-amplitude is equivalent to the one
induced by a four Earth minimum mass planet in
the habitable zone of the star

So do we take it from this, that planets of 4 Earth masses and above are ruled out in the habitable zone? (Bearing in mind that the super-Mercury reported is apparently close to the detection limit.) I wonder what is the minimum mass of planet that would have been detected in the HZ?

Don Alexander
2012-Oct-18, 12:44 PM
Wasn't obvious to me, either.

Your previous post, which I quoted in part, mentioned that you had been contacted by a 'renowned' researcher who did not believe this discovery was real. That was what I was questioning. I've read the ESO page (or I did yesterday), both before and after you suggested I do so. They seem to be ecstatic and give no hint of reservation about the findings. Perhaps you misread my first post.
Oh, sorry, seems there were multiple misunderstandings...

At the time I wrote that, this had been "private communication" and I had not wanted to reveal the name.

Now, though, said researcher has spoken up anyway on Sky & Telescope:

http://www.skyandtelescope.com/news/home/Planet-Found-in-Alpha-Centauri-System-174559561.html

"This tiny wobble is on the edge of modern detection capabilities. It’s also one-third the strength of the stellar-activity signal, leading Artie Hatzes (Thuringian State Observatory, Germany) to wonder whether the planet is actually there."

He's one of the PIs of the CoRoT mission and the lead author of the paper on CoRoT-7b, the first rocky exoplanet found, as well as the director of the institute I have worked at for years.

Of course the press release has no hints of reservations. Those do not sell to the public. Which also means, that, of course, in the eyes of the public, if this turns out to be a fluke, "the scientists will have gotten it all wrong yet again"...

Swift
2012-Oct-18, 01:04 PM
Finally saw something about this in the general media: a story on CNN Headline News this morning. It was only about a 30 second spot, but didn't seem to get anything wrong.

geonuc
2012-Oct-18, 01:44 PM
Oh, sorry, seems there were multiple misunderstandings...

At the time I wrote that, this had been "private communication" and I had not wanted to reveal the name.

Now, though, said researcher has spoken up anyway on Sky & Telescope:

http://www.skyandtelescope.com/news/home/Planet-Found-in-Alpha-Centauri-System-174559561.html

"This tiny wobble is on the edge of modern detection capabilities. It’s also one-third the strength of the stellar-activity signal, leading Artie Hatzes (Thuringian State Observatory, Germany) to wonder whether the planet is actually there."

He's one of the PIs of the CoRoT mission and the lead author of the paper on CoRoT-7b, the first rocky exoplanet found, as well as the director of the institute I have worked at for years.

Of course the press release has no hints of reservations. Those do not sell to the public. Which also means, that, of course, in the eyes of the public, if this turns out to be a fluke, "the scientists will have gotten it all wrong yet again"...

Thanks for the clarification. I agree with your assessment although I haven't seen any of my usual go-to people say anything to suggest it isn't real either. Bad Astronomer, Fraser, etc.

StupendousMan
2012-Oct-18, 01:48 PM
So do we take it from this, that planets of 4 Earth masses and above are ruled out in the habitable zone? (Bearing in mind that the super-Mercury reported is apparently close to the detection limit.) I wonder what is the minimum mass of planet that would have been detected in the HZ?

How long would it take a planet in the habitable zone to orbit the star?
(Hint: would be similar to orbit of Earth)

How long as the team been making high-precision RV measurements?
(Hint: read paper)

How many orbits of a planet in the habitable zone could they have seen by now?
(not nearly as many as those of the putative planet)

The limits on a planet in the habitable zone will be weaker than the limits
on a planet close to the star, simply due to the smaller number of
cycles in the radial velocity measurements. When one is looking for
a very small periodic signal, having many cycles helps a LOT.

chornedsnorkack
2012-Oct-18, 02:01 PM
How long would it take a planet in the habitable zone to orbit the star?
(Hint: would be similar to orbit of Earth)

About 220 days. Or 65 times the orbital period of Bb


How long as the team been making high-precision RV measurements?
(Hint: read paper)

4 years


How many orbits of a planet in the habitable zone could they have seen by now?
(not nearly as many as those of the putative planet)

About 6.


The limits on a planet in the habitable zone will be weaker than the limits
on a planet close to the star, simply due to the smaller number of
cycles in the radial velocity measurements. When one is looking for
a very small periodic signal, having many cycles helps a LOT.

But a single cycle of a small periodic signal is much more easily lost in a noise.

Over an equal total timespan and count of measurements, what is easier to resolve from noise - a short period signal with many cycles, or a long period signal with only a few cycles but many observations per cycle?

IsaacKuo
2012-Oct-18, 02:52 PM
Over an equal total timespan and count of measurements, what is easier to resolve from noise - a short period signal with many cycles, or a long period signal with only a few cycles but many observations per cycle?

