A Neptune-sized transiting planet closely orbiting a 5-10-million-year-old star

TL;DR

This paper reports the discovery of a young, Neptune-sized transiting planet orbiting a 5-10 million-year-old star, providing insights into early planet formation and migration processes.

Contribution

It presents the first detection of a fully formed, close-in planet around a very young star, challenging existing theories of planet formation timelines.

Findings

The planet is 50% larger than Neptune.

Its mass is less than 3.6 times Jupiter's, likely near Neptune's mass.

The star hosts a dust disk and a close-in planet at less than one-twentieth AU.

Abstract

Theories of the formation and early evolution of planetary systems postulate that planets are born in circumstellar disks, and undergo radial migration during and after dissipation of the dust and gas disk from which they formed. The precise ages of meteorites indicate that planetesimals - the building blocks of planets - are produced within the first million years of a star's life. A prominent question is: how early can one find fully formed planets like those frequently detected on short orbital periods around mature stars? Some theories suggest the in situ formation of planets close to their host stars is unlikely and the existence of such planets is evidence for large scale migration. Other theories posit that planet assembly at small orbital separations may be common. Here we report on a newly-born, transiting planet orbiting its star every 5.4 days. The planet is 50 per cent larger than Neptune, and its mass is less than 3.6 times Jupiter (at 99.7 per cent confidence), with a true mass likely to be within a factor of several of Neptune's. The 5-10 million year old star has a tenuous dust disk extending outwards from about 2 times the Earth-Sun separation, in addition to the large planet located at less than one-twentieth the Earth-Sun separation.