HD 111998 b
Astrophysical Synthesis & Habitability Characterization
HD 111998 b is a confirmed gas giant exoplanet orbiting the star HD 111998, located approximately 108.4 light-years (33.22 parsecs) from the Solar System. First announced in 2016 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 12.9 Earth radii (1.15 Jupiter radii) and has a measured mass of 1525.576 Earth masses (4.8 Jupiter masses). Combining its mass and radius yields a mean bulk density of 3.92 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 9.17 g⊕ (89.93 m/s²), and an escape velocity of 121.6 km/s.
In its orbital architecture around HD 111998, HD 111998 b completes one full revolution every 810 Earth days (2.22Julian years) at a semi-major axis of 1.91 AU (corresponding to the middle-system regime between Mars at 1.52 AU and Jupiter at 5.20 AU). Its mean orbital velocity is approximately 25.7 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.13 carries the world between 1.6617 AU at periapsis and 2.1583 AU at apoapsis, driving measurable seasonal insolation cycles.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 12.900 R⊕, HD 111998 b 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 HD 111998 is classified as a warm F-type star of spectral type F6 V with an effective photospheric temperature of 6,557 K, a radius of 1.45 R☉, a mass of 1.4 M☉, an estimated bolometric luminosity of 3.487 L☉. Stellar evolution modeling indicates an estimated stellar age of 1.7 Gyr and a metallicity of [Fe/H] = 0.07 dex (metal-rich relative to the Sun). From Earth, HD 111998 shines at apparent V-band magnitude 6.11 (visible to the unaided human eye under dark skies) in the Southern 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: La Silla Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 111998 |
| Spectral Type | F6 V |
| Effective Temp (Teff) | 6,557 K |
| Stellar Radius | 1.4500 R☉ |
| Stellar Mass | 1.4000 M☉ |
| Bolometric Luminosity | 3.487 L☉ |
| Metallicity [Fe/H] | 0.070 dex |
| Stellar Age | 1.700 Gyr |
| Apparent Magnitude | V: 6.110 · G: 5.995 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.910000 AU |
| Orbital Period | 810 days |
| Mean Orbital Velocity | 25.7 km/s |
| Orbital Eccentricity (e) | 0.13000 |
| Orbital Inclination (i) | 90.0000° |
| Mean Bulk Density | 3.92 g/cm³ (121.6 km/s vesc) |
| Insolation Flux | 0.8918 S⊕ (~1,214 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 108.400 LY (33.224 pc) |