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PhilCo126
Well-known exoplanet researcher Dr Michel Mayor ( discoverer of Peg 51b with Dr Didier Queloz in 1995 ) today announced the discovery of the lightest exoplanet found so far. The planet, “e”, in the famous system Gliese 581, is only about twice the mass of our Earth. The team also refined the orbit of the planet Gliese 581 d, first discovered in 2007, placing it well within the habitable zone, where liquid water oceans could exist:
http://www.eso.org/public/outreach/press-r...9/pr-15-09.html

belleraphon1
32 New Exoplanets Found - 10/19/09 ESO release

"Today, at an international ESO/CAUP exoplanet conference in Porto, the team who built the High Accuracy Radial Velocity Planet Searcher, better known as HARPS, the spectrograph for ESO's 3.6-metre telescope, reports on the incredible discovery of some 32 new exoplanets, cementing HARPS's position as the world’s foremost exoplanet hunter. This result also increases the number of known low-mass planets by an impressive 30%. Over the past five years HARPS has spotted more than 75 of the roughly 400 or so exoplanets now known"

http://www.eso.org/public/outreach/press-r...9/pr-39-09.html

From searching Extrasolar Planets Encyclopedia catalog I find 6 of the new planets seem to be Neptune mass or less.
http://exoplanet.eu/catalog-all.php?&m...de=-7&more=

BD-082823b at .045 Jmass
GJ 433b at .019 Jmass
GJ 667Cb at .018 Jmass
HD 1255995b at .045 Jmass
HD 215497b at .017Jmass
HD 90156b .055Jmass

Craig
Julius
How can they be so sure that the super earths detected represent one planetary body ie.could it not be that 8 earth masses could represent 2 terrestrial planets and other planetary dust the likes of asteroids in orbit round the parent star?!
qraal
QUOTE (Julius @ Oct 20 2009, 10:10 PM) *
How can they be so sure that the super earths detected represent one planetary body ie.could it not be that 8 earth masses could represent 2 terrestrial planets and other planetary dust the likes of asteroids in orbit round the parent star?!


Because the radial velocity detection method detects a periodic signal that only a planet can cause - though some data is too patchy to be sure we're seeing one planet and not two. A diffuse asteroid belt would produce a symmetric 'tug' on the star it orbits, thus producing no radial velocity signal.
Greg Hullender
There's a branch of mathematics called "Fourier Analysis" which, among other things, let's you take a complex signal and break it into a collection of sine waves. It's pretty cool, if you haven't seen it before.

So if there's just one planet, then the velocity plot ought to be a pretty clean simple sine wave over time. If there are multiple planets (let's say three) around the same star, then it'll be a mess, but a fourier analysis ought to result in just three sine curves and very little else.

--Greg

tfisher
QUOTE (Greg Hullender @ Oct 20 2009, 02:47 PM) *
So if there's just one planet, then the velocity plot ought to be a pretty clean simple sine wave over time. If there are multiple planets (let's say three) around the same star, then it'll be a mess, but a fourier analysis ought to result in just three sine curves and very little else.


I'm afraid this skips over a few important complexities. One is that with eccentric orbits (which are common!), the radial velocity signal of a planet is not a single sine wave, but may have significantly different shape. Another problem is that in reality we never have continuous or even a complete discrete series of radial velocity observations of a given target. Instead of seeing a continuous curve, we just have a non-uniformly spaced discrete sampling from the curve. So Fourier analysis can't really be directly applied to work out the component curves. A third problem is that there is a lot of noise in the observed radial velocities, coming from stellar activity of the host star and limitations of the observation instruments. In many cases (smaller, more distant planets or younger, more active stars) this noise is of a similar or even much greater strength to the signals we are looking for.

You can get a really good understanding of all of this playing with the amazing "systemic console" free tool for fitting candidate planetary systems to radial velocity datasets. You can get this at oklo.org. I highly recommend it!
Greg Hullender
QUOTE (tfisher @ Oct 21 2009, 05:30 PM) *
I'm afraid this skips over a few important complexities.

