Extrasolar Planets

Tidal Distortions As A Bottleneck On Constraining Exoplanet Compositions

By Keith Cowing
Status Report
January 24, 2023
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Tidal Distortions As A Bottleneck On Constraining Exoplanet Compositions
Mass-Radius relationships along with data points (and error-bars) for the sample of planets considered in this work. The left and right panels refer to low and high mass planets respectively. Black curves in the left figure are taken from Zeng et al. (2019). Colored bands represent variations of these curves by up to 4.7% in radius, corresponding to density variations of up to 15%. The right hand panel shows a similar phenomenon for high mass planets, where we show constant-density relations corresponding to solar system gas giants giant densities, as well as a planet with half the density of Saturn and a planet with a density of 0.2g/cm3 representative of ‘super puffs’. The planets highlighted in red are those mentioned in Table 2 whose density uncertainty is less than the deviations caused by tides.

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 4{\sigma} bias on their density estimates.

David Berardo, Julien de Wit

Comments: 8 pages, 7 figures, 2 tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2301.08755 [astro-ph.EP] (or arXiv:2301.08755v1 [astro-ph.EP] for this version)
Journal reference: ApJ 941 155 (2022)
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Submission history
From: David Berardo
[v1] Fri, 20 Jan 2023 19:00:00 UTC (2,363 KB)

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