K2-233 d
Astrophysical Synthesis & Habitability Characterization
K2-233 d is a confirmed sub-neptune exoplanet orbiting the star K2-233, located approximately 220.2 light-years (67.51 parsecs) from the Solar System. First announced in 2018 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0931% across the stellar disk), this world measures 2.363 Earth radii and has a measured mass of 10.3 Earth masses. Combining its mass and radius yields a mean bulk density of 4.3 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 1.84 g⊕ (18.04 m/s²), and an escape velocity of 23.4 km/s.
In its orbital architecture around K2-233, K2-233 d completes one full revolution every 24.368 Earth days at a semi-major axis of 0.1516 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). Its moderate orbital eccentricity of e = 0.18 carries the world between 0.1243 AU at periapsis and 0.1789 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 525 K (+252°C / +486°F) and receiving 12.70 S⊕ (~17,285 W/m²), K2-233 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-233 is classified as an orange K-type star of spectral type K3 with an effective photospheric temperature of 4,796 K, a radius of 0.71 R☉, a mass of 0.79 M☉, an estimated bolometric luminosity of 0.239 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.36 Gyr and a metallicity of [Fe/H] = -0.082 dex (near-solar heavy-element abundance). From Earth, K2-233 shines at apparent V-band magnitude 10.883 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The K2-233 system is a multi-planet architecture hosting 3 confirmed worlds, with K2-233 d sharing its stellar neighborhood alongside K2-233 b, K2-233 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 | K2-233 |
| Spectral Type | K3 |
| Effective Temp (Teff) | 4,796 K |
| Stellar Radius | 0.7100 R☉ |
| Stellar Mass | 0.7900 M☉ |
| Bolometric Luminosity | 0.239 L☉ |
| Metallicity [Fe/H] | -0.082 dex |
| Stellar Age | 0.360 Gyr |
| Apparent Magnitude | V: 10.883 · G: 10.419 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.151600 AU |
| Orbital Period | 24.368 days |
| Mean Orbital Velocity | 67.7 km/s |
| Orbital Eccentricity (e) | 0.18000 |
| Orbital Inclination (i) | 89.6200° |
| Mean Bulk Density | 4.3 g/cm³ (23.4 km/s vesc) |
| Insolation Flux | 12.7000 S⊕ (~17,285 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 220.200 LY (67.506 pc) |