An anomalous planetary system that challenges current models of planetary formation is discovered

Figure: artistic representation of the star GJ 3512 with the newly discovered giant planet. ©CARMENES/RenderArea/J.Bollaín/C.Gallego consortium.


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A study led by IEEC researchers at ICE (CSIC) and involving the Centro de Astrobiología (CAB, CSIC-INTA) has discovered an unusual planetary system around the red dwarf star GJ 3512, which owns at least one gas giant planet. Since current models of planetary formation do not contemplate the presence of gaseous giants around small stars, it is suggested that the planet may have formed from the fragmentation of an unstable disk around the star when it was still young.
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Astronomers of the CARMENES consortium, led by Juan Carlos Morales, researcher at the Instituto de Estudios Espaciales de Cataluña (IECC) at the Instituto de Ciencias del Espacio (ICE, CSIC), have discovered one, and even two, giant gaseous planets orbiting around the red dwarf star GJ 351, located about 30 light-years from Earth. The results of this discovery have been published in the journal Science.

To discover the planets, astronomers have used the Doppler technique, which measures the round-trip movement of a star when orbiting one or more planets and the spectrograph planethunter CARMENES (Calar Alto High-Resolution Search for M dwarfs with Exoearths with Near-infrared and optical Échelle Spectrographs), installed in the 3.5-meter telescope of the Calar Alto Observatory in Almería. In addition, the CARMENES consortium has used the Joan Oró Telescope (TJO) of the IECC located in the Observatori Astronomic del Montsec and the facilities of the Sierra Nevada Observatory (IAA, CSIC).

GJ 3512 is a star practically identical to Proxima Centauri and, with a tenth of the mass of the Sun, only slightly more massive than the Star of Teegarden and TRAPPIST-1. All of these stars are home to Earth-like planets in temperate and compact orbits, but none have gaseous giants. 

"Big stars like the Sun have gas giant planets because they have large protoplanetary disks. Small stars, such as GJ 3512, typically have small protoplanetary discs that result in small planets such as Uranus or Earth," explains José Antonio Caballero, researcher at the Centro de Astrobiología and co-author of the study. "How can a small star get to have at least one giant planet? Was the system formed as a two-star binary system? Or did the protoplanetary disk have anything special? Either way, the giant planet of the star GJ 3512 has broken all existing planet formation schemes and new models need to be found to give it an explanation," Concludes Caballero. 

Models of planetary formation should be able to explain how planetary systems come to exist both around stars and the Sun, as well as around smaller stars. The most accepted model for planet formation, called the nucleus accretion model, was considered sufficient to explain the formation of planets such as Jupiter and Saturn in our Solar System, and also that of many gaseous giants discovered around other stars. This model assumes that the planets are formed in two phases. First solid rocky nuclei, of a few land masses, are created in the protoplanetary disk; and then, when a critical mass is reached, these nuclei begin to accumulate large amounts of gas until they reach the size of Jupiter, or even larger.

 

Fuente: UCC-CAB

 

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