Linking the formation history of planets with their spectrum

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• Christoph Mordasini (University of Bern, Switzerland)
• Tuesday 26 May 2015, 14:00-15:00
• Martin Ryle Seminar Room, Kavli Institute.

If you have a question about this talk, please contact David Titterington.

Despite the enormous increase in observational data on extrasolar planets in the past two decades, many aspects of their formation are still not well understood to date. In particular, the formation mechanism of the oldest known class of exoplanets, the hot Jupiters like 51 Peg b, is still not clear. A new approach to disentangle different formation mechanisms might be offered by an observational technique that has recently seen a lot of progress, which is the spectroscopy of planetary atmospheres. This is because the spectrum represent a window into the composition of a planet. In my talk I will show how it might be possible to find the traces of the planetary formation history in the spectrum of an exoplanet, based on the results of a planet formation and evolution model and assumptions about the refractive and volatile composition of the planetary building blocks. In particular, different migration mechanisms (disk migration versus migration due to the Kozai mechanism or planet-planet scattering) might lead to distinct imprints, which is very important from a planet formation point of view. To this end we simulate a planet’s formation using a global planet formation model, tracing the material abundances in the accreted material. We then consider the planet’s subsequent evolution, evolving the radius, internal, and atmospheric structure to an age of several Gyrs when exoplanets are typically observed spectroscopically. Using an atmospheric radiative transfer and chemistry model we finally calculate the spectrum of the planets at this age. With this, we can study differences in the spectra resulting from, e.g. different C/O ratios due to different migration histories. We find that a formation inside the water ice line can lead to a strong imprint, but only if planetesimals in the inner system contain refractory carbon grains in significant quantities. It is then discussed whether these imprints can be observed with current and future instruments like JWST , and which steps need to be taken in the theoretical models to better understand the link between formation and spectra.

This talk is part of the Cavendish Astrophysics Seminars series.

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