HD 23472 d
Astrophysical Synthesis & Habitability Characterization
HD 23472 d is a confirmed sub-earth exoplanet orbiting the star HD 23472, located approximately 127.3 light-years (39.03 parsecs) from the Solar System. First announced in 2022 by Transiting Exoplanet Survey Satellite (TESS) using the Transit detection technique (producing an estimated primary transit depth of 0.0094% across the stellar disk), this world measures 0.75 Earth radii and has a measured mass of 0.55 Earth masses. Combining its mass and radius yields a mean bulk density of 7.19 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 0.98 g⊕ (9.61 m/s²), and an escape velocity of 9.6 km/s.
In its orbital architecture around HD 23472, HD 23472 d completes one full revolution every 3.977 Earth days at a semi-major axis of 0.04298 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 117.6 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.07 carries the world between 0.04 AU at periapsis and 0.046 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 909 K (+636°C / +1177°F) and receiving 117.00 S⊕ (~159,237 W/m²), HD 23472 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 23472 is classified as an orange K-type star of spectral type K4 V with an effective photospheric temperature of 4,684 K, a radius of 0.71 R☉, a mass of 0.67 M☉, an estimated bolometric luminosity of 0.218 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.2 dex (metal-poor relative to the Sun). From Earth, HD 23472 shines at apparent V-band magnitude 9.73 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The HD 23472 system is a multi-planet architecture hosting 5 confirmed worlds, with HD 23472 d sharing its stellar neighborhood alongside HD 23472 e, HD 23472 f, HD 23472 b, HD 23472 c.
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 23472 |
| Spectral Type | K4 V |
| Effective Temp (Teff) | 4,684 K |
| Stellar Radius | 0.7100 R☉ |
| Stellar Mass | 0.6700 M☉ |
| Bolometric Luminosity | 0.218 L☉ |
| Metallicity [Fe/H] | -0.200 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 9.730 · G: 9.385 |
| System Architecture | 1 Star, 5 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.042980 AU |
| Orbital Period | 3.977 days |
| Mean Orbital Velocity | 117.6 km/s |
| Orbital Eccentricity (e) | 0.07000 |
| Orbital Inclination (i) | 87.9500° |
| Mean Bulk Density | 7.19 g/cm³ (9.6 km/s vesc) |
| Insolation Flux | 117.0000 S⊕ (~159,237 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 127.300 LY (39.034 pc) |