TOI-5398 c
Astrophysical Synthesis & Habitability Characterization
TOI-5398 c is a confirmed sub-neptune exoplanet orbiting the star TOI-5398, located approximately 426.8 light-years (130.86 parsecs) from the Solar System. First announced in 2023 by Transiting Exoplanet Survey Satellite (TESS) using the Transit detection technique (producing an estimated primary transit depth of 0.0943% across the stellar disk), this world measures 3.52 Earth radii (0.31 Jupiter radii) and has a measured mass of 11.8 Earth masses. Combining its mass and radius yields a mean bulk density of 1.49 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.95 g⊕ (9.32 m/s²), and an escape velocity of 20.5 km/s.
In its orbital architecture around TOI-5398, TOI-5398 c completes one full revolution every 4.773 Earth days at a semi-major axis of 0.057 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 129.9 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.14 carries the world between 0.049 AU at periapsis and 0.065 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1242 K (+969°C / +1776°F) and receiving 370.60 S⊕ (~504,391 W/m²), TOI-5398 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star TOI-5398 is classified as a solar-type yellow star of spectral type G V with an effective photospheric temperature of 6,000 K, a radius of 1.051 R☉, a mass of 1.146 M☉, an estimated bolometric luminosity of 1.284 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.65 Gyr and a metallicity of [Fe/H] = 0.09 dex (metal-rich relative to the Sun). From Earth, TOI-5398 shines at apparent V-band magnitude 10.059 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The TOI-5398 system is a multi-planet architecture hosting 2 confirmed worlds, with TOI-5398 c sharing its stellar neighborhood alongside TOI-5398 b.
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-5398 |
| Spectral Type | G V |
| Effective Temp (Teff) | 6,000 K |
| Stellar Radius | 1.0510 R☉ |
| Stellar Mass | 1.1460 M☉ |
| Bolometric Luminosity | 1.284 L☉ |
| Metallicity [Fe/H] | 0.090 dex |
| Stellar Age | 0.650 Gyr |
| Apparent Magnitude | V: 10.059 · G: 9.982 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.057000 AU |
| Orbital Period | 4.773 days |
| Mean Orbital Velocity | 129.9 km/s |
| Orbital Eccentricity (e) | 0.14000 |
| Orbital Inclination (i) | 88.4000° |
| Mean Bulk Density | 1.49 g/cm³ (20.5 km/s vesc) |
| Insolation Flux | 370.6030 S⊕ (~504,391 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 426.800 LY (130.855 pc) |