Kepler-77 b
Kepler-77 b is a hot Jupiter orbiting the G5 V star Kepler-77 in the constellation Cygnus. It lies about 2,086 light-years from Earth and was discovered in 2013 using the transit method.
How Big Is Kepler-77 b?
Kepler-77 b has a radius of 10.76 times that of Earth, or 0.96 times the radius of Jupiter. Its mass is 137 times that of Earth, giving it a density of 0.60 g/cm³ — closer to gas planets like Jupiter (1.33 g/cm³).
Is Kepler-77 b in the Habitable Zone?
Kepler-77 b orbits inside the inner edge of the habitable zone of Kepler-77. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of Kepler-77: 0.688–1.634 AU (conservative: 0.872–1.549 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 ›
Temperature on Kepler-77 b
The equilibrium temperature of Kepler-77 b is about 1,440 K (1,167 °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.
Orbit and Year Length
A year on Kepler-77 b — one full orbit around Kepler-77 — lasts 3.58 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.045 AU — closer to its star than Mercury is to the Sun.
How Was Kepler-77 b Discovered?
Kepler-77 b was discovered in 2013 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-77 b?
Kepler-77 b is 2,085.5 light-years (639.4 parsecs) from Earth. Light arriving here tonight left the planet about 2,086 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 36,704,800 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-77 b scores 0.08, ranking #4,604 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-77
Kepler-77
- Spectral type
- G5 V
- Surface temperature
- 5,520 K (Sun: 5,772 K)
- Mass
- 0.95 M☉
- Radius
- 0.99 R☉
- Age
- 7.5 billion years (Sun: 4.6)
Planetary System
Kepler-77 b is the only planet known to orbit Kepler-77 so far.
Kepler-77 b — Complete Data
| Radius | 10.761 Earth radii (0.960 Jupiter radii) |
|---|---|
| Mass | 136.66 Earth masses (0.430 Jupiter masses) |
| Density | 0.60 g/cm³ (Earth: 5.51) |
| Orbital period | 3.58 days |
| Orbital distance | 0.045 AU |
| Equilibrium temperature | 1,440 K (1,167 °C) |
| Earth Similarity Index | 0.08 |
| Distance from Earth | 2,085.5 light-years (639.4 parsecs) |
| Constellation | Cygnus |
| Discovery method | Transit |
| Discovery facility | Kepler |
| Discovery year | 2013 |
Data: NASA Exoplanet Archive, last updated 2014-05-14. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About Kepler-77 b
Is Kepler-77 b habitable?
No — Kepler-77 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Kepler-77 b?
Kepler-77 b is about 2,086 light-years from Earth in the constellation Cygnus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 36,704,800 years to get there.
How big is Kepler-77 b compared to Earth?
Kepler-77 b has 10.76 times the radius of Earth and about 137 times its mass.
How long is a year on Kepler-77 b?
One orbit around Kepler-77 takes 3.6 Earth days — short enough that 102 of its years would fit into one Earth year.
Explore Kepler-77 b in the app
Browse, filter and compare 6,000+ exoplanets on iPhone, iPad and Apple Watch — with habitable-zone views, widgets and offline data.
