HATS-28 b
Astrophysical Synthesis & Habitability Characterization
HATS-28 b is a confirmed gas giant exoplanet orbiting the star HATS-28, located approximately 1746.2 light-years (535.38 parsecs) from the Solar System. First announced in 2016 by HATSouth using the Transit detection technique (producing an estimated primary transit depth of 1.7711% across the stellar disk), this world measures 13.384 Earth radii (1.19 Jupiter radii) and has a measured mass of 213.582 Earth masses (0.67 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.49 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.19 g⊕ (11.67 m/s²), and an escape velocity of 44.7 km/s.
In its orbital architecture around HATS-28, HATS-28 b completes one full revolution every 3.181 Earth days at a semi-major axis of 0.04131 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 141.3 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.202 carries the world between 0.033 AU at periapsis and 0.0497 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1253 K (+980°C / +1796°F) and receiving 407.85 S⊕ (~555,082 W/m²), HATS-28 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HATS-28 is classified as a solar-type yellow star of spectral type G with an effective photospheric temperature of 5,498 K, a radius of 0.922 R☉, a mass of 0.929 M☉, an estimated bolometric luminosity of 0.697 L☉. Stellar evolution modeling indicates an estimated stellar age of 6.2 Gyr and a metallicity of [Fe/H] = 0.01 dex (near-solar heavy-element abundance). From Earth, HATS-28 shines at apparent V-band magnitude 13.981 (faint and requiring research-grade or CCD telescopic photometry) 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: HATSouth · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HATS-28 |
| Spectral Type | G |
| Effective Temp (Teff) | 5,498 K |
| Stellar Radius | 0.9220 R☉ |
| Stellar Mass | 0.9290 M☉ |
| Bolometric Luminosity | 0.697 L☉ |
| Metallicity [Fe/H] | 0.010 dex |
| Stellar Age | 6.200 Gyr |
| Apparent Magnitude | V: 13.981 · G: 13.793 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.041310 AU |
| Orbital Period | 3.181 days |
| Mean Orbital Velocity | 141.3 km/s |
| Orbital Eccentricity (e) | 0.20200 |
| Orbital Inclination (i) | 86.1700° |
| Mean Bulk Density | 0.49 g/cm³ (44.7 km/s vesc) |
| Insolation Flux | 407.8485 S⊕ (~555,082 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1746.200 LY (535.383 pc) |