Kepler-261 b
Kepler-261 b is a mini-Neptune orbiting Kepler-261 in the constellation Lyra. It lies about 1,036 light-years from Earth and was discovered in 2014 using the transit method.
How Big Is Kepler-261 b?
Kepler-261 b has a radius of 2.18 times that of Earth.
Is Kepler-261 b in the Habitable Zone?
Kepler-261 b orbits inside the inner edge of the habitable zone of Kepler-261. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of Kepler-261: 0.482–1.161 AU (conservative: 0.610–1.100 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-261 b — one full orbit around Kepler-261 — lasts 10.4 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.088 AU — closer to its star than Mercury is to the Sun.
How Was Kepler-261 b Discovered?
Kepler-261 b 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-261 b?
Kepler-261 b is 1,035.5 light-years (317.5 parsecs) from Earth. Light arriving here tonight left the planet about 1,036 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 18,224,800 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-261 b scores 0.28, ranking #2,414 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-261
Kepler-261
- Surface temperature
- 5,098 K (Sun: 5,772 K)
- Radius
- 0.79 R☉
The Kepler-261 Planetary System
Kepler-261 b is one of 2 known planets in the Kepler-261 system. Its siblings:
- Kepler-261 c (Super Earth)
Kepler-261 b — Complete Data
| Radius | 2.180 Earth radii (0.194 Jupiter radii) |
|---|---|
| Orbital period | 10.38 days |
| Orbital distance | 0.088 AU |
| Earth Similarity Index | 0.28 |
| Distance from Earth | 1,035.5 light-years (317.5 parsecs) |
| Constellation | Lyra |
| 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-261 b
Is Kepler-261 b habitable?
No — Kepler-261 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Kepler-261 b?
Kepler-261 b is about 1,036 light-years from Earth in the constellation Lyra. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 18,224,800 years to get there.
How big is Kepler-261 b compared to Earth?
Kepler-261 b has 2.18 times the radius of Earth.
How long is a year on Kepler-261 b?
One orbit around Kepler-261 takes 10.4 Earth days — short enough that 35 of its years would fit into one Earth year.
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