K2-187 d
Astrophysical Synthesis & Habitability Characterization
K2-187 d is a confirmed sub-neptune exoplanet orbiting the star K2-187, located approximately 1079.3 light-years (330.92 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0703% across the stellar disk), this world measures 2.4 Earth radii and has a measured mass of 6.35 Earth masses. Combining its mass and radius yields a mean bulk density of 2.53 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.1 g⊕ (10.79 m/s²), and an escape velocity of 18.2 km/s.
In its orbital architecture around K2-187, K2-187 d completes one full revolution every 7.15 Earth days at a semi-major axis of 0.072 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 109.6 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 865 K (+592°C / +1098°F) and receiving 122.82 S⊕ (~167,157 W/m²), K2-187 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-187 is classified as a stellar host with an effective photospheric temperature of 5,438 K, a radius of 0.83 R☉, a mass of 0.967 M☉, an estimated bolometric luminosity of 0.541 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0 dex (near-solar heavy-element abundance). From Earth, K2-187 shines at apparent V-band magnitude 13.102 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The K2-187 system is a multi-planet architecture hosting 4 confirmed worlds, with K2-187 d sharing its stellar neighborhood alongside K2-187 b, K2-187 c, K2-187 e.
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 | K2-187 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,438 K |
| Stellar Radius | 0.8300 R☉ |
| Stellar Mass | 0.9670 M☉ |
| Bolometric Luminosity | 0.541 L☉ |
| Metallicity [Fe/H] | 0.000 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 13.102 · G: 12.867 |
| System Architecture | 1 Star, 4 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.072000 AU |
| Orbital Period | 7.15 days |
| Mean Orbital Velocity | 109.6 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | 90.3000° |
| Mean Bulk Density | 2.53 g/cm³ (18.2 km/s vesc) |
| Insolation Flux | 122.8195 S⊕ (~167,157 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1079.300 LY (330.916 pc) |