Super-young protoplanet challenges planet formation theory

An international team of astronomers has photographed the youngest planet recorded to date – and it might tell us more about planetary formation.

The protoplanet, which is a planet in its developmental stages, is still shrouded in the matter it’s forming from and orbits the star AB Aurigae, about 531 light-years from our Sun.

The researchers identified the protoplanet with imagery of AB Aurigae taken by the Hubble Space Telescope and the Subaru Telescope, in Hawaii, US. They’ve published their findings in Nature Astronomy.

Swirling image labelled subaru telescope image of ab aurigae, with circle showing neptunes orbit and arrow pointing to protoplanet in bright spot
AB Aurigae, taken by the Subaru Telescope. The star has been masked and is represented by a 5-point star, and the protoplanet spot is pointed out. Credit: T. Currie/Subaru Telescope

Analysis of the images shows that the anomaly in the star’s orbit can’t be reflected starlight, and it can’t be an older planet. The researchers say that the best fit is a protoplanet, still surrounded by a protoplanetary disc. The protoplanet is likely becoming a gas giant, like Jupiter (a Jovian planet).

The most unusual thing about the protoplanet is its distance from its star: it’s 93 AU (astronomical units) away. For context, Earth is one AU away from our Sun, and Neptune is only 30.

Read more: How was the asteroid belt formed?

Previously, it was thought that the rocky cores of Jovian planets had to form much closer to the centre of stars than this. But if this discovery pans out, then the canonical theory of Jovian planet formation needs work.

“This study sheds new light on our understanding of the different ways that planets form,” says lead author Dr Thayne Currie, an astrophysicist at the NASA-Ames Research Center, US, and the Subaru Telescope.

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