WASP-77 A b
WASP-77 A b is a hot Jupiter orbiting WASP-77 A in the constellation Cetus. It lies about 343 light-years from Earth and was discovered in 2012 using the transit method.
Is WASP-77 A b in the Habitable Zone?
WASP-77 A b orbits inside the inner edge of the habitable zone of WASP-77 A. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of WASP-77 A: 0.653–1.546 AU (conservative: 0.827–1.465 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 WASP-77 A b — one full orbit around WASP-77 A — lasts just 32.6 hours, shorter than Mercury's 88-day year. It orbits at an average distance of 0.023 AU — closer to its star than Mercury is to the Sun. Its orbit is nearly circular (eccentricity 0.014).
How Was WASP-77 A b Discovered?
WASP-77 A b was discovered in 2012 using the transit method, with observations from SuperWASP.
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 WASP-77 A b?
WASP-77 A b is 343.0 light-years (105.2 parsecs) from Earth. Light arriving here tonight left the planet around the year 1683. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 6,036,800 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. WASP-77 A b scores 0.07, ranking #5,033 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: WASP-77 A
WASP-77 A b belongs to a system of 2 stars; it orbits WASP-77 A.
WASP-77 A
- Surface temperature
- 5,617 K (Sun: 5,772 K)
- Mass
- 0.90 M☉
- Radius
- 0.91 R☉
- Luminosity
- 0.7430 L☉
- Age
- 6.2 billion years (Sun: 4.6)
Planetary System
WASP-77 A b is the only planet known to orbit WASP-77 A so far.
WASP-77 A b — Complete Data
| Mass | 529.31 Earth masses (1.665 Jupiter masses) |
|---|---|
| Orbital period | 1.36 days |
| Orbital distance | 0.023 AU |
| Eccentricity | 0.014 |
| Earth Similarity Index | 0.07 |
| Distance from Earth | 343.0 light-years (105.2 parsecs) |
| Constellation | Cetus |
| Discovery method | Transit |
| Discovery facility | SuperWASP |
| Discovery year | 2012 |
Data: NASA Exoplanet Archive, last updated 2025-05-19. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About WASP-77 A b
Is WASP-77 A b habitable?
No — WASP-77 A b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is WASP-77 A b?
WASP-77 A b is about 343 light-years from Earth in the constellation Cetus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 6,036,800 years to get there.
How long is a year on WASP-77 A b?
One orbit around WASP-77 A takes 1.4 Earth days — short enough that 269 of its years would fit into one Earth year.
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