Kepler-1998 b
Astrophysical Synthesis & Habitability Characterization
Kepler-1998 b is a confirmed sub-earth exoplanet orbiting the star Kepler-1998, located approximately 1112.1 light-years (340.97 parsecs) from the Solar System. First announced in 2023 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0036% across the stellar disk), this world measures 0.6 Earth radii and has a measured mass of 0.156 Earth masses. Combining its mass and radius yields a mean bulk density of 3.98 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 0.43 g⊕ (4.22 m/s²), and an escape velocity of 5.7 km/s.
In its orbital architecture around Kepler-1998, Kepler-1998 b completes one full revolution every 3.033 Earth days at a semi-major axis of 0.0405 AU (an ultra-close orbit less than one-seventh of Mercury's 0.387 AU distance from the Sun, where strong stellar tidal forces typically induce synchronous rotation). Its mean orbital velocity is approximately 145.3 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 1187 K (+914°C / +1677°F) and receiving 468.31 S⊕ (~637,370 W/m²), Kepler-1998 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-1998 is classified as a stellar host with an effective photospheric temperature of 5,640 K, a radius of 0.921 R☉, a mass of 0.962 M☉, an estimated bolometric luminosity of 0.77 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.27 Gyr and a metallicity of [Fe/H] = 0.06 dex (metal-rich relative to the Sun). From Earth, Kepler-1998 shines at apparent V-band magnitude 12.74 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.
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-1998 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,640 K |
| Stellar Radius | 0.9210 R☉ |
| Stellar Mass | 0.9620 M☉ |
| Bolometric Luminosity | 0.77 L☉ |
| Metallicity [Fe/H] | 0.060 dex |
| Stellar Age | 4.270 Gyr |
| Apparent Magnitude | V: 12.740 · G: 12.602 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.040500 AU |
| Orbital Period | 3.033 days |
| Mean Orbital Velocity | 145.3 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 88.9300° |
| Mean Bulk Density | 3.98 g/cm³ (5.7 km/s vesc) |
| Insolation Flux | 468.3100 S⊕ (~637,370 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1112.100 LY (340.965 pc) |