GJ 357 b
Astrophysical Synthesis & Habitability Characterization
GJ 357 b is a confirmed terrestrial exoplanet orbiting the star GJ 357, located approximately 30.8 light-years (9.44 parsecs) from the Solar System. First announced in 2019 by Transiting Exoplanet Survey Satellite (TESS) using the Transit detection technique (producing an estimated primary transit depth of 0.1066% across the stellar disk), this world measures 1.2 Earth radii and has a measured mass of 1.83 Earth masses. Combining its mass and radius yields a mean bulk density of 5.84 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 1.27 g⊕ (12.45 m/s²), and an escape velocity of 13.8 km/s.
In its orbital architecture around GJ 357, GJ 357 b completes one full revolution every 3.931 Earth days at a semi-major axis of 0.036 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 99.6 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 518 K (+245°C / +473°F) and receiving 12.60 S⊕ (~17,149 W/m²), GJ 357 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star GJ 357 is classified as a low-mass red dwarf of spectral type M2.5 V with an effective photospheric temperature of 3,505 K, a radius of 0.337 R☉, a mass of 0.342 M☉, an estimated bolometric luminosity of 0.015 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.12 dex (metal-poor relative to the Sun). From Earth, GJ 357 shines at apparent V-band magnitude 10.91 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The GJ 357 system is a multi-planet architecture hosting 3 confirmed worlds, with GJ 357 b sharing its stellar neighborhood alongside GJ 357 c, GJ 357 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: Transiting Exoplanet Survey Satellite (TESS) · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | GJ 357 |
| Spectral Type | M2.5 V |
| Effective Temp (Teff) | 3,505 K |
| Stellar Radius | 0.3370 R☉ |
| Stellar Mass | 0.3420 M☉ |
| Bolometric Luminosity | 0.015 L☉ |
| Metallicity [Fe/H] | -0.120 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 10.910 · G: 9.880 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.036000 AU |
| Orbital Period | 3.931 days |
| Mean Orbital Velocity | 99.6 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | 89.2280° |
| Mean Bulk Density | 5.84 g/cm³ (13.8 km/s vesc) |
| Insolation Flux | 12.6000 S⊕ (~17,149 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 30.800 LY (9.442 pc) |