Transit of giant exoplanet HIP 41378 f shows significant timing variations

Star system: HIP 41378 | Distance from the Sun: 346 light years

The giant exoplanet HIP 41378 f, which orbits its host star every 542 days, has been observed during a 19-hour transit event. This rare long-period planet, roughly 9.5 times the radius of Earth, provides researchers with a look into planetary systems that are difficult to study. By capturing this transit, the timing of the planet's passage was measured, confirming significant deviations from expected patterns known as transit timing variations.

Transit timing variations occur when the gravitational pull of other planets in a system causes a planet to arrive at its transit point earlier or later than calculated. In the case of HIP 41378 f, the planet arrived approximately 7 hours ahead of its predicted schedule. This discovery marks the planet as having the longest orbital period of any known exoplanet to exhibit such measurable timing shifts.

The data was collected through a global campaign using a variety of ground-based and space-based telescopes, including NEOSSat and the Las Cumbres Observatory Global Telescope network. By combining this new timing measurement with previous observations of the other outer planets in the system, HIP 41378 d and HIP 41378 e, researchers were able to refine the orbital models and predict future transits for the outer planets.

Key findings
- HIP 41378 f is confirmed as the longest-period exoplanet to show measurable transit timing variations.
- The transit on October 31, 2025, occurred 7 hours earlier than linear predictions suggested.
- Dynamical modeling of the system allows for more accurate predictions of future transit events for the outer planets.
- The transit duration of 19 hours was captured through a coordinated multi-site observing campaign.

Scientific study

Observing a 542-day transiting giant with large TTVs: The 2025 transit of HIP 41378 f and new constraints on the outer system (external link)