Periodic transit timing variations measured for Neptune-like planet HAT-P-18 b

Researchers have used the James Webb Space Telescope to monitor the transit timings of 37 exoplanets. Among the findings, the Neptune-like planet HAT-P-18 b displays a periodic signal in the timing of its transits, suggesting complex planetary dynamics. These observations highlight the telescope's ability to track subtle orbital changes across various types of planets.

Star system: HAT-P-18 A | Distance from the Sun: 527 light years

Transit timing variations occur when a planet crosses in front of its host star at slightly different times than expected. These small shifts provide information about the orbital path of a planet and the presence of other gravitational forces in the system. By measuring these variations, observers can understand the dynamics and evolution of distant planetary systems.

The James Webb Space Telescope provides the high-precision data necessary to track these subtle events across a wide range of exoplanet sizes. By analyzing 84 transit light curves, which are graphs showing the dip in brightness as a planet passes its star, the project successfully updated transit records for 37 different worlds. This group included hot Jupiters, super-Earths, and Neptune-like planets, allowing for a broad comparison of orbital behaviors.

The analysis of HAT-P-18 b indicates a clear periodic signal in its transit timing with an amplitude of 92.9 seconds. This regular fluctuation suggests that the planet's orbit is influenced by external factors, distinguishing it from planets that maintain perfectly predictable paths. Continued observation of this system will help determine the specific cause of these variations and refine our understanding of its orbital stability.

Key findings
The Neptune-like planet HAT-P-18 b exhibits periodic transit timing variations of 92.9 seconds.
The hot Jupiter HATS-6 b shows a long-term trend in its transit period, likely caused by tidal interactions with its host star.
New data for the exoplanet WASP-121 b does not support previously reported positive period changes.
The study demonstrates that high-precision transit timing is effective for lower-mass planets in addition to larger gas giants.

Scientific study

ExoEcho: Exoplanet Ephemerides Change Observations. III. A JWST Survey for Transit Timing Variations of 37 Exoplanets (external link)