Kepler-1991 c
Kepler-1991 c is a mini-Neptune orbiting Kepler-1991 in the constellation Lyra. It lies about 2,791 light-years from Earth and was discovered in 2023 using the transit method.
How Big Is Kepler-1991 c?
Kepler-1991 c has a radius of 2.57 times that of Earth.
Is Kepler-1991 c in the Habitable Zone?
Kepler-1991 c orbits inside the inner edge of the habitable zone of Kepler-1991. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of Kepler-1991: 0.723–1.718 AU (conservative: 0.916–1.629 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on Kepler-1991 c
The equilibrium temperature of Kepler-1991 c is about 634 K (361 °C) — hot enough to melt many metals. This estimate ignores any atmosphere, which could change surface temperatures dramatically — Earth's greenhouse effect adds about 33 °C. It receives 38.27 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on Kepler-1991 c — one full orbit around Kepler-1991 — lasts 22.8 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.153 AU — closer to its star than Mercury is to the Sun.
How Was Kepler-1991 c Discovered?
Kepler-1991 c was discovered in 2023 using the transit method, with observations from Kepler.
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 Kepler-1991 c?
Kepler-1991 c is 2,791.3 light-years (855.8 parsecs) from Earth. Light arriving here tonight left the planet about 2,791 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 49,126,880 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. Kepler-1991 c scores 0.26, ranking #2,736 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-1991
Kepler-1991
- Surface temperature
- 5,478 K (Sun: 5,772 K)
- Mass
- 0.91 M☉
- Radius
- 1.05 R☉
The Kepler-1991 Planetary System
Kepler-1991 c is one of 2 known planets in the Kepler-1991 system. Its siblings:
- Kepler-1991 b (Super Earth)
Kepler-1991 c — Complete Data
| Radius | 2.570 Earth radii (0.229 Jupiter radii) |
|---|---|
| Orbital period | 22.79 days |
| Orbital distance | 0.153 AU |
| Equilibrium temperature | 634 K (361 °C) |
| Stellar irradiation | 38.27× Earth |
| Earth Similarity Index | 0.26 |
| Distance from Earth | 2,791.3 light-years (855.8 parsecs) |
| Constellation | Lyra |
| Discovery method | Transit |
| Discovery facility | Kepler |
| Discovery year | 2023 |
Data: NASA Exoplanet Archive, last updated 2017-05-08. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About Kepler-1991 c
Is Kepler-1991 c habitable?
No — Kepler-1991 c orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Kepler-1991 c?
Kepler-1991 c is about 2,791 light-years from Earth in the constellation Lyra. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 49,126,880 years to get there.
How big is Kepler-1991 c compared to Earth?
Kepler-1991 c has 2.57 times the radius of Earth.
How long is a year on Kepler-1991 c?
One orbit around Kepler-1991 takes 22.8 Earth days — short enough that 16 of its years would fit into one Earth year.
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