K2-273 b
Astrophysical Synthesis & Habitability Characterization
K2-273 b is a confirmed sub-neptune exoplanet orbiting the star K2-273, located approximately 1004.9 light-years (308.11 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.1082% across the stellar disk), this world measures 3.05 Earth radii (0.27 Jupiter radii) and has a measured mass of 9.53 Earth masses. Combining its mass and radius yields a mean bulk density of 1.85 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.02 g⊕ (10 m/s²), and an escape velocity of 19.8 km/s.
In its orbital architecture around K2-273, K2-273 b completes one full revolution every 11.72 Earth days at a semi-major axis of 0.0729 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 67.7 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 849 K (+576°C / +1069°F) and receiving 83.51 S⊕ (~113,661 W/m²), K2-273 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-273 is classified as a stellar host with an effective photospheric temperature of 5,161 K, a radius of 0.85 R☉, a mass of 0.89 M☉, an estimated bolometric luminosity of 0.46 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.2 dex (metal-rich relative to the Sun). From Earth, K2-273 shines at apparent V-band magnitude 13.246 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.
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 | K2-273 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,161 K |
| Stellar Radius | 0.8500 R☉ |
| Stellar Mass | 0.8900 M☉ |
| Bolometric Luminosity | 0.46 L☉ |
| Metallicity [Fe/H] | 0.200 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 13.246 · G: 13.146 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.072900 AU |
| Orbital Period | 11.72 days |
| Mean Orbital Velocity | 67.7 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | 90.0000° |
| Mean Bulk Density | 1.85 g/cm³ (19.8 km/s vesc) |
| Insolation Flux | 83.5129 S⊕ (~113,661 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1004.900 LY (308.105 pc) |