Gas giant planets form by the transfer of material from the circumstellar disk, through a circumplanetary disk (CPD) and onto the planet. In the last stages of formation, the circumstellar material is exhausted and the remaining CPD accretes onto the gas giant planet, with moons forming and carving out transient ring-like structures in the planet’s Hill sphere. These exorings can be hundreds of times larger than Saturn’s rings, up to one astronomical unit in diameter.
In 2015, the young star J1407 underwent a complex and deep 56 day eclipse that had photometric variations down to timescales of hours. We interpret this as the transit of a giant ring system within the Hill sphere of a substellar companion. Amongst the follow up observations, the ALMA array detected a sub-mm source consistent with emission from warm dust in a giant ring system near J1407, and over the past year, we have been intensively monitoring another potential transiting ring system towards the nearby star J0600.
In this talk we discuss our observations of J1407 and J0600, and show how they can provide insight into the last stages of giant planet and moon formation.