Additional Planets at Gliese 581

jyril wrote:

Seems they did not see any signs of planets f or g.

The HARPS search for southern extra-solar planets XXXII. Only 4 planets in the Gl~581 system
http://arxiv.org/abs/1109.2505

Quote :

The Gl 581 planetary system has generated wide interest, because its 4 planets include both the lowest mass planet known around a main sequence star other than the Sun and the first super-Earth planet in the habitable zone of its star. A recent paper announced the possible discovery of two additional super-Earth planets in that system, one of which would be in the middle of the habitable zone of Gl 581. The statistical significance of those two discoveries has, however, been questioned. We have obtained 121 new radial velocity measurements of Gl 581 with the HARPS spectrograph on the ESO 3.6 m telescope, and analyse those together with our previous 119 measurements of that star to examine these potential additional planets. We find that neither is likely to exist with their proposed parameters. We also obtained photometric observations with the 2.5 m Isaac Newton Telescope during a potential transit of the inner planet, Gl 581e, which had a 5% geometric transit probability. Those observations exclude transits for planet densities under 4 times the Earth density within -0.2 sigma to +2.7 sigma of the predicted transit center.

Their updated four-planet model for the e planet has an oddly eccentric orbit.

The Vogt team assumed circular orbits, and only then the planets popped out, am I right?

They simply can not see the planet g in the data maybe the mass of the planet is under the mass of earth? or simply is not existing but planet f??Nobody cares because if existing is frigid but probably is ghost is well as g or still signal to noise can not definetely solve the problem

Of course there can be a small planet in the HZ (say, 1 M_Earth ) hiding under the detection limit.

1 earth mass planet would be great reward for all uncertainities according existence or not that planet.Is planet f more likely anybody knows?

jyril wrote:

The Vogt team assumed circular orbits, and only then the planets popped out, am I right?

looks like you still don't get them even if you assume circular orbits. This was much the same as I found when I looked at the individual datasets, the HARPS dataset didn't contain much convincing signs of additional planets, and the HIRES data seemed only good enough to recover planets b and c.

It certainly looks like these claims were an artifact of merging the datasets.

Here we go again! Vogt et al. back for more...

GJ 581 Update: An Independent Re-analysis Of The HARPS Data Set

The Vogt presentation has now been withdrawn from the conference...

A new analysis of the GJ581 extrasolar planetary system
http://arxiv.org/abs/1203.3140

Quote :

We have done a new analysis of the available observations for the GJ581 exoplanetary system. Today this system is controversial due to choices that can be done in the orbital determination. The main ones are the ocurrence of aliases and the additional bodies - the planets f and g - announced in Vogt et al. 2010. Any dynamical study of exoplanets requires the good knowledge of the orbital elements and the investigations involving the planet g are particularly interesting, since this body would lie in the Habitable Zone (HZ) of the star GJ581. This region,for this system, is very attractive of the dynamical point of view due to several resonances of two and three bodies present there. In this work, we investigate the conditions under which the planet g may exist. We stress the fact that the planet g is intimately related with the orbital elements of the planet d; more precisely, we conclude that it is not possible to disconnect its existence from the determination of the eccentricity of the planet d. Concerning the planet f, we have found one solution with period $\approx 450$ days, but we are judicious about any affirmation concernig this body because its signal is in the threshold of detection and the high period is in a spectral region where the ocorruence of aliases is very common. Besides, we outline some dynamical features of the habitable zone with the dynamical map and point out the role played by some resonances laying there.

That one does not include the latest HARPS dataset though...

Quote :

Of course, additional observations can help solving the dilemma about planet g. Forveille et al. 2011, using new observations, were not able to confirm the existence of the planets g and f. But, this statement could not be verified because the new data were not yet made available in public domain.

Never ending story I wonder if any transit b,c,d,e would solve anything

GJ 581 update: Additional Evidence for a Super-Earth in the Habitable Zone
http://arxiv.org/abs/1207.4515

Here we go again...

Gliese 581 g welcome back

tommi59 wrote:

Gliese 581 g welcome back

Since the original Gliese 581 f appears to have gone desaparecido, the potentially habitable super-Earth ought to be renamed Gliese 581 f(2)

Or it goes the way of Capella, where large numbers of letters were "wasted" on objects that are not part of the system, so the companion binary ended up designated as H and L...

Peak at 191 and 450 days?

Galzi wrote:

Since the original Gliese 581 f appears to have gone desaparecido, the potentially habitable super-Earth ought to be renamed Gliese 581 f(2)

Yeah I was thinking more or less the same.

I'll hold off on calling this one "confirmed" until this can be reliably, independently confirmed.

Well you are right sirius.Neverthelles mass of planet with slightly shorter period is significantly lower

Lower mass is better for habitability because the lower core pressure makes it easier for the iron to be liquid and therefore generate a magnetic dynamo.

Not to mention that a higher mass planet could be a mini-Neptune instead of a super-Earth.

With the apparent migration history of the GJ 581 system, I would be surprised if the planets (except b*) we observe at the star aren't mini-Neptunes.

* Corrected/edited.

Because they created beyond snow line?Hard to tell but both transiting planets around M dwarf (gj 436 b ,gj 1214 b)have density 1.5g/cm3 and kepler 11 d,e,f however less.I am not so sure rather water worlds

Be interesting to see what the Bayesians have to say about the new HARPS data...

Commenting on the new Vogt et al. paper, Xavier Bonfils of the HARPS team notes that the roughly 4% chance of their finding still being an error makes "not acceptable" for astronomers to accept the existence of former Gliese 581g

http://www.usatoday.com/tech/science/columnist/vergano/story/2012-07-21/goldilocks-planet-debate/56381428/1

Another interesting part of the article said:

Quote :

"Vogt says a new telescope is becoming available at the Lick Observatory near San Jose, Calif., where his team is based. It allows year-round viewing of Gliese 581 to make more measurements, so he hopes this means "we will be able to pound this (problem) into submission"

It seems Vogt is planning to observe Gliese 581 with the Automated Planet Finder. With its high cadence observations, that would help a lot.