HAT-P-2 b
HAT-P-2 b is a hot Jupiter orbiting the F8 star HAT-P-2 in the constellation Hercules. It lies about 417 light-years from Earth and was discovered in 2007 using the transit method.
Is HAT-P-2 b in the Habitable Zone?
HAT-P-2 b orbits inside the inner edge of the habitable zone of HAT-P-2. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of HAT-P-2: 1.332–3.098 AU (conservative: 1.687–2.937 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Orbit and Year Length
A year on HAT-P-2 b — one full orbit around HAT-P-2 — lasts 5.63 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.068 AU — closer to its star than Mercury is to the Sun. Its orbit is highly elliptical (eccentricity 0.52), swinging dramatically closer to and farther from its star.
How Was HAT-P-2 b Discovered?
HAT-P-2 b was discovered in 2007 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-2 b?
HAT-P-2 b is 416.7 light-years (127.8 parsecs) from Earth. Light arriving here tonight left the planet around the year 1610. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 7,333,920 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-2 b scores 0.07, ranking #4,903 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: HAT-P-2
HAT-P-2
- Spectral type
- F8
- Surface temperature
- 6,380 K (Sun: 5,772 K)
- Mass
- 1.33 M☉
- Radius
- 1.39 R☉
- Luminosity
- 3.3884 L☉
- Age
- 1.4 billion years (Sun: 4.6)
The HAT-P-2 Planetary System
HAT-P-2 b is one of 2 known planets in the HAT-P-2 system. Its siblings:
- HAT-P-2 c (Cold Gas Giant)
HAT-P-2 b — Complete Data
| Mass (best estimate) | 2,739.69 Earth masses |
|---|---|
| Orbital period | 5.63 days |
| Orbital distance | 0.068 AU |
| Eccentricity | 0.517 |
| Earth Similarity Index | 0.07 |
| Distance from Earth | 416.7 light-years (127.8 parsecs) |
| Constellation | Hercules |
| Discovery method | Transit |
| Discovery facility | HATNet |
| Discovery year | 2007 |
Data: NASA Exoplanet Archive, last updated 2018-09-25. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About HAT-P-2 b
Is HAT-P-2 b habitable?
No — HAT-P-2 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-2 b?
HAT-P-2 b is about 417 light-years from Earth in the constellation Hercules. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 7,333,920 years to get there.
How long is a year on HAT-P-2 b?
One orbit around HAT-P-2 takes 5.6 Earth days — short enough that 65 of its years would fit into one Earth year.
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