Refined Orbital Period Decay Analysis Reinforces the Migration Theory for the Formation and Evolution of HD 189733 & Other Hot Jupiter Systems

Hot Jupiters are extrasolar planets with similar masses and radii to Jupiter. They are “hot” because they orbit very close (a < 0.2 au) to their host stars, resulting in very short orbital periods. Hot Jupiters are the easiest exoplanets to detect using planetary transits and Doppler-effect radial velocity observations due to their significant sizes and masses. The first major theory of Hot Jupiter planet formation and evolution is the migration theory, which speculates that these planets form far away from their host stars and migrate inward due to tidal and magnetic interactions with their host stars. Whereas, the “In Situ” hypothesis suggests that these planets were once the cores of super-Earths that then became Hot Jupiters without much change in their period over time. HD 189733 is perhaps the most important Hot Jupiter system because of its proximity to Earth (d≈ 19.8 pc) and brightness (V≈ +7.67 mag). This system has been photometrically observed at Villanova University since 2007, leading to the creation of a catalog of transit eclipse timings. These timings provide an orbital period decrease which suggests that the migration theory is correct. With new observations of HD 189733 and data from the Exoplanet Transit Database, or ETD, the most refined orbital decay rate of the system has been calculated. This decrease in orbital period is supported by the observed age discrepancy between HD 189733 A, the host star, and its red dwarf companion star, HD 189733 B. The orbital decay rates of eight other short period Hot Jupiter systems have also been refined. The discovery of orbital decay within the HD 189733 system and six of the other systems reinforces the migration theory and the inevitable death spiral of all Hot Jupiters.

This research is supported by grants from NASA. We also acknowledge financial support from the Villanova Undergraduate Research Fellowship (VURF) Program for 2019 and 2020.