LTT 3780 c
Astrophysical Synthesis & Habitability Characterization
LTT 3780 c is a confirmed sub-neptune exoplanet orbiting the star LTT 3780, located approximately 71.7 light-years (21.98 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 0.3325% across the stellar disk), this world measures 2.39 Earth radii and has a measured mass of 8.04 Earth masses. Combining its mass and radius yields a mean bulk density of 3.25 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.41 g⊕ (13.83 m/s²), and an escape velocity of 20.5 km/s.
In its orbital architecture around LTT 3780, LTT 3780 c completes one full revolution every 12.252 Earth days at a semi-major axis of 0.0757 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 67.2 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.024 (ranging from 0.0739 AU at periapsis to 0.0775 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 359 K (+86°C / +187°F) and receiving 2.76 S⊕ (~3,756 W/m²), LTT 3780 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star LTT 3780 is classified as a low-mass red dwarf of spectral type M3.5 V with an effective photospheric temperature of 3,358 K, a radius of 0.38 R☉, a mass of 0.381 M☉, an estimated bolometric luminosity of 0.016 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.1 Gyr and a metallicity of [Fe/H] = 0.06 dex (metal-rich relative to the Sun). From Earth, LTT 3780 shines at apparent V-band magnitude 13.14 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The LTT 3780 system is a multi-planet architecture hosting 2 confirmed worlds, with LTT 3780 c sharing its stellar neighborhood alongside LTT 3780 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 | LTT 3780 |
| Spectral Type | M3.5 V |
| Effective Temp (Teff) | 3,358 K |
| Stellar Radius | 0.3800 R☉ |
| Stellar Mass | 0.3810 M☉ |
| Bolometric Luminosity | 0.016 L☉ |
| Metallicity [Fe/H] | 0.060 dex |
| Stellar Age | 3.100 Gyr |
| Apparent Magnitude | V: 13.140 · G: 11.847 |
| System Architecture | 2 Stars, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.075700 AU |
| Orbital Period | 12.252 days |
| Mean Orbital Velocity | 67.2 km/s |
| Orbital Eccentricity (e) | 0.02400 |
| Orbital Inclination (i) | 88.9580° |
| Mean Bulk Density | 3.25 g/cm³ (20.5 km/s vesc) |
| Insolation Flux | 2.7600 S⊕ (~3,756 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 71.700 LY (21.981 pc) |