18 Del b
Astrophysical Synthesis & Habitability Characterization
18 Del b is a confirmed gas giant exoplanet orbiting the star 18 Del, located approximately 248.6 light-years (76.22 parsecs) from the Solar System. First announced in 2008 by Okayama Astrophysical Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 12.5 Earth radii (1.12 Jupiter radii) and has a measured mass of 2926.246 Earth masses (9.21 Jupiter masses). Combining its mass and radius yields a mean bulk density of 8.26 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 18.73 g⊕ (183.68 m/s²), and an escape velocity of 171.1 km/s.
In its orbital architecture around 18 Del, 18 Del b completes one full revolution every 982.85 Earth days (2.69Julian years) at a semi-major axis of 2.476 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 27.4 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.024 (ranging from 2.4166 AU at periapsis to 2.5354 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 453 K (+180°C / +356°F) and receiving 7.02 S⊕ (~9,551 W/m²), 18 Del b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star 18 Del is classified as a solar-type yellow star of spectral type G6 III with an effective photospheric temperature of 4,980 K, a radius of 8.8 R☉, a mass of 2.1 M☉, an estimated bolometric luminosity of 42.734 L☉. Stellar evolution modeling indicates an estimated stellar age of 1.1 Gyr and a metallicity of [Fe/H] = -0.06 dex (near-solar heavy-element abundance). From Earth, 18 Del shines at apparent V-band magnitude 5.51 (visible to the unaided human eye under dark skies) 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: Okayama Astrophysical Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | 18 Del |
| Spectral Type | G6 III |
| Effective Temp (Teff) | 4,980 K |
| Stellar Radius | 8.8000 R☉ |
| Stellar Mass | 2.1000 M☉ |
| Bolometric Luminosity | 42.734 L☉ |
| Metallicity [Fe/H] | -0.060 dex |
| Stellar Age | 1.100 Gyr |
| Apparent Magnitude | V: 5.510 · G: 5.275 |
| System Architecture | 2 Stars, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 2.476000 AU |
| Orbital Period | 982.85 days |
| Mean Orbital Velocity | 27.4 km/s |
| Orbital Eccentricity (e) | 0.02400 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 8.26 g/cm³ (171.1 km/s vesc) |
| Insolation Flux | 7.0173 S⊕ (~9,551 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 248.600 LY (76.222 pc) |