GJ 3138 b
Astrophysical Synthesis & Habitability Characterization
GJ 3138 b is a confirmed terrestrial exoplanet orbiting the star GJ 3138, located approximately 92.9 light-years (28.47 parsecs) from the Solar System. First announced in 2017 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 1.18 Earth radii and has a measured mass of 1.78 Earth masses. Combining its mass and radius yields a mean bulk density of 5.97 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 1.28 g⊕ (12.55 m/s²), and an escape velocity of 13.7 km/s.
In its orbital architecture around GJ 3138, GJ 3138 b completes one full revolution every 1.22 Earth days at a semi-major axis of 0.0197 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 175.7 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.19 carries the world between 0.016 AU at periapsis and 0.0234 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 903 K (+630°C / +1166°F) and receiving 118.10 S⊕ (~160,734 W/m²), GJ 3138 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star GJ 3138 is classified as a low-mass red dwarf of spectral type M0 with an effective photospheric temperature of 3,717 K, a radius of 0.5 R☉, a mass of 0.681 M☉, an estimated bolometric luminosity of 0.043 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.3 dex (metal-poor relative to the Sun). From Earth, GJ 3138 shines at apparent V-band magnitude 10.828 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The GJ 3138 system is a multi-planet architecture hosting 3 confirmed worlds, with GJ 3138 b sharing its stellar neighborhood alongside GJ 3138 c, GJ 3138 d.
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: La Silla Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | GJ 3138 |
| Spectral Type | M0 |
| Effective Temp (Teff) | 3,717 K |
| Stellar Radius | 0.5000 R☉ |
| Stellar Mass | 0.6810 M☉ |
| Bolometric Luminosity | 0.043 L☉ |
| Metallicity [Fe/H] | -0.300 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 10.828 · G: 10.192 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.019700 AU |
| Orbital Period | 1.22 days |
| Mean Orbital Velocity | 175.7 km/s |
| Orbital Eccentricity (e) | 0.19000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 5.97 g/cm³ (13.7 km/s vesc) |
| Insolation Flux | 118.1000 S⊕ (~160,734 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 92.900 LY (28.471 pc) |