HAT-P-20 b
HAT-P-20 b is a hot Jupiter orbiting the K3 star HAT-P-20 in the constellation Gemini. It lies about 232 light-years from Earth and was discovered in 2010 using the transit method.
How Big Is HAT-P-20 b?
HAT-P-20 b has a radius of 9.72 times that of Earth, or 0.87 times the radius of Jupiter. Its mass is 2,303 times that of Earth, giving it a density of 13.78 g/cm³ — comparable to rocky planets like Earth (5.51 g/cm³).
Is HAT-P-20 b in the Habitable Zone?
HAT-P-20 b orbits inside the inner edge of the habitable zone of HAT-P-20. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of HAT-P-20: 0.347–0.855 AU (conservative: 0.440–0.810 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 HAT-P-20 b
The equilibrium temperature of HAT-P-20 b is about 970 K (697 °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 HAT-P-20 b — one full orbit around HAT-P-20 — lasts 2.88 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.036 AU — closer to its star than Mercury is to the Sun. Its orbit is nearly circular (eccentricity 0.015).
How Was HAT-P-20 b Discovered?
HAT-P-20 b was discovered in 2010 using the transit method, with observations from HATNet.
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 HAT-P-20 b?
HAT-P-20 b is 231.7 light-years (71.0 parsecs) from Earth. Light arriving here tonight left the planet around the year 1795. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 4,077,920 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. HAT-P-20 b scores 0.10, ranking #4,472 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: HAT-P-20
HAT-P-20
- Spectral type
- K3
- Surface temperature
- 4,595 K (Sun: 5,772 K)
- Mass
- 0.76 M☉
- Radius
- 0.69 R☉
- Luminosity
- 0.1901 L☉
- Age
- 6.7 billion years (Sun: 4.6)
Planetary System
HAT-P-20 b is the only planet known to orbit HAT-P-20 so far.
HAT-P-20 b — Complete Data
| Radius | 9.718 Earth radii (0.867 Jupiter radii) |
|---|---|
| Mass | 2,302.90 Earth masses (7.246 Jupiter masses) |
| Density | 13.78 g/cm³ (Earth: 5.51) |
| Orbital period | 2.88 days |
| Orbital distance | 0.036 AU |
| Eccentricity | 0.015 |
| Equilibrium temperature | 970 K (697 °C) |
| Earth Similarity Index | 0.10 |
| Distance from Earth | 231.7 light-years (71.0 parsecs) |
| Constellation | Gemini |
| Discovery method | Transit |
| Discovery facility | HATNet |
| Discovery year | 2010 |
Data: NASA Exoplanet Archive, last updated 2014-05-14. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About HAT-P-20 b
Is HAT-P-20 b habitable?
No — HAT-P-20 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is HAT-P-20 b?
HAT-P-20 b is about 232 light-years from Earth in the constellation Gemini. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 4,077,920 years to get there.
How big is HAT-P-20 b compared to Earth?
HAT-P-20 b has 9.72 times the radius of Earth and about 2,303 times its mass.
How long is a year on HAT-P-20 b?
One orbit around HAT-P-20 takes 2.9 Earth days — short enough that 127 of its years would fit into one Earth year.
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