It depends on the noise spectrum. For example, if the power of the noise is roughly equivalent at the low and high frequencies, then the long period signal would be harder to detect (it's power, given a particular amplitude, would be far lower). However, I doubt the noise spectrum is flat with respect to power. I don't know enough about radial velocity measurements to know what the noise spectrum is like.

BTW, I think this thread has a very unhelpful subject title.

eburacum45
2012-Oct-19, 09:10 AM
Here's my interpretation of the planet from the available info;
http://www.orionsarm.com/im_store/ixion.jpg
(Ixion is the provisional name we've given it in Orion's Arm)

The planet is tidally locked, and has a dayside temperature of around 1500K , which is the temperature of many lavas. I've shown the surface broken up into numerous microplates, but it might have Io-like volcanoes instead.
The amount of tidal heating isn't yet known; it might be minimal, or considerable if there are several other planets in the system (which one hopes there are)
If you were to see this planet in real life, the day side would be dazzlingly bright, drowning out the glow from the lava - so this image doesn't really show what you would see with the unaided eye.

IsaacKuo
2012-Oct-19, 09:58 AM
What sort of atmosphere, if any, do you imagine? Is 1500K hot enough for a primarily sodium atmosphere?

Noclevername
2012-Oct-19, 10:52 AM
BTW, I think this thread has a very unhelpful subject title.

Not a Niven fan?

Don Alexander
2012-Oct-19, 11:27 AM
Ixion's already the name of a TNO, might want to rethink that.

IsaacKuo
2012-Oct-19, 11:30 AM
Not a Niven fan?
Already, at least one person missed this thread, and was called out for starting a new thread instead. The funny thing is, this thread wasn't even the first, either. This one was:http://cosmoquest.org/forum/showthread.php/138823-Next-Door-Neighbors-Earth-Sized-Planet-Discovered-in-Nearest-Star-System-to-Us

kzb
2012-Oct-19, 12:02 PM
What sort of atmosphere, if any, do you imagine? Is 1500K hot enough for a primarily sodium atmosphere?

I found this atmosphere plotter the other day:


http://astro.unl.edu/naap/atmosphere/animations/gasRetentionPlot.html

It does not go up to 1500 degrees unfortunately. BUT, I have to say it is not necessarily a given that this world must have some exotic atmosphere, or no atmosphere at all.

Maybe it has a strong magnetic field: it should be high in iron, and it rotates every three days. Maybe, like Mercury, it is not exactly tide-locked, and it is in spin-orbit resonance.

You'd also expect it to be dense, therefore a relatively high surface gravity for its mass.

Using that plotter and extrapolating a bit, ACBb may have held on to xenon, even CO2 and N2.

chornedsnorkack
2012-Oct-19, 12:21 PM
What is the silica vapour pressure at 1200 Celsius? (It is 1 bar at 2230 Celsius.)

lpetrich
2012-Oct-19, 01:17 PM
Sudarsky extrasolar planet classification - Wikipedia (http://en.wikipedia.org/wiki/Sudarsky_extrasolar_planet_classification)
It would be class V: silicate and iron clouds, but only a little past class IV: alkali-metal clouds.

chornedsnorkack
2012-Oct-19, 02:37 PM
Sudarshy classification is applicable to gas giants, which are massive enough and/or cold enough to hold excess hydrogen. It is inapplicable to rocky planets!

Swift
2012-Oct-19, 03:29 PM
Already, at least one person missed this thread, and was called out for starting a new thread instead. The funny thing is, this thread wasn't even the first, either. This one was:http://cosmoquest.org/forum/showthread.php/138823-Next-Door-Neighbors-Earth-Sized-Planet-Discovered-in-Nearest-Star-System-to-Us
I rather like the thread title (I did get the reference), but decided to make a small clarifying modification. No foul, no harm Don Alexander, thank you for starting the thread.

Long experience has shown that even very clear titles don't stop people from starting new threads on topics; I'm rather surprisied we haven't seen more (though I'm also rather surprised by the lack of interest in this topic).

kzb
2012-Oct-19, 03:29 PM
Silica wouldn't even melt at this temperature, never mind be an atmospheric constituent. Impure silica might melt (glass).

I'd have thought heavy volcanic gases like sulfur dioxide could be candidates for atmospheric constituents.

If this planet is tidally-locked, could there be a ring around the terminator of piled-up volatiles, distilled from the hot side and condensed in the transition zone ?

IsaacKuo
2012-Oct-19, 03:52 PM
Sudarshy classification is applicable to gas giants, which are massive enough and/or cold enough to hold excess hydrogen. It is inapplicable to rocky planets!

