GJ 2126 b
Astrophysical Synthesis & Habitability Characterization
GJ 2126 b is a confirmed gas giant exoplanet orbiting the star GJ 2126, located approximately 124.4 light-years (38.13 parsecs) from the Solar System. First announced in 2025 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 13.6 Earth radii (1.21 Jupiter radii) and has a measured mass of 413.177 Earth masses (1.3 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.91 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 2.23 g⊕ (21.87 m/s²), and an escape velocity of 61.7 km/s.
In its orbital architecture around GJ 2126, GJ 2126 b completes one full revolution every 272.7 Earth days at a semi-major axis of 0.71 AU (situated at an orbital separation between Mercury's 0.39 AU and Venus's 0.72 AU). Its mean orbital velocity is approximately 28.3 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.85, swinging from 0.1065 AU at periapsis out to 1.3135 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 13.600 R⊕, GJ 2126 b 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 2126 is classified as a low-mass red dwarf of spectral type M0 V with an effective photospheric temperature of 4,159 K, a radius of 0.728 R☉, a mass of 0.65 M☉, an estimated bolometric luminosity of 0.142 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.6 dex (metal-rich relative to the Sun). From Earth, GJ 2126 shines at apparent V-band magnitude 10.7 (faint and requiring research-grade or CCD telescopic photometry) in the Southern 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: La Silla Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | GJ 2126 |
| Spectral Type | M0 V |
| Effective Temp (Teff) | 4,159 K |
| Stellar Radius | 0.7280 R☉ |
| Stellar Mass | 0.6500 M☉ |
| Bolometric Luminosity | 0.142 L☉ |
| Metallicity [Fe/H] | 0.600 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 10.700 · G: 10.150 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.710000 AU |
| Orbital Period | 272.7 days |
| Mean Orbital Velocity | 28.3 km/s |
| Orbital Eccentricity (e) | 0.85000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.91 g/cm³ (61.7 km/s vesc) |
| Insolation Flux | 0.2833 S⊕ (~386 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 124.400 LY (38.129 pc) |