HD 2638 b
Astrophysical Synthesis & Habitability Characterization
HD 2638 b is a confirmed gas giant exoplanet orbiting the star HD 2638, located approximately 179.3 light-years (54.96 parsecs) from the Solar System. First announced in 2005 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 14.3 Earth radii (1.28 Jupiter radii) and has a measured mass of 133.489 Earth masses (0.42 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.25 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.65 g⊕ (6.37 m/s²), and an escape velocity of 34.2 km/s.
In its orbital architecture around HD 2638, HD 2638 b completes one full revolution every 3.444 Earth days at a semi-major axis of 0.04 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 126.3 km/s (compared to Earth's 29.8 km/s). The orbit is modeled as circular (e = 0.00), maintaining a constant stellar distance throughout its year.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1212 K (+939°C / +1722°F) and receiving 292.33 S⊕ (~397,867 W/m²), HD 2638 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 2638 is classified as an orange K-type star of spectral type K1 V with an effective photospheric temperature of 5,186 K, a radius of 0.94 R☉, a mass of 0.77 M☉, an estimated bolometric luminosity of 0.573 L☉. Stellar evolution modeling indicates an estimated stellar age of 3 Gyr and a metallicity of [Fe/H] = 0.13 dex (metal-rich relative to the Sun). From Earth, HD 2638 shines at apparent V-band magnitude 9.44 (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 2638 |
| Spectral Type | K1 V |
| Effective Temp (Teff) | 5,186 K |
| Stellar Radius | 0.9400 R☉ |
| Stellar Mass | 0.7700 M☉ |
| Bolometric Luminosity | 0.573 L☉ |
| Metallicity [Fe/H] | 0.130 dex |
| Stellar Age | 3.000 Gyr |
| Apparent Magnitude | V: 9.440 · G: 9.193 |
| System Architecture | 3 Stars, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.040000 AU |
| Orbital Period | 3.444 days |
| Mean Orbital Velocity | 126.3 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.25 g/cm³ (34.2 km/s vesc) |
| Insolation Flux | 292.3345 S⊕ (~397,867 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 179.300 LY (54.962 pc) |