Right. I'm trying to apply results from this study:

CHEMISTRY OF SILICATE ATMOSPHERES OF EVAPORATING SUPER-EARTHS
Laura Schaefer and Bruce Fegley

http://iopscience.iop.org/1538-4357/703/2/L113/fulltext/apjl_703_2_113.text.html
http://iopscience.iop.org/1538-4357/703/2/L113
http://arxiv.org/abs/0906.1204

This study involved hot super-Earths, with the assumption that the usual lightweight volatiles have all been baked away already.

I don't really understand the results, and don't know how applicable they are, since they assume a super-Earth rather than something of roughly Earth mass.

If the main gas in the atmosphere is silicon monoxide, then that would be, to me, very interesting from an ISRU perspective. Silicon might not be quite the super-resource that carbon is, but it's still a pretty promising universal building block.

kzb
2012-Oct-19, 04:16 PM
CHEMISTRY OF SILICATE ATMOSPHERES OF EVAPORATING SUPER-EARTHS
Laura Schaefer and Bruce Fegley

Thanks for the link that looks interesting. A quick look at it: notice the y-axis is in molecules per sq cm of surface. At the lower temperatures, when you work it out, there are micromoles per sq cm of surface. This is almost a vacuum.

I also find it surprising at first sight that we can apparently have atomic sodium and molecular oxygen co-existing. Again, I think this could only happen in near-vacuum conditions.

eburacum45
2012-Oct-19, 04:43 PM
If the atmosphere is thin enough, there might be water ice or CO2 on the cold side. But that seems a remote possibility.

Githyanki
2012-Oct-19, 05:12 PM
Though I'm happy for this discovery (if really true), but I am also disappointed; I always thought a world like this was orbiting Alpha Centauri A not B!

Just one question: could this be the remains of a gas-giant that fell in sucking up all the other terrestrial worlds of ACb and this is all that's left of it?

Also, I expect since AC3 has more metallicity, that any Sol-System, "Twin", would be more massive, ie, a larger Mars etc.

IsaacKuo
2012-Oct-19, 06:58 PM
If the atmosphere is thin enough, there might be water ice or CO2 on the cold side. But that seems a remote possibility.

Is it really remote? It seems inevitable to me, assuming there were comets to deliver ice there.

If ice can apparently find a foothold on Mercury, among the tiny potential footholds of polar craters, the gigantic foothold of a hemisphere of cold darkness seems like a sure thing.

That is, unless (tidal heated?) volcanic activity is so violent that it sublimates ice away everywhere.

My interest in atmospheric scooping is that it would involve much simpler ISRU hardware than anything that would have to land on the surface. A somewhat thin atmosphere is okay--you don't want too much drag at orbital speeds anyway. But something ridiculously thin like Mercury's "atmosphere" is far too thin even at orbital speeds.

IsaacKuo
2012-Oct-19, 07:11 PM
I found this atmosphere plotter the other day:

http://astro.unl.edu/naap/atmosphere/animations/gasRetentionPlot.html

It does not go up to 1500 degrees unfortunately. [...]
Using that plotter and extrapolating a bit, ACBb may have held on to xenon, even CO2 and N2.

Thanks! I'm not sure, but assuming this planet is roughly Venus-like in escape velocity it looks pretty good for CO2 but borderline for N2. So, it's at least plausible for this planet to have a CO2 atmosphere. That would be my dream atmosphere, anyway. ;) I have a lot of thoughts about atmospheric scooping of CO2 as a general purpose raw material. Conveniently, we have two planets nearby to exploit using this technology, and it would be awesome if atmospheric scooping factory probes could be used more or less off-the-shelf for an Alpha Centauri mission.


CHEMISTRY OF SILICATE ATMOSPHERES OF EVAPORATING SUPER-EARTHS
Laura Schaefer and Bruce Fegley

Thanks for the link that looks interesting. A quick look at it: notice the y-axis is in molecules per sq cm of surface. At the lower temperatures, when you work it out, there are micromoles per sq cm of surface. This is almost a vacuum.

So basically, too cold for a significant sodium or silicate atmosphere.

Bearing in mind that atmospheric scooping would involve plowing through the atmosphere at orbital speeds, so you don't need something as thick as Mars's atmosphere--but there's still such a thing as too thin.

chornedsnorkack
2012-Oct-19, 08:36 PM
http://iopscience.iop.org/1538-4357/703/2/L113/fulltext/apjl_703_2_113.text.html

This study involved hot super-Earths, with the assumption that the usual lightweight volatiles have all been baked away already.



Not quite safe assumptions:

Given the extreme heating experienced by many super-Earths, we consider here the nature of atmospheres that may be produced if a super-Earth is volatile (e.g., H, C, N, S)-free.
CO is volatile (vapour pressure 1 bar at -180 degrees), and so is CO2 (-78 degrees).

