K2-73 b
Astrophysical Synthesis & Habitability Characterization
K2-73 b is a confirmed sub-neptune exoplanet orbiting the star K2-73, located approximately 878 light-years (269.18 parsecs) from the Solar System. First announced in 2016 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.05% across the stellar disk), this world measures 2.58 Earth radii and has a measured mass of 9.2 Earth masses. Combining its mass and radius yields a mean bulk density of 2.95 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.38 g⊕ (13.53 m/s²), and an escape velocity of 21.1 km/s.
In its orbital architecture around K2-73, K2-73 b completes one full revolution every 7.496 Earth days at a semi-major axis of 0.07619 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 110.6 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 968 K (+695°C / +1283°F) and receiving 209.00 S⊕ (~284,449 W/m²), K2-73 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-73 is classified as a stellar host with an effective photospheric temperature of 5,867 K, a radius of 1.058 R☉, a mass of 1.02 M☉, an estimated bolometric luminosity of 1.19 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.04 dex (near-solar heavy-element abundance). From Earth, K2-73 shines at apparent V-band magnitude 11.345 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The K2-73 system is a multi-planet architecture hosting 2 confirmed worlds, with K2-73 b sharing its stellar neighborhood alongside K2-73 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 | K2-73 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,867 K |
| Stellar Radius | 1.0580 R☉ |
| Stellar Mass | 1.0200 M☉ |
| Bolometric Luminosity | 1.19 L☉ |
| Metallicity [Fe/H] | 0.040 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 11.345 · G: 11.715 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.076190 AU |
| Orbital Period | 7.496 days |
| Mean Orbital Velocity | 110.6 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | 88.4430° |
| Mean Bulk Density | 2.95 g/cm³ (21.1 km/s vesc) |
| Insolation Flux | 209.0000 S⊕ (~284,449 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 878.000 LY (269.183 pc) |