Discovered in 2015 by the Kepler satellite, the exoplanet HIP 41378 f has an abnormal density, less than one tenth that of water. Akinsanmi et al. suggest that HIP 41378 is probably denser and smaller, but surrounded by rings.
Abstract: The presence of rings around a transiting planet can cause its radius to be overestimated and lead to an underestimation of its densityif the mass is known. We employed a Bayesian framework to show that the anomalously low density (∼0.09 g cm^−3) of the transitinglong-period planet HIP 41378f might be due to the presence of opaque circum-planetary rings. Given our adopted model priorsand data from the K2 mission, we find the statistical evidence for the ringed planet scenario to be comparable to that of the planet-only scenario. The ringed planet solution suggests a larger planetary density of ∼1.23 g cm^−3 similar to Uranus. The associated ringextends from 1.05 to 2.59 times the planetary radius and is inclined away from the sky plane by ∼25 degree. Future high-precision transitobservations of HIP 41378f would be necessary to confirm/dismiss the presence of planetary rings.