LHS 1678 b
Astrophysical Synthesis & Habitability Characterization
LHS 1678 b is a confirmed sub-earth exoplanet orbiting the star LHS 1678, located approximately 64.8 light-years (19.88 parsecs) from the Solar System. First announced in 2021 by Transiting Exoplanet Survey Satellite (TESS) using the Transit detection technique (producing an estimated primary transit depth of 0.0364% across the stellar disk), this world measures 0.685 Earth radii and has a measured mass of 0.35 Earth masses. Combining its mass and radius yields a mean bulk density of 6 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 0.75 g⊕ (7.35 m/s²), and an escape velocity of 8 km/s.
In its orbital architecture around LHS 1678, LHS 1678 b completes one full revolution every 0.86 Earth days at a semi-major axis of 0.01239 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 156.7 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.033 (ranging from 0.012 AU at periapsis to 0.0128 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 830 K (+557°C / +1035°F) and receiving 94.30 S⊕ (~128,342 W/m²), LHS 1678 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star LHS 1678 is classified as a low-mass red dwarf of spectral type M2.0 V with an effective photospheric temperature of 3,490 K, a radius of 0.329 R☉, a mass of 0.345 M☉, an estimated bolometric luminosity of 0.014 L☉. Stellar evolution modeling indicates an estimated stellar age of 7 Gyr. From Earth, LHS 1678 shines at apparent V-band magnitude 12.6 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The LHS 1678 system is a multi-planet architecture hosting 3 confirmed worlds, with LHS 1678 b sharing its stellar neighborhood alongside LHS 1678 c, LHS 1678 d.
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 | LHS 1678 |
| Spectral Type | M2.0 V |
| Effective Temp (Teff) | 3,490 K |
| Stellar Radius | 0.3290 R☉ |
| Stellar Mass | 0.3450 M☉ |
| Bolometric Luminosity | 0.014 L☉ |
| Metallicity [Fe/H] | — |
| Stellar Age | 7.000 Gyr |
| Apparent Magnitude | V: 12.600 · G: 11.540 |
| System Architecture | 2 Stars, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.012390 AU |
| Orbital Period | 0.86 days |
| Mean Orbital Velocity | 156.7 km/s |
| Orbital Eccentricity (e) | 0.03300 |
| Orbital Inclination (i) | 88.5300° |
| Mean Bulk Density | 6 g/cm³ (8 km/s vesc) |
| Insolation Flux | 94.3000 S⊕ (~128,342 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 64.800 LY (19.878 pc) |