For those of you whose favorite planet is Saturn, due to its ring system, prepare to meet your new favorite planet! Astronomers have discovered an exoplanet around star J1407 with a set of rings 120,000 kilometers across–two hundred times larger than the rings of Saturn–with the planet itself being between 10-40 times as large as Jupiter, the largest planet in our solar system. The ring system is so large, it would be appear larger than the moon if it were as distant as Saturn.
The ring system was discovered by observing unusual light curves in the brightness of it’s host star. One of the means by which astronomers find exoplanets is by observing the brightness of a star over time. If a planet happens to come between us and a star we observe, then we can “see” that planet by the star’s diminished brightness.
The exoplanet in question had particularly long transit of 56 days, but a very odd dip in brightness. Other possibilities were ruled out and it was concluded that this planet had a particularly massive ring system.
Our solar system has four planets with ring systems (Jupiter, Saturn, Uranus, Neptune) with Saturn being the most notable. Ring systems form because of a phenomenon called the Roche Limit. Debris around planets often clumps together to form moons. If a moon is too close to a planet, the tidal forces of the planet will eventually tear the moon apart into moonlets, forming rings; the likely cause of the ring systems in our solar system today. The ring system around J1407b is likely caused in part by the youth of the solar system; the rings have not yet had enough time to condense into moons. The planets in our solar system may have had larger ring systems as well. As time passes J1407b’s ring system may shrink to within the Roche Limit.