Astronomers have obtained 12 new high-precision transit observations of WASP-103b — a planet almost twice the size of Jupiter with 1.5 times its mass — with ESA’s CHaracterising ExOplanet Satellite (CHEOPS) to study the tidal interaction with its host star, WASP-103.
“It’s incredible that CHEOPS was actually able to reveal this tiny deformation,” said Dr. Jacques Laskar, an astronomer with Paris Observatory at the Université Paris Sciences et Lettres.
“This is the first time such analysis has been made, and we can hope that observing over a longer time interval will strengthen this observation and lead to better knowledge of the planet’s internal structure.”
“Because of its great proximity to its star, we had already suspected that very large tides are caused on the planet. But, we had not yet been able to verify this,” said Professor Yann Alibert, an astronomer at the University of Bern.
WASP-103b is significantly more massive (1.5 Jupiter masses) and larger (2 Jupiter radii) than Jupiter.
Discovered in 2014, it orbits the F8-type main-sequence star WASP-103 once every 22 hours.
Also known as TIC 276754403 and 2MASS J16371556+0711000, the star is about 1.7 times larger and 200 degrees Celsius hotter than the Sun.
The system is located approximately 1,800 light-years (552 parsecs) away in the constellation of Hercules.
Dr. Lask, Professor Alibert and their colleagues were able to use the transit light curve of WASP-103b to derive a parameter — the Love number — that measures how mass is distributed within a planet.
Understanding how mass is distributed can reveal details on the internal structure of the planet.
“The resistance of a material to being deformed depends on its composition,” said Dr. Susana Barros, an astronomer at the Instituto de Astrofísica e Ciências do Espaço and the University of Porto.
“For example, here on Earth we have tides due to the Moon and the Sun but we can only see tides in the oceans.”
“The rocky part doesn’t move that much. By measuring how much the planet is deformed we can tell how much of it is rocky, gaseous or water.”
The Love number for WASP-103b is similar to Jupiter, which tentatively suggests that the internal structure is similar.
“In principle we would expect a planet with 1.5 times the mass of the Jupiter to be roughly the same size, so WASP-103b must be very inflated due to heating from its star and maybe other mechanisms,” Dr. Barros said.
“If we can confirm the details of its internal structure with future observations maybe we could better understand what makes it so inflated.”
“Knowing the size of the core of this exoplanet will also be important to better understand how it formed.”
The study was published in the journal Astronomy & Astrophysics.
S.C.C. Barros et al. 2022. Detection of the tidal deformation of WASP-103b at 3 σ with CHEOPS. A&A 657, A52; doi: 10.1051/0004-6361/202142196
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