Kepler-309 c
Kepler-309 c is a mini-Neptune orbiting Kepler-309 in the constellation Cygnus. It lies about 1,776 light-years from Earth and was discovered in 2014 using the transit method. It orbits within the habitable zone of its star — the region where liquid water could exist on a planet's surface.
How Big Is Kepler-309 c?
Kepler-309 c has a radius of 2.51 times that of Earth.
Is Kepler-309 c in the Habitable Zone?
Kepler-309 c orbits within the optimistic habitable zone of Kepler-309 — the broader region where liquid water might be possible under favorable atmospheric conditions.
Habitable zone of Kepler-309: 0.381–0.931 AU (conservative: 0.482–0.883 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-309 c — one full orbit around Kepler-309 — lasts 105.4 Earth days, between the years of Mercury (88 days) and Earth (365 days). It orbits at an average distance of 0.401 AU — comparable to the inner Solar System.
How Was Kepler-309 c Discovered?
Kepler-309 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-309 c?
Kepler-309 c is 1,776.1 light-years (544.6 parsecs) from Earth. Light arriving here tonight left the planet about 1,776 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 31,259,360 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-309 c scores 0.65, ranking #95 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-309
Kepler-309
- Surface temperature
- 4,713 K (Sun: 5,772 K)
- Radius
- 0.72 R☉
The Kepler-309 Planetary System
Kepler-309 c is one of 2 known planets in the Kepler-309 system. Its siblings:
- Kepler-309 b (Super Earth)
Kepler-309 c — Complete Data
| Radius | 2.510 Earth radii (0.224 Jupiter radii) |
|---|---|
| Orbital period | 105.36 days |
| Orbital distance | 0.401 AU |
| Earth Similarity Index | 0.65 |
| Distance from Earth | 1,776.1 light-years (544.6 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-309 c
Is Kepler-309 c habitable?
Kepler-309 c orbits within the habitable zone of Kepler-309, the region where liquid water could exist on a planet's surface. Whether it is actually habitable depends on its atmosphere and composition, which remain unknown.
How far away is Kepler-309 c?
Kepler-309 c is about 1,776 light-years from Earth in the constellation Cygnus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 31,259,360 years to get there.
How big is Kepler-309 c compared to Earth?
Kepler-309 c has 2.51 times the radius of Earth.
How long is a year on Kepler-309 c?
One orbit around Kepler-309 takes 105.4 Earth days.
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