K2-155 d
Astrophysical Synthesis & Habitability Characterization
K2-155 d is a confirmed super-earth exoplanet orbiting the star K2-155, located approximately 237.4 light-years (72.8 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0902% across the stellar disk), this world measures 1.9 Earth radii and has a measured mass of 4.27 Earth masses. Combining its mass and radius yields a mean bulk density of 3.43 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.18 g⊕ (11.57 m/s²), and an escape velocity of 16.8 km/s.
In its orbital architecture around K2-155, K2-155 d completes one full revolution every 40.718 Earth days at a semi-major axis of 0.1937 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 51.8 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 381 K (+108°C / +226°F) and receiving 1.67 S⊕ (~2,273 W/m²), K2-155 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-155 is classified as an orange K-type star of spectral type K7 with an effective photospheric temperature of 4,258 K, a radius of 0.58 R☉, a mass of 0.65 M☉, an estimated bolometric luminosity of 0.099 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.3 dex (metal-poor relative to the Sun). From Earth, K2-155 shines at apparent V-band magnitude 12.773 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The K2-155 system is a multi-planet architecture hosting 3 confirmed worlds, with K2-155 d sharing its stellar neighborhood alongside K2-155 b, K2-155 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 | K2-155 |
| Spectral Type | K7 |
| Effective Temp (Teff) | 4,258 K |
| Stellar Radius | 0.5800 R☉ |
| Stellar Mass | 0.6500 M☉ |
| Bolometric Luminosity | 0.099 L☉ |
| Metallicity [Fe/H] | -0.300 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 12.773 · G: 12.253 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.193700 AU |
| Orbital Period | 40.718 days |
| Mean Orbital Velocity | 51.8 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | 89.6100° |
| Mean Bulk Density | 3.43 g/cm³ (16.8 km/s vesc) |
| Insolation Flux | 1.6700 S⊕ (~2,273 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 237.400 LY (72.800 pc) |