Artist's impression of Corot-7b

Exoplanet CoRoT-7b (artist’s impression) orbits a relatively low-mass star. Credit: ESO/L. Calçada

ASTRONOMY AND ASTROPHYSICS

 


During formation, the planets can draw a greater amount of hydrogen and helium around themselves, causing them to increase in size.
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Planets that form around more-massive stars can efficiently wrap themselves in a blanket of gas — making them larger than planets around less-massive stars.

More than 4,400 planets are confirmed to exist outside the Solar System. Among parent stars that have a mass lower than that of the Sun, comparably more-massive stars tend to host larger planets than do lower-mass stars. Astronomers have puzzled over why this might be.

Michael Lozovsky at the University of Zurich in Switzerland and his colleagues analysed data from NASA’s database of exoplanets, and modelled what planets of different sizes and masses might be made of.

The authors’ calculations suggest that planets around relatively massive stars are more efficient at accreting hydrogen and helium gas from the swirling disks of gas and dust from which they form. These planets grow more quickly and so grow larger before the disk runs out of material and dissipates.

Other possible explanations, such as the host star heating up the planet and causing it to balloon in size, are less plausible, the researchers say.

Astron. Astrophys. (2021)