TOI-4438 b
Astrophysical Synthesis & Habitability Characterization
TOI-4438 b is a confirmed sub-neptune exoplanet orbiting the star TOI-4438, located approximately 98 light-years (30.04 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 0.3634% across the stellar disk), this world measures 2.4 Earth radii and has a measured mass of 4.11 Earth masses. Combining its mass and radius yields a mean bulk density of 1.64 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.71 g⊕ (6.96 m/s²), and an escape velocity of 14.6 km/s.
In its orbital architecture around TOI-4438, TOI-4438 b completes one full revolution every 7.446 Earth days at a semi-major axis of 0.0523 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 76.4 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.07 carries the world between 0.0486 AU at periapsis and 0.056 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 446 K (+173°C / +343°F) and receiving 6.00 S⊕ (~8,166 W/m²), TOI-4438 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star TOI-4438 is classified as a low-mass red dwarf of spectral type M3.5 V with an effective photospheric temperature of 3,501 K, a radius of 0.365 R☉, a mass of 0.345 M☉, an estimated bolometric luminosity of 0.018 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.8 Gyr and a metallicity of [Fe/H] = 0.07 dex (metal-rich relative to the Sun). From Earth, TOI-4438 shines at apparent V-band magnitude 13.69 (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-4438 |
| Spectral Type | M3.5 V |
| Effective Temp (Teff) | 3,501 K |
| Stellar Radius | 0.3650 R☉ |
| Stellar Mass | 0.3450 M☉ |
| Bolometric Luminosity | 0.018 L☉ |
| Metallicity [Fe/H] | 0.070 dex |
| Stellar Age | 4.800 Gyr |
| Apparent Magnitude | V: 13.690 · G: 12.520 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.052300 AU |
| Orbital Period | 7.446 days |
| Mean Orbital Velocity | 76.4 km/s |
| Orbital Eccentricity (e) | 0.07000 |
| Orbital Inclination (i) | 89.7000° |
| Mean Bulk Density | 1.64 g/cm³ (14.6 km/s vesc) |
| Insolation Flux | 6.0000 S⊕ (~8,166 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 98.000 LY (30.035 pc) |