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First evidence of an oval exoplanet

First evidence of an oval exoplanet

On Earth there are tides in the oceans, mainly due to the Moon slightly ‘pulling’ on our planet as it orbits us. The Sun also has a small but significant effect on the tides, although it is too far away to cause major deformations here.

The exoplanet WASP-103b has been warped by powerful tidal forces acting in close proximity to its host star, WASP-103, which is hotter and larger than our Sun.

Now, an international scientific team, with the participation of the Center for Astrobiology (CAB, CSIC-INTA), has detected the first oval-shaped exoplanet due to these powerful tidal forces: WASP-103b. The results are published in the journal Astronomy and Astrophysics.

The star around which this exoplanet revolves, called WASP-103, at the constellation of Hercules, is about 1.7 times larger than our Sun and has a temperature 200 degrees higher.

On the other hand, WASP-103b is a planet gas giant nearly twice the size of Jupiter and 1.5 times its mass. Its extreme proximity to its host star can cause gigantic tides, something that has so far been unconfirmed.

rugby ball shape

“This exoplanet takes less than a day to go around its star and its shape is more like a rugby ball than a sphere,” he says. Jorge Lillo-Box, a CAB researcher who participated in this study, who adds: “We had theorized about these planetary deformations, but this is the first time that we have verified this with observations.”

The infographic shows how powerful tidal forces from the star WASP-103 warped the planet WASP-103b. / AT THAT

Using new data from Cheops Space Telescope From the European Space Agency (ESA), combined with previous data obtained by the Hubble and Spitzer space telescopes, the astronomical community was able to detect how tidal forces warp the exoplanet WASP-103b, giving it an oval shape.

These data were complemented with high spatial resolution images from the instrument. AstraLux, at the Calar Alto Observatory (Almería), thanks to which it was possible to confirm the origin of the signal.

The CHEOPS mission and Love’s numbers

cheops measures the exoplanet transits, that is, the faint decrease in light caused when a planet passes in front of its star from our point of view. Typically, studying the shape of the light curve reveals details about the planet, such as its size. But in this case, Cheops’ high accuracy, along with its pointing flexibility, which allows the satellite to return to a target and observe multiple transits, made it possible to detect the tiny signal that indicates WASP-103b is being warped. by tidal forces.

This is the first time that a study of this type has been carried out, which also made it possible to use the WASP-103b traffic light curve to derive a parameter, the love number.

This number measures how mass is distributed within a planet, something that can reveal details about its internal structure, giving us information about the strength of materials and determining in what proportion it can have a rocky, gaseous or liquid composition.

We had theorized about these planetary deformations, but this is the first time we’ve verified this with observations.

Jorge Lillo-Box (CAB)

“Understanding this internal structure is essential for understanding the processes of formation and evolution of planetary systems,” says Lillo-Box.

The exoplanet WASP-103b’s Love number is similar to that of Jupiter, suggesting that the internal structure may be similar despite WASP-103b being twice the radius. This is because it is ‘inflated’, probably by the heat emanating from its host star and by other mechanisms that could be studied in the future with more observations, both with CHEOPS and the James Webb Space Telescope.

The great precision that the latter will achieve will improve measurements of the deformation caused by the tidal force on exoplanets, helping to know more about their internal structure and, specifically, about their core, which could reveal how they were formed.

mysterious movements

But WASP-103b holds more mysteries. Tidal interactions between a star and a Jupiter-sized planet so close should cause the planet’s orbital period to decrease, gradually bringing it closer to the star before it is finally engulfed by it.

WASP-103b’s measurements seem to indicate that it is slowly moving away from the star, which would indicate that, in addition to tidal forces, there must be another factor influencing the planet: a companion star?

However, measurements from WASP-103b seem to indicate that the orbital period may be increasing and that the planet is slowly moving away from the star. This would indicate that, in addition to tidal forces, there must be another factor that is influencing the planet.

“The team raised the possibility of the presence of a companion star that can affect the dynamics of the system’s movements or make the orbit slightly elliptical”, says the co-author david barrado, a CAB researcher, who anticipates: “We have not been able to confirm or disprove this possibility, so it will be necessary to carry out more observations of the system to reveal what is causing the planet to move away from the star.”


SCC Barros et al. “Cheops reveals WASP-103b’s tidal deformation”. Astronomy and Astrophysics, 2022.

Spanish participation in Cheops: The company responsible for the design and construction of the spacecraft was Airbus Defense and Space, and the Operations Center for this ESA mission is located at the premises of the Instituto Nacional de Tecnologia Aeroespacial (INTA) in the city of Torrejón de Ardoz, Madrid. .

Rights: Creative Commons.


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