GJ 4276 b
Astrophysical Synthesis & Habitability Characterization
GJ 4276 b is a confirmed sub-neptune exoplanet orbiting the star GJ 4276, located approximately 69.6 light-years (21.34 parsecs) from the Solar System. First announced in 2019 by Calar Alto Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 4.22 Earth radii (0.38 Jupiter radii) and has a measured mass of 16.57 Earth masses. Combining its mass and radius yields a mean bulk density of 1.22 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.93 g⊕ (9.12 m/s²), and an escape velocity of 22.2 km/s.
In its orbital architecture around GJ 4276, GJ 4276 b completes one full revolution every 13.352 Earth days at a semi-major axis of 0.082 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 66.8 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.37, swinging from 0.0517 AU at periapsis out to 0.1123 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 364 K (+91°C / +196°F) and receiving 2.93 S⊕ (~3,987 W/m²), GJ 4276 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star GJ 4276 is classified as a low-mass red dwarf of spectral type M4.0 with an effective photospheric temperature of 3,387 K, a radius of 0.407 R☉, a mass of 0.406 M☉, an estimated bolometric luminosity of 0.02 L☉. Stellar evolution modeling indicates an estimated stellar age of 6.9 Gyr and a metallicity of [Fe/H] = 0.12 dex (metal-rich relative to the Sun). From Earth, GJ 4276 shines at apparent V-band magnitude 12.903 (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: Calar Alto Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | GJ 4276 |
| Spectral Type | M4.0 |
| Effective Temp (Teff) | 3,387 K |
| Stellar Radius | 0.4070 R☉ |
| Stellar Mass | 0.4060 M☉ |
| Bolometric Luminosity | 0.02 L☉ |
| Metallicity [Fe/H] | 0.120 dex |
| Stellar Age | 6.900 Gyr |
| Apparent Magnitude | V: 12.903 · G: 11.661 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.082000 AU |
| Orbital Period | 13.352 days |
| Mean Orbital Velocity | 66.8 km/s |
| Orbital Eccentricity (e) | 0.37000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.22 g/cm³ (22.2 km/s vesc) |
| Insolation Flux | 2.9298 S⊕ (~3,987 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 69.600 LY (21.336 pc) |