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Excitation of Planetary Obliquities through Planet-Disk Interactions

Millholland, Sarah and Batygin, Konstantin (2019) Excitation of Planetary Obliquities through Planet-Disk Interactions. Astrophysical Journal, 876 (2). Art. No. 119. ISSN 1538-4357.

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The tilt of a planet's spin axis off its orbital axis ("obliquity") is a basic physical characteristic that plays a central role in determining the planet's global circulation and energy redistribution. Moreover, recent studies have also highlighted the importance of obliquities in sculpting not only the physical features of exoplanets but also their orbital architectures. It is therefore of key importance to identify and characterize the dominant processes of excitation of nonzero axial tilts. Here we highlight a simple mechanism that operates early on and is likely fundamental for many extrasolar planets and perhaps even solar system planets. While planets are still forming in the protoplanetary disk, the gravitational potential of the disk induces nodal recession of the orbits. The frequency of this recession decreases as the disk dissipates, and when it crosses the frequency of a planet's spin axis precession, large planetary obliquities may be excited through capture into a secular spin–orbit resonance. We study the conditions for encountering this resonance and calculate the resulting obliquity excitation over a wide range of parameter space. Planets with semimajor axes in the range 0.3 au ≾ a ≾ 2 au are the most readily affected, but large-a planets can also be impacted. We present a case study of Uranus and Neptune, and show that this mechanism likely cannot help explain their high obliquities. While it could have played a role if finely tuned and envisioned to operate in isolation, large-scale obliquity excitation was likely inhibited by gravitational planet–planet perturbations.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Millholland, Sarah0000-0003-3130-2282
Batygin, Konstantin0000-0002-7094-7908
Alternate Title:Excitation of Planetary Obliquities through Planet–Disk Interactions
Additional Information:© 2019. The American Astronomical Society. Received 2019 January 9; revised 2019 April 2; accepted 2019 April 14; published 2019 May 10. We wish to thank Chris Spalding, Alessandro Morbidelli, and Greg Laughlin for their helpful insights and comments. We also thank the referee for a useful report. S.M. is supported by the NSF Graduate Research Fellowship Program under grant DGE-1122492. K.B. is grateful to the David and Lucile Packard Foundation and the Alfred P. Sloan Foundation for their support.
Group:Astronomy Department
Funding AgencyGrant Number
NSF Graduate Research FellowshipDGE-1122492
David and Lucile Packard FoundationUNSPECIFIED
Alfred P. Sloan FoundationUNSPECIFIED
Subject Keywords:planet–disk interactions; planets and satellites: dynamical evolution and stability; planets and satellites: formation; planets and satellites: fundamental parameters; planets and satellites: physical evolution
Issue or Number:2
Record Number:CaltechAUTHORS:20190510-105529664
Persistent URL:
Official Citation:Sarah Millholland and Konstantin Batygin 2019 ApJ 876 119
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95394
Deposited By: George Porter
Deposited On:13 May 2019 17:01
Last Modified:20 Apr 2020 08:47

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