Fair enough. I still maintain that a Fourier Transform would work fine for a system whose planets had circular orbits and ought to be a great way to eliminate the high-frequency noise in any case, but, yeah, I agree it won't be very good for elliptical orbits.
QUOTE (tfisher @ Oct 21 2009, 05:30 PM) *
You can get a really good understanding of all of this playing with the amazing "systemic console" free tool for fitting candidate planetary systems to radial velocity datasets. You can get this at oklo.org. I highly recommend it!

This is pretty cool. Without actually downloading the program, is there a link to a document that describes the actual algorithms they're using? From what I could glean from their blog, it could be anything from Expectation Maximization to Markov Chain Monte Carlo.

Thanks!

--Greg
Hungry4info
QUOTE (Greg Hullender @ Oct 21 2009, 08:26 PM) *
This is pretty cool. Without actually downloading the program, is there a link to a document that describes the actual algorithms they're using? From what I could glean from their blog, it could be anything from Expectation Maximization to Markov Chain Monte Carlo.
There's a paper describing Systemic in such level of detail here.
http://arxiv.org/abs/0907.1675
Greg Hullender
QUOTE (Hungry4info @ Oct 22 2009, 04:33 AM) *
There's a paper describing Systemic in such level of detail here.
http://arxiv.org/abs/0907.1675

Excellent! Thank you very much!

This paper's a pretty good read, if you've got the math for it, and offers a very comprehensive answer to the original question. A point they mentioned that I hadn't thought about before is that they don't yet make relativistic corrections, which actually ought to matter considering how many of these planets are in very close orbits. It'll be fun to see what happens once they start to get their hands on the Kepler data.

--Greg
imipak
'Spherical cow' now has it's very own Wikipedia entry smile.gif
PhilCo126
Team of Astronomers using Japanese Subaru Telescope at Mauna Kea - Hawaii makes major discovery: GJ 758 B


http://www.princeton.edu/main/news/archive...tion=topstories
Hungry4info
I'm quite unsure as to why this is being made into such a big deal. The mass of the two objects are quite unconstrained (and in the case of c, it's not even known for sure if it's bound to the system). Even the minimum mass of 10 M_J for B is so high that it's hard to say for sure that this object would be a planet. Also, another object like this was imaged at 1RXS J160929.1-210524 with a mass of 8 M_J, but it's unknown if the object is bound to the system.
centsworth_II
QUOTE (Hungry4info @ Dec 5 2009, 11:00 PM) *
I'm quite unsure as to why this is being made into such a big deal....
I'm not surprised that a site titled "News at Princeton" would make a big deal of any new discovery involving a Princeton scientist. How big a deal anyone else makes of it is up to them.

It is the first discovery of a new instrument and validates its usefulness in imaging sub-stellar objects orbiting stars. That seems pretty exciting to me. Isn't this just the second time such a feat has been accomplished?
ngunn
On a different topic, I've not noticed discussion here of the planets/lithium anticorrelation announced a few weeks back.
http://www.eso.org/public/outreach/press-r...9/pr-42-09.html

Thinking about what could create a planetary system and also flush a star clean of lithium led me to the idea of a self-ejecting supernova companion. A little digging tracked that idea back 65 years to Fred Hoyle and it seems to have been seriously considered by at least some astronomers in the intervening time. It appears towards the end of this free sample page:
http://resources.metapress.com/pdf-preview...mp;size=largest

Any thoughts?
Hungry4info
QUOTE ("centsworth_II")
Isn't this just the second time such a feat has been accomplished?


Maybe not the second, if you count 51 Sagittae B (first brown dwarf discovered around a sun-like star, in 2002, directly imaged) and 54 Piscium B (from 2006, also directly imaged). Spectral types G1V and K0V, respectively, with true masses of ~50 M_J for both objects. But I can see why such a high mass would cause these sub-stellar companions to be sort-of ignored. I guess it all depends on perspective. Epsilon Indi also has a pair of imaged brown dwarfs.

ngunn,

According to recent papers on the current theories, which the authors admit are incomplete, tidal interactions of a planet with its host star allow mixing of the stellar interior. This lets lithium descend deeper into the star than possible without the presence of a planetary companion. The lithium gets roasted alive and no longer shows up in stellar spectra.

