LP 791-18 c
LP 791-18 c is a mini-Neptune orbiting the M(6.1 +/- 0.7) V star LP 791-18 in the constellation Crater. It lies about 86 light-years from Earth and was discovered in 2019 using the transit method.
How Big Is LP 791-18 c?
LP 791-18 c has a radius of 2.49 times that of Earth. Its mass is 7.2 times that of Earth, giving it a density of 2.56 g/cm³ — between that of rocky and gaseous planets.
Is LP 791-18 c in the Habitable Zone?
LP 791-18 c orbits inside the inner edge of the habitable zone of LP 791-18. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of LP 791-18: 0.039–0.105 AU (conservative: 0.050–0.100 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Orbit and Year Length
A year on LP 791-18 c — one full orbit around LP 791-18 — lasts 4.99 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.030 AU — closer to its star than Mercury is to the Sun. Its orbit is nearly circular (eccentricity 0.000).
How Was LP 791-18 c Discovered?
LP 791-18 c was discovered in 2019 using the transit method, with observations from Transiting Exoplanet Survey Satellite (TESS).
The transit method watches a star for the tiny, regular dip in brightness that occurs when a planet crosses in front of it. The depth and timing of these dips reveal the planet's size and orbital period.
How Far Away Is LP 791-18 c?
LP 791-18 c is 86.4 light-years (26.5 parsecs) from Earth. Light arriving here tonight left the planet around the year 1940. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 1,520,640 years to make the journey.
Earth Similarity Index
The Earth Similarity Index (ESI) scores how physically similar a planet is to Earth, from 0 to 1, based on radius, density, escape velocity and surface temperature. LP 791-18 c scores 0.57, ranking #172 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: LP 791-18
LP 791-18
- Spectral type
- M(6.1 +/- 0.7) V
- Surface temperature
- 2,960 K (Sun: 5,772 K)
- Mass
- 0.14 M☉
- Radius
- 0.18 R☉
- Luminosity
- 0.0023 L☉
- Age
- 0.5 billion years (Sun: 4.6)
The LP 791-18 Planetary System
LP 791-18 c is one of 3 known planets in the LP 791-18 system. Its siblings:
- LP 791-18 b (Terrestrial)
- LP 791-18 d (Terrestrial)
LP 791-18 c — Complete Data
| Radius | 2.488 Earth radii (0.222 Jupiter radii) |
|---|---|
| Mass | 7.16 Earth masses (0.023 Jupiter masses) |
| Density | 2.56 g/cm³ (Earth: 5.51) |
| Orbital period | 4.99 days |
| Orbital distance | 0.030 AU |
| Eccentricity | 0.000 |
| Earth Similarity Index | 0.57 |
| Distance from Earth | 86.4 light-years (26.5 parsecs) |
| Constellation | Crater |
| Discovery method | Transit |
| Discovery facility | Transiting Exoplanet Survey Satellite (TESS) |
| Discovery year | 2019 |
Data: NASA Exoplanet Archive, last updated 2026-02-26. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About LP 791-18 c
Is LP 791-18 c habitable?
No — LP 791-18 c orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is LP 791-18 c?
LP 791-18 c is about 86 light-years from Earth in the constellation Crater. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 1,520,640 years to get there.
How big is LP 791-18 c compared to Earth?
LP 791-18 c has 2.49 times the radius of Earth and about 7.2 times its mass.
How long is a year on LP 791-18 c?
One orbit around LP 791-18 takes 5.0 Earth days — short enough that 73 of its years would fit into one Earth year.
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