TOI 813 b is a newly validated Saturn-sized exoplanet orbiting a bright subgiant star on an 84-day orbital period, discovered through a combination of NASA’s Transiting Exoplanet Survey Satellite (TESS) photometry and citizen science analysis via the Planet Hunters TESS project, according to an arxiv.org report.
Citizen Science Finds Planet Orbiting Evolved Subgiant Star
- The newly confirmed planet orbits an evolved subgiant star, providing a rare benchmark to study planetary system evolution as host stars expand.
- Detection relied on non-standard citizen science methods rather than automated search pipelines, which typically miss single-transit events outside short orbital windows.
- The host star’s bright visual magnitude of under 11 enables future radial velocity mass measurements with an expected semi-amplitude of approximately 6 meters per second.
Uncovering Long-Period Planets in TESS Sector Data
The Transiting Exoplanet Survey Satellite (Ricker et al., 2015, TESS) operates as an all-sky space mission designed to monitor roughly 85 percent of the sky across 26 observational sectors. Targets in low ecliptic latitudes receive approximately 27.4 days of continuous monitoring. This short baseline heavily skews early automated returns toward rapid orbits. Data shows that 88 percent of the first 1,075 TESS Objects of Interest exhibit periods under 15 days, while 95 percent stay under 30 days. Standard detection pipelines demand two or three transit events to secure the signal-to-noise ratio necessary for confirmation. Consequently, identifying wider orbits requires alternative frameworks, including machine learning, probabilistic transit model comparison, and citizen science platforms.
Citizen Science Detection of TIC 55525572 b
The candidate designated as TOI 813 b (TIC 55525572 b) first surfaced as a single-transit event flagged by volunteer participants in the Planet Hunters TESS project. Subsequent identification of additional transit windows allowed researchers to constrain the orbital period to approximately 84 days. This makes it the longest-period validated planet found by TESS. The host star is actively transitioning away from the main sequence onto the red giant branch. Evolved subgiants are rarely targeted by transit surveys because their enlarged radii generate shallower, longer transit signatures that complicate automated detection. Their rotational velocity profiles make precise radial velocity follow-up work more difficult.
Future Radial Velocity Mass Constraints
Despite the challenges posed by evolved host stars, the brightness profile of the subgiant alongside a calculated Doppler semi-amplitude of roughly 6 meters per second positions TOI 813 b for precise mass determination. Because subgiant and giant phases represent short-lived evolutionary states in the solar neighborhood, known planets around these stars remain scarce. This target supplies a unique observational laboratory to examine how mature planetary structures react to rising stellar flux and physical proximity as parent stars expand.
| Parameter | Observed Value |
|---|---|
| Host Star Designation | TIC 55525572 (TOI 813) |
| Planet Designation | TOI 813 b |
| Planetary Size Class | Saturn-sized |
| Orbital Period | ~84 days |
| Doppler Semi-Amplitude | ~6 m s-1 |