C is not - vapour pressure 1 bar at about 3800 degrees.
Less volatile than Si (3300 degrees), SiO (1880 degrees), SiO2 (2230 degrees), Al2O3 (2980 degrees), Al (2520 degrees), MgO (3600 degrees), CaO (2850 degrees), Ti (3290 degrees), TiO2 (2970 degrees), Fe (2860 degrees) or FeO (3410 degrees)

Garrison
2012-Oct-19, 09:49 PM
The planet itself is interesting but I'm wondering just how likely it is that there are others around Alpha Centauri in more congenial orbits? Is it fair to say that at the least where there's one planet there are likely others?

eburacum45
2012-Oct-20, 08:28 AM
The chances are that any CO2 or H2O would be lost early in the history of this planet, so that there might not be much of either species left to freeze out, even if the antisolar point is cold enough to support ice (which is possible).

If the planet has any respectable atmosphere at all, the three-day spin would distribute heat quite well, so to have a cold spot it would need to be nearly as airless as Mercury.

eburacum45
2012-Oct-20, 09:19 AM
Just to show how extreme the environment is on this planet, here is a comparison between the local stellar disk as seen from Earth, Mercury and Alpha Centauri Bb
http://www.orionsarm.com/im_store/tolimanb.jpg
Admittedly the B star is slightly less bright than the Sun, but at that distance it would still be extraordinarily bright.

kzb
2012-Oct-20, 04:44 PM
Isaackuo, surely we expect the escape velocity of ACBb (is it "PH1" now ?), to be significantly higher than Venus, and actually higher than that of Earth?

eburacum45 wrote:
The chances are that any CO2 or H2O would be lost early in the history of this planet

Maybe, but I don't think it is a certainty. This planet more than likely was formed further out than it is now. On the other hand, there are reasons to think the AC system planets would be pretty dry anyway. There's no gas giants to throw comets inwards, and anyway there are no comets to throw in.

chornedsnorkack
2012-Oct-20, 04:50 PM
On the other hand, there are reasons to think the AC system planets would be pretty dry anyway. There's no gas giants to throw comets inwards, and anyway there are no comets to throw in.
On the other hands, there are the stars themselves - AB pair and Proxima - perturbing comet orbits.

Kullat Nunu
2012-Oct-21, 02:22 AM
The planet itself is interesting but I'm wondering just how likely it is that there are others around Alpha Centauri in more congenial orbits? Is it fair to say that at the least where there's one planet there are likely others?

It is! At least according to Kepler results, small planets tend to be in multi-planet systems. There could be several more Earth-size planets further out, but their detection is too difficult for now.

Jovians however are unlikely around any of the Alpha Centauri stars.

Kullat Nunu
2012-Oct-21, 03:56 AM
On the other hand, nature seems to prefer compact systems instead of sparse ones like ours. Therefore I see the detection of Alpha Centauri Bb both very exciting and worrying...

publiusr
2012-Oct-21, 08:46 PM
Something I was thinking of in terms of an extrasolar mission. This hell world may be pretty dismal, but the location of so many large objects near each other in this system allows for novel gravity assists, or so one would think.

Now solar probe + is supposed to dump all kinds of momentum off at Jupiter to free fall to our Sun. With Three stars and an Earth Sized planet, you have perhaps mulitple opportunities to slow down.

Hornblower
2012-Oct-21, 08:55 PM
On the other hand, nature seems to prefer compact systems instead of sparse ones like ours. Therefore I see the detection of Alpha Centauri Bb both very exciting and worrying...

Excitement, yes, but why worrying?

Noclevername
2012-Oct-21, 09:13 PM
On the other hand, nature seems to prefer compact systems instead of sparse ones like ours. Therefore I see the detection of Alpha Centauri Bb both very exciting and worrying...

Compact systems are easier to detect using our current observational methods. We can see what's large and close enough to dim the star during transit, or what's massive enough to move the star, or what's hot enough or brightly lit enough to be visible across interstellar distances, or what's fourtunate enough to be in exactly the right position to spot with gravitational lensing.

Kullat Nunu
2012-Oct-22, 02:12 AM
Excitement, yes, but why worrying?

Well, Alpha Cen B system could turn up being yet another compact system with only hot terrestrials. Also, the discovery strengthens the impression that our Solar System seems to be quite atypical planetary system.

Kullat Nunu
2012-Oct-22, 02:14 AM
Compact systems are easier to detect using our current observational methods. We can see what's large and close enough to dim the star during transit, or what's massive enough to move the star, or what's hot enough or brightly lit enough to be visible across interstellar distances, or what's fourtunate enough to be in exactly the right position to spot with gravitational lensing.