The lithium anti-correlation is only applicable to a very narrow temperature range of about 100 K on either side of the temperature of Sol. M, K, F and A stars do not seem to have this trend (the population of planets around A stars is mostly inferred from the detection of planets around stars that have evolved and cooled to become cool giant stars, while too few planets are known to exist around OB stars).

Interestingly, sun-like stars with close stellar companions do not seem to have this anti-correlation. If stellar mixing is the cause, then one would expect stellar companions would do better at that than planetary companions. The orbits of close stellar companions are statistically indistinguishable from the orbits of planetary companions.

Another idea is that a star will magnetically interact with its protoplanetary disk and somehow allow the lithium to be transported deeper into the star and destroyed that way.
ngunn
Yes I noticed the range of hypotheses offered, but they seem to focus on how A might cause B and sound a bit convoluted. I just think Hoyle's blast-your-neighbour-and-scram idea is more exciting, and it could neatly provide a single cause for both A and B.

QUOTE (Hungry4info @ Dec 6 2009, 02:26 PM) *
Interestingly, sun-like stars with close stellar companions do not seem to have this anti-correlation.


Well they wouldn't, would they? Their companions haven't exploded. smile.gif
Hungry4info
Of course it's more exciting, but only in the "All stars are actually anti-matter/matter reaction driven" sort of sense. There's no reason to support it, and there's already other ideas that better explain what is observed.

Planet hosts are lithium poor. Planets not known to have stars are lithium rich.
(anti)correlation has something to do with planets (or planet formation).

This trend only shows up for stars within +/- 100 K of Sol's effective temperature.
(anti)correlation has something to do with the structures of stars +/- 100 K of Sol's effective temperature.

Even in our solar system, the planets (or the process of their formation) were able to cause Sol to become lithium poor. There is no evidence for any of our planets having exploded in the past.

Does the idea of a exploding companions explain why only near-stellar Teff stars display this correlation?
Does it explain why binary stars in the same temperature range do not?
Is there any evidence for planetary companions blasting their neighbors and screaming?

Consider the 16 Cygni system. Two sun-like stars: the lithium-poor star hosts a planet. The lithium-rich star hosts an M-dwarf.
ngunn
QUOTE (Hungry4info @ Dec 6 2009, 05:07 PM) *
1 (anti)correlation has something to do with planets (or planet formation).

2 (anti)correlation has something to do with the structures of stars +/- 100 K of Sol's effective temperature.

3 There is no evidence for any of our planets having exploded in the past.

4 Is there any evidence for planetary companions blasting their neighbors and screaming?


1 - Agreed.
2 - Agreed.
3 - I didn't say that, and neither did Fred Hoyle. The explosion would have predated (and lead to) planet formation.
4 - I didn't say 'scream' either(!) I said scram, as in 'rapidly leave the area'.

There has also been quite a lot written over the years about the trauma to a close companion star when a supernova occurs, and about binaries becoming unbound following stellar explosions. I don't think it's far fetched to imagine that the trauma might involve lithium destruction for certain classes of star but not others.

16 Cygni B is around 1000AU from the AC pair, maybe far enough for a supernova to destroy the lithium in one but not the other.

There may be better theories as you say, but as you also say they are not complete and there is no clear winner yet so I don't think broader speculation is out of order at this stage.
scalbers
I guess we can mention GJ1214b and the MEarth project in this thread...

http://arxiv1.library.cornell.edu/abs/0912.3229

http://en.wikipedia.org/wiki/GJ_1214_b
PhilCo126
Keck telescopes on Mauna Kea - Hawaii discovered 2nd smallest exo-planet HD156668b at 80 light years in the constellation Hercules
http://spacefellowship.com/news/art17807/s...anet-found.html
Mongo
I will charitably assume that the reporters left out the bolded part: 2nd smallest exoplanet discovered by radial velocity variations.

I count at least 5 smaller exoplanets, one of which was discovered by radial velocity variations.
belleraphon1
Agreed Mongo...

