HD 21749 c
Astrophysical Synthesis & Habitability Characterization
HD 21749 c is a confirmed terrestrial exoplanet orbiting the star GJ 143, located approximately 53.2 light-years (16.32 parsecs) from the Solar System. First announced in 2019 by Transiting Exoplanet Survey Satellite (TESS) using the Transit detection technique (producing an estimated primary transit depth of 0.0138% across the stellar disk), this world measures 0.892 Earth radii and has a measured mass of 3.7 Earth masses. Combining its mass and radius yields a mean bulk density of 28.75 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 4.65 g⊕ (45.6 m/s²), and an escape velocity of 22.8 km/s.
In its orbital architecture around GJ 143, HD 21749 c completes one full revolution every 7.79 Earth days at a semi-major axis of 0.0695 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 97.1 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 701 K (+428°C / +802°F) and receiving 305.94 S⊕ (~416,388 W/m²), HD 21749 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star GJ 143 is classified as an orange K-type star of spectral type K4.5 with an effective photospheric temperature of 4,640 K, a radius of 0.695 R☉, a mass of 0.73 M☉, an estimated bolometric luminosity of 0.201 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.8 Gyr and a metallicity of [Fe/H] = 0.003 dex (near-solar heavy-element abundance). From Earth, GJ 143 shines at apparent V-band magnitude 8.08 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The GJ 143 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 21749 c sharing its stellar neighborhood alongside GJ 143 b.
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 | GJ 143 |
| Spectral Type | K4.5 |
| Effective Temp (Teff) | 4,640 K |
| Stellar Radius | 0.6950 R☉ |
| Stellar Mass | 0.7300 M☉ |
| Bolometric Luminosity | 0.201 L☉ |
| Metallicity [Fe/H] | 0.003 dex |
| Stellar Age | 3.800 Gyr |
| Apparent Magnitude | V: 8.080 · G: 7.679 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.069500 AU |
| Orbital Period | 7.79 days |
| Mean Orbital Velocity | 97.1 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | 88.9000° |
| Mean Bulk Density | 28.75 g/cm³ (22.8 km/s vesc) |
| Insolation Flux | 305.9425 S⊕ (~416,388 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 53.200 LY (16.320 pc) |