Gl 378 b
Astrophysical Synthesis & Habitability Characterization
Gl 378 b is a confirmed sub-neptune exoplanet orbiting the star Gl 378, located approximately 48.8 light-years (14.96 parsecs) from the Solar System. First announced in 2019 by Haute-Provence Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 3.66 Earth radii (0.33 Jupiter radii) and has a measured mass of 13.02 Earth masses. Combining its mass and radius yields a mean bulk density of 1.46 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.97 g⊕ (9.51 m/s²), and an escape velocity of 21.1 km/s.
In its orbital architecture around Gl 378, Gl 378 b completes one full revolution every 3.822 Earth days at a semi-major axis of 0.039435 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 112.2 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.109 carries the world between 0.0351 AU at periapsis and 0.0437 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 830 K (+557°C / +1035°F) and receiving 38.58 S⊕ (~52,511 W/m²), Gl 378 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Gl 378 is classified as a low-mass red dwarf of spectral type M1 with an effective photospheric temperature of 3,879 K, a radius of 0.56 R☉, a mass of 0.56 M☉, an estimated bolometric luminosity of 0.064 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.06 dex (metal-rich relative to the Sun). From Earth, Gl 378 shines at apparent V-band magnitude 10.03 (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: Haute-Provence Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | Gl 378 |
| Spectral Type | M1 |
| Effective Temp (Teff) | 3,879 K |
| Stellar Radius | 0.5600 R☉ |
| Stellar Mass | 0.5600 M☉ |
| Bolometric Luminosity | 0.064 L☉ |
| Metallicity [Fe/H] | 0.060 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 10.030 · G: 9.265 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.039435 AU |
| Orbital Period | 3.822 days |
| Mean Orbital Velocity | 112.2 km/s |
| Orbital Eccentricity (e) | 0.10900 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.46 g/cm³ (21.1 km/s vesc) |
| Insolation Flux | 38.5823 S⊕ (~52,511 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 48.800 LY (14.955 pc) |