HAT-P-42 b
HAT-P-42 b is a hot Jupiter orbiting HAT-P-42 in the constellation Hydra. It lies about 1,322 light-years from Earth and was discovered in 2012 using the transit method.
How Big Is HAT-P-42 b?
HAT-P-42 b has a radius of 14.35 times that of Earth, or 1.28 times the radius of Jupiter. Its mass is 332 times that of Earth, giving it a density of 0.61 g/cm³ — closer to gas planets like Jupiter (1.33 g/cm³).
Is HAT-P-42 b in the Habitable Zone?
HAT-P-42 b orbits inside the inner edge of the habitable zone of HAT-P-42. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of HAT-P-42: 1.133–2.672 AU (conservative: 1.435–2.533 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on HAT-P-42 b
The equilibrium temperature of HAT-P-42 b is about 1,428 K (1,155 °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-42 b — one full orbit around HAT-P-42 — lasts 4.64 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.058 AU — closer to its star than Mercury is to the Sun.
How Was HAT-P-42 b Discovered?
HAT-P-42 b was discovered in 2012 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-42 b?
HAT-P-42 b is 1,321.7 light-years (405.2 parsecs) from Earth. Light arriving here tonight left the planet about 1,322 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 23,261,920 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-42 b scores 0.06, ranking #5,066 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: HAT-P-42
HAT-P-42
- Surface temperature
- 5,743 K (Sun: 5,772 K)
- Mass
- 1.18 M☉
- Radius
- 1.53 R☉
- Luminosity
- 2.2699 L☉
- Age
- 5.2 billion years (Sun: 4.6)
Planetary System
HAT-P-42 b is the only planet known to orbit HAT-P-42 so far.
HAT-P-42 b — Complete Data
| Radius | 14.348 Earth radii (1.280 Jupiter radii) |
|---|---|
| Mass | 331.80 Earth masses (1.044 Jupiter masses) |
| Density | 0.61 g/cm³ (Earth: 5.51) |
| Orbital period | 4.64 days |
| Orbital distance | 0.058 AU |
| Equilibrium temperature | 1,428 K (1,155 °C) |
| Earth Similarity Index | 0.06 |
| Distance from Earth | 1,321.7 light-years (405.2 parsecs) |
| Constellation | Hydra |
| Discovery method | Transit |
| Discovery facility | HATNet |
| Discovery year | 2012 |
Data: NASA Exoplanet Archive, last updated 2014-05-14. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About HAT-P-42 b
Is HAT-P-42 b habitable?
No — HAT-P-42 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-42 b?
HAT-P-42 b is about 1,322 light-years from Earth in the constellation Hydra. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 23,261,920 years to get there.
How big is HAT-P-42 b compared to Earth?
HAT-P-42 b has 14.35 times the radius of Earth and about 332 times its mass.
How long is a year on HAT-P-42 b?
One orbit around HAT-P-42 takes 4.6 Earth days — short enough that 79 of its years would fit into one Earth year.
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