Two weeks ago, U.S.-based astronomers announced the discovery of the first Goldilocks planet circling another star: just the right size and just the right temperature to harbor alien life. But yesterday at an exoplanet meeting in Turin, Italy, Switzerland-based astronomers announced that they could find no trace of the prized planet in their observations of the same planetary system. 
 
 All the excitement has been over the subtlest of wiggles in the motion of the star Gliese 581 that lies just 20 light-years from the sun in the direction of the constellation Libra. A consortium of institutions led by the Observatory of Geneva in Switzerland had already discovered four planets circling Gliese 581 by sorting out the subtle motions of the star that are induced by the gravitational tugs of any orbiting planets. 
 
 On 29 September, a U.S.-based team led by astronomer Steven Vogt of the University of California, Santa Cruz, announced that it had discovered a fifth planet. The American team used a combined set of observations: One 11-year-long set consisted of 122 measurements made by the team, while the other set was 4.3 years long and consisted of 119 measurements published by the consortium. 
 
 Designated Gliese 581g, the new planet has at least three times the mass of Earth—large enough to hold on to a watery atmosphere—and orbits at a distance from its star that would allow any water to remain liquid. That would make 581g a happy home for life as we know it. 
 
 But at this week's Astrophysics of Planetary Systems meeting, astronomer Francesco Pepe of the Geneva Observatory and the Swiss group reported that he and his colleagues could find no reliable sign of a fifth planet in Gliese 581's habitable zone. They used only their own observations, but they expanded their published data set from what the U.S. group included in its analysis to a length of 6.5 years and 180 measurements. "We do not see any evidence for a fifth planet ... as announced by Vogt et al.," Pepe wrote Science in an e-mail from the meeting. On the other hand, "we can't prove there is no fifth planet." No one yet has the required precision in their observations to prove the absence of such a small exoplanet, he notes. 
 
 Astronomer Paul Butler, a member of the U.S. team who is at the Carnegie Institution for Science in Washington, D.C., says he can't comment on the Swiss work because he wasn't at the meeting and the data are unpublished. He notes, however, that more observations will likely be needed to solidify the existence of Gliese 581g. "I would expect that on the time scale of a year or two this should be settled." ||||| 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: 
 
 " ‎"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.
– US-based researchers may have gotten a tad carried away when they announced the discovery of a new, potentially life-sustaining planet a couple weeks back. Yesterday, a team of Switzerland-based astronomers said their own observations of star Gliese 581g didn’t back up the American team at all. “We do not see any evidence for a fifth planet,” astronomer Francesco Pepe told ScienceNow. The team also said that, if they were forced to draw a conclusion from their data, they would get a negative signal, which implies that the planet isn’t there, not that they just haven’t been able to find it, notes Steinn Sigurðsson on his blog. Meanwhile, a member of the US team admits that more data is necessary to confirm Gliese 581g’s existence. “I would expect that on the time scale of a year or two, this should be settled.”