Additional Planets at Gliese 581

http://www.universetoday.com/74640/new-earth-sized-exoplanet-is-in-star%E2%80%99s-habitable-zone/#more-74640

Edit: Mongo beat me to the posting of the paper's link.

Paper:
http://www.ucolick.org/~vogt/ms_press-1.pdf


Gliese 581 f → 7 M_e planet at 0.758 AU (beyond the orbit of d).
Gliese 581 g → 3 M_e planet in the HZ (between c and d).

Nature blog on the discovery

Link to paper

ABSTRACT

We present 11 years of HIRES precision radial velocities (RV) of the nearby M3V star Gliese 581, combining our data set of 122 precision RVs with an existing published 4.3-year set of 119 HARPS precision RVs. The velocity set now indicates 6 companions in Keplerian motion around this star. Differential photometry indicates a likely stellar rotation period of  94 days and reveals no significant periodic variability at any of the Keplerian periods, supporting planetary orbital motion as the cause of all the radial velocity variations. The combined data set strongly confirms the 5.37-day, 12.9-day, 3.15-day, and 67-day planets previously announced by Bonls et al. (2005), Udry et al. (2007), and Mayor et al. (2009). The observations also indicate a 5th planet in the system, GJ 581f, a minimum-mass 7.0M planet orbiting in a 0.758 AU orbit of period 433 days and a 6th planet, GJ 581g, a minimum-mass 3.1M planet orbiting at 0.146 AU with a period of 36.6 days. The estimated equilibrium temperature of GJ 581g is 228 K, placing it squarely in the middle of the habitable zone of the star and offering a very compelling case for a potentially habitable planet around a very nearby star. That a system harboring a potentially habitable planet has been found this nearby, and this soon in the relatively early history of precision RV surveys, indicates that , the fraction of stars with potentially habitable planets, is likely to be substantial. This detection, coupled with statistics of the incompleteness of present-day precision RV surveys for volume-limited samples of stars in the immediate solar neighborhood suggests that  could well be on the order of a few tens of percent. If the local stellar neighborhood is a representative sample of the galaxy as a whole, our Milky Way could be teeming with potentially habitable planets.

Furthermore, Gliese 581 d is safely at the 67-day period, instead of the < 2 day period.

I guess that makes it less likely that planet d is habitable, since the lower the eccentricity, the lower the orbit-averaged insolation.

Probably this is the same planet, which Vogt said in December 2009
https://solar-flux.forumotion.com/extrasolar-news-and-discoveries-f2/two-new-super-earths-61-vir-and-hd1461-t465-15.htm#4392

Well, I think this may be the closest thing to Earth so far found, this time. Ain't it?

Edasich wrote:

Well, I think this may be the closest thing to Earth so far found, this time. Ain't it?

As far as its equilibrium temperature and mass, yes.

Lazarus wrote:

I guess that makes it less likely that planet d is habitable, since the lower the eccentricity, the lower the orbit-averaged insolation.

The new fit has the semi-major axis of d coming inward just a bit. I don't know if that compensates fully.

The equilibrum temperature of the Earth is about -18°C isn't it?

Yes indeed.

Quote :

To discover " g " and his big sister " f ", of 7 Earth's masses, «our American colleagues used for a half their own measures of radial velocity, got with the telescope Keck in Hawaii, and for other one those, more definite, which we published thanks to HARPS until 2009», explains Xavier Bonfils. Problem, it is that the data of Keck, only, «allow to find only two of first four planets of the system», follows the researcher. Where from a reservation on the existence of Gliese 581g (and f): even when are those of Harps the data of the American telescope added them are really of sufficient quality to discern six planets at the same time?

http://www.cieletespace.fr/node/6035

I think that's mentioned in the paper: neither individual dataset is sufficient to reveal the entire system, you need to combine them. That's why they seem to be very cautious about the status of planet g, regarding it as unconfirmed.

