GJ 3942 b
Astrophysical Synthesis & Habitability Characterization
GJ 3942 b is a confirmed sub-neptune exoplanet orbiting the star GJ 3942, located approximately 55.2 light-years (16.93 parsecs) from the Solar System. First announced in 2017 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 2.57 Earth radii and has a measured mass of 7.14 Earth masses. Combining its mass and radius yields a mean bulk density of 2.32 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.08 g⊕ (10.59 m/s²), and an escape velocity of 18.6 km/s.
In its orbital architecture around GJ 3942, GJ 3942 b completes one full revolution every 6.905 Earth days at a semi-major axis of 0.0608 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 95.8 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.121 carries the world between 0.0534 AU at periapsis and 0.0682 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 590 K (+317°C / +603°F) and receiving 20.52 S⊕ (~27,929 W/m²), GJ 3942 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star GJ 3942 is classified as a low-mass red dwarf of spectral type M0 with an effective photospheric temperature of 3,867 K, a radius of 0.61 R☉, a mass of 0.63 M☉, an estimated bolometric luminosity of 0.075 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.04 dex (near-solar heavy-element abundance). From Earth, GJ 3942 shines at apparent V-band magnitude 10.166 (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 3942 |
| Spectral Type | M0 |
| Effective Temp (Teff) | 3,867 K |
| Stellar Radius | 0.6100 R☉ |
| Stellar Mass | 0.6300 M☉ |
| Bolometric Luminosity | 0.075 L☉ |
| Metallicity [Fe/H] | -0.040 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 10.166 · G: 9.408 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.060800 AU |
| Orbital Period | 6.905 days |
| Mean Orbital Velocity | 95.8 km/s |
| Orbital Eccentricity (e) | 0.12100 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 2.32 g/cm³ (18.6 km/s vesc) |
| Insolation Flux | 20.5207 S⊕ (~27,929 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 55.200 LY (16.929 pc) |