HD 159243 c
Astrophysical Synthesis & Habitability Characterization
HD 159243 c is a confirmed gas giant exoplanet orbiting the star HD 159243, located approximately 239.1 light-years (73.31 parsecs) from the Solar System. First announced in 2013 by Haute-Provence Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 13.4 Earth radii (1.2 Jupiter radii) and has a measured mass of 603.9 Earth masses (1.9 Jupiter masses). Combining its mass and radius yields a mean bulk density of 1.38 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 3.36 g⊕ (32.95 m/s²), and an escape velocity of 75.1 km/s.
In its orbital architecture around HD 159243, HD 159243 c completes one full revolution every 248.4 Earth days at a semi-major axis of 0.8 AU (comparable to the inner terrestrial zone between Venus, Earth at 1.00 AU, and Mars at 1.52 AU). Its mean orbital velocity is approximately 35 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.075 carries the world between 0.74 AU at periapsis and 0.86 AU at apoapsis, driving measurable seasonal insolation cycles.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 13.400 R⊕, HD 159243 c 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 159243 is classified as a solar-type yellow star of spectral type G0 V with an effective photospheric temperature of 6,123 K, a radius of 1.12 R☉, a mass of 1.125 M☉, an estimated bolometric luminosity of 1.582 L☉. Stellar evolution modeling indicates an estimated stellar age of 1.25 Gyr and a metallicity of [Fe/H] = 0.05 dex (near-solar heavy-element abundance). From Earth, HD 159243 shines at apparent V-band magnitude 8.65 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere. The HD 159243 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 159243 c sharing its stellar neighborhood alongside HD 159243 b.
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: Haute-Provence Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 159243 |
| Spectral Type | G0 V |
| Effective Temp (Teff) | 6,123 K |
| Stellar Radius | 1.1200 R☉ |
| Stellar Mass | 1.1250 M☉ |
| Bolometric Luminosity | 1.582 L☉ |
| Metallicity [Fe/H] | 0.050 dex |
| Stellar Age | 1.250 Gyr |
| Apparent Magnitude | V: 8.650 · G: 8.512 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.800000 AU |
| Orbital Period | 248.4 days |
| Mean Orbital Velocity | 35 km/s |
| Orbital Eccentricity (e) | 0.07500 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.38 g/cm³ (75.1 km/s vesc) |
| Insolation Flux | 2.0315 S⊕ (~2,765 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 239.100 LY (73.306 pc) |