WASP-42 b
WASP-42 b is a hot Jupiter orbiting WASP-42 in the constellation Centaurus. It lies about 578 light-years from Earth and was discovered in 2012 using the transit method.
How Big Is WASP-42 b?
WASP-42 b has a radius of 12.58 times that of Earth, or 1.12 times the radius of Jupiter. Its mass is 167 times that of Earth, giving it a density of 0.46 g/cm³ — closer to gas planets like Jupiter (1.33 g/cm³).
Is WASP-42 b in the Habitable Zone?
WASP-42 b orbits inside the inner edge of the habitable zone of WASP-42. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of WASP-42: 0.582–1.390 AU (conservative: 0.737–1.318 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on WASP-42 b
The equilibrium temperature of WASP-42 b is about 1,021 K (748 °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 WASP-42 b — one full orbit around WASP-42 — lasts 4.98 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.056 AU — closer to its star than Mercury is to the Sun.
How Was WASP-42 b Discovered?
WASP-42 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-42 b?
WASP-42 b is 578.2 light-years (177.3 parsecs) from Earth. Light arriving here tonight left the planet around the year 1448. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 10,176,320 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-42 b scores 0.08, ranking #4,701 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: WASP-42
WASP-42
- Surface temperature
- 5,315 K (Sun: 5,772 K)
- Mass
- 0.95 M☉
- Radius
- 0.89 R☉
- Age
- 4.4 billion years (Sun: 4.6)
Planetary System
WASP-42 b is the only planet known to orbit WASP-42 so far.
WASP-42 b — Complete Data
| Radius | 12.576 Earth radii (1.122 Jupiter radii) |
|---|---|
| Mass | 167.50 Earth masses (0.527 Jupiter masses) |
| Density | 0.46 g/cm³ (Earth: 5.51) |
| Orbital period | 4.98 days |
| Orbital distance | 0.056 AU |
| Equilibrium temperature | 1,021 K (748 °C) |
| Earth Similarity Index | 0.08 |
| Distance from Earth | 578.2 light-years (177.3 parsecs) |
| Constellation | Centaurus |
| Discovery method | Transit |
| Discovery facility | SuperWASP |
| Discovery year | 2012 |
Data: NASA Exoplanet Archive, last updated 2016-02-24. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About WASP-42 b
Is WASP-42 b habitable?
No — WASP-42 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is WASP-42 b?
WASP-42 b is about 578 light-years from Earth in the constellation Centaurus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 10,176,320 years to get there.
How big is WASP-42 b compared to Earth?
WASP-42 b has 12.58 times the radius of Earth and about 167 times its mass.
How long is a year on WASP-42 b?
One orbit around WASP-42 takes 5.0 Earth days — short enough that 73 of its years would fit into one Earth year.
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