Kepler-221 c
Kepler-221 c is a mini-Neptune orbiting Kepler-221 in the constellation Cygnus. It lies about 1,257 light-years from Earth and was discovered in 2014 using the transit method.
How Big Is Kepler-221 c?
Kepler-221 c has a radius of 2.93 times that of Earth.
Is Kepler-221 c in the Habitable Zone?
Kepler-221 c orbits inside the inner edge of the habitable zone of Kepler-221. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of Kepler-221: 0.523–1.253 AU (conservative: 0.663–1.188 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
See the full interactive habitable-zone view in the Exoplanet Explorer app ›
Orbit and Year Length
A year on Kepler-221 c — one full orbit around Kepler-221 — lasts 5.69 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.059 AU — closer to its star than Mercury is to the Sun.
How Was Kepler-221 c Discovered?
Kepler-221 c was discovered in 2014 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-221 c?
Kepler-221 c is 1,256.5 light-years (385.2 parsecs) from Earth. Light arriving here tonight left the planet about 1,257 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 22,114,400 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-221 c scores 0.22, ranking #3,605 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-221
Kepler-221
- Surface temperature
- 5,243 K (Sun: 5,772 K)
- Radius
- 0.82 R☉
The Kepler-221 Planetary System
Kepler-221 c is one of 4 known planets in the Kepler-221 system. Its siblings:
- Kepler-221 b (Super Earth)
- Kepler-221 d (Mini Neptune)
- Kepler-221 e (Mini Neptune)
Kepler-221 c — Complete Data
| Radius | 2.930 Earth radii (0.261 Jupiter radii) |
|---|---|
| Orbital period | 5.69 days |
| Orbital distance | 0.059 AU |
| Earth Similarity Index | 0.22 |
| Distance from Earth | 1,256.5 light-years (385.2 parsecs) |
| Constellation | Cygnus |
| Discovery method | Transit |
| Discovery facility | Kepler |
| Discovery year | 2014 |
Data: NASA Exoplanet Archive, last updated 2014-05-14. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About Kepler-221 c
Is Kepler-221 c habitable?
No — Kepler-221 c orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Kepler-221 c?
Kepler-221 c is about 1,257 light-years from Earth in the constellation Cygnus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 22,114,400 years to get there.
How big is Kepler-221 c compared to Earth?
Kepler-221 c has 2.93 times the radius of Earth.
How long is a year on Kepler-221 c?
One orbit around Kepler-221 takes 5.7 Earth days — short enough that 64 of its years would fit into one Earth year.
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