TOI-5800 b
Astrophysical Synthesis & Habitability Characterization
TOI-5800 b is a confirmed sub-neptune exoplanet orbiting the star TOI-5800, located approximately 139.9 light-years (42.91 parsecs) from the Solar System. First announced in 2025 by Transiting Exoplanet Survey Satellite (TESS) using the Transit detection technique (producing an estimated primary transit depth of 0.0851% across the stellar disk), this world measures 2.46 Earth radii and has a measured mass of 9.5 Earth masses. Combining its mass and radius yields a mean bulk density of 3.52 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.57 g⊕ (15.4 m/s²), and an escape velocity of 22 km/s.
In its orbital architecture around TOI-5800, TOI-5800 b completes one full revolution every 2.628 Earth days at a semi-major axis of 0.0344 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 142.4 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.3, swinging from 0.0241 AU at periapsis out to 0.0447 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1108 K (+835°C / +1535°F) and receiving 274.16 S⊕ (~373,136 W/m²), TOI-5800 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star TOI-5800 is classified as an orange K-type star of spectral type K3 V with an effective photospheric temperature of 4,850 K, a radius of 0.773 R☉, a mass of 0.778 M☉, an estimated bolometric luminosity of 0.297 L☉. Stellar evolution modeling indicates an estimated stellar age of 8.1 Gyr and a metallicity of [Fe/H] = -0.04 dex (near-solar heavy-element abundance). From Earth, TOI-5800 shines at apparent V-band magnitude 9.553 (accessible to binoculars and small amateur telescopes) in the Southern 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-5800 |
| Spectral Type | K3 V |
| Effective Temp (Teff) | 4,850 K |
| Stellar Radius | 0.7730 R☉ |
| Stellar Mass | 0.7780 M☉ |
| Bolometric Luminosity | 0.297 L☉ |
| Metallicity [Fe/H] | -0.040 dex |
| Stellar Age | 8.100 Gyr |
| Apparent Magnitude | V: 9.553 · G: 9.218 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.034400 AU |
| Orbital Period | 2.628 days |
| Mean Orbital Velocity | 142.4 km/s |
| Orbital Eccentricity (e) | 0.30000 |
| Orbital Inclination (i) | 85.0800° |
| Mean Bulk Density | 3.52 g/cm³ (22 km/s vesc) |
| Insolation Flux | 274.1630 S⊕ (~373,136 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 139.900 LY (42.905 pc) |