Detectability of shape deformation in short-period exoplanets

Abstract

Short-period planets suffer from extreme tidal forces from their parent stars causing them to deform and attain non-spherical shapes. The planet shapes, modeled here as triaxial ellipsoids, can have an impact on the observed transit light curves and the planetary parameters derived. We investigate the detectability of tidal deformation in short-period planets from their transit light curves and the instrumental precision needed. We show how the detection of deformation from the light curve allows us to obtain an observational estimate of the second fluid Love number which gives valuable insight about the planet's internal structure. We adopted a model to calculate the shape of a planet due to the external potentials acting on it and used this model to modify the ellc transit tool. Our model is parameterized by the Love number, hence for a given light curve we can derive the value of the Love number that best matches the observations. We simulated the known cases of WASP-103b and WASP-121b expected to be highly deformed. Our analyses showed that instrumental precision $\le$50ppm/min is needed to reliably estimate the Love number and detect tidal deformation. This precision can be achieved for WASP-103b in ~40 transits using HST and in ~300 transits using the forthcoming CHEOPS. However, fewer transits will be required for short-period planets that may be found around bright stars in the TESS and PLATO survey missions. The unprecedented precisions expected from PLATO and JWST can permit the detection of deformation with a single transit. However, the effects of instrumental and astrophysical noise must be well-considered as they can increase the number of transits required to reach the 50 ppm/min detection limit. We also show that improper modeling of limb darkening can act to bury signals related to the planet's shape thereby leading us to infer sphericity for a deformed planet.

9 pages, 10 figures, 2 tables, accepted for publication in A&A

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Cited by in corpus (20)

• The CHEOPS mission
• Spinning Black Holes Fall in Love
• Analysis of Early Science observations with the CHaracterising ExOPlanets Satellite (CHEOPS) using pycheops
• Detection of the tidal deformation of WASP-103b at $3\sigma$ with CHEOPS
• Machine learning inference of the interior structure of low-mass exoplanets
• ExoMDN: Rapid characterization of exoplanet interior structures with Mixture Density Networks
• Retrieval of the fluid Love number $k_2$ in exoplanetary transit curves
• Diagnosing limb asymmetries in hot and ultra-hot Jupiters with high-resolution transmission spectroscopy
• The GAPS Programme with HARPS-N at TNG. XXXI. The WASP-33 system revisited with HARPS-N
• Spitzer thermal phase curve of WASP-121 b
• HST/STIS capability for Love number measurement of WASP-121b
• Tidal Response and Shape of Hot Jupiters
• Stability and detectability of exomoons orbiting HIP 41378 f, a temperate Jovian planet with an anomalously low apparent density
• The impact of tidal friction evolution on the orbital decay of ultra-short period planets
• Constraining the oblateness of transiting planets with photometry and spectroscopy
• Signature of the atmospheric asymmetries of hot and ultra-hot Jupiters in lightcurves
• Relationship between the moment of inertia and the $k_2$ Love number of fluid extra-solar planets
• Exo-Geoscience Perspectives Beyond Habitability
• Tidal Distortions as a Bottleneck on Constraining Exoplanet Compositions
• TOI-2458 b: A mini-Neptune consistent with in situ hot Jupiter formation