K2-172 c
Astrophysical Synthesis & Habitability Characterization
K2-172 c is a confirmed sub-neptune exoplanet orbiting the star K2-172, located approximately 814.5 light-years (249.74 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.1144% across the stellar disk), this world measures 3.206 Earth radii (0.29 Jupiter radii) and has a measured mass of 10.4 Earth masses. Combining its mass and radius yields a mean bulk density of 1.74 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.01 g⊕ (9.9 m/s²), and an escape velocity of 20.1 km/s.
In its orbital architecture around K2-172, K2-172 c completes one full revolution every 29.627 Earth days.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 3.206 R⊕, K2-172 c exceeds the empirical ~1.8–2.2 R⊕ Fulton radius valley threshold, indicating a substantial hydrogen-helium or supercritical volatile envelope without a conventional solid terrestrial surface.
The host star K2-172 is classified as a stellar host with an effective photospheric temperature of 5,569 K, a radius of 0.8689 R☉, a mass of 0.9344 M☉, an estimated bolometric luminosity of 0.652 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.06 dex (near-solar heavy-element abundance). From Earth, K2-172 shines at apparent V-band magnitude 12.5 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The K2-172 system is a multi-planet architecture hosting 2 confirmed worlds, with K2-172 c sharing its stellar neighborhood alongside K2-172 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 | K2-172 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,569 K |
| Stellar Radius | 0.8689 R☉ |
| Stellar Mass | 0.9344 M☉ |
| Bolometric Luminosity | 0.652 L☉ |
| Metallicity [Fe/H] | -0.060 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 12.500 · G: 12.281 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | — |
| Orbital Period | 29.627 days |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | 89.4973° |
| Mean Bulk Density | 1.74 g/cm³ (20.1 km/s vesc) |
| Insolation Flux | — |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 814.500 LY (249.742 pc) |