How does a forming planet behave?

Planets form inside protoplanetary disks, structures of gas and dust that revolve around young stars. As these planets grow, gravitational potential energy is transformed into kinetic energy and heat, which can have a great impact on the surrounding material, heating and even expelling gas and dust.

In recent years, different teams have obtained images of protoplanetary disks in which a “hot spot” is observed (candidates that can be counted on the fingers of one hand), which is thought to be a planet in formation, however, it is necessary to better understand what we are really seeing in these images and, if this point does correspond to a planet, to study how it is growing.

A team of astrophysicists, in which Jorge Cuadra, associate researcher at the Millennium Nucleus of Planet Formation, and Matías Montesinos, a postdoctoral researcher at the same center, participated, carried out numerical simulations of a protoplanetary disk with a growing planet, to analyze how fast it accretes (gains) material and how much energy is released by this process, something new in this type of work. This research was published this month in the prestigious scientific journal Monthly Notices of the Royal Astronomical Society, in an article led by Matías Gárate, who did his master’s thesis with Cuadra and currently a postdoctoral researcher at the Max Planck Institute for Astronomy in Germany.

“Our first important result is that the energy released does not stop the growth of the planet, but it  does slow it, since it is more difficult for the planet to accrete hot gas, which tends to escape”, explains Jorge Cuadra, who also is an academic in the Department of Sciences of the Faculty of Liberal Arts of the Universidad Adolfo Ibáñez.

The scientist adds that it was found that the release of energy causes the planet to gain mass in a variable way: at times faster, at times slower. In principle, this effect could be measured by making repeated observations of a growing planet, which would change its brightness in this way.

The research was carried out using the publicly available numerical code FARGO, specially designed to simulate protoplanetary disks, which the team modified to be able to calculate the growth of the planet and the release of energy.

“These results are relevant because we are trying to understand the details of the planetary formation process. Today there are still very few observations of this process, and they are not very clear either because they are at the limit of what telescopes can do. So the computational models help us better understand what should be happening, and thus interpret the observations well”, Cuadra emphasizes.

Regarding the next steps of this study, Cuadra indicates that the immediate thing is to improve the simulations, for example, going from two dimensions to three, which is more realistic but much more challenging to simulate. “In the longer term, in this study we are proposing how future observations of growing planets can give us details of this process. These observations are not possible today, but at NPF we are trying to contribute to the development of the Planet Formation Imager observatory, which will be capable of doing so ”, he concludes.

Scientific publication 

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