Go to Extrsolar Planets Encyclopedia catalog http://exoplanet.eu/catalog-all.php and sort by Mass you will find the three pulsar planets, MOA-2007-BLG-192-L-b (microlensing find) and GJ581e (the smaller of the RV finds).

Actually I think the discovery of GJ1214b is far more exciting. Close enough we can learn things about it's atmosphere from current space telescopes. GO MEarth team!!!

Craig
ngunn
There is nothing like new data for shaking things up. smile.gif

http://www.sciencedaily.com/releases/2010/...00413071749.htm
Ron Hobbs
The VLT has taken pictures of a planet orbiting beta Pic.

"For the first time, astronomers have been able to directly follow the motion of an exoplanet as it moves from one side of its host star to the other. The planet has the smallest orbit so far of all directly imaged exoplanets, lying almost as close to its parent star as Saturn is to the Sun. Scientists believe that it may have formed in a similar way to the giant planets in the Solar System. Because the star is so young, this discovery proves that gas giant planets can form within discs in only a few million years, a short time in cosmic terms."

Exoplanet Caught on the Move

I want to give a shout out to the folks at ESO; they provide some really cool graphics of their discoveries.
remcook
Doing observations from the ground can have its advantages... smile.gif

http://news.bbc.co.uk/2/hi/science_and_env...nt/10393633.stm
Drkskywxlt
Confirmation of the first directly imaged planet around a sun-like star thanks to Gemini. An 8Jup-mass planet at over 300AU!
http://www.space.com/scienceastronomy/firs...med-100629.html
ustrax
It's extragalactastic! biggrin.gif
http://www.eso.org/public/news/eso1045/
ustrax
500! and 2... biggrin.gif
Wow! And to think that we just opened our eyes in 1988...what's ahead? smile.gif
remcook
Well, finally that mysterious DPS presentation got cleared up
http://www.jpl.nasa.gov/news/news.cfm?rele...mp;auid=7439932
High density atmosphere or clouds on super-Earth GJ1214b
ngunn
Free floating planets found by microlensing: http://science.nasa.gov/science-news/scien..._orphanplanets/

Food for WISE is probably out there. Go get 'em WISE!
TheAnt
Some years ago we were given the impression that quite some stellar systems had hot Jupiters. That turned out to be an observational bias since such planets are easy to detect.
But such systems have been found again in quite a number in a study where HARPS were the main instrument though also Hubble and a few others were used.
It appear that in the open star cluster M67 about one out of twenty stellar systems have a hot Jupiter.


(Sorry for awakening this very old thread. But I were once asked by a moderator not to start to many new topics.)
Explorer1
A Proxima Centauri planet!? ohmy.gif
http://phys.org/news/2016-08-scientists-un...ike-planet.html
No official confirmation or denial, but an announcement set for the end of August (if true!).
Translated Der Spiegel article that has source: https://translate.google.ca/translate?hl=en...amp;prev=search

Just hype, or something more?
Gerald
Seems, they found a hint to a small deviation of Proxima Centauri's trajectory close to the limits of statistical evidence.
The press tends to make a sensation of exciting preliminary hypotheses. So, let's wait, how statistically significant the findings actually turn out to be.
HSchirmer
Just noticed that Der Spiegel and other online sources are reporting a pre-announcement about a
a terrestrial planet with liquid water around alpha centauri...

Anybody hearing anything?
JRehling
Google searches limited to the last week show several results; this is one:

http://phys.org/news/2016-08-scientists-un...ike-planet.html

It is Proxima Centauri that is the host star; Proxima Centauri is believed to be part of the Alpha Centauri system, but it is quite remote from the other two and it is not certain that they are gravitationally bound. However, their distance from us is nearly equal.

Any discovery like this would be very exciting, but I'm quite sure that at this point, the only thing anyone could say about liquid water would be speculation based on the amount of insolation a planet receives; actually detecting liquid water would be a much harder feat.

