HD 18015 b
Astrophysical Synthesis & Habitability Characterization
HD 18015 b is a confirmed gas giant exoplanet orbiting the star HD 18015, located approximately 403.8 light-years (123.8 parsecs) from the Solar System. First announced in 2018 by W. M. Keck Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 13.1 Earth radii (1.17 Jupiter radii) and has a measured mass of 1048.834 Earth masses (3.3 Jupiter masses). Combining its mass and radius yields a mean bulk density of 2.57 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 6.11 g⊕ (59.92 m/s²), and an escape velocity of 100.1 km/s.
In its orbital architecture around HD 18015, HD 18015 b completes one full revolution every 2278 Earth days (6.24Julian years) at a semi-major axis of 3.87 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 18.5 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.148 carries the world between 3.2972 AU at periapsis and 4.4428 AU at apoapsis, driving measurable seasonal insolation cycles.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 13.100 R⊕, HD 18015 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 18015 is classified as a solar-type yellow star of spectral type G6 IV with an effective photospheric temperature of 5,603 K, a radius of 3.13 R☉, a mass of 1.49 M☉, an estimated bolometric luminosity of 8.663 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.14 dex (metal-poor relative to the Sun). From Earth, HD 18015 shines at apparent V-band magnitude 7.89 (accessible to binoculars and small amateur telescopes) 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: W. M. Keck Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 18015 |
| Spectral Type | G6 IV |
| Effective Temp (Teff) | 5,603 K |
| Stellar Radius | 3.1300 R☉ |
| Stellar Mass | 1.4900 M☉ |
| Bolometric Luminosity | 8.663 L☉ |
| Metallicity [Fe/H] | -0.140 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 7.890 · G: 7.722 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 3.870000 AU |
| Orbital Period | 2278 days |
| Mean Orbital Velocity | 18.5 km/s |
| Orbital Eccentricity (e) | 0.14800 |
| Orbital Inclination (i) | 69.0000° |
| Mean Bulk Density | 2.57 g/cm³ (100.1 km/s vesc) |
| Insolation Flux | 0.6286 S⊕ (~856 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 403.800 LY (123.801 pc) |