K2-77 b
K2-77 b is a mini-Neptune orbiting K2-77 in the constellation Taurus. It lies about 462 light-years from Earth and was discovered in 2016 using the transit method.
How Big Is K2-77 b?
K2-77 b has a radius of 2.50 times that of Earth.
Is K2-77 b in the Habitable Zone?
K2-77 b orbits inside the inner edge of the habitable zone of K2-77. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of K2-77: 0.492–1.182 AU (conservative: 0.623–1.121 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on K2-77 b
The equilibrium temperature of K2-77 b is about 806 K (533 °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 K2-77 b — one full orbit around K2-77 — lasts 8.20 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.075 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.29).
How Was K2-77 b Discovered?
K2-77 b was discovered in 2016 using the transit method, with observations from K2.
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 K2-77 b?
K2-77 b is 462.3 light-years (141.7 parsecs) from Earth. Light arriving here tonight left the planet around the year 1564. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 8,136,480 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. K2-77 b scores 0.26, ranking #2,782 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: K2-77
K2-77
- Surface temperature
- 5,160 K (Sun: 5,772 K)
- Mass
- 0.85 M☉
- Radius
- 0.79 R☉
- Luminosity
- 0.4010 L☉
- Age
- 4.7 billion years (Sun: 4.6)
Planetary System
K2-77 b is the only planet known to orbit K2-77 so far.
K2-77 b — Complete Data
| Radius | 2.500 Earth radii (0.223 Jupiter radii) |
|---|---|
| Orbital period | 8.20 days |
| Orbital distance | 0.075 AU |
| Eccentricity | 0.290 |
| Equilibrium temperature | 806 K (533 °C) |
| Earth Similarity Index | 0.26 |
| Distance from Earth | 462.3 light-years (141.7 parsecs) |
| Constellation | Taurus |
| Discovery method | Transit |
| Discovery facility | K2 |
| Discovery year | 2016 |
Data: NASA Exoplanet Archive, last updated 2024-11-20. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About K2-77 b
Is K2-77 b habitable?
No — K2-77 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is K2-77 b?
K2-77 b is about 462 light-years from Earth in the constellation Taurus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 8,136,480 years to get there.
How big is K2-77 b compared to Earth?
K2-77 b has 2.50 times the radius of Earth.
How long is a year on K2-77 b?
One orbit around K2-77 takes 8.2 Earth days — short enough that 45 of its years would fit into one Earth year.
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