Exoplanetology: Exoplanets & Exomoons

More Likely Than You Think: Inclination-Driving Secular Resonances are Common in Known Exoplanet Systems

By Keith Cowing
Status Report
astro-ph.EP
June 14, 2024
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More Likely Than You Think: Inclination-Driving Secular Resonances are Common in Known Exoplanet Systems
Left: Relationship between companion planet semimajor axis ratios (axes) and maximum inclination induced on candidate inner planet via resonance (color bar). Planets 1 and 2 were initialized with a 4◦ mutual inclination Right: Effects of the variation of the masses of the outer two planets at four different sets of semimajor axis ratios shown on the leftmost panel corresponding to the four different qualitative regions shown: A) ain and a1 are too close and a2 too far away for the system to enter resonance; B) a1 and a2 are such that the inner planet is in resonance with the outer two at J2 = 0; C) a1 and a2 are such that the inner planet is in resonance with the outer two for some particular J2 ̸= 0; D) a1 and a2 are such that the inner planet will never be in resonance with the outer two for any of the J2 values the star will explore. The green stars mark the mass ratio assumed in the left panel. — astro-ph.EP

Multi-planet systems face significant challenges to detection. For example, further orbiting planets have reduced signal-to-noise ratio in radial velocity detection methods, and small mutual inclinations between planets can prevent them from all transiting.

One mechanism to excite mutual inclination between planets is secular resonance, where the nodal precession frequencies of the planets align such as to greatly increase the efficiency of angular momentum transport between planets.

These resonances can significantly misalign planets from one another, hindering detection, and typically can only occur when there are three or more planets in the system. Naively, systems can only be in resonance for particular combinations of planet semimajor axes and masses; however, effects that alter the nodal precession frequencies of the planets, such as the decay of stellar oblateness, can significantly expand the region of parameter space where resonances occur.

In this work, we explore known three-planet systems, determine whether they are in (or were in) secular resonance due to evolving stellar oblateness, and demonstrate the implications of resonance on their detectability and stability. We show that about 20% of a sample of three planet transiting systems seem to undergo these resonances early in their lives.

Thea Faridani, Smadar Naoz, Gongjie Li, Malena Rice, Nicholas Inzunza

Comments: 23 pages, 11 figures, 5 tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2406.09359 [astro-ph.EP] (or arXiv:2406.09359v1 [astro-ph.EP] for this version)
Submission history
From: Thea Faridani
[v1] Thu, 13 Jun 2024 17:44:06 UTC (1,991 KB)
https://arxiv.org/abs/2406.09359

Astrobiology

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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