New Insights Into Planet Formation
August 17, 2012

Low Mass Planets Need Metal To Form: HARPS

April Flowers for - Your Universe Online

An international team of researchers led by EXOEarth scientists from Centro de Astrofisica daUniversidade do Porto (CAUP) argues that metals like Magnesium might have an important role to play in the formation of low mass planets.

Using the European Southern Observatory's (ESO) HARPS spectrograph, the team analyzed high resolution spectra of 1,111 sun-like stars. Of these stars, 109 are known to harbor high mass planets similar to Jupiter, and 26 have Neptune-like planetary companions.

HARPS is the High Accuracy Radial velocity Planet Searcher at ESO's La Silla 3.6m telescope. HARPS is dedicated to the discovery of extrasolar planets. Extrasolar, or exoplanets, are planets outside of our Solar System.

The focus of the research was especially focused on the abundance of Alpha Elements in these stars, like Magnesium (Mg), Silicon (Si), or Titanium (Ti). Alpha elements are integer multiples of the mass of the Helium (He) nucleus. This is also known as the alpha particle. Adding an alpha particle (He nucleus) to a Carbon atom results in an Oxygen atom, and adding an alpha particle to that originates a Neon atom.

The study, published in the July issue of Astronomy & Astrophysics, found that the ratio of these alpha elements, compared with the amount of Iron (Fe), was consistently higher in stars with planets. The greatest discrepancy was observed for Magnesium.

“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," commented CAUP Astronomer Vardan Zh. Adibekyan

The current leading theories of planet formation suggest that planets form by clumping smaller particles of heavy elements, or metals, into larger and larger bodies. The results of this study suggest that planets need a minimum amount of these heavy elements to be formed. The formation of planets, even the lowest mass ones, is dependent on the dust content of the debris cloud that gave the star and the planetary system their origin.