I should say that Kepler data indicate that very roughly 8% of red dwarfs have Earth-sized planets in their habitable zone and roughly 8% have a Super Earth in their habitable zone… obviously this depends on definitions of HZ and the size bounds used. With a looser definition, the sum of those probabilities plus Mars-sized planets might climb over 50%. Which is to say: Without making any observations of Proxima Centauri, one could already saw that there's a good chance of a terrestrial planet with temperatures that could permit liquid water. One might even say that it's probable for each red dwarf. (Although this packs a lot of uncertainty into the "could permit liquid water" and definition of "terrestrial planet.") Furthermore, it seems nearly certain that one of the four or so closest red dwarfs should have a planet that meets those loose definitions.

I'll be eager to hear more, though. Proxima Centauri is the absolute easiest star in the universe for follow-up science on its planetary system. It would be a nice bit of luck if a candidate "earthlike" planet were there.
nprev
MOD MODE: Merged topic created for this alleged Proxima planet into this topic. There is absolutely no way that liquid water could have possibly been detected on this purported planet via the espoused (ground-based) discovery method. Media reports are spinning rapidly out of control. The characterization 'Earth-like" is inherently misleading; "Earth-sized" is much more plausible and accurate.

Furthermore, this is the same team that 'discovered' Alpha Centauri Bb, which was subsequently not confirmed. All these points should produce some healthy skepticism.

Bottom line is that this story is extremely speculative at this point--and therefore of extremely questionable quality as subject matter for UMSF. Discussion will be allowed using reputably sourced information, but not obvious sensationalism as seems to be the case for this thus far. This thread will be closed immediately if the discussion does not meet Forum standards.

"Extraordinary claims require extraordinary evidence"- Sagan's Law
JRehling
This is indeed a good time to invoke Sagan's Law.

The notion that Proxima Centauri might have a planet is not a wild one at all – in fact, it may be nearly certain that any given red dwarf have at least one planet. The remarkable claim is about how much it might be like Earth, and those words "might" and "like" are packed full of opportunities to be vague and say nothing meaningful.

Here are key statements from the Spiegel article:

• The research involved in this took place at the limit of what measurements technically feasible.
• The method used involved "variations in the motion of the star."

The second statement is ambiguous. The Doppler method that measures radial (towards or away from Earth) movement of the star has been one of the two most productive methods for discovering exoplanets. Another method – long-discussed, but never-yet successful – has been to look at how a star wobbles side-to-side. The Doppler method works equally well for stars that are far or near, whereas the wobble method would be more successful for close stars – and Proxima Centauri is the closest – than any other. The Doppler method is also blind to planets in orbits that we see face-on, whereas the wobble method would work just fine for those… if it works for any cases at all, which is not clear. Finding Earth-mass planets has been elusive even for the Doppler method, with the smallest so far confirmed having a mass of about 3.7 mass[Earth] with an uncertainty of about 0.7. When the uncertainty in one of the best cases is 0.7 mass[Earth], it gives you an idea of the hopelessness of determining that any subsequent discovery would be very close to 1.0 mass[Earth] without very large relative uncertainty.

The first statement is of paramount importance: If the results come at the limit of what is technically feasible, then they almost inherently contain uncertainty, which would mean that there could be doubt as to whether or not they detected a planet as opposed to noise, and if they did detect a planet, even if it happened to be very much Earth-sized and getting Earth-like amounts of sunlight, the measurements would have too large of an error for us to be confident about the nature of the planet yet.

Given what we know in general about exoplanet occurrence, it would be surprising if Proxima Centauri didn't have some planets smaller than Neptune orbiting it, and it wouldn't be surprising if it had one about the size of Earth and getting about that much sunlight… but "not surprising" is a long way from confirmed.
Explorer1
Presumably they wouldn't have published the article if they knew they would be embarrassed by another false positive, right? The lack of flat denial from ESO also makes me anticipate that there really will be some announcement by the end of the month. Then we'll see where the chips fall, and the next step of the scientific method (attempts to replicate/confirm results) can be put in practice.
Gerald
Pale Red Dot has submitted a paper for peer review, and "Our paper has got positive referee reports!"
But at the same time "#PaleRedDot team says the Proxima Centauri planet report in @DerSPIEGEL didn't come from them."

