Kepler-865 c
Kepler-865 c is a terrestrial planet orbiting Kepler-865 in the constellation Cygnus. It lies about 1,912 light-years from Earth and was discovered in 2023 using the transit method.
How Big Is Kepler-865 c?
Kepler-865 c has a radius of 0.89 times that of Earth.
Is Kepler-865 c in the Habitable Zone?
Kepler-865 c orbits inside the inner edge of the habitable zone of Kepler-865. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of Kepler-865: 0.650–1.539 AU (conservative: 0.823–1.460 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on Kepler-865 c
The equilibrium temperature of Kepler-865 c is about 914 K (641 °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 165 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on Kepler-865 c — one full orbit around Kepler-865 — lasts 6.21 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.061 AU — closer to its star than Mercury is to the Sun.
How Was Kepler-865 c Discovered?
Kepler-865 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-865 c?
Kepler-865 c is 1,911.7 light-years (586.1 parsecs) from Earth. Light arriving here tonight left the planet about 1,912 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 33,645,920 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-865 c scores 0.30, ranking #1,315 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-865
Kepler-865
- Surface temperature
- 5,570 K (Sun: 5,772 K)
- Mass
- 0.93 M☉
- Radius
- 0.92 R☉
- Age
- 4.3 billion years (Sun: 4.6)
The Kepler-865 Planetary System
Kepler-865 c is one of 2 known planets in the Kepler-865 system. Its siblings:
- Kepler-865 b (Mini Neptune)
Kepler-865 c — Complete Data
| Radius | 0.890 Earth radii (0.079 Jupiter radii) |
|---|---|
| Orbital period | 6.21 days |
| Orbital distance | 0.061 AU |
| Equilibrium temperature | 914 K (641 °C) |
| Stellar irradiation | 164.98× Earth |
| Earth Similarity Index | 0.30 |
| Distance from Earth | 1,911.7 light-years (586.1 parsecs) |
| Constellation | Cygnus |
| 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-865 c
Is Kepler-865 c habitable?
No — Kepler-865 c orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Kepler-865 c?
Kepler-865 c is about 1,912 light-years from Earth in the constellation Cygnus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 33,645,920 years to get there.
How big is Kepler-865 c compared to Earth?
Kepler-865 c has 0.89 times the radius of Earth.
How long is a year on Kepler-865 c?
One orbit around Kepler-865 takes 6.2 Earth days — short enough that 59 of its years would fit into one Earth year.
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