Additional Planets at Gliese 581

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.

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
http://solar-flux.forumandco.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?

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

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...

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.