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Understanding how Hot Jupiters Form
Understanding how Hot Jupiters Form
Named to JPL's list of the top 20 Most Intriguing Exoplanets, the WASP-47 system (Michigan press release linked here) was the first system containing a hot Jupiter to be found to also contain additional, close-in planetary companions. In this work, we also confirmed the planetary nature of the ~9 day period candidate and predicted the planetary masses in the WASP-47 system by fitting the transit timing variations. The masses derived with this method are consistent with the RV masses later measured by other methods (see their paper here; collaborator Andrew Vanderburg also led an RV analysis, to which I contributed, here; Lauren Weiss led a simultaneous RV and TTV analysis here). Ideally, the discovery of more systems of this nature will enable an eventual statistical study of the differences between hot Jupiters with and without nearby companions.
I discussed this project at the 2019 KITP Conference, Planet-Star Connections in the Era of TESS and Gaia. The talk I gave is online, and serves as a good summary of both this project and my work on WASP-47!
The obliquities of cool stars hosting hot Jupiters tend to be aligned. Some of these systems have extra companions, with orbits well exterior to the hot Jupiter's orbit. Because these companions were discovered with RVs, we do not know their inclinations relative to the hot Jupiter's orbit (see schematic above).
Below, I show three videos, showing what happens if you give different inclinations to these exterior companions in some example systems:
Movie 1: When all planets are set to have no minimal mutual inclinations, the exterior companion will remain in the same plane as the hot Jupiter.
Movie 2: When the exterior companion is given a small mutual inclination to the orbit of the hot Jupiter, the orbit of the hot Jupiter will precess and appear to be "pointing" different directions at different times.
Movie 3: When the exterior companion starts with an orbit that is more tilted relative to the hot Jupiter, the hot Jupiter's orbit will evolve wildly over time.
When a companion has a high inclination relative to the hot Jupiter, it leads the orbit of the hot Jupiter to precess (change over time) relative to the spin axis of the star. Since we see cool stars hosting hot Jupiters to have low obliquities, this suggests that those exterior companions generally (but we can't say "always") have inclinations similar to the hot Jupiter's (so, the orbital behavior will be much more similar to Movie 1 than Movie 3).
Next up, we are planning to do further analysis to determine exactly what the implications of this result are on planet formation.
Solar System Dynamics
Solar System Dynamics
Working with Fred Adams and David Gerdes, I have been attempting to understand the dynamics of the outer solar system. Part of this is finding cool new objects (like this one!) that help us better understand exactly what is in the outer solar system. Another part of understanding this is assessing whether the proposed solar system member Planet Nine exists, and (if it does) what its dynamical implications are. In this work, we evaluated the dynamical stability of extreme TNOs in the presence of Planet Nine, and identified that objects may hop between resonances with Planet Nine.
res_hopping_w_p9.movSimulated orbits for a TNO (green) and Planet Nine (yellow), demonstrating the 'hopping' behavior that TNOs can experience under the gravitational influence of Planet Nine. The central circle and ring denote the sun and the orbit of Neptune.
In work that got a large amount of press coverage, Tali Khain and I used Dark Energy Survey data to discover 2015 BP519, a Trans-Neptunian Object (TNO) with a uniquely large inclination for its orbital period.
This object is not only useful because it helps constrain the Planet Nine hypothesis, but its high inclination is not predicted by most solar system formation models. As such, its existence can be used to determine which models are correct (and can produce the proper number of these objects).
A plot of the (top panel) inclination and (bottom panel) eccentricity versus semi-major axis for all known TNOs. Regular TNOs are in grey, 'extreme' TNOs are in red, and BP519 is denoted by a star and label. BP519 is both eccentric and inclined relative to the plane of the solar system.
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