Astronomers Discover Largest Ever Cache Of Exoplanets

August 24, 2010

Astronomers at the European Southern Observatory (ESO) have discovered five planets orbiting a star in what is being called by the AFP news agency “the biggest discovery of so-called exoplanets since the first was logged 15 years ago.”

The ESO astronomers discovered the planetary system around a sun-like star called HD 10180. Using the HARPS spectrograph, they also reportedly discovered evidence which suggests that there may be two additional planets present in orbit around the celestial body, including one which would have the lowest recorded exoplanetary mass in history.

“We have found what is most likely the system with the most planets yet discovered,” Christophe Lovis, the lead author of a paper describing the findings, said in a press release dated August 24. “This remarkable discovery also highlights the fact that we are now entering a new era in exoplanet research: the study of complex planetary systems and not just of individual planets. Studies of planetary motions in the new system reveal complex gravitational interactions between the planets and give us insights into the long-term evolution of the system.”

Lovis and his team, who have submitted their findings to the journal Astronomy and Astrophysics (A&A), took 190 individual measurements of HD 10180 using equipment stationed at the ESO’s La Silla, Chile facility. With the organization’s 3.6-meter telescope and the HARPS sectrograph, they discovered back and forth motions in the star that would be caused by the gravitational pull of at least five planets.

According to the ESO press release, the strongest gravitational signals come from planets with a mass roughly equivelant to Neptune, with orbits ranging from 6 to 600 days. Furthermore, Lovis said that his team has “good reasons to believe that two other planets are present,” including one with a mass similar to Saturn and another that would be about 1.4 times that of the Earth’s, making it the least-massive exoplanet discovered to date. The Saturn-like planet would possess an orbit of approximately 2,200 days, while a year on the smaller planet would last a mere 1.18 days.

“The newly discovered system of planets around HD 10180 is unique in several respects,” the press release states. “First of all, with at least five Neptune-like planets lying within a distance equivalent to the orbit of Mars, this system is more populated than our Solar System in its inner region, and has many more massive planets there. Furthermore, the system probably has no Jupiter-like gas giant. In addition, all the planets seem to have almost circular orbits.”

“If confirmed, that would bring the distant star system to seven planets, compared with eight in our own Solar System,” reported the AFP on Tuesday. “A total of 402 stars with planets have been logged since the first was detected in 1995, according to NASA’s Jet Propulsion Laboratory (JPL). The tally of exoplanets stands at 472″¦ None, though, is even remotely similar to Earth.”

“The HD 10180 system represents an interesting example of the various outcomes of planet formation,” Lovis wrote in the conclusion section of his paper, which is entitled ‘The HARPS search for southern extra-solar planets. XXVII. Up to seven planets orbiting HD 10180: probing the architecture of low-mass planetary systems.’

“No massive gas giant was formed, but instead a large number of still relatively massive objects survived, and migrated to the inner regions. Building a significant sample of such low-mass systems will show what are the relative influences of the different physical processes at play during planet formation and evolution,” he added.

The ESO announced their findings during a presentation at the Observatoire de Haute-Provence, France on Tuesday. Those credited as joining Lovis on the ESO research team are D. S©gransan, M. Mayor, S. Udry, F. Pepe, and D. Queloz of Observatoire de Genve, Universit© de Genve, Switzerland; W. Benz of Universität Bern, Switzerland; F. Bouchy of Institut d’Astrophysique de Paris, France; C. Mordasini of the Max-Planck-Institut fr Astronomie, Heidelberg, Germany;  N. C. Santos from Universidade do Porto, Portugal; J. Laskar of Observatoire de Paris, France; A. Correia from Universidade de Aveiro, Portugal; J.-L. Bertaux from Universit© Versailles Saint-Quentin, France; and G. Lo Curto of the ESO.

Image 1: This artist’s impression shows the remarkable planetary system around the Sun-like star HD 10180. Observations with the HARPS spectrograph, attached to ESO’s 3.6-meter telescope at La Silla, Chile, have revealed the definite presence of five planets and evidence for two more in orbit around this star. This system is similar to the Solar System in terms of number of planets and the presence of a regular pattern in the sizes of the orbits. If confirmed the closest planet detected would be the lightest yet known outside the Solar System, with a mass that could be only about 1.4 times that of the Earth. The large crescent is the third world in the system (HD 10180d), which is comparable to the planet Neptune in mass. The two inner planets appear as silhouettes in transit across the bright disc of the star. The outer planets in the system appear in the background sky. Credit: ESO/L. Calçada

Image 2: This wide-field image shows the sky around the star HD 10180, which appears as a fairly bright star just below the center. The picture was created from photographs taken through red and blue filters and forming part of the Digitized Sky Survey 2. The field of view is approximately three degrees across. The colored halos around the stars are artifacts of the photographic process and are not real. The remarkable planetary system around this star is far too faint and close in to be visible in this image. Credit: ESO, Digitized Sky Survey 2. Acknowledgement: Davide De Martin

Image 3: This image shows a close-up of the sky around the star HD 10180. The picture was created from photographs taken through red and blue filters and forming part of the Digitized Sky Survey 2. The field of view is approximately eleven arcminutes across. The blue and orange halos around the star, and the eight spikes of light, are artifacts of the imaging process and are not real. The remarkable planetary system around this star is far too faint and close in to be visible in this image. Credit: ESO and Digitized Sky Survey 2. Acknowledgment: Davide De Martin

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