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Science in Washington, D.C., says he can't comment on the Swiss work because he wasn't at the meeting and the data are unpublished.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. ||||| An artist's illustration of the strange Earth-like rocky planet Kepler-78b, which orbits a sun-like star 400 light-years from Earth. The planet is 20 percent wider and 80 percent more massive than Earth. 
 
 Credit: David A. Aguilar (CfA) View full size image 
 
 A puzzling alien planet is the closest thing to an Earth twin in size and composition known beyond our solar system, though it's far too hot to support life, scientists say. 
 
 The exoplanet Kepler-78b, whose supertight orbit baffles astronomers, is just 20 percent wider and about 80 percent more massive than Earth, with a density nearly identical to that of our planet, two research teams report in separate papers published online today (Oct. 30) in the journal Nature. 
 
 "This is the planet that, in many respects, is the most like Earth that's been discovered outside our solar system," said Andrew Howard, of the University of Hawaii at Manoa's Institute for Astronomy and lead author of one of the studies. "It has approximately the same size. It has the same density, which means it's made out of the same stuff as Earth, in all likelihood." [The Strangest Alien Planets (Gallery)] 
 
 Studying a lava world 
 
 Kepler-78b, whose discovery was announced last month, orbits a sunlike star in the constellation Cygnus, about 400 light-years from Earth. 
 
 The alien world circles 900,000 miles (1.5 million kilometers) or so from its parent star — just 1 percent of the distance between Earth and the sun— and completes one lap every 8.5 hours. Surface temperatures on Kepler-78b likely top 3,680 degrees Fahrenheit (2,000 degrees Celsius), Howard said. 
 
 The planet was found by NASA's prolific Kepler space telescope, which has spotted nearly 3,600 potential exoplanets since its March 2009 launch. (Kepler was hobbled in May of this year when the second of its orientation-maintaining reaction wheels failed, but scientists are still sifting through the instrument's huge databases.) 
 
 Kepler flagged alien worlds by noting the telltale brightness dips they caused when passing in front of, or transiting, their parent stars from the spacecraft's perspective. Kepler's measurements allow researchers to estimate an exoplanet's size but not its mass, meaning that other strategies are required to get a handle on a world's density and composition. [Gallery: A World of Kepler Planets] 
 
 One such method is the radial velocity technique, which measures the wobble in a host star's light induced by the gravitational pull of an orbiting planet. Both new studies employed this method to investigate the Kepler-78 system, with Howard's group using the HIRES spectrograph at Hawaii's Keck Observatory and another team, led by Francesco Pepe of the University of Geneva, relying on the new HARPS-N instrument on the Telescopio Nazionale Galileo in the Canary Islands. 
 
 The two teams came to very similar conclusions. Howard's group determined Kepler-78b's mass to be 1.69 times greater than that of Earth, while Pepe's team calculated it to be 1.86 times higher than Earth's. The results of the Pepe-led study suggest a density of 5.57 grams per cubic centimeter for Kepler-78b, while those of Howard's team imply a density of 5.3 grams per cubic cm. 
 
 These numbers agree to within the error range independently estimated by both teams, suggesting that they are quite accurate, Howard said. 
 
 "The fact that we agree to within our errors — in science, that's basically as good as you can do," Howard told SPACE.com. 
 
 Earth's density is about 5.5 grams per cubic cm, so Kepler-78b probably has an Earth-like composition, complete with a rocky interior and an iron core, both studies suggest. 
 
 A mysterious origin 
 
 The extremely tight orbit of Kepler-78b puzzles astronomers. According to prevailing theory, the alien world shouldn't exist where it does, because its host star was significantly larger when the planet was taking shape. 
 
 "It couldn't have formed in place because you can't form a planet inside a star," Dimitar Sasselov, of the Harvard-Smithsonian Center for Astrophysics and a member of the Pepe-led team, said in a statement. "It couldn't have formed further out and migrated inward, because it would have migrated all the way into the star. This planet is an enigma." 
 
 What is clear, however, is that Kepler-78b's days are numbered. The planet will continue circling lower and lower until the immense gravity of its host star tears it apart, likely within 3 billion years or so. 
 
 "Kepler-78b is going to end up in the star very soon, astronomically speaking," Sasselov said. 
 
 The search for another Earth 
 
 The hellishly hot Kepler-78b is not a good place to hunt for alien life. But the determination of its density marks a milestone in the ongoing search for a true "Earth twin" — a planet very much like Earth in size, composition and surface temperature. 
 
 "The existence of Kepler-78b shows that, at the very least, extrasolar planets of Earth-like composition are not rare," astronomer Drake Deming, of the University of Maryland, writes in an accompanying commentary article today in the same issue of Nature. 
 
 Deming points to NASA's upcoming Transiting Exoplanet Survey Satellite mission, or TESS, which is slated to launch in 2017 to hunt for transiting planets around nearby stars (as contrasted with Kepler, whose gaze was more distant). 
 
 "By focusing particularly on small stars cooler than the sun, TESS should find exo-Earths whose mass can be measured by trading the close-in orbit of Kepler-78b for more distant orbits around low-mass stars, approaching orbital zones where life is possi­ble," Deming writes. "That trade-off probably cannot be pushed to the point of measuring an Earth twin orbiting once per year around a sun twin, but it will allow future scientific teams to probe habitable planets orbiting small stars." 
 
 Follow Mike Wall on Twitter @michaeldwall and Google+. Follow us @Spacedotcom, Facebook or Google+. Originally published on SPACE.com.
– 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.”