Kepler-298 d
Astrophysical Synthesis & Habitability Characterization
Kepler-298 d is a confirmed sub-neptune exoplanet orbiting the star Kepler-298, located approximately 1690.2 light-years (518.2 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.1551% across the stellar disk), this world measures 2.5 Earth radii and has a measured mass of 6.8 Earth masses. Combining its mass and radius yields a mean bulk density of 2.4 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.09 g⊕ (10.69 m/s²), and an escape velocity of 18.4 km/s.
In its orbital architecture around Kepler-298, Kepler-298 d completes one full revolution every 77.474 Earth days at a semi-major axis of 0.305 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 42.8 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.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 2.500 R⊕, Kepler-298 d exceeds the empirical ~1.8–2.2 R⊕ Fulton radius valley threshold, indicating a substantial hydrogen-helium or supercritical volatile envelope without a conventional solid terrestrial surface.
The host star Kepler-298 is classified as a stellar host with an effective photospheric temperature of 4,465 K, a radius of 0.582 R☉, a mass of 0.66 M☉, an estimated bolometric luminosity of 0.121 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.4 Gyr and a metallicity of [Fe/H] = -0.21 dex (metal-poor relative to the Sun). From Earth, Kepler-298 shines at apparent V-band magnitude 15.617 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-298 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-298 d sharing its stellar neighborhood alongside Kepler-298 b, Kepler-298 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: Kepler · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | Kepler-298 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 4,465 K |
| Stellar Radius | 0.5820 R☉ |
| Stellar Mass | 0.6600 M☉ |
| Bolometric Luminosity | 0.121 L☉ |
| Metallicity [Fe/H] | -0.210 dex |
| Stellar Age | 2.400 Gyr |
| Apparent Magnitude | V: 15.617 · G: 15.418 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.305000 AU |
| Orbital Period | 77.474 days |
| Mean Orbital Velocity | 42.8 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.5700° |
| Mean Bulk Density | 2.4 g/cm³ (18.4 km/s vesc) |
| Insolation Flux | 1.7150 S⊕ (~2,334 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1690.200 LY (518.204 pc) |