!Gliese 581g

There are reports from Torino about HARPS observations of Gliese 581(g)

Vogt et al reported on additional possible planets in the multi-planet low mass Gliese 581(g) system.

In particular they showed a ~ 3 sigma detection of a possible 3+ earth mass planet in a circular orbit with an orbital period consistent with a temperate surface.

The paper used a combination of historic Keck data, published HARPS data up through 2008 and new high cadence Keck data.
There was some concern when the paper came out that the False Alarm Probability was underestimated (see Cumming et al for discussion of False Alarm Probability estimates and general considerations ).

The two new planets reported by Vogt et al, were both coming in close to the detection threshold and there have been problems disentangllng closely packed multi-planet systems, due to aliasing and harmonic contamination. Gliese 581, in particular, has had a couple of claims about its planets backed out before.

What everyone in the community was waiting for is what the HARPS group could say, since they ought to have a couple of years more data, presumably with high cadence also, and very high velocity precision.

IAU 276 The Astrophysics of Planetary Systems: Formation, Structure, and Dynamical Evolution just got underway in Torino, Italy (good week to be in Italy - meeting in Sardinia also, Wish I Was There).

Ray Jay reports on social networks:

" â"We cannot confirm it [Gliese 581g] in our HARPS data" - Francesco Pepe (Geneva team) at IAU 276 in Torino."

This is interesting, but not totally surprising.
It will be very interesting to see the HARPS paper, and how this shakes out.

Gliese 581g could still be there, it could be in the orbit reported, but this needs some more work.

PS: additional oral reports from the meeting.
HARPS statement is stronger than "we don't see it" - they find that if they force a solution they get a negative signal appearing, implying the planet is not there, not just that they are not sensitive to it.
50% more data since 2008 published series.

This could get interesting.

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Any indications about the status of planet f in the HARPS data? Extrasolar Planets Encyclopaedia has demoted it to unconfirmed, but all the reports I've come across seem to be talking about planet g only.

Wow..just saw this...I have students in an astronomy lab right now looking at the exoplanet catalog...

By Pat Durrell (not verified) on 11 Oct 2010 #permalink

Uh oh ...

Did they think they were in direct competition with the Geneva group to publish this result first and thus rushed it to publication, or did they really think that they had a solid detection and didn't need to collect more data for confirmation?

The abstract and Section 6 of the paper seem to imply the former, but then there's this strange passage in the summary:
"And to be completely fair, the HIRES data set could also have undiscovered systematic errors lurking within. This is very difficult work and there is no shame or dishonor in
uncovering residual systematic errors at these levels of precision.

...Confirmation by other teams through additional high-precision RVs would be most welcome. But if GJ 581g is confirmed by further RV scrutiny ..."

This makes it seem like the detection isn't quite as clear-cut.

Considering the marginal (3-sigma!) significance of their detection, I don't understand why Vogt et al. presented their study as "indicating the presence" of a 6th planet in the habitable zone (exact words from the abstract) rather than cast it as a "candidate" detection that may or may not be real and needs follow-up observations for confirmation.

Raises the question of which instruments can get comparable precision to HARPS. There have been worrying suggestions about systematic errors in the HARPS measurements, particularly with the dim stars that are being surveyed by the space-based transit missions. For example, there was a recent paper on the arXiv that suggested that there is no convincing radial velocity detection of planets around CoRoT-7.

Good. Dog fights between careless press-release driven scientists. Hopefully they cross-check all their ridiculous "discoveries".

By stop_the_press (not verified) on 12 Oct 2010 #permalink

I suspect the vast majority of extrasolar planets detected by this method, may now be in doubt & the number of 'confirmed' extrasolar planets will now fall sharply. I expect though once better imaging techniques are in place, James Webb Telescope is launched & on station, KEPLER has been observing longer, etc, they will start rising once again. The very few imaged directly like Fomalhaut b, H788 a,b,c, Beta Pictoris b, etc do physically exist for sure as well as those that have passed the transiting method (three consecutive observed transits across their parent stars).

This is a bitter disappointment for sure, perhaps Gliese 581g does exist, but we cannot be sure now, in fact the others thought to be orbiting the red dwarf star Gliese 581 may not really exist either as they were 'detected' the same way.

Perhaps the Peer Review process really needs to be tightened up. It gives science a very bad name, mistakes happen, that's part of being human, but wild speculation & hyperbole, of which Gliese 581g was a great example, does not do science any favours.

Also the wild speculation & hyperbole about supposed subsurface oceans on Europa & Enceladus needs to stop, until we have more direct concrete information.

