GJ 9404 b
Astrophysical Synthesis & Habitability Characterization
GJ 9404 b is a confirmed sub-neptune exoplanet orbiting the star GJ 9404, located approximately 77.9 light-years (23.88 parsecs) from the Solar System. First announced in 2023 by Roque de los Muchachos Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 3.48 Earth radii (0.31 Jupiter radii) and has a measured mass of 11.9 Earth masses. Combining its mass and radius yields a mean bulk density of 1.56 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.98 g⊕ (9.61 m/s²), and an escape velocity of 20.7 km/s.
In its orbital architecture around GJ 9404, GJ 9404 b completes one full revolution every 13.459 Earth days at a semi-major axis of 0.0943 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 76.2 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.49, swinging from 0.0481 AU at periapsis out to 0.1405 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 474 K (+201°C / +394°F) and receiving 11.25 S⊕ (~15,305 W/m²), GJ 9404 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star GJ 9404 is classified as a low-mass red dwarf of spectral type M2V with an effective photospheric temperature of 3,811 K, a radius of 0.626 R☉, a mass of 0.62 M☉, an estimated bolometric luminosity of 0.074 L☉. From Earth, GJ 9404 shines at apparent V-band magnitude 10.62 (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: Roque de los Muchachos Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | GJ 9404 |
| Spectral Type | M2V |
| Effective Temp (Teff) | 3,811 K |
| Stellar Radius | 0.6260 R☉ |
| Stellar Mass | 0.6200 M☉ |
| Bolometric Luminosity | 0.074 L☉ |
| Metallicity [Fe/H] | — |
| Stellar Age | — |
| Apparent Magnitude | V: 10.620 · G: 9.870 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.094300 AU |
| Orbital Period | 13.459 days |
| Mean Orbital Velocity | 76.2 km/s |
| Orbital Eccentricity (e) | 0.49000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.56 g/cm³ (20.7 km/s vesc) |
| Insolation Flux | 11.2454 S⊕ (~15,305 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 77.900 LY (23.884 pc) |