GJ 1265 b
Astrophysical Synthesis & Habitability Characterization
GJ 1265 b is a confirmed sub-neptune exoplanet orbiting the star GJ 1265, located approximately 33.4 light-years (10.25 parsecs) from the Solar System. First announced in 2018 by Calar Alto Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 2.63 Earth radii and has a measured mass of 7.4 Earth masses. Combining its mass and radius yields a mean bulk density of 2.24 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.07 g⊕ (10.49 m/s²), and an escape velocity of 18.8 km/s.
In its orbital architecture around GJ 1265, GJ 1265 b completes one full revolution every 3.651 Earth days at a semi-major axis of 0.026 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 77.5 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.04 (ranging from 0.025 AU at periapsis to 0.027 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 424 K (+151°C / +304°F) and receiving 5.38 S⊕ (~7,328 W/m²), GJ 1265 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star GJ 1265 is classified as a low-mass red dwarf of spectral type M4.5 V with an effective photospheric temperature of 3,236 K, a radius of 0.192 R☉, a mass of 0.178 M☉, an estimated bolometric luminosity of 0.00363 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.04 dex (near-solar heavy-element abundance). From Earth, GJ 1265 shines at apparent V-band magnitude 14.01 (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: Calar Alto Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | GJ 1265 |
| Spectral Type | M4.5 V |
| Effective Temp (Teff) | 3,236 K |
| Stellar Radius | 0.1920 R☉ |
| Stellar Mass | 0.1780 M☉ |
| Bolometric Luminosity | 0.00363 L☉ |
| Metallicity [Fe/H] | -0.040 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 14.010 · G: 12.081 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.026000 AU |
| Orbital Period | 3.651 days |
| Mean Orbital Velocity | 77.5 km/s |
| Orbital Eccentricity (e) | 0.04000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 2.24 g/cm³ (18.8 km/s vesc) |
| Insolation Flux | 5.3846 S⊕ (~7,328 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 33.400 LY (10.253 pc) |