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Published November 20, 2016 | Submitted + Published
Journal Article Open

The imprint of exoplanet formation history on observable present-day spectra of hot Jupiters

Abstract

The composition of a planet's atmosphere is determined by its formation, evolution, and present-day insolation. A planet's spectrum therefore may hold clues on its origins. We present a "chain" of models, linking the formation of a planet to its observable present-day spectrum. The chain links include (1) the planet's formation and migration, (2) its long-term thermodynamic evolution, (3) a variety of disk chemistry models, (4) a non-gray atmospheric model, and (5) a radiometric model to obtain simulated spectroscopic observations with James Webb Space Telescope and ARIEL. In our standard chemistry model the inner disk is depleted in refractory carbon as in the Solar System and in white dwarfs polluted by extrasolar planetesimals. Our main findings are: (1) envelope enrichment by planetesimal impacts during formation dominates the final planetary atmospheric composition of hot Jupiters. We investigate two, under this finding, prototypical formation pathways: a formation inside or outside the water iceline, called "dry" and "wet" planets, respectively. (2) Both the "dry" and "wet" planets are oxygen-rich (C/O < 1) due to the oxygen-rich nature of the solid building blocks. The "dry" planet's C/O ratio is <0.2 for standard carbon depletion, while the "wet" planet has typical C/O values between 0.1 and 0.5 depending mainly on the clathrate formation efficiency. Only non-standard disk chemistries without carbon depletion lead to carbon-rich C/O ratios >1 for the "dry" planet. (3) While we consistently find C/O ratios <1, they still vary significantly. To link a formation history to a specific C/O, a better understanding of the disk chemistry is thus needed.

Additional Information

© 2016 American Astronomical Society. Received 2016 January 19; revised 2016 August 17; accepted 2016 September 10; published 2016 November 15. We thank K. Dullemond, U. Marboeuf, and A. Thiabaud for useful discussions. C.M. acknowledges the support of the Swiss National Science Foundation via grant BSSGI0_155816 "PlanetsInTime." Parts of this work have been carried out within the frame of the National Centre for Competence in Research "PlanetS" supported by the Swiss National Science Foundation (SNSF).

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Published - Mordasini_2016_ApJ_832_41.pdf

Submitted - 1609.03019v1.pdf

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