K2-98 b
Astrophysical Synthesis & Habitability Characterization
K2-98 b is a confirmed sub-neptune exoplanet orbiting the star K2-98, located approximately 1691.5 light-years (518.63 parsecs) from the Solar System. First announced in 2016 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0936% across the stellar disk), this world measures 5.066 Earth radii (0.45 Jupiter radii) and has a measured mass of 34.008 Earth masses (0.11 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.44 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.33 g⊕ (13.04 m/s²), and an escape velocity of 29 km/s.
In its orbital architecture around K2-98, K2-98 b completes one full revolution every 10.137 Earth days at a semi-major axis of 0.0986 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 105.8 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.119 carries the world between 0.0869 AU at periapsis and 0.1103 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1185 K (+912°C / +1674°F) and receiving 339.00 S⊕ (~461,379 W/m²), K2-98 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-98 is classified as a warm F-type star of spectral type F8 V with an effective photospheric temperature of 6,260 K, a radius of 1.518 R☉, a mass of 1.246 M☉, an estimated bolometric luminosity of 3.175 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.4 Gyr and a metallicity of [Fe/H] = -0.044 dex (near-solar heavy-element abundance). From Earth, K2-98 shines at apparent V-band magnitude 12.216 (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: K2 · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | K2-98 |
| Spectral Type | F8 V |
| Effective Temp (Teff) | 6,260 K |
| Stellar Radius | 1.5180 R☉ |
| Stellar Mass | 1.2460 M☉ |
| Bolometric Luminosity | 3.175 L☉ |
| Metallicity [Fe/H] | -0.044 dex |
| Stellar Age | 3.400 Gyr |
| Apparent Magnitude | V: 12.216 · G: 12.040 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.098600 AU |
| Orbital Period | 10.137 days |
| Mean Orbital Velocity | 105.8 km/s |
| Orbital Eccentricity (e) | 0.11900 |
| Orbital Inclination (i) | 88.3900° |
| Mean Bulk Density | 1.44 g/cm³ (29 km/s vesc) |
| Insolation Flux | 339.0000 S⊕ (~461,379 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1691.500 LY (518.625 pc) |