Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published February 1, 2020 | Published + Submitted
Journal Article Open

X-Ray Ionization of Planet-Opened Gaps in Protostellar Disks

Abstract

Young planets with masses approaching Jupiter's have tides strong enough to clear gaps around their orbits in the protostellar disk. Gas flow through the gaps regulates the planets' further growth and governs the disk's evolution. Magnetic forces may drive that flow if the gas is sufficiently ionized to couple to the fields. We compute the ionizing effects of the X-rays from the central young star, using Monte Carlo radiative transfer calculations to find the spectrum of Compton-scattered photons reaching the planet's vicinity. The scattered X-rays ionize the gas at rates similar to or greater than the interstellar cosmic-ray rate near planets with the masses of Saturn and of Jupiter, located at 5 au and at 10 au, in disks with the interstellar mass fraction of sub-micron dust and with the dust depleted by a factor 100. Solving a gas–grain recombination reaction network yields charged particle populations whose ability to carry currents is sufficient to partly couple the magnetic fields to the gas around the planet. Most cases can undergo Hall-shear instability, and some can launch magnetocentrifugal winds. However, the material on the planet's orbit has diffusivities so large in all the cases we examine that magnetorotational turbulence is prevented and the non-ideal terms govern the magnetic field's evolution. Thus the flow of gas in the gaps opened by young giant planets depends crucially on the finite conductivity.

Additional Information

© 2020 The American Astronomical Society. Received 2018 April 11; revised 2019 December 28; accepted 2019 December 30; published 2020 February 4. We are grateful to Barbara Ercolano for advice on the X-ray opacities, Wilhelm Kley and Stephen Lubow for advice on the depths of planet-opened gaps, and Satoshi Okuzumi for providing his subroutine implementing the Bethell & Bergin cross sections. Lynne Hillenbrand's sponsorship of S.Y.K. at Caltech enabled this work to begin. The research was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration, and with the support of the NASA Origins of Solar Systems program through grant 13-OSS13-0114 and Exoplanets Research Program through grant 17-XRP17_2-0081. Government sponsorship acknowledged.

Attached Files

Published - Kim_2020_ApJ_889_159.pdf

Submitted - 1804.04265.pdf

Files

Kim_2020_ApJ_889_159.pdf
Files (1.6 MB)
Name Size Download all
md5:e19472400e392dca4438cd8da1751547
930.4 kB Preview Download
md5:eee52a5329b84eee38455e09ff318cd1
665.4 kB Preview Download

Additional details

Created:
August 22, 2023
Modified:
October 20, 2023