K2-32 d
Astrophysical Synthesis & Habitability Characterization
K2-32 d is a confirmed sub-neptune exoplanet orbiting the star K2-32, located approximately 514.3 light-years (157.68 parsecs) from the Solar System. First announced in 2016 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.1379% across the stellar disk), this world measures 3.484 Earth radii (0.31 Jupiter radii) and has a measured mass of 6.7 Earth masses. Combining its mass and radius yields a mean bulk density of 0.87 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.55 g⊕ (5.39 m/s²), and an escape velocity of 15.5 km/s.
In its orbital architecture around K2-32, K2-32 d completes one full revolution every 31.717 Earth days at a semi-major axis of 0.18422 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 63.2 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.05 carries the world between 0.175 AU at periapsis and 0.1934 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 550 K (+277°C / +531°F) and receiving 14.80 S⊕ (~20,143 W/m²), K2-32 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-32 is classified as a solar-type yellow star of spectral type G9 V with an effective photospheric temperature of 5,271 K, a radius of 0.86 R☉, a mass of 0.83 M☉, an estimated bolometric luminosity of 0.512 L☉. Stellar evolution modeling indicates an estimated stellar age of 7.9 Gyr and a metallicity of [Fe/H] = -0.06 dex (near-solar heavy-element abundance). From Earth, K2-32 shines at apparent V-band magnitude 12.304 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The K2-32 system is a multi-planet architecture hosting 4 confirmed worlds, with K2-32 d sharing its stellar neighborhood alongside K2-32 e, K2-32 b, K2-32 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: K2 · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | K2-32 |
| Spectral Type | G9 V |
| Effective Temp (Teff) | 5,271 K |
| Stellar Radius | 0.8600 R☉ |
| Stellar Mass | 0.8300 M☉ |
| Bolometric Luminosity | 0.512 L☉ |
| Metallicity [Fe/H] | -0.060 dex |
| Stellar Age | 7.900 Gyr |
| Apparent Magnitude | V: 12.304 · G: 12.004 |
| System Architecture | 2 Stars, 4 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.184220 AU |
| Orbital Period | 31.717 days |
| Mean Orbital Velocity | 63.2 km/s |
| Orbital Eccentricity (e) | 0.05000 |
| Orbital Inclination (i) | 89.4000° |
| Mean Bulk Density | 0.87 g/cm³ (15.5 km/s vesc) |
| Insolation Flux | 14.8000 S⊕ (~20,143 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 514.300 LY (157.682 pc) |