K2-133 d
Astrophysical Synthesis & Habitability Characterization
K2-133 d is a confirmed sub-neptune exoplanet orbiting the star K2-133, located approximately 245.2 light-years (75.17 parsecs) from the Solar System. First announced in 2017 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.1629% across the stellar disk), this world measures 2.003 Earth radii and has a measured mass of 4.67 Earth masses. Combining its mass and radius yields a mean bulk density of 3.2 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.16 g⊕ (11.38 m/s²), and an escape velocity of 17.1 km/s.
In its orbital architecture around K2-133, K2-133 d completes one full revolution every 11.025 Earth days at a semi-major axis of 0.07487 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 73.9 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 734 K (+461°C / +862°F) and receiving 48.33 S⊕ (~65,770 W/m²), K2-133 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-133 is classified as a low-mass red dwarf of spectral type M1.5 V with an effective photospheric temperature of 3,655 K, a radius of 0.455 R☉, a mass of 0.461 M☉, an estimated bolometric luminosity of 0.033 L☉. From Earth, K2-133 shines at apparent V-band magnitude 14.073 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The K2-133 system is a multi-planet architecture hosting 4 confirmed worlds, with K2-133 d sharing its stellar neighborhood alongside K2-133 b, K2-133 c, K2-133 e.
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 | K2-133 |
| Spectral Type | M1.5 V |
| Effective Temp (Teff) | 3,655 K |
| Stellar Radius | 0.4550 R☉ |
| Stellar Mass | 0.4610 M☉ |
| Bolometric Luminosity | 0.033 L☉ |
| Metallicity [Fe/H] | — |
| Stellar Age | — |
| Apparent Magnitude | V: 14.073 · G: 13.325 |
| System Architecture | 1 Star, 4 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.074870 AU |
| Orbital Period | 11.025 days |
| Mean Orbital Velocity | 73.9 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | 89.4000° |
| Mean Bulk Density | 3.2 g/cm³ (17.1 km/s vesc) |
| Insolation Flux | 48.3251 S⊕ (~65,770 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 245.200 LY (75.170 pc) |