ESA exoplanet The Cheops mission has revealed that an exoplanet orbiting its host star in a day has a distorted shape closer to that of a rugby ball than a sphere. This is the first time that the deformation of an exoplanet has been detected, offering new information on the internal structure of these planets close to stars.
The planet, known as WASP-103b, is located in the constellation of Hercules. It was distorted by strong tidal forces between the planet and its host star WASP-103, which is about 200 degrees hotter and 1.7 times larger than the Sun.
We experience tides in Earth’s oceans primarily due to the Moon’s slight tug on our planet as it orbits us. The Sun also has a small but significant effect on the tides, however it is too far from Earth to cause major deformations of our planet. The same cannot be said for WASP-103b, a planet almost twice the size of Jupiter with 1.5 times its mass, orbiting its host star in less than a day. Astronomers suspected that such proximity would cause monumental tides, but so far they have not been able to measure them.
Using new data from ESA’s Cheops space telescope, combined with data already obtained by the ">Nasa/ESA The Hubble Space Telescope and NASA’s Spitzer Space Telescope, astronomers have now been able to detect how tidal forces are warping exoplanet WASP-103b from a usual sphere into a rugby ball shape.
Cheops measures exoplanet transits – the dip in light caused when a planet passes in front of its star from our perspective. Ordinarily, studying the shape of the light curve will reveal details about the planet such as its size. Cheops’ high accuracy coupled with its pointing flexibility, which allows the satellite to return to a target and observe multiple transits, allowed astronomers to detect the tiny signal of WASP-103b’s tidal warping. This distinct signature can be used to reveal even more about the planet.
“It’s amazing that Cheops was able to reveal this tiny deformation,” says Jacques Laskar of the Paris Observatory, University of Paris Sciences and Letters, and co-author of the research. “This is the first time that such an analysis has been done, and we can hope that observation over a longer time interval will strengthen this observation and lead to a better understanding of the internal structure of the planet.”
The team was able to use WASP-103b’s transit light curve to derive a parameter – the love count – that measures the distribution of mass on a planet. Understanding how mass is distributed can reveal details about the internal structure of the planet.
“A material’s resistance to deformation depends on its composition,” says Susana Barros of the Instituto de Astrofísica e Ciências do Espaço and the University of Porto, Portugal, and lead author of the research. “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 much. By measuring how distorted the planet is, we can tell how rocky, gassy, or watery it is.
The love number for WASP-103b is similar to Jupiter, which tentatively suggests that the internal structure is similar, although WASP-103b has twice the radius.
“In principle, we would expect a planet with 1.5 times the mass of Jupiter to be about the same size, so WASP-103b must be very puffy due to its star heating and possibly d ‘other mechanisms’, explains Susana.
“If we can confirm the details of its internal structure with future observations, we might be able to better understand what makes it so puffy. Knowing the size of the core of this exoplanet will also be important to better understand how it formed. .
Since the uncertainty in Love’s number is still quite high, it will take future observations with Cheops and the James Webb (Webb) Space Telescope to decipher the details. Webb’s extremely high precision will improve measurements of exoplanet tidal warping, allowing better comparison between these so-called “hot Jupiters” and the giant planets of the solar system.
Another mystery also surrounds WASP-103b. Tidal interactions between a star and a planet very close to the size of Jupiter would typically cause the planet’s orbital period to shorten, gradually bringing it closer to the star before it was eventually engulfed by the parent star. However, measurements from WASP-103b seem to indicate that the orbital period may be increasing and the planet is slowly moving away from the star. This would indicate that something other than tidal forces is the dominant factor affecting this planet.
Susana and her colleagues looked at other potential scenarios, such as a host companion star affecting the system’s dynamics or the planet’s slightly elliptical orbit. They weren’t able to confirm these scenarios, but they couldn’t rule them out either. It is also possible that the orbital period is decreasing rather than increasing, but only further observations of WASP-103b’s transits with Cheops and other telescopes will help unravel this mystery.
“The magnitude of the effect of tidal warping on an exoplanet transit light curve is very small, but thanks to the very high precision of Cheops, we are able to see it for the first time,” says Kate Isaak, ESA’s Cheops project scientist. “This study is an excellent example of the wide-ranging questions that exoplanet scientists are able to address with Cheops, illustrating the importance of this flexible tracking mission.”
Reference: “Tidal deformation detection of WASP-103b at 3 σ with CHEOPS” by SCC Barrosg, B. Akinsanmi, G. Boué, AMS Smith, J. Laskar, S. Ulmer-Moll, J. Lillo-Box , D Queloz, A. Collier Cameron, SG Sousa, D. Ehrenreich, MJ Hooton, G. Bruno, B.-O. Demory, ACM Correia, ODS Demangeon, TG Wilson, A. Bonfanti, S. Hoyer, Y. Alibert, R. Alonso, G. Anglada Escudé, D. Barbato, T. Bárczy, D. Barrado, W. Baumjohann, M. Beck, T. Beck, W. Benz, M. Bergomi, N. Billot, X. Bonfils, F. Bouchy, A. Brandeker, C. Broeg, J. Cabrera, V. Cessa, S. Charnoz, CCV Damme, MB Davies, M. Deleuil, A. Deline, L. Delrez, A. Erikson, A. Fortier, L. Fossati, M. Fridlund, D. Gandolfi, A. García Muñoz, M. Gillon, M. Güdel, KG Isaak, K. Heng, L. Kiss, A. Lecavelier des Etangs, M. Lendl, C. Lovis, D. Magrin, V. Nascimbeni, PFL Maxted, G. Olofsson, R. Ottensamer, I. Pagano, E. Pallé, H Parviainen, G. Peter, G. Piotto, D. Pollacco, R. Ragazzoni, N. Rando, H. Rauer, I. Ribas, NC Santos, G. Scandariato, D. Ségransan, AE Simon, M. Steller, Gy . M. Szabó, N. Thomas, S. Udry, B. Ulmer, V. Van Grootel and NA Walton, January 11, 2022, Astronomy & Astrophysics.