LP 791-18 c
Astrophysical Synthesis & Habitability Characterization
LP 791-18 c is a confirmed sub-neptune exoplanet orbiting the star LP 791-18, located approximately 86.4 light-years (26.49 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 1.5707% across the stellar disk), this world measures 2.488 Earth radii and has a measured mass of 7.16 Earth masses. Combining its mass and radius yields a mean bulk density of 2.56 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.16 g⊕ (11.38 m/s²), and an escape velocity of 19 km/s.
In its orbital architecture around LP 791-18, LP 791-18 c completes one full revolution every 4.99 Earth days at a semi-major axis of 0.02961 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 64.6 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.0001 (ranging from 0.0296 AU at periapsis to 0.0296 AU at apoapsis), the planet experiences minimal orbital distance variation.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 2.488 R⊕, LP 791-18 c exceeds the empirical ~1.8–2.2 R⊕ Fulton radius valley threshold, indicating a substantial hydrogen-helium or supercritical volatile envelope without a conventional solid terrestrial surface.
The host star LP 791-18 is classified as a low-mass red dwarf of spectral type M(6.1 +/- 0.7) V with an effective photospheric temperature of 2,960 K, a radius of 0.182 R☉, a mass of 0.139 M☉, an estimated bolometric luminosity of 0.00228 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.5 Gyr and a metallicity of [Fe/H] = -0.09 dex (near-solar heavy-element abundance). From Earth, LP 791-18 shines at apparent V-band magnitude 16.91 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The LP 791-18 system is a multi-planet architecture hosting 3 confirmed worlds, with LP 791-18 c sharing its stellar neighborhood alongside LP 791-18 b, LP 791-18 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 | LP 791-18 |
| Spectral Type | M(6.1 +/- 0.7) V |
| Effective Temp (Teff) | 2,960 K |
| Stellar Radius | 0.1820 R☉ |
| Stellar Mass | 0.1390 M☉ |
| Bolometric Luminosity | 0.00228 L☉ |
| Metallicity [Fe/H] | -0.090 dex |
| Stellar Age | 0.500 Gyr |
| Apparent Magnitude | V: 16.910 · G: 15.072 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.029610 AU |
| Orbital Period | 4.99 days |
| Mean Orbital Velocity | 64.6 km/s |
| Orbital Eccentricity (e) | 0.00010 |
| Orbital Inclination (i) | 89.9400° |
| Mean Bulk Density | 2.56 g/cm³ (19 km/s vesc) |
| Insolation Flux | 2.6370 S⊕ (~3,589 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 86.400 LY (26.493 pc) |