Imperial College London
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DrJamesOwen

Faculty of Natural Sciences, Department of Physics

Senior Lecturer in Exoplanet Physics
 
 
 
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Contact

 

+44 (0)20 7594 5785james.owen CV

 
 
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Location

 

Blackett LaboratorySouth Kensington Campus

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Summary

 

Publications

Citation

BibTex format

@article{Owen:2017:1538-4357/aa890a,
author = {Owen, JE and Wu, Y},
doi = {1538-4357/aa890a},
journal = {The Astrophysical Journal: an international review of astronomy and astronomical physics},
title = {The evaporation valley in the Kepler planets},
url = {http://dx.doi.org/10.3847/1538-4357/aa890a},
volume = {847},
year = {2017}
}
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RIS format (EndNote, RefMan)

TY  - JOUR
AB  - A new piece of evidence supporting the photoevaporation-driven evolution model for low-mass, close-in exoplanets was recently presented by the California–Kepler Survey. The radius distribution of the Kepler planets is shown to be bimodal, with a "valley" separating two peaks at 1.3 and 2.6 R ⊕. Such an "evaporation valley" had been predicted by numerical models previously. Here, we develop a minimal model to demonstrate that this valley results from the following fact: the timescale for envelope erosion is the longest for those planets with hydrogen/helium-rich envelopes that, while only a few percent in weight, double its radius. The timescale falls for envelopes lighter than this because the planet's radius remains largely constant for tenuous envelopes. The timescale also drops for heavier envelopes because the planet swells up faster than the addition of envelope mass. Photoevaporation therefore herds planets into either bare cores (~1.3 R ⊕), or those with double the core's radius (~2.6 R ⊕). This process mostly occurs during the first 100 Myr when the stars' high-energy fluxes are high and nearly constant. The observed radius distribution further requires the Kepler planets to be clustered around 3 M ⊕ in mass, born with H/He envelopes more than a few percent in mass, and that their cores are similar to the Earth in composition. Such envelopes must have been accreted before the dispersal of the gas disks, while the core composition indicates formation inside the ice line. Lastly, the photoevaporation model fails to account for bare planets beyond ~30–60 days; if these planets are abundant, they may point to a significant second channel for planet formation, resembling the solar system terrestrial planets.
AU  - Owen,JE
AU  - Wu,Y
DO  - 1538-4357/aa890a
PY  - 2017///
SN  - 0004-637X
TI  - The evaporation valley in the Kepler planets
T2  - The Astrophysical Journal: an international review of astronomy and astronomical physics
UR  - http://dx.doi.org/10.3847/1538-4357/aa890a
UR  - http://hdl.handle.net/10044/1/59065
VL  - 847
ER  -
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