That is of course true, there are several factors which makes the detection of close-in systems much easier.

Hornblower
2012-Oct-22, 02:27 AM
Well, Alpha Cen B system could turn up being yet another compact system with only hot terrestrials. Also, the discovery strengthens the impression that our Solar System seems to be quite atypical planetary system.

I still don't see what there is to worry about.

chornedsnorkack
2012-Oct-22, 08:31 AM
Solar System is not atypical - merely inconspicuous. The radial velocity method simply detects hot Jupiters best, followed by hot Uranuses and super-Mercuries.

Just because we see the super-Mercury on Toliman B does not mean that the system does not also have Earth like or Mars like planets we simply cannot detect.

kzb
2012-Oct-22, 11:47 AM
Yes, my understanding is that Earth wouldn't have been detected yet, and that is by any method.

If anyone has not seen this paper before, it is interesting to see the prediction versus the facts:

Formation and Detectability of Terrestrial Planets around alpha-Centauri B Guedes et al 2008 (there's no pay wall):

http://iopscience.iop.org/0004-637X/679/2/1582

If you look at their Table 1 (p. 12), you'll notice that Bb does not feature in any of their model outcomes. But Earth mass planets within the habitable zone feature heavily.

So that could be slightly worrying, in that this model predicted a high probability of Earths, but no Bb. So maybe that model is flawed and its prediction of Earths in the HZ will also turn out to be wrong. Time will tell.

kzb
2012-Oct-22, 12:30 PM
On the other hands, there are the stars themselves - AB pair and Proxima - perturbing comet orbits.

Yes true enough, but I read somewhere that AC apparently doesn't have an Oort Cloud. There's an "on the other hand" to that argument also: the the idea that a lot of Earth's volatiles were delivered by asteroids, not comets. So I guess it is still on the cards that some water, ammonia et al were delivered to Bb, but the hydrogen part of the molecule at least is long gone.

When you think that Bb surely must be very volcanic, and all the sulfur and its compounds that come out of volcanoes on Earth (and Io and Venus), surely this element must feature heavily in the Bb atmospheric composition (if it has an atmosphere of course).

George
2012-Oct-22, 01:53 PM
Yes true enough, but I read somewhere that AC apparently doesn't have an Oort Cloud. "Absense of evidence is not evidence of absense". I think they simply have not detected an Oort cloud, but I don't think our Oort cloud has been directly observed either, though indirect evidence exists.

Kullat Nunu
2012-Oct-22, 03:56 PM
I don't think our Oort cloud has been directly observed either, though indirect evidence exists.

That is true, the existence is based on the distribution of orbits of long period comets.

Kullat Nunu
2012-Oct-22, 03:59 PM
Solar System is not atypical - merely inconspicuous. The radial velocity method simply detects hot Jupiters best, followed by hot Uranuses and super-Mercuries.

Just because we see the super-Mercury on Toliman B does not mean that the system does not also have Earth like or Mars like planets we simply cannot detect.

I know, and I really hope that is the case here. But (1) this planet has clearly migrated, which suggests other planets may have done that too and (2) if you're been following Kepler results, more "normal" planetary systems with terrestrials in wide orbits don't seem to be as common as anticipated based on initial results (though this may be an artifact due to higher than expected noise).

Jens
2012-Oct-23, 08:54 AM
I've read the ESO page (or I did yesterday), both before and after you suggested I do so. They seem to be ecstatic and give no hint of reservation about the findings.

Researchers can sometimes appear ecstatic and fail to express reservations about things that later turn out not to be true. The problem is partly that the press wants stories that are expressed as certainty, not with reservations. I mean this as a general phenomenon, not something in this specific case.

kzb
2012-Oct-23, 12:01 PM
"Absense of evidence is not evidence of absense". I think they simply have not detected an Oort cloud, but I don't think our Oort cloud has been directly observed either, though indirect evidence exists.

I read previously that our Oort cloud originated from our gas giants throwing material outwards during the early days of the solar system. I suppose the reasoning was then Alpha Centauri-no gas giants- therefore no AC Oort cloud.

But I now see that an alternative origin for most of the Oort cloud objects is that they were stolen from neighbouring star's accretion disks when the sun first formed in its birth cluster. That being the case, I suppose there's no reason why AC should not have an Oort cloud.

That's all the more reason not to give up on the idea that Bb might have some kind of atmosphere, consisting of heavy gases and inert gases like krypton and xenon. These could've been delivered as ices and persisted to this day.

IsaacKuo
2012-Oct-23, 12:11 PM
That's all the more reason not to give up on the idea that Bb might have some kind of atmosphere, consisting of heavy gases and inert gases like krypton and xenon. These could've been delivered as ices and persisted to this day.
If those Oort cloud objects are anything like our comets, they don't have any krypton or xenon in solid ice form--but they do have a lot of water ice.

