HD 103720 b
Astrophysical Synthesis & Habitability Characterization
HD 103720 b is a confirmed gas giant exoplanet orbiting the star HD 103720, located approximately 148.5 light-years (45.54 parsecs) from the Solar System. First announced in 2014 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 14.1 Earth radii (1.26 Jupiter radii) and has a measured mass of 197.046 Earth masses (0.62 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.39 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.99 g⊕ (9.71 m/s²), and an escape velocity of 41.8 km/s.
In its orbital architecture around HD 103720, HD 103720 b completes one full revolution every 4.556 Earth days at a semi-major axis of 0.0498 AU (an ultra-close orbit less than one-seventh of Mercury's 0.387 AU distance from the Sun, where strong stellar tidal forces typically induce synchronous rotation). Its mean orbital velocity is approximately 118.9 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.086 carries the world between 0.0455 AU at periapsis and 0.0541 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 926 K (+653°C / +1207°F) and receiving 140.35 S⊕ (~191,013 W/m²), HD 103720 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 103720 is classified as an orange K-type star of spectral type K3 V with an effective photospheric temperature of 5,017 K, a radius of 0.73 R☉, a mass of 0.794 M☉, an estimated bolometric luminosity of 0.303 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.8 Gyr and a metallicity of [Fe/H] = -0.02 dex (near-solar heavy-element abundance). From Earth, HD 103720 shines at apparent V-band magnitude 9.5 (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: La Silla Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 103720 |
| Spectral Type | K3 V |
| Effective Temp (Teff) | 5,017 K |
| Stellar Radius | 0.7300 R☉ |
| Stellar Mass | 0.7940 M☉ |
| Bolometric Luminosity | 0.303 L☉ |
| Metallicity [Fe/H] | -0.020 dex |
| Stellar Age | 3.800 Gyr |
| Apparent Magnitude | V: 9.500 · G: 9.224 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.049800 AU |
| Orbital Period | 4.556 days |
| Mean Orbital Velocity | 118.9 km/s |
| Orbital Eccentricity (e) | 0.08600 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.39 g/cm³ (41.8 km/s vesc) |
| Insolation Flux | 140.3478 S⊕ (~191,013 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 148.500 LY (45.535 pc) |