HD 18742 b
Astrophysical Synthesis & Habitability Characterization
HD 18742 b is a confirmed gas giant exoplanet orbiting the star HD 18742, located approximately 530.6 light-years (162.69 parsecs) from the Solar System. First announced in 2011 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 1080.622 Earth masses (3.4 Jupiter masses). Combining its mass and radius yields a mean bulk density of 2.65 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 6.3 g⊕ (61.78 m/s²), and an escape velocity of 101.6 km/s.
In its orbital architecture around HD 18742, HD 18742 b completes one full revolution every 766 Earth days (2.1Julian years) at a semi-major axis of 1.82 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 25.8 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.04 (ranging from 1.7472 AU at periapsis to 1.8928 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 400 K (+127°C / +261°F) and receiving 4.20 S⊕ (~5,711 W/m²), HD 18742 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 18742 is classified as a solar-type yellow star of spectral type G8/K0 IV with an effective photospheric temperature of 4,940 K, a radius of 5.13 R☉, a mass of 1.36 M☉, an estimated bolometric luminosity of 14.062 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.3 Gyr and a metallicity of [Fe/H] = -0.04 dex (near-solar heavy-element abundance). From Earth, HD 18742 shines at apparent V-band magnitude 7.81 (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 18742 |
| Spectral Type | G8/K0 IV |
| Effective Temp (Teff) | 4,940 K |
| Stellar Radius | 5.1300 R☉ |
| Stellar Mass | 1.3600 M☉ |
| Bolometric Luminosity | 14.062 L☉ |
| Metallicity [Fe/H] | -0.040 dex |
| Stellar Age | 2.300 Gyr |
| Apparent Magnitude | V: 7.810 · G: 7.555 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.820000 AU |
| Orbital Period | 766 days |
| Mean Orbital Velocity | 25.8 km/s |
| Orbital Eccentricity (e) | 0.04000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 2.65 g/cm³ (101.6 km/s vesc) |
| Insolation Flux | 4.1964 S⊕ (~5,711 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 530.600 LY (162.685 pc) |