Exoplanetology: Exoplanets & Exomoons

Searching For The Grand Tack In Exoplanetary Data

By Keith Cowing
Status Report
astro-ph.EP
July 25, 2024
Filed under , , , ,
Searching For The Grand Tack In Exoplanetary Data
Orbital data extracted from the NASA Exoplanet Archive on May 2, 2024, for a set of planetary systems that (at least) partially meet the requirements for the Masset and Snellgrove mechanism. Left: Period ratio of planet pair in a ‘grand tack’ mass arrangement (i.e. the interior planet is more massive) in the exoplanet population, as well as for Jupiter and Saturn (labelled ‘Solar System’). Some systems contain more than one pair and are thus represented by multiple points. The orange crosses show the period ratio if the secondary planet orbits at an orbital distance of 3 Hill radii of the primary. Three of the systems (at the bottom of the plot) orbit near this arrangement. The three vertical lines show, from left to right, orbital period ratios of exactly 3:2, 2:1, and 3:1, respectively. Middle: Orbital separation of each planet from their host star in units of AU. The size of each marker is proportional to the mass of the planets; the black points show the orbital structure of Jupiter and Saturn in our own Solar System. Right: Eccentricity of the inner planet as well as the mass ratio of each planetary pair. A wide range of eccentricities is seen for the exoplanet population; however the planets with high period ratios (top of the figure) seem to generally have higher eccentricities on average. — astro-ph.EP

The grand tack model, more generally called the Masset and Snellgrove mechanism, is a planetary migration model whereby two giant planets via interactions with their natal disk migrated to larger orbital radii.

While its relevance in our own Solar System remains in question, the fact that the Masset and Snellgrove mechanism is a general hydrodynamical effect implies that it may have occurred in another planetary system.

In this study I searched through exoplanet data for evidence of the Masset and Snellgrove mechanism, which requires that (1) the inner of the two planets is more massive than the outer planet; (2) the planets are sufficiently massive that their gravity-induced gap overlaps; and (3) they orbit at sufficiently close radii that their co-rotation regions also overlap.

The last two requirements are met when the planets orbit with a 3:2 mean motion resonance. I do not find conclusive evidence for a grand tack-like system, but find some evidence for planet formation at the edge of a planet-induced protoplanetary disk gap in three systems.

A.J. Cridland

Comments: 4 pages, 1 figure, accepted for publications in A&A letters, updated with language correction
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2407.11574 [astro-ph.EP] (or arXiv:2407.11574v2 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2407.11574
Focus to learn more
Submission history
From: Alex Cridland
[v1] Tue, 16 Jul 2024 10:31:38 UTC (411 KB)
[v2] Thu, 18 Jul 2024 07:41:06 UTC (411 KB)
https://arxiv.org/abs/2407.11574
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) 🖖🏻

Follow on Twitter
MORE FROM Exoplanetology: Exoplanets & Exomoons