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A football-shaped exoplanet

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According to astrophysicist Susana Barros and her colleagues, the exoplanet discovered in 2014 has been distorted by tidal forces between the planet and its host star, which is about 1.7 times the size of the Sun.

This planet, called WASP-103b, is located in the constellation of Hercules at a distance of about 1,800 light years from our solar system. Detected using data collected by the European Space Agency’s (ESA) Cheops Space Telescope, it is about 50 times closer to its star WASP-103 than Earth is to the Sun. For this reason, the exoplanet circles its star in just 22 hours, compared to 365 days for Earth.

Because of this, WASP-103b experiences an extreme tidal force which, failing to destroy it, gives it a rare form.

This is the first time that the deformation of an exoplanet has been detected, offering new information on the internal structure of these planets extremely close to their star, explains the Observatory in a press release.

The oceanic tides on Earth are mainly due to the pull of the Moon. The Sun has a weak, nonetheless significant effect on the tides, but it is too far from our planet to cause significant deformations.

For its part, WASP-103b is almost twice the size of Jupiter at 1.5 times its mass. While astronomers suspected that such proximity would cause monumental tides, they had failed to measure them until now.

It was by analyzing data collected by Cheops, which they combined with data obtained by the Hubble and Spitzer telescopes, that astronomers were able to determine how tidal forces distort the exoplanet.

Its deformation should eventually make it possible to determine its internal structure, rocky or gaseous, because the resistance of a material to deformation depends on its composition, notes Susanna Barros.

Cheops was placed in orbit in December 2019. The telescope measures the transits of exoplanets, that is to say the decrease in light caused when a planet passes in front of its star. Usually, this technique can detect exoplanets and reveal certain details, such as their size. Cheops’ high accuracy allowed detection of the tiny tidal deformation signal from WASP-103b.

A symbiotic relationship

This work also sheds light on another mystery surrounding WASP-103b. Usually, tidal interactions between a star and a planet very close to the size of Jupiter would lead to a shortening of the planet’s orbital period. This reality would gradually bring her closer to the star before she was engulfed by it.

However, the data seems to show that WASP-103b seems to indicate that its orbital period is increasing and that it is slowly moving away from the star. This would indicate that something other than tidal forces is affecting this planet, say the researchers in the press release.

According to them, several scenarios can explain this phenomenon. For example, another star in a binary system could influence the dynamics of the system or the orbit of the slightly elliptical planet. Future observations of WASP-103b transits may explain the mystery.

Details of this work are published in the journal Astronomy & AstrophysicsHave (New window)Have (in English).

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