TOI-3362b: A Proto Hot Jupiter Undergoing High-eccentricity Tidal Migration

Abstract

High-eccentricity tidal migration is a possible way for giant planets to be placed in short-period orbits. If this happens often, one would expect to catch proto hot Jupiters on highly elliptical orbits undergoing high-eccentricity tidal migration. As of yet, few such systems have been discovered. Here, we introduce TOI-3362b (TIC-464300749b), an 18.1 day, 5 M Jup planet orbiting a main-sequence F-type star that is likely undergoing higheccentricity tidal migration. The orbital eccentricity is 0.815 -+ 0.032 0.023 . With a semimajor axis of 0.153 -+ 0.003 0.002 au, the planet's orbit is expected to shrink to a final orbital radius of 0.051 -+ 0.006 0.008 au after complete tidal circularization. Several mechanisms could explain the extreme value of the planet's eccentricity, such as planet-planet scattering and secular interactions. Such hypotheses can be tested with follow-up observations of the system, e.g., measuring the stellar obliquity and searching for companions in the system with precise, long-term radial-velocity observations. The variation in the planet's equilibrium temperature as it orbits the host star and the tidal heating at periapse make this planet an intriguing target for atmospheric modeling and observation. Because the planet's orbital period of 18.1 days is near the limit of TESS's period sensitivity, even a few such discoveries suggest that proto hot Jupiters may be quite common.

HD 83443c: A Highly Eccentric Giant Planet on a 22 yr Orbit

“…In this context, the presence of HD 83443c in its highly eccentric orbit is of particular interest, since it points to the possibility that HD 83443b achieved its current hot Jupiter status as a result of chaotic encounters with that outer planet (i.e., the second mechanism noted above). As a consequence, the remaining planet is left in a short and highly eccentric orbit (e.g., Rasio & Ford 1996;Weidenschilling & Marzari 1996;Chatterjee et al 2008) and undergoes tidal circularization (Nagasawa et al 2008;Bonomo et al 2017;Dong et al 2021). Wu & Lithwick (2011) proposed a secular migration mechanism to explain the pile-up of hot Jupiters on ∼3 day orbits, the generally lower masses (<1 M J ) of hot Jupiters, and the low frequency of additional planets in hot Jupiter systems within a few au (and noting that more distant eccentric companions were likely).…”

Tidal evolution and diffusive growth during high-eccentricity planet migration: revisiting the eccentricity distribution of hot Jupiters

“…Detecting proto-HJs with 0.8 < e < 0.9 would more fully test the viability of high-eccentricity migration under the action of the diffusive tide. The recently discovered proto-HJ TOI-3362b by TESS (Dong et al 2021) with e = 0.815 is consistent with a planet that has ended the rapid phase of diffusive evolution and entered the slow circularization phase (Equation ( 5)). The discovery of additional systems like TOI-3362b should help test the diffusive evolution scenario and constrain the termination eccentricity e term .…”

The TESS Grand Unified Hot Jupiter Survey. I. Ten TESS Planets

“…While the shortest period hot Jupiters are expected to be on circular orbits due to tides raised by the star on the planet, the tidal circularization timescale increases rapidly with orbital distance. Tidal circularization might be too slow to have affected planets with periods approaching 10 days or longer, with an extreme example being the recently discovered TOI-3362b, a potential proto-hot Jupiter on a P = 18.1 day, e = 0.82 orbit (Dong et al 2021). Indeed, the two longest period planets in our sample, TOI-2207b (P = 8.00 days) and TOI-3693b (P = 9.09 days) have theoretical tidal circularization timescales of 12 ± 5 and 22 ± 6 Gyr, based on Equation (3) of Adams & Laughlin (2006), who extended the work of Goldreich & Soter (1966), and assuming a tidal quality factor of Q P = 10 6 .…”