K2-72 d
Astrophysical Synthesis & Habitability Characterization
K2-72 d is a confirmed terrestrial exoplanet orbiting the star K2-72, located approximately 216.7 light-years (66.43 parsecs) from the Solar System. First announced in 2016 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0783% across the stellar disk), this world measures 1.01 Earth radii and has a measured mass of 1.01 Earth masses. Combining its mass and radius yields a mean bulk density of 5.41 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 0.99 g⊕ (9.71 m/s²), and an escape velocity of 11.2 km/s.
In its orbital architecture around K2-72, K2-72 d completes one full revolution every 7.76 Earth days at a semi-major axis of 0.05 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 70.1 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.11 carries the world between 0.0445 AU at periapsis and 0.0555 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 417 K (+144°C / +291°F) and receiving 5.40 S⊕ (~7,349 W/m²), K2-72 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-72 is classified as a stellar host with an effective photospheric temperature of 3,360 K, a radius of 0.331 R☉, a mass of 0.2714 M☉, an estimated bolometric luminosity of 0.013 L☉. From Earth, K2-72 shines at apparent V-band magnitude 15.37 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The K2-72 system is a multi-planet architecture hosting 4 confirmed worlds, with K2-72 d sharing its stellar neighborhood alongside K2-72 b, K2-72 c, K2-72 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 | K2-72 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 3,360 K |
| Stellar Radius | 0.3310 R☉ |
| Stellar Mass | 0.2714 M☉ |
| Bolometric Luminosity | 0.013 L☉ |
| Metallicity [Fe/H] | — |
| Stellar Age | — |
| Apparent Magnitude | V: 15.370 · G: 14.279 |
| System Architecture | 1 Star, 4 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.050000 AU |
| Orbital Period | 7.76 days |
| Mean Orbital Velocity | 70.1 km/s |
| Orbital Eccentricity (e) | 0.11000 |
| Orbital Inclination (i) | 89.2600° |
| Mean Bulk Density | 5.41 g/cm³ (11.2 km/s vesc) |
| Insolation Flux | 5.4000 S⊕ (~7,349 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 216.700 LY (66.432 pc) |