G 9-40 b
Astrophysical Synthesis & Habitability Characterization
G 9-40 b is a confirmed super-earth exoplanet orbiting the star G 9-40, located approximately 91.1 light-years (27.93 parsecs) from the Solar System. First announced in 2019 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.3314% across the stellar disk), this world measures 1.9 Earth radii and has a measured mass of 4 Earth masses. Combining its mass and radius yields a mean bulk density of 3.22 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 16.2 km/s.
In its orbital architecture around G 9-40, G 9-40 b completes one full revolution every 5.746 Earth days at a semi-major axis of 0.0418 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 79.1 km/s (compared to Earth's 29.8 km/s). The orbit is modeled as circular (e = 0.00), maintaining a constant stellar distance throughout its year.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 441 K (+168°C / +334°F) and receiving 6.27 S⊕ (~8,533 W/m²), G 9-40 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star G 9-40 is classified as a low-mass red dwarf of spectral type M2.5 V with an effective photospheric temperature of 3,395 K, a radius of 0.3026 R☉, a mass of 0.2952 M☉, an estimated bolometric luminosity of 0.011 L☉. Stellar evolution modeling indicates an estimated stellar age of 9.9 Gyr and a metallicity of [Fe/H] = -0.07 dex (near-solar heavy-element abundance). From Earth, G 9-40 shines at apparent V-band magnitude 13.821 (faint and requiring research-grade or CCD telescopic photometry) in the Northern 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: K2 · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | G 9-40 |
| Spectral Type | M2.5 V |
| Effective Temp (Teff) | 3,395 K |
| Stellar Radius | 0.3026 R☉ |
| Stellar Mass | 0.2952 M☉ |
| Bolometric Luminosity | 0.011 L☉ |
| Metallicity [Fe/H] | -0.070 dex |
| Stellar Age | 9.900 Gyr |
| Apparent Magnitude | V: 13.821 · G: 12.733 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.041800 AU |
| Orbital Period | 5.746 days |
| Mean Orbital Velocity | 79.1 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.0300° |
| Mean Bulk Density | 3.22 g/cm³ (16.2 km/s vesc) |
| Insolation Flux | 6.2700 S⊕ (~8,533 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 91.100 LY (27.928 pc) |