Kepler-197 d
Astrophysical Synthesis & Habitability Characterization
Kepler-197 d is a confirmed terrestrial exoplanet orbiting the star Kepler-197, located approximately 1078.2 light-years (330.58 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.01% across the stellar disk), this world measures 1.22 Earth radii and has a measured mass of 1.98 Earth masses. Combining its mass and radius yields a mean bulk density of 6.01 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 1.33 g⊕ (13.04 m/s²), and an escape velocity of 14.3 km/s.
In its orbital architecture around Kepler-197, Kepler-197 d completes one full revolution every 15.678 Earth days at a semi-major axis of 0.119 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 82.6 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.03 (ranging from 0.1154 AU at periapsis to 0.1226 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 810 K (+537°C / +999°F) and receiving 109.09 S⊕ (~148,473 W/m²), Kepler-197 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-197 is classified as a stellar host with an effective photospheric temperature of 6,004 K, a radius of 1.12 R☉, a mass of 0.857 M☉, an estimated bolometric luminosity of 1.462 L☉. Stellar evolution modeling indicates an estimated stellar age of 5.37 Gyr and a metallicity of [Fe/H] = -0.441 dex (metal-poor relative to the Sun). From Earth, Kepler-197 shines at apparent V-band magnitude 11.775 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-197 system is a multi-planet architecture hosting 4 confirmed worlds, with Kepler-197 d sharing its stellar neighborhood alongside Kepler-197 b, Kepler-197 c, Kepler-197 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-197 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 6,004 K |
| Stellar Radius | 1.1200 R☉ |
| Stellar Mass | 0.8570 M☉ |
| Bolometric Luminosity | 1.462 L☉ |
| Metallicity [Fe/H] | -0.441 dex |
| Stellar Age | 5.370 Gyr |
| Apparent Magnitude | V: 11.775 · G: 11.780 |
| System Architecture | 2 Stars, 4 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.119000 AU |
| Orbital Period | 15.678 days |
| Mean Orbital Velocity | 82.6 km/s |
| Orbital Eccentricity (e) | 0.03000 |
| Orbital Inclination (i) | 84.5500° |
| Mean Bulk Density | 6.01 g/cm³ (14.3 km/s vesc) |
| Insolation Flux | 109.0910 S⊕ (~148,473 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1078.200 LY (330.575 pc) |