Astronomers using three space telescopes were the first to directly detect the tidal deformation of an exoplanet while observing its transits along the disk of its star. It turned out that the internal structure of WASP-103b may be similar to Jupiter, despite the difference in size and radiation levels from the side of the stars. The most distinctive feature of the exoplanet is its shape – it is not a sphere.
Exoplanets with short orbital periods
Exoplanets with an ultrashort period include bodies whose orbital period is less than one Earth day. These planets are exposed to intense radiation and tidal forces from the star, which allows astronomers to study the interaction of planets with stars.
In particular, tidal forces are responsible for the synchronization of the rotation periods of the planet and the star, the deformation of the planet, and even the reduction of its orbit, which ultimately can lead to the fall of the exoplanet onto the star along a spiral trajectory.
If the planet’s shape is distorted, the effect will be most pronounced for large objects that almost fill their Roche lobes, such as superhot Jupiters. The radial deformation of a planet can be estimated using the Love number, which characterizes the distribution of mass within the planet depending on the concentration of heavy elements in the core relative to the outer shell of the planet.
Scientists discovered WASP-103b, an exoplanet that is not a sphere
A group of astronomers led by Susana Barros from the Institute of Astrophysics and Space Sciences in Porto has published the results of studies of the interaction of the exoplanet WASP-103b with its star.
Scientists analyzed the data of observations of the passage of WASP-103b on the disk of the star, which were obtained by the CHEOPS space telescope, as well as archived observational data obtained by the Hubble and Spitzer space telescopes.
WASP-103b is located near an F-type star at a distance of 1,532 light-years from the Sun, in the constellation Hercules. The exoplanet’s mass is 1.5 times the mass of Jupiter, the radius is 1.5 times the radius of Jupiter, and a year on it lasts 22 hours.
Analysis of the observational data made it possible to determine the value of the radial Love number hf for WASP-103b, which is slightly higher than the value obtained for Saturn and is similar to the value obtained for Jupiter.
This means that the two planets can be similar in internal structure, despite the different sizes and levels of radiation from the stars. The shape of exoplanet WASP-103b looks more like an ellipsoid rather than a sphere, due to the tidal forces from the side of the star.
An unusual conclusion of the work was that the exoplanet’s orbital period is increasing, rather than decreasing, as predicted in theory, as a result of which WASP-103b slowly drifts away from the star.
Possible explanations could be a companion star in the system, statistical artifacts, the Applegate effect, or apsidal precession, but none of these hypotheses has yet been confirmed or refuted. Scientists need new observational data from WASP-103b in order to understand the peculiarities of the planet’s orbital motion and more accurately assess its internal structure.
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• Barros, S. C. C., Akinsanmi, B., & Boué, G. (n.d.). Detection of the tidal deformation of WASP-103b at 3 σ with CHEOPS. Astronomy & Astrophysics.
• ESA. (n.d.). Cheops reveals a rugby ball-shaped exoplanet.
• Howell, E. (2022, January 11). Weird ‘hot Jupiter’ exoplanet is shaped like a football. Space.com.
• Tran, T. (2022, January 11). Scientists just discovered a planet that’s not a sphere. Futurism.