GJ 357 d
Astrophysical Synthesis & Habitability Characterization
GJ 357 d is a confirmed sub-neptune exoplanet orbiting the star GJ 357, located approximately 30.8 light-years (9.44 parsecs) from the Solar System. First announced in 2019 by Multiple Observatories using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 2.34 Earth radii and has a measured mass of 6.1 Earth masses. Combining its mass and radius yields a mean bulk density of 2.63 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.11 g⊕ (10.89 m/s²), and an escape velocity of 18.1 km/s.
In its orbital architecture around GJ 357, GJ 357 d completes one full revolution every 55.661 Earth days at a semi-major axis of 0.204 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 39.9 km/s (compared to Earth's 29.8 km/s).
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 2.340 R⊕, GJ 357 d exceeds the empirical ~1.8–2.2 R⊕ Fulton radius valley threshold, indicating a substantial hydrogen-helium or supercritical volatile envelope without a conventional solid terrestrial surface.
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 d sharing its stellar neighborhood alongside GJ 357 b, GJ 357 c.
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: Multiple Observatories · 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) | 0.204000 AU |
| Orbital Period | 55.661 days |
| Mean Orbital Velocity | 39.9 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 2.63 g/cm³ (18.1 km/s vesc) |
| Insolation Flux | 0.3800 S⊕ (~517 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 30.800 LY (9.442 pc) |