Rapid contraction of giant planets orbiting the 20 million-years old star V1298 Tau

TL;DR

This study observes two giant planets around the 20-million-year-old star V1298 Tau, revealing rapid contraction in young giant planets, which challenges existing planetary evolution models.

Contribution

First direct mass and density measurements of young giant planets, providing evidence for faster contraction than current theories predict.

Findings

Planet b has a density similar to older giant planets.

Planet e has a higher density than most known young giant planets.

Results suggest some giant planets evolve and contract faster than models currently assume.

Abstract

Current theories of planetary evolution predict that infant giant planets have large radii and very low densities before they slowly contract to reach their final size after about several hundred million years. These theoretical expectations remain untested to date, despite the increasing number of exoplanetary discoveries, as the detection and characterisation of very young planets is extremely challenging due to the intense stellar activity of their host stars. However, the recent discoveries of young planetary transiting systems allow to place initial constraints on evolutionary models. With an estimated age of 20 million years, V1298\,Tau is one of the youngest solar-type stars known to host transiting planets: it harbours a multiple system composed of two Neptune-sized, one Saturn-sized, and one Jupiter-sized planets. Here we report the analysis of an intense radial velocity campaign, revealing the presence of two periodic signals compatible with the orbits of two of its planets. We find that planet b, with an orbital period of 24 days, has a mass of 0.64 Jupiter masses and a density similar to the giant planets of the Solar System and other known giant exoplanets with significantly older ages. Planet e, with an orbital period of 40 days, has a mass of 1.16 Jupiter masses and a density larger than most giant exoplanets. This is unexpected for planets at such a young age and suggests that some giant planets might evolve and contract faster than anticipated, thus challenging current models of planetary evolution.