Additional Planets at Gliese 581

Planets f and g do not exist: arxiv.org/abs/1208.0814

efroimsk wrote:

Planets f and g do not exist: arxiv.org/abs/1208.0814

Indeed, see Galzi's post a couple months ago, and just upthread.

Lazarus wrote:

That paper doesn't seem to reference the Forveille et al. (2011) paper which contains the extended HARPS dataset, instead they are using the older Mayor et al. (2009) dataset.

That was an early version. In the published version (see also the recent update in arxiv) we did use the data by Forveille (2011).

efroimsk wrote:

In the published version (see also the recent update in arxiv) we did use the data by Forveille (2011).

Ah I see. Sorry about that!

efroimsk wrote:

Planets f and g do not exist: arxiv.org/abs/1208.0814

That's true regarding the solution provided by Vogt et al. (2010); on the other hand the study seems to tentatively support the detection of a 32.1 day planet proposed by Vogt et al. (2012), assuming zero eccentricities for all the planets:

Quote :

In their most recent update on the GJ 581 system, Vogt et al. (2012) used the yet unpublished, much expanded set of RV data from the HARPS (Forveille et al. 2011). They found that a fifth planet (f) can be detected if the eccentricity of the 66.7 day planet (d) is set to zero. Using the same data set, but not rejecting any data points in it, we were able to confirm this statement with our detection algorithm by forcing the eccentricity of the four planets b–e to zero. A 32.1 day planet with a projected mass of 1.99ME emerges at a confidence level above 99%. It is likely therefore that we are dealing with the second harmonic in the signal of an eccentric planet, which can be confused with a separate nearly commensurate planet.

The eccentricity issue needs to be solved. Maybe HARPS, with the latest improvements, has the potential to do that.

Eccentricity over 0.25 for planet d at 0.215 au is in my opinion very unlikely

efroimsk wrote:

Lazarus wrote:

That paper doesn't seem to reference the Forveille et al. (2011) paper which contains the extended HARPS dataset, instead they are using the older Mayor et al. (2009) dataset.

That was an early version. In the published version (see also the recent update in arxiv) we did use the data by Forveille (2011).

Thanks for the information!

Seems the case for planets f and g is getting progressively weaker. Seems to me that the claimed period for g is close to several plausible "artifact" periods...

Robertson et al. (2012) say that periodicity of planet f is actually correlated to stellar cycle rather to an orbital period.

Another failure to detect the f and g planets.
http://arxiv.org/abs/1307.1246

Well no surprise.I expect like in case gliese 436 sub earth size planet is causing non zero eccentricity for 436 b, sub earth mass planet can cause the same for. 581d.There could be couple (sub)earth mass planets in gj 581 under threshold detection that is why we can not find any reliable signals beside b,c,d,e

There they go...

Stellar activity masquerading as planets in the habitable zone of the M dwarf Gliese 581
http://www.sciencemag.org/content/early/2014/07/02/science.1253253

Quote :

The M dwarf Gliese 581 is believed to host four planets, including one (GJ 581d) near the habitable zone that could possibly support liquid water on its surface if it is a rocky planet. The detection of another habitable-zone planet—GJ 581 g—is disputed, as its significance depends on the eccentricity assumed for d. Analyzing stellar activity using the Hα line, we measure a stellar rotation period of 130 ± 2 days and a correlation for Hα modulation with radial velocity. Correcting for activity greatly diminishes the signal of GJ 581d (to 1.5σ) while significantly boosting the signals of the other known super-Earth planets. GJ 581d does not exist, but is an artifact of stellar activity which, when incompletely corrected, causes the false detection of planet g.

OUCH

on the other hand, I guess that frees up the HZ for lower-mass terrestrial planets... surely there's got to be something in the gap between c and the debris disc?

Additional Planets at Gliese 581 lol  

Good news : planets e, b & c are real !!    

http://www.space.com/26432-potentially-habitable-exoplanets-gliese-581-existence.html

Other good news: we don't have to worry about being obliterated in 2049 by the relativistic missile response to the Bebo spamfest beamed towards the system.

Or Battleship-playing aliens from Gliese 581g for that matter.

Will the three confirmed planets keep their current lettering? I'm not sure of any precedent for this.

I don't see why they would rename them, this would create a lot of confusion with the established literature. Note that candidate g was not renamed even when f basically disappeared from all the orbital analyses.

Precedents also exist from the naming of binary/multiple stars, which is why the Capella system has ended up with components Aa, Ab, H and L.

If 67 days planet does not exist so 3 days should be named d

Don't you think that would be a little confusing to people who are unaware of the change in name?

Since the non-existence of d was predicted by red noise analysis, I'd be interested to see what would happen if the methods of the Robertson et al. (2014) paper are applied to GJ 667C.

Ok...this is getting a bit confusing to me (and apparently to the others here).

So...

...which of the Gliese 581 planets are believed to be 'real'?

...can a good case still be made for any of the other Gliese 581 planets? Or is the dismissal reasonably solid?

...and are any of the 'real' Gliese 581 planets in the habitable zone?

The first discovered "b", the most massive of the system (hot neptune) is real.
The smallest planet discovered by RV, "e" is real too.
The first "habitable" planet ever announced "c" is real too but it's too hot, more like Venus, not realy habitable.

Now on arXiv.
http://arxiv.org/abs/1407.1049

Stalker - thank you for that clarification.

Aha, so the activity correction also removes the suspiciously high eccentricity estimate for planet e.