K2-389 b
Astrophysical Synthesis & Habitability Characterization
K2-389 b is a confirmed sub-neptune exoplanet orbiting the star K2-389, located approximately 845.4 light-years (259.21 parsecs) from the Solar System. First announced in 2022 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0381% across the stellar disk), this world measures 2.33 Earth radii and has a measured mass of 6.04 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 km/s.
In its orbital architecture around K2-389, K2-389 b completes one full revolution every 8.583 Earth days.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 932 K (+659°C / +1218°F) and receiving 179.00 S⊕ (~243,619 W/m²), K2-389 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-389 is classified as a solar-type yellow star of spectral type G3 with an effective photospheric temperature of 5,773 K, a radius of 1.094 R☉, a mass of 0.99 M☉, an estimated bolometric luminosity of 1.193 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.038 dex (near-solar heavy-element abundance). From Earth, K2-389 shines at apparent V-band magnitude 11.827 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The K2-389 system is a multi-planet architecture hosting 2 confirmed worlds, with K2-389 b sharing its stellar neighborhood alongside K2-389 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 | K2-389 |
| Spectral Type | G3 |
| Effective Temp (Teff) | 5,773 K |
| Stellar Radius | 1.0940 R☉ |
| Stellar Mass | 0.9900 M☉ |
| Bolometric Luminosity | 1.193 L☉ |
| Metallicity [Fe/H] | 0.038 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 11.827 · G: 11.570 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | — |
| Orbital Period | 8.583 days |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 2.63 g/cm³ (18 km/s vesc) |
| Insolation Flux | 179.0000 S⊕ (~243,619 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 845.400 LY (259.208 pc) |