Kepler-172 d
Astrophysical Synthesis & Habitability Characterization
Kepler-172 d is a confirmed sub-neptune exoplanet orbiting the star Kepler-172, located approximately 2702.5 light-years (828.59 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0361% across the stellar disk), this world measures 2.25 Earth radii and has a measured mass of 5.69 Earth masses. Combining its mass and radius yields a mean bulk density of 2.75 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.12 g⊕ (10.98 m/s²), and an escape velocity of 17.8 km/s.
In its orbital architecture around Kepler-172, Kepler-172 d completes one full revolution every 14.627 Earth days at a semi-major axis of 0.118 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 87.8 km/s (compared to Earth's 29.8 km/s). The orbit is modeled as circular (e = 0.00), maintaining a constant stellar distance throughout its year.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 736 K (+463°C / +865°F) and receiving 75.29 S⊕ (~102,470 W/m²), Kepler-172 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-172 is classified as a stellar host with an effective photospheric temperature of 5,526 K, a radius of 1.085 R☉, a mass of 1.081 M☉, an estimated bolometric luminosity of 0.985 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.69 Gyr and a metallicity of [Fe/H] = 0.39 dex (metal-rich relative to the Sun). From Earth, Kepler-172 shines at apparent V-band magnitude 14.703 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-172 system is a multi-planet architecture hosting 4 confirmed worlds, with Kepler-172 d sharing its stellar neighborhood alongside Kepler-172 b, Kepler-172 c, Kepler-172 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: Kepler · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | Kepler-172 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,526 K |
| Stellar Radius | 1.0850 R☉ |
| Stellar Mass | 1.0810 M☉ |
| Bolometric Luminosity | 0.985 L☉ |
| Metallicity [Fe/H] | 0.390 dex |
| Stellar Age | 2.690 Gyr |
| Apparent Magnitude | V: 14.703 · G: 14.537 |
| System Architecture | 1 Star, 4 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.118000 AU |
| Orbital Period | 14.627 days |
| Mean Orbital Velocity | 87.8 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 84.9700° |
| Mean Bulk Density | 2.75 g/cm³ (17.8 km/s vesc) |
| Insolation Flux | 75.2900 S⊕ (~102,470 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2702.500 LY (828.592 pc) |