Given the examples of the Moon and Mercury, I'd expect insignificant amounts of atmospheric krypton/xenon, but plenty of water to deliver water ice to the dark side (if tide locked).

Hornblower
2012-Oct-23, 12:21 PM
As I see it, the popular media could have extra-scientific gut excitement about it when it is scientifically no more important than a similar discovery around a similar star much farther away.

George
2012-Oct-23, 02:06 PM
As I see it, the popular media could have extra-scientific gut excitement about it when it is scientifically no more important than a similar discovery around a similar star much farther away. Yep. The gut factor is likely the fact that Alpha Centauri is both our closest neighbor and the two main stars are within 10% of our Sun's mass. But I wonder if the level of excitement is age related since so many of the early Sci Fi books fired our imaginations by using our neighboring star system? Do Sci Fi authors use Alpha Centauri as they once did? It seems to me they are not, but I am not an avid reader.

George
2012-Oct-23, 02:23 PM
I read previously that our Oort cloud originated from our gas giants throwing material outwards during the early days of the solar system. I suppose the reasoning was then Alpha Centauri-no gas giants- therefore no AC Oort cloud. That seems reasonable. I wonder how far a gas giant can be from either star before instability is created by the binary? Of course, both stars (ignoring Proxima) are gas giants. :) Can one or both spit out an Oort cloud during the early days?

I think it is hard to recognize just how difficult it is too see objects in the Oort cloud. Reflected light from the Sun off these distant objects varies as the inverse 4th power of distance from us. Jupiter, for example, would vanish from the HST view if it were moved to only about 10,000 au. [It would be seen in IR, however.]

IsaacKuo
2012-Oct-23, 02:50 PM
As I see it, the popular media could have extra-scientific gut excitement about it when it is scientifically no more important than a similar discovery around a similar star much farther away.
It is more important than a similar discovery around a similar star much farther away. There are numerous possible methods of sending an interstellar mission at relativistic speeds, but they all share one aspect--they could all get to Alpha Centauri far more quickly than Gliese 876.

The fact is, Alpha Centauri is irresistably the juiciest scientific target for a first interstellar mission. It's the only place vaguely nearby which lets us visit both a red dwarf--the most common type of star, and two sun-like stars. It's three for the price of one, and it also happens to be the closest target by a good margin!

But if Alpha Centauri had no planets? In that case, there would be an unfortunate trade-off between a quicker easier mission to a system with interesting stars but no planets, vs a longer harder mission to a system with just one star but planet(s).

Now? There is no trade-off necessary. Alpha Centauri is easily the best of all interstellar mission targets, no question. And it happens to be the closest one around, also!

Swift
2012-Oct-23, 03:09 PM
Do Sci Fi authors use Alpha Centauri as they once did?
The movie Avatar takes place in the Alpha Centauri system. So the answer is yes.

antoniseb
2012-Oct-23, 03:26 PM
It is more important than a similar discovery around a similar star much farther away. ...

I agree. I expect that we are 50 to 200 years away from having the technology to a degree that it is politically possible to get the money together for a 100-300 year long (i.e very delayed payoff) robotic expedition to explore the stars and planets of Alpha Centauri up close. We're much further (time-wise) from a similar mission to a place eight times as far away... without the planets, it would probably be yet another century before we'd consider such a mission.

Kullat Nunu
2012-Oct-23, 03:58 PM
It is more important than a similar discovery around a similar star much farther away. There are numerous possible methods of sending an interstellar mission at relativistic speeds, but they all share one aspect--they could all get to Alpha Centauri far more quickly than Gliese 876.

Not to mention that possible planets would be much easier to study as long as the interference from the bright stars can be eliminated...

kzb
2012-Oct-23, 05:00 PM
If those Oort cloud objects are anything like our comets, they don't have any krypton or xenon in solid ice form--but they do have a lot of water ice.

How did we get our krypton and xenon? If even our water had to be delivered later, surely the more volatile and much less chemically reactive Kr and Xe did? (I can tell you from bitter experience just how hot minerals have to get before you have driven off all the water !)

I can understand where we got most of our argon: from K-40 decay. This mechanism should also have supplied Bb with argon, but Ar looks a bit too light to be retained at these temperatures.

IsaacKuo
2012-Oct-23, 07:43 PM
How did we get our krypton and xenon?
We don't have much krypton and xenon. It's just trace amounts. If krypton and/or xenon are the main components of this hypothetical "atmosphere", it wouldn't be thick enough to seriously threaten deposits of water ice on the dark side. (Again, assuming tide lock.)

