Exoplanet hosting stars give further insights on planet formation

Aug 16, 2012
Swirling disk of planet-building dust. (Credit: NASA/JPL-Caltech/T. Pyle (SSC)

An international team, led by EXOEarths researchers (Centro de Astrofísica da Universidade do Porto), proposes that metals like magnesium might have an important role in the formation of low mass planets.

The team, lead by CAUP researcher Vardan Zh. Adibekyan, analyzed high resolution spectra of 1111 sun-like , obtained by the HARPS spectrograph (ESO). Of these stars, 109 are known to harbor high mass (Jupiter-like) , and 26 have Neptune-like planetary companions.

The team focused especially on studying the abundance of Alpha Elements in these stars, like Magnesium (Mg), Silicon (Si) or Titanium (Ti). The research found that the ratio of these, compared with the amount of Iron (Fe), was consistently higher in stars with planets, with the greatest discrepancy observed for Mg.

The lead author of the paper, CAUP Astronomer Vardan Zh. Adibekyan commented “These findings indicate that some metals other than iron are involved in the process of planet formation, especially when the amount of iron is lower than solar. These results may provide strong constraints for the models of planet formation, especially for planets with low mass.”

The leading theories of suggest that planets form by clumping smaller particles of heavy elements (metals), into larger and larger bodies. The results put forward by the present study suggest that planets need a minimum amount of “metals” to be formed. The formation of planets, even the lowest mass ones, is dependent on the dust content of the cloud that gave origin to the star and planetary system.

Explore further: Mixing in star-forming clouds explains why sibling stars look alike

More information: "Overabundance of alpha-elements in exoplanet-hosting", Vardan Zh. Adibekyan, Nuno Cardoso Santos, Sérgio Sousa, Garik Israelian, Elisa Delgado Mena, Jonay González Hernández, Michel Mayor, Christophe Lovis, Stephan Udry. Astronomy & Astrophysics Volume 543, July 2012, Article Number A89 (DOI: 10.1051/0004-6361/201219564 ).

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SnowballSolarSystem _SSS_
1 / 5 (3) Aug 28, 2012
(Exo)planets often occur in pairs (or triads) of similar mass orbiting at similar distances from their host star, such as Venus & Earth, Saturn & Jupiter and Uranus & Neptune, which may form by gravitational collapse of enriched dust clouds in figure-eight orbits around protostars, before the binary stars ignite and enter the main sequence. The collapsing dust clouds fragment due to excess angular momentum, tending to form quasi-stellar-planet (QSP) pairs.

Core collapse lifts the QSP orbits at the expense of energy and angular momentum of the binary stellar pairs, causing the stellar components to spiral in and merge, creating nucleosynthesis alpha elements in luminous red novae, so alpha elements may be an effect rather than a cause of binary stellar pairs that also happen to form QSPs.