K2-146 c
Astrophysical Synthesis & Habitability Characterization
K2-146 c is a confirmed sub-neptune exoplanet orbiting the star K2-146, located approximately 258.6 light-years (79.3 parsecs) from the Solar System. First announced in 2019 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.3702% across the stellar disk), this world measures 2.19 Earth radii and has a measured mass of 7.49 Earth masses. Combining its mass and radius yields a mean bulk density of 3.93 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.56 g⊕ (15.3 m/s²), and an escape velocity of 20.7 km/s.
In its orbital architecture around K2-146, K2-146 c completes one full revolution every 4.005 Earth days at a semi-major axis of 0.0327 AU (an ultra-close orbit less than one-seventh of Mercury's 0.387 AU distance from the Sun, where strong stellar tidal forces typically induce synchronous rotation). Its mean orbital velocity is approximately 88.8 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.075 carries the world between 0.0302 AU at periapsis and 0.0352 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 519 K (+246°C / +475°F) and receiving 14.03 S⊕ (~19,092 W/m²), K2-146 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-146 is classified as a low-mass red dwarf of spectral type M3.0 V with an effective photospheric temperature of 3,385 K, a radius of 0.33 R☉, a mass of 0.331 M☉, an estimated bolometric luminosity of 0.013 L☉. Stellar evolution modeling indicates an estimated stellar age of 5 Gyr and a metallicity of [Fe/H] = -0.02 dex (near-solar heavy-element abundance). From Earth, K2-146 shines at apparent V-band magnitude 16.7 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The K2-146 system is a multi-planet architecture hosting 2 confirmed worlds, with K2-146 c sharing its stellar neighborhood alongside K2-146 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 | K2-146 |
| Spectral Type | M3.0 V |
| Effective Temp (Teff) | 3,385 K |
| Stellar Radius | 0.3300 R☉ |
| Stellar Mass | 0.3310 M☉ |
| Bolometric Luminosity | 0.013 L☉ |
| Metallicity [Fe/H] | -0.020 dex |
| Stellar Age | 5.000 Gyr |
| Apparent Magnitude | V: 16.700 · G: 14.983 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.032700 AU |
| Orbital Period | 4.005 days |
| Mean Orbital Velocity | 88.8 km/s |
| Orbital Eccentricity (e) | 0.07500 |
| Orbital Inclination (i) | 87.5400° |
| Mean Bulk Density | 3.93 g/cm³ (20.7 km/s vesc) |
| Insolation Flux | 14.0280 S⊕ (~19,092 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 258.600 LY (79.300 pc) |