George
2012-Oct-23, 08:39 PM
The movie Avatar takes place in the Alpha Centauri system. So the answer is yes. Thanks. I think I remember smiling when I heard that mentioned in the movie, now that you reminded me about it.

Don Alexander
2012-Oct-23, 11:46 PM
I daresay Alpha Centauri is important far beyond any pipe dreams of interstellar travel. It's the nearest planetary system, the stars are extremely bright, yielding high signal to noise even with short integration times. If this planet transits, it would be an incredible bonanza.

IF IT EXISTS. Which seems doubtful.

Swift
2012-Oct-24, 12:23 AM
IF IT EXISTS. Which seems doubtful.
Is that your interpretation of the data? As a professional in the field, and the starter of this thread, I am curious about your opinion on this. Could you elaborate, for those of us who have not read the paper?

StupendousMan
2012-Oct-24, 11:46 AM
Those who don't have time to read the original paper

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

might look at a very quick summary which includes figures from the paper

http://spiff.rit.edu/classes/phys200/lectures/alpha_cen/alpha_cen.html

kzb
2012-Oct-24, 11:47 AM
We don't have much krypton and xenon. It's just trace amounts. If krypton and/or xenon are the main components of this hypothetical "atmosphere", it wouldn't be thick enough to seriously threaten deposits of water ice on the dark side. (Again, assuming tide lock.)

Agreed there are only trace amounts of Kr and Xe. I don't see how they threaten deposits of water ice on the dark side, quite the reverse. The reasoning was, if on Earth, much cooler than Bb of course, we have to hypothesise that most water was delivered to the planet after its formation, then how much more true this would be for Kr and Xe. In other words, if the part of the disk that formed Earth was too warm for water to exist, it surely must have been too warm for these inert gases also. What we have must've been delivered by comets and maybe asteroids.

I'm not necessarily saying these are the major part of any atmosphere on Bb. I'm just saying there does not seem any reason for them not to be there, and in similar amounts to on Earth. Even in these small amounts, there is still much more of them than SiO2 gas or whatever was in that paper.

I'm sure this is a fantasy, but when you think about it, Bb could even have an oxygen/nitrogen atmosphere, with liquid water somewhere around the day side/dark side transition zone. The oxygen and nitrogen come from photolysis of water and ammonia delivered from comets, with loss of hydrogen due to the high temperature. Although water is being consumed, there is such a huge pile of it frozen on the dark side, that not all the water has gone yet.

What was that Van Diesel film, the planet where there was a hot wind at sunrise, which incinerated everything in its path? That could be Bb....

Swift
2012-Oct-24, 02:22 PM
Those who don't have time to read the original paper

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

might look at a very quick summary which includes figures from the paper

http://spiff.rit.edu/classes/phys200/lectures/alpha_cen/alpha_cen.html
Thanks StupendousMan, that summary was excellent.

I'm not an astronomer, but I deal with data all the time. Yeah... that's pretty thin, and the last graph, with the actual data after all the subtractions and the fit is pretty ugly. I would have to agree that I'm pretty far from convinced.

Don Alexander
2012-Oct-24, 04:14 PM
Is that your interpretation of the data? As a professional in the field, and the starter of this thread, I am curious about your opinion on this. Could you elaborate, for those of us who have not read the paper?
I'm actually not a professional in THIS exact field, but I'm conveying the opinion of at least one person who IS a professional in the field...

The thing is, as you state yourself, the evidence is pretty thin. The final RV plot does not look too bad if you consider the binned data, but remember, the shape of the binned data curve depends on the period, and that has to be measured from the raw data, which shows incredible scatter. Once you put in 3.2something days, then bin, yeah, it looks pretty good, but what would it look like if the period was taken to be two days, or five? Could you get a similar nicely binned plot with other periods?

With the huge amount of modeling they did to remove all the contaminating effects, one does wonder if they might not have underestimated the systematics somewhere along the line. Finding a planet around Alpha Centauri is for sure a great discovery, and they put an enormous effort into it... With so much effort, and so much at stake, it is not astonishing that they actually do think they found something...

Anyway, it seems an American team has also been obtaining data, from Magellan or so?? Let's see what that data says. Also, I'm hoping maybe MOST can be trained on A Cen B and try to detect a transit. Even if it rules out a transit, that gives a lower limit on the sin i, implying the planet has to be a bit more massive than claimed.

@Kzb: The Chronicles of Riddick. I love that movie, but the planet (Crematoria) is sooo terribly unrealistic... Anyway, it's not tidally locked, and A Cen Bb assuredly would be.

chornedsnorkack
2012-Oct-24, 04:22 PM
A planet notorious for being nearest AND for not having got CONFIRMED is that of Barnardīs Runaway, after all.

