Rugby ball instead of ball: exoplanet WASP-103b elongated by its star

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The giant exoplanet WASP-103b orbits so close to its star that it is deformed by its gravity and looks more like a rugby ball than a sphere. This is what an international research team found out using ESA’s Cheops space telescope, which is the first time ever such an analysis has been carried out. They also worked out details of the exoplanet’s structure and found that the world is about twice the size of Jupiter, even though it is only about one and a half times the mass of the largest planet in the solar system. So far they can only formulate theories about why it is so bloated.

WASP-103b, discovered in 2014, is 1,225 light-years from Earth and orbits its star just 0.02 astronomical units (AU) away. In the solar system that would be about halfway between Mercury and the sun. The exoplanet needs less than one earth day to orbit its star – which is almost twice the size of the sun. All of this ensures the extreme conditions that prevail there, explain the astronomers. While large bodies of water on earth are deformed by the gravitational pull of the moon in such a way that tides are formed, the gas planet WASP-103b as a whole is being elongated. This makes it more like a rugby ball than a ball.

The researchers had already suspected that WASP-103b had large tides due to the short distance to the star, explain now. With Cheops (Characterizing ExOPlanet Satellite) they would also have an instrument at their disposal to investigate this. The extremely precise observatory was aligned in such a way that it could observe several transits of the exoplanet in front of its star, and the light curves then made the deformation visible. Furthermore, it was even possible to determine how mass is distributed inside the exoplanet. It has been shown that WASP-103b is apparently inflated compared to Jupiter. This could be due to the heat of the nearby star, but also to other mechanisms.

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Finally, the movement of WASP-103b puzzles. Actually, it is to be expected that a huge planet that circled so closely around its star would be drawn closer and closer to it until it crashes into it at some point. However, initial measurements on WASP-103b instead suggest that it is even slowly moving away from its star. There are various attempts to explain this, but so far none of them can be confirmed or excluded. Further analyzes are necessary. The research work is now published in the journal Astronomy & Astrophysics turn into.


(mho)

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