HD 108236 e
Astrophysical Synthesis & Habitability Characterization
HD 108236 e is a confirmed sub-neptune exoplanet orbiting the star HD 108236, located approximately 210.7 light-years (64.6 parsecs) from the Solar System. First announced in 2020 by Transiting Exoplanet Survey Satellite (TESS) using the Transit detection technique (producing an estimated primary transit depth of 0.1039% across the stellar disk), this world measures 3.083 Earth radii (0.28 Jupiter radii) and has a measured mass of 9.71 Earth masses. Combining its mass and radius yields a mean bulk density of 1.83 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.02 g⊕ (10 m/s²), and an escape velocity of 19.9 km/s.
In its orbital architecture around HD 108236, HD 108236 e completes one full revolution every 19.59 Earth days at a semi-major axis of 0.1367 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 75.9 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.058 carries the world between 0.1288 AU at periapsis and 0.1446 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 636 K (+363°C / +685°F) and receiving 35.00 S⊕ (~47,639 W/m²), HD 108236 e orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 108236 is classified as a solar-type yellow star of spectral type G3 V with an effective photospheric temperature of 5,660 K, a radius of 0.877 R☉, a mass of 0.869 M☉, an estimated bolometric luminosity of 0.708 L☉. Stellar evolution modeling indicates an estimated stellar age of 6.7 Gyr and a metallicity of [Fe/H] = -0.28 dex (metal-poor relative to the Sun). From Earth, HD 108236 shines at apparent V-band magnitude 9.25 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The HD 108236 system is a multi-planet architecture hosting 5 confirmed worlds, with HD 108236 e sharing its stellar neighborhood alongside HD 108236 b, HD 108236 c, TOI-1233.01, HD 108236 f.
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: Transiting Exoplanet Survey Satellite (TESS) · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 108236 |
| Spectral Type | G3 V |
| Effective Temp (Teff) | 5,660 K |
| Stellar Radius | 0.8770 R☉ |
| Stellar Mass | 0.8690 M☉ |
| Bolometric Luminosity | 0.708 L☉ |
| Metallicity [Fe/H] | -0.280 dex |
| Stellar Age | 6.700 Gyr |
| Apparent Magnitude | V: 9.250 · G: 9.087 |
| System Architecture | 1 Star, 5 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.136700 AU |
| Orbital Period | 19.59 days |
| Mean Orbital Velocity | 75.9 km/s |
| Orbital Eccentricity (e) | 0.05800 |
| Orbital Inclination (i) | 89.2450° |
| Mean Bulk Density | 1.83 g/cm³ (19.9 km/s vesc) |
| Insolation Flux | 35.0031 S⊕ (~47,639 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 210.700 LY (64.598 pc) |