Perhaps the Geneva team will revise their data publishing policy

Planet g is not present in new HARPS data, according to result presented at IAU Symposium 276. EPE note does not mention planet f, but both f and g have been relegated to the list of unconfirmed planets.

Dynamics of Cats is not encouraging...

Quote :

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.

News article at Space.com - planet f is not found in the HARPS data either.

Lazarus wrote:

News article at Space.com - planet f is not found in the HARPS data either.

Some pretty strong emotions expressed in the comment thread on Space.com.
As Steinn wrote: "This could get interesting"

I wonder how Vogt et al. (2010)'s data pointed to these additional planets now disproved.

As far as I can make out, the HIRES data is only sufficient to confirm the existence of planets b and c. In combination with the HARPS data it may also help resolve the aliasing issues with the orbital period of planet d. Why it was used to assert the existence of additional planets I don't know. Certainly it should not have gone to the media at this stage.

Moreover Vogt et al. (2010)'s radial velocity sets were weirdly short, unable to be integrated with any previous RV datasets.

If I wished to make a Systemic console simulation to search for such planets, it could not be done.

Edasich: the arXiv paper has a truncated set of RV measurements. The version of the paper linked in the first post in this thread has the complete dataset.

I doubt even in true period planet d because signal 82 days seemed to be more likely.This is very strange at all because Vogt was sure existence of planets g,f now unconfirmed

tommi59 wrote:

I doubt even in true period planet d because signal 82 days seemed to be more likely.

The 82-day period was shown to be an alias of the ~60-day period in the paper that described the discovery of Gliese 581 e.

Steven Vogt casts doubt on conclusions based on additional HARPS measurements because
they have not been published in a peer-reviewed journal

http://www.space.com/scienceastronomy/gliese-581g-discoverer-responds-101013.html

Certainly it's hard for discoverers to retract their own finding, but sure we all would like to hear author's reason for non retractions.

http://www.sciencenews.org/view/generic/id/64308/title/Existence_of_habitable_exoplanet_questioned

Quote :

Vogt says he and his colleagues stand by their results, which analyzed a larger set of data and also found evidence for a sixth planet. “I feel confident that we have accurately and honestly reported our uncertainties and done a thorough and responsible job extracting what information this dataset has to offer,” he says.
Vogt’s team combined the Swiss group’s 119 measurements with 122 measurements recorded by his team over a span of 11 years using the HIRES spectrograph at the Keck Observatory atop Hawaii’s Mauna Kea. The wobble induced in the parent star by Gliese 581g can be detected only when the two data sets are combined, Vogt and his colleagues note in an article posted September 29 at arXiv.org and scheduled to be published in Astrophysical Journal.
“I am not overly surprised,” says Vogt, that even with some new data, the Swiss team does not find evidence of Gliese 581g “as these are very weak signals, and adding 60 points onto 119 does not necessarily translate to big gains in sensitivity.”
“As the Swiss group has our data,” Vogt adds, “I am also wondering why they have not already combined all the data together into a more complete analysis themselves.”
Pepe declined to say when and if he and his colleagues would add the U.S. Keck data to their analysis.

Quote :

Seager, who is attending the conference, called Pepe’s presentation “striking.” She notes that, unlike Vogt’s, the Swiss team’s analysis doesn’t assume that all the planets orbiting Gliese 581 have perfectly circular orbits.
That difference in approach could be the crux of the disagreement between the teams, says Alan Boss of the Carnegie Institution for Science in Washington, D.C., who is also at the Torino conference. Allowing the known planets orbiting Gliese 581 to have eccentric, or elongated, orbits could mask the signal from an additional planet, he notes. On the other hand, Seager says, assuming perfectly circular orbits, as Vogt’s team has done, could produce false signals that appear to be additional small planets.
“I don't know if we should be in such a hurry to say one way or the other,” says MIT astronomer Sara Seager. “We will have consensus at some point; I don't think we need to vote right now."