Tidal Distortions as a Bottleneck on Constraining Exoplanet Compositions

Abstract

Improvements in the number of confirmed planets and the precision of observations imply a need to better understand subtle effects that may bias interpretations of exoplanet observations. One such effect is the distortion of a short period planet by its host star, affecting its derived density. We extend the work of Burton et al., Correia, and others, using a gravitational potential formulation to a sample of nearly 200 planets with periods less than 3 days. We find five planets exhibiting density variations of >10% and as many as 20 planets with deviations >5%. We derive an analytic approximation for this deviation as a function of the orbital period, transit depth, and mass ratio between the planet and host star, allowing for rapid determination of such tidal effects. We find that current density error bars are typically larger than tidal deviations but that reducing the uncertainty on transit depth and radial velocity (RV) amplitude by a factor of 3 causes tidal effects to dominate density errors (>50%) in >40% of planets in our sample, implying that in the near future upgraded observational precision will cause shape deviations to become a bottleneck with regards to analysis of exoplanet compositions. These two parameters are found to dominate uncertainties compared to errors on stellar mass and radius. We identify a group of eight planets (including WASP-19 b, HAT-P-7 b, and WASP-12 b) for which current density uncertainties are as much as 4x smaller than the potential shift due to tides, implying a possible 4σ bias on their density estimates.

11 pages, 7 figures, 2 tables

References in corpus (12)

• Growth Model Interpretation of Planet Size Distribution
• HAT-P-7b: An Extremely Hot Massive Planet Transiting a Bright Star in the Kepler Field
• Tidal Locking of Habitable Exoplanets
• Changing Phases of Alien Worlds: Probing Atmospheres of Kepler Planets with High-Precision Photometry
• WASP-4b Arrived Early for the TESS Mission
• Transit light curve and inner structure of close-in planets
• Detection of the tidal deformation of WASP-103b at $3\sigma$ with CHEOPS
• Fundamental physics with Espresso: Towards an accurate wavelength calibration for a precision test of the fine-structure constant
• Detectability of shape deformation in short-period exoplanets
• Tidally Distorted Exoplanets: Density Corrections for Short-Period Hot-Jupiters based solely on Observable Parameters
• Precession, nutation, and space geodetic determination of the Earth's variable gravity field
• On the Effects of Planetary Oblateness on Exoplanet Studies