K2-5 c
Astrophysical Synthesis & Habitability Characterization
K2-5 c is a confirmed sub-neptune exoplanet orbiting the star K2-5, located approximately 661.9 light-years (202.94 parsecs) from the Solar System. First announced in 2015 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.1321% across the stellar disk), this world measures 2.26 Earth radii and has a measured mass of 5.73 Earth masses. Combining its mass and radius yields a mean bulk density of 2.74 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.12 g⊕ (10.98 m/s²), and an escape velocity of 17.8 km/s.
In its orbital architecture around K2-5, K2-5 c completes one full revolution every 10.932 Earth days at a semi-major axis of 0.0818 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 81.4 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 456 K (+183°C / +361°F) and receiving 10.20 S⊕ (~13,882 W/m²), K2-5 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-5 is classified as an orange K-type star of spectral type K7.5 V with an effective photospheric temperature of 3,930 K, a radius of 0.57 R☉, a mass of 0.61 M☉, an estimated bolometric luminosity of 0.07 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.33 dex (metal-poor relative to the Sun). From Earth, K2-5 shines at apparent V-band magnitude 14.974 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The K2-5 system is a multi-planet architecture hosting 2 confirmed worlds, with K2-5 c sharing its stellar neighborhood alongside K2-5 b.
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 | K2-5 |
| Spectral Type | K7.5 V |
| Effective Temp (Teff) | 3,930 K |
| Stellar Radius | 0.5700 R☉ |
| Stellar Mass | 0.6100 M☉ |
| Bolometric Luminosity | 0.07 L☉ |
| Metallicity [Fe/H] | -0.330 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 14.974 · G: 14.339 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.081800 AU |
| Orbital Period | 10.932 days |
| Mean Orbital Velocity | 81.4 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | 86.9500° |
| Mean Bulk Density | 2.74 g/cm³ (17.8 km/s vesc) |
| Insolation Flux | 10.2000 S⊕ (~13,882 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 661.900 LY (202.943 pc) |