HAT-P-23 b
HAT-P-23 b is a hot Jupiter orbiting the G0 star HAT-P-23 in the constellation Delphinus. It lies about 1,190 light-years from Earth and was discovered in 2010 using the transit method.
How Big Is HAT-P-23 b?
HAT-P-23 b has a radius of 15.33 times that of Earth, or 1.37 times the radius of Jupiter. Its mass is 664 times that of Earth, giving it a density of 1.01 g/cm³ — closer to gas planets like Jupiter (1.33 g/cm³).
Is HAT-P-23 b in the Habitable Zone?
HAT-P-23 b orbits inside the inner edge of the habitable zone of HAT-P-23. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of HAT-P-23: 0.936–2.199 AU (conservative: 1.186–2.085 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-23 b
The equilibrium temperature of HAT-P-23 b is about 2,056 K (1,783 °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-23 b — one full orbit around HAT-P-23 — lasts just 29.1 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 mildly elliptical (eccentricity 0.11).
How Was HAT-P-23 b Discovered?
HAT-P-23 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-23 b?
HAT-P-23 b is 1,189.9 light-years (364.8 parsecs) from Earth. Light arriving here tonight left the planet about 1,190 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 20,942,240 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-23 b scores 0.06, ranking #5,154 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: HAT-P-23
HAT-P-23
- Spectral type
- G0
- Surface temperature
- 5,905 K (Sun: 5,772 K)
- Mass
- 1.13 M☉
- Radius
- 1.20 R☉
- Luminosity
- 1.5812 L☉
- Age
- 4.0 billion years (Sun: 4.6)
Planetary System
HAT-P-23 b is the only planet known to orbit HAT-P-23 so far.
HAT-P-23 b — Complete Data
| Radius | 15.334 Earth radii (1.368 Jupiter radii) |
|---|---|
| Mass | 664.24 Earth masses (2.090 Jupiter masses) |
| Density | 1.01 g/cm³ (Earth: 5.51) |
| Orbital period | 1.21 days |
| Orbital distance | 0.023 AU |
| Eccentricity | 0.106 |
| Equilibrium temperature | 2,056 K (1,783 °C) |
| Earth Similarity Index | 0.06 |
| Distance from Earth | 1,189.9 light-years (364.8 parsecs) |
| Constellation | Delphinus |
| Discovery method | Transit |
| Discovery facility | HATNet |
| Discovery year | 2010 |
Data: NASA Exoplanet Archive, last updated 2018-04-25. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About HAT-P-23 b
Is HAT-P-23 b habitable?
No — HAT-P-23 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-23 b?
HAT-P-23 b is about 1,190 light-years from Earth in the constellation Delphinus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 20,942,240 years to get there.
How big is HAT-P-23 b compared to Earth?
HAT-P-23 b has 15.33 times the radius of Earth and about 664 times its mass.
How long is a year on HAT-P-23 b?
One orbit around HAT-P-23 takes 1.2 Earth days — short enough that 301 of its years would fit into one Earth year.
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