Noclevername
2012-Oct-24, 06:34 PM
@Kzb: The Chronicles of Riddick. I love that movie, but the planet (Crematoria) is sooo terribly unrealistic...

It could have the chemistry of an Oxygen Candle (http://en.wikipedia.org/wiki/Chemical_oxygen_generator#Oxygen_candle), with O2 released from the rocks by heat, then re-oxydized at night. (I know, I'm putting more thought into it than the filmmakers did.)

George
2012-Oct-25, 01:24 AM
....might look at a very quick summary which includes figures from the paper

http://spiff.rit.edu/classes/phys200/lectures/alpha_cen/alpha_cen.html
Thanks for that helpful explanation. I wonder what the sigma value is for such a scatter?

kzb
2012-Oct-25, 12:02 PM
@Kzb: The Chronicles of Riddick. I love that movie, but the planet (Crematoria) is sooo terribly unrealistic... Anyway, it's not tidally locked, and A Cen Bb assuredly would be.

Maybe we can fantasize that Bb is in a spin-orbit resonance. However, if you imagine that, it then could not have the dark-side ices feeding its oxygen atmosphere...but then again we could still have the "oxygen candle"....

Onwards...
I've been trying to find more about the chemical composition of the AC system. I know already that it is enriched in iron and magnesium relative to the sun, but if we had more detail it might drive the discussion forward.

If you look at the link below, you will see there was a presentation on this very topic by Charles Lineweaver at the 9th Australian Space Sciences Conference in 2009:

Starlight reveals chemistry of planets
http://www.cosmosmagazine.com/news/3056/stars-light-reveals-chemistry-planets

Quote:
...the chemical compositions of extrasolar rocky planets can be estimated from the spectra elemental abundances of their host stars, the researchers argue.

But I'm unable to find any text or publication from this study. The conference proceedings are here, but they don't include this presentation. Anyone seen this?

http://www.nssa.com.au/9assc/downloads/9assc-proceedings-lores.pdf

neilzero
2012-Dec-05, 04:43 AM
The planet is perhaps 1500 k near the center of the hot side (assuming tide lock) but the always dark side could be 200 k to 300 k which would tolerable for advanced beings similar to humans. Ice could be mined for water. Rarely Centari A would be tiny, but about as bright as our full moon, but lighting is not difficult, even for photosythesis. Perhaps as much atmosphere as Mars, but some oxygen, nitrogen, water vapor as well as carbon dioxide. Steam can be made just barely on the sun lit side (near sunshine terminator) and the turbine condencer can be in the shade of a mountain, so possibly energy is abundent. Not pleasent, but livable.
Some compounds decompose at 1500k or less. Possibly volitiles will condence out just inside the dark side, such as water. Elements that vaporize significantly between 300k and 1500 k are typically chemically active and would form compouds with the stuff I suggested for the atmosphere, so I don't think free alkali metals, or hydrocarbons if there is an atmosphere of significance.
I read Centari A in wikipedia including the talk page = much like this thread. I agree, near zero chance intelegent beings can evolve on the dark side assuming tide locked, but sufficiently advance colonists can likely form a dependent colony almost anywhere. Neil

kzb
2012-Dec-05, 12:54 PM
The planet is perhaps 1500 k near the center of the hot side (assuming tide lock) but the always dark side could be 200 k to 300 k which would tolerable for advanced beings similar to humans. Ice could be mined for water. Rarely Centari B would be tiny, but about as bright as our full moon, but lighting is not difficult, even for photosythesis. Perhaps as much atmosphere as Mars, but some oxygen, nitrogen, hydrocarbons, water vapor as well as carbon dioxide. Steam can be made just barely on the sun lit side (near sunshine terminator) and the turbine condencer can be in the shade of a mountain, so possibly energy is abundent. Not pleasent, but livable.
Some compounds decompose at 1500k or less. Possibly volitiles will condence out just inside the dark side, such as water. Elements that vaporize significantly between 300k and 1500 k are typically chemically active and would form compouds with the stuff I suggested for the atmosphere, so I don't think free alkali metals, or hydrocarbons if there is an atmosphere of significance. Neil

It's certainly interesting to speculate isn't it ! (I think you mean Centauri A, not B. It wouldn't provide enough illumination for useful photosynthesis on the dark side of Bb unfortunately.)

If there is some sort of atmosphere on Bb, there could be a thin strip of terminator zone where the illumination level is about right. Imagine, there is permanent cloud in the atmosphere in this region due to volatile compounds from the hot side circulating back to the cold side, and condensing as cloud in the terminator zone. In this zone, the light reflected off clouds could give us a comfortable level of insolation, and also in the correct range for plant growth.

I think we have to concede though, that any atmosphere is not going to be of the correct composition for Earth life. Colonies would have to be under transparent domes or something.