| HIP 41378 f | |
| Discoverer: | K2 (Vanderburg et al.) |
| Discovered: | June 2016 |
| Discovery Method: | Transit |
| Apsis: | astron |
| Star: | HIP 41378 |
| Mean Radius: | (or with rings) |
| Density: | (or with rings) |
| Single Temperature: | Teq 294K |
HIP 41378 f (also known as EPIC 211311380 f) is an exoplanet orbiting around the F-type star HIP 41378. It is the outermost planet of its system and notable for the possibility that the planet may host circumplanetary debris rings. It has an anomalously large radius (9.2) for a planet of its size and temperature. This radius, combined with its measured mass of (12), suggest that its core is a maximum of 3 and subsequently the planet has an envelope fraction of 75% or greater.[1] This envelope fraction is larger than would be possible in the core accretion model of planet formation for a planet with its core mass, which is consistent with the hypothesis that the planet's radius may be observed to be larger than it actually is due to an optically thick ring system.[2] One proposed origin for such a ring system is an exomoon, which migrated and disintegrated in the past.[3] It is located within the optimistic habitable zone of its parent star. No atmospheric signatures were found as of 2022, further reinforcing the hypothesis of opaque circumplanetary rings.
A 2023 study analyzed the orbital stability and detectability of a hypothetical Mars-sized exomoon orbiting HIP 41378 f, finding that the existence of such a moon is feasible but is currently unlikely to be detectable.