From a tv channel:
QUOTE
." ESO-Sprecher Richard Hook erklärte jedoch zu dem angeblichen Sensationsfund, die Angaben basierten offenbar "größtenteils auf Gerüchten". Er könne den Inhalt des "Spiegel"-Berichts "nicht bestätigen". Die Ergebnisse der Suche nach einem möglichen Planeten bei Proxima Centauri würden "zur rechten Zeit bekanntgegeben", betonte Hook.

ESO-speaker Richard Hook, however, explained regarding the presumed sensational findings, the statements are obviously based "mostly on rumors". He "can't confirm" the contents of the "Spiegel" report. The results of the search for a possible planet near Proxima Centauri will be "reported in due time", emphasized Hook.
nprev
Thanks, Gerald. That's the kind of clarifying information that's needed concerning this story at this point.
alphasam
I'll just leave this here cool.gif

From BBC The Sky at Night presenter Chris Lintott;
https://twitter.com/chrislintott/status/766171247256412160


JRehling
Der Spiegel has published a new article that almost looks like the previous rumor-level article but with slightly less hedging:

http://www.spiegel.de/international/zeitge...-a-1107983.html

It'll be nice to have absolute confirmation that Proxima Centauri has planets but, to recap, it is somewhere between expected and very likely for any given red dwarf to have planets, and because they tend to have small planets, it is more or less expected for it to have a planet that's roughly earth-sized.

What would be nice to know is what uncertainty exists concerning any such detection. If the result is a detection with an estimated radius between 0.5 and 2.5 Earth radii, and/or similar uncertainty regarding its illumination, that's not going to mean much.

It would also be great, and surprising, if Proxima Centauri's planetary plane is aligned such that we see its planets transit, but there's no indication that this is going to be part of the announcement.

If Der Spiegel is accurate, we'll know within a couple of weeks what the team has found.
alphasam
There will be a press conference at ESO headquarters this Wednesday at 1pm CET, 7am EDT.
TheAnt
Hmm, if Der Spiegel is to believed, it is now claimed that the source was from the PaleRedDot team after all.
Lets see about this ESO announcement tomorrow. =)
Gerald
ESO on twitter:
QUOTE
Dear friends we will be making an announcement today at 19:00 CEST. Please stay tuned until then
alphasam
Yeah, there is a conference with the press going on now but not being broadcast :-( , the end of the embargo has been set for the evening.
DEChengst
ESOcast 87: Pale Red Dot Results:

https://www.eso.org/public/unitedkingdom/videos/eso1629a/

Mass is at least 1.3 Earth masses and the orbital period is 11.2 days.

And the actual press briefing that was given earlier this afternoon.

https://t.co/vC5zgpfB8s
TheAnt
Here we got the full facts, a 'year' lasting 11 days, that's a tight orbit for the Proxima C planet ESO press release.

Edit, adding resources that popped up after the embargo was lifted:

The Icecat page The habitability of Proxima Centauri b concludes that the planet is not Earth's twin.

A terrestrial planet candidate in a temperate orbit around Proxima Centauri (PDF)
Gladstoner
FYI, Centauri Dreams is a good resource for exoplanets as well as general interstellar exploration topics:

http://www.centauri-dreams.org/
JRehling
This work contains, also, an interesting hint of the cup-half-empty: The detection of this planet and not any other apparent signal that interferes appreciably with it says something about a lack of other planets within certain parameters. There must be no planet that is closer to Proxima Centauri and more than a fraction of the mass of Proxima b, nor any planet a bit further out and a few times more massive. This is interesting because, a priori, there could be space for another terrestrial planet with prospects for liquid water on the surface. Proxima Centauri may still – and very likely does – have other planets, but this work places bounds on their size and orbits.

Hopefully, we'll soon get some information on the systems of Alpha Centauri A and Alpha Centauri B. Planets with earthlike temperatures would have much longer orbital periods than 11 days (more like 150 to 500 days) and so much longer studies will be needed. On the plus side, planets orbiting one of those could be observed directly a bit more easily, using a chronograph to block a star that is 0.4 to 1.1 AU away from the planet, which is easier due to the larger angular separation than blocking Proxima Centauri to observe Proxima b.
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