A spectroscopic study aims at shedding some light on the formation mechanism of hot Jupiters. The study “Chemical fingerprints of hot Jupiter planet formation” of J. Maldonado (INAF-OAPA) recently published by A&A
The discovery of hot Jupiters (e.g. Jupiter-like exoplanets with orbital period shorter than 10 days) was completely unexpected since no such planets are present in the Solar System. This has forced us to change our view of how giant planets can form.
Two hypotheses are used to explain how hot Jupiters form. The most accredited theory is that hot Jupiters form at large distances from their star, beyond the “snow line” where temperature are low enough so that water ice can exist. Once formed, these planets migrate inward at close orbits around their central stars. Recently it has been also suggested that hot Jupiters may form in situ. This may explain why hot Jupiters are on average smaller than cold Jupiters. Besides, the distribution of Jupiter-like planets orbital period shows two evident peaks with almost no planets in between: one peak with periods shorter than 3 days (hot Jupiters) and one for periods between 100 and 3000 days (cold Jupiters). This suggests that Jupiters-like exoplanets may form with both mechanisms.
The study “Chemical fingerprints of hot Jupiter planet formation” of J. Maldonado (INAF-OAPA), recently published by Astronomy & Astrophysics, shows how stars hosting hot Jupiters have different chemical properties than those hosting cold Jupiters. The authors have analyzed high resolution spectra of 88 stars hosting Jupiter-like exoplanets in order to measure their chemical abundance of various elements with respect to hydrogen (e.g. the metallicity). They have found that stars hosting hot Jupiters have on average larger metallicity than stars hosting cold Jupiters. Together with the confirmation that hot Jupiters are on average smaller than cold Jupiters, this study supports the hypothesis that hot Jupiters may have formed in situ.
The figure (link) shows the distribution of metallicity as a function of orbital period as found in this study
