天文学：近くの恒星を周回する若いトランジット惑星が発見される

The detection of a giant planet that transits a very young star is reported in Nature. The findings indicate that this is the youngest transiting planet found to date.

Scientists have previously discovered more than a dozen transiting planets (planets that pass between a star and an observer such as Earth) around stars that are 10–40 million years old. However, there have been no detections of younger transiting planets; this is perhaps because the planets have not fully formed yet, or because our view of such planets is blocked by a residual protoplanetary disk (the ring of dense gas and dust surrounding a newly formed star from which the planets form).

Madyson Barber and colleagues analysed data from NASA’s Transiting Exoplanet Survey Satellite and observed a young (3-million-year-old) star, IRAS 04125+2902, which is located relatively close to Earth (160 parsecs). The outer protoplanetary disk surrounding this star is misaligned and presents almost face on, as opposed to side on, while also having a depleted inner disk; this combination of features has enabled the observation of the transiting protoplanet IRAS 04125+2902 b. This planet has been shown to have an orbital period of 8.83 days, a radius 10.7 times larger than Earth, and approximately 30% of the mass of Jupiter. The authors suggest that it could be a precursor of the super-Earth and sub-Neptune planets that are frequently found orbiting main-sequence stars.

Given the young age of this star and planet, the rare disk misalignment, and the relatively close proximity to Earth, the authors suggest that this system could be a useful target for studying the early stages of planet formation.