By Andrew Brown 3488 (not verified) on 12 Oct 2010 #permalink

Well I decided to play around with the datasets using the Systemic Console to see what was there.

Fitting the HIRES data alone, I recover planets b and c, so these planets do seem fairly secure. The next peak is at 26-days, with a FAP of 0.3%. I do not find planets d or e in this dataset (let alone f or g). Conclusion is not affected particularly by adding eccentricities.

Fitting the HARPS 2009 data alone, I recover planets b, c, d and e. After these planets the top 3 peaks are at 1.06d, 17.2d, 196d, none of which lies above the lowest FAP line in the periodogram. I'm not seeing planets f or g here.

Fitting the combined dataset, I recover planets b, c, d and e. If I allow the eccentricities to float during the fitting procedure, I get a peak at ~430 days just below the lowest FAP line. After fitting this planet, the next peaks are at 4.7 and 25 days, I therefore do not find planet g. I only find g if I constrain all the orbits to be circular during the fitting process.

So the detection of planets b and c seem to be pretty solid. Planets d and e are at least not contradicted by the HIRES data when used in combination with the HARPS data, and according to the Space.com article they are still recovered in the as-yet-unpublished expanded HARPS dataset. Planets f and g are definitely suspicious.

Planet g is definitely "unconfirmed", the long period planet may be there, time will tell.

Most of the radial velocity discoveries are solid, they are large signal-to-noise, and the nice thing about periodic signals is once you lock onto a real signal it builds very rapidly.
Also remember that a fraction of the radial velocity detections are confirmed by transits. They're there.

Necessarily the marginal detections, the lowest amplitude signals, the lowest mass planets, are those most likely to be false positives. Those are also among the most interesting and the hottest targets.

Another thing to note is that the periodogram of sampling contains strong peaks at 29.5 days (probably the Moon) and 180 days (roughly half a year). The difference of the two frequencies comes out as representing a period of roughly 35 days, quite close to the claimed period for g. I am now even more suspicious that g is an artifact of data sampling.

I think that, far from giving science a bad name, this sort of development makes the hunt for extrasolar planets even more interesting. I've said this sort of thing here before, so I'll keep it brief, but I think the story of why a candidate planet may or may not be there is fascinating and it should be shared with the public. Rather than deriding science-by-press-release and calling for better peer review, I think members of the lay public (such as myself) should be invited to watch the process unfold, particularly when the research is tax-payer funded. Retracted confirmations and tentative results can be just as educational and thrilling as final results, if not more so, and of course, no result is ever really final.

By Eric Goldstein (not verified) on 13 Oct 2010 #permalink

Remember that announcement of 32 planets discovered by HARPS that happened last year? One year on, a large fraction of them still have not been published, and today EPE just demoted the super-Earths Gliese 667Cb and Gliese 433b to "unconfirmed" status.

These low-mass planets are proving tricky to pin down, no?

Sounds like we need the Terrestrial Planet Finder, stat.

The claim form the Vogt group is that the Geneva team have allowed the gl581g signal to be swallowed up by the eccentricity of the gl581d planet. They claim that planets d and g with circular orbits are a better fit than the eccentric d orbit that the Geneva team claims. Both groups promise that all the data will be released within a few weeks, so then everyone can try to work this out for themselves.

Of course, Gliese 581g confirmation is still up in the air. But I began to have some concerns about the authenticity of the find when Vogt said, during the NSF video announcement, that he felt that there was a "100%" certainty that Gliese 581g had life. To make such a statement, based upon such scant (nonexistent?) evidence revealed him to be, shall we say, a very "optimistic" fellow. But being optimistic is not the same thing as being correct. In the excitement of the possible discovery, I think the human, Steven Vogt, momentarily forgot to be a scientist.

By Steve Bergman (not verified) on 08 Nov 2010 #permalink

What happened to the Space.com links? Theye're all dead? That's a BIG site to be down. Is this something that the naysayers are trying to throw up as a smoke screen? Sure Vogt et al may have overreacted so quickly, but afterall, they ARE HUMAN! My take on all this is that there is a weak signal there that comes and goes (see #3 tc above about the ~3sigma difference in detection) and give HIRES a chance to retrieve more data and combine with the HARPS and other research data to confirm or deny the existence of GJ581g, f, e; and for now just leave the as unconfirmed! Keep the ball rolling. Don't just stop it in it's tracks now that we're finally going somewhere! And HEY,cardsharing ... get a life!!!!!!!!!

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Joy
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