TOI-1855 b
Astrophysical Synthesis & Habitability Characterization
TOI-1855 b is a confirmed gas giant exoplanet orbiting the star TOI-1855, located approximately 576.8 light-years (176.83 parsecs) from the Solar System. First announced in 2024 by Transiting Exoplanet Survey Satellite (TESS) using the Transit detection technique (producing an estimated primary transit depth of 2.6531% across the stellar disk), this world measures 18.495 Earth radii (1.65 Jupiter radii) and has a measured mass of 360.1 Earth masses (1.13 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.31 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.05 g⊕ (10.3 m/s²), and an escape velocity of 49.4 km/s.
In its orbital architecture around TOI-1855, TOI-1855 b completes one full revolution every 1.364 Earth days at a semi-major axis of 0.02398 AU (an ultra-close orbit less than one-seventh of Mercury's 0.387 AU distance from the Sun, where strong stellar tidal forces typically induce synchronous rotation). Its mean orbital velocity is approximately 191.2 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.033 (ranging from 0.0232 AU at periapsis to 0.0248 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1701 K (+1428°C / +2602°F) and receiving 852.16 S⊕ (~1,159,792 W/m²), TOI-1855 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star TOI-1855 is classified as a stellar host with an effective photospheric temperature of 5,359 K, a radius of 1.041 R☉, a mass of 0.987 M☉, an estimated bolometric luminosity of 0.802 L☉. Stellar evolution modeling indicates an estimated stellar age of 8.2 Gyr and a metallicity of [Fe/H] = 0.399 dex (metal-rich relative to the Sun). From Earth, TOI-1855 shines at apparent V-band magnitude 11.197 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.
Methodology: Computed using the Schulze-Makuch et al. (2011) weighted metric comparing physical interior (radius, estimated density) and surface thermal regime (escape velocity, equilibrium temperature).
Discovery Facility: Transiting Exoplanet Survey Satellite (TESS) · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | TOI-1855 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,359 K |
| Stellar Radius | 1.0410 R☉ |
| Stellar Mass | 0.9870 M☉ |
| Bolometric Luminosity | 0.802 L☉ |
| Metallicity [Fe/H] | 0.399 dex |
| Stellar Age | 8.200 Gyr |
| Apparent Magnitude | V: 11.197 · G: 11.161 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.023980 AU |
| Orbital Period | 1.364 days |
| Mean Orbital Velocity | 191.2 km/s |
| Orbital Eccentricity (e) | 0.03300 |
| Orbital Inclination (i) | 78.1000° |
| Mean Bulk Density | 0.31 g/cm³ (49.4 km/s vesc) |
| Insolation Flux | 852.1620 S⊕ (~1,159,792 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 576.800 LY (176.833 pc) |