WASP-18 b
WASP-18 b is a hot Jupiter orbiting WASP-18 in the constellation Phoenix. It lies about 403 light-years from Earth and was discovered in 2009 using the transit method.
How Big Is WASP-18 b?
WASP-18 b has a radius of 13.90 times that of Earth, or 1.24 times the radius of Jupiter. Its mass is 3,242 times that of Earth, giving it a density of 6.60 g/cm³ — comparable to rocky planets like Earth (5.51 g/cm³).
Is WASP-18 b in the Habitable Zone?
WASP-18 b orbits inside the inner edge of the habitable zone of WASP-18. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of WASP-18: 1.181–2.744 AU (conservative: 1.496–2.602 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 WASP-18 b
The equilibrium temperature of WASP-18 b is about 2,429 K (2,156 °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. It receives 5,805 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on WASP-18 b — one full orbit around WASP-18 — lasts just 22.6 hours, shorter than Mercury's 88-day year. It orbits at an average distance of 0.020 AU — closer to its star than Mercury is to the Sun. Its orbit is nearly circular (eccentricity 0.005).
How Was WASP-18 b Discovered?
WASP-18 b was discovered in 2009 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-18 b?
WASP-18 b is 402.7 light-years (123.5 parsecs) from Earth. Light arriving here tonight left the planet around the year 1624. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 7,087,520 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-18 b scores 0.06, ranking #5,058 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: WASP-18
WASP-18 b belongs to a system of 2 stars; it orbits WASP-18.
WASP-18
- Surface temperature
- 6,432 K (Sun: 5,772 K)
- Mass
- 1.29 M☉
- Radius
- 1.32 R☉
- Luminosity
- 2.6800 L☉
- Age
- 1.6 billion years (Sun: 4.6)
The WASP-18 Planetary System
WASP-18 b is one of 2 known planets in the WASP-18 system. Its siblings:
- WASP-18 c (Hot Jupiter)
WASP-18 b — Complete Data
| Radius | 13.899 Earth radii (1.240 Jupiter radii) |
|---|---|
| Mass | 3,241.85 Earth masses (10.200 Jupiter masses) |
| Density | 6.60 g/cm³ (Earth: 5.51) |
| Orbital period | 0.94 days |
| Orbital distance | 0.020 AU |
| Eccentricity | 0.005 |
| Equilibrium temperature | 2,429 K (2,156 °C) |
| Stellar irradiation | 5,805.00× Earth |
| Earth Similarity Index | 0.06 |
| Distance from Earth | 402.7 light-years (123.5 parsecs) |
| Constellation | Phoenix |
| Discovery method | Transit |
| Discovery facility | SuperWASP |
| Discovery year | 2009 |
Data: NASA Exoplanet Archive, last updated 2022-01-31. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About WASP-18 b
Is WASP-18 b habitable?
No — WASP-18 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is WASP-18 b?
WASP-18 b is about 403 light-years from Earth in the constellation Phoenix. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 7,087,520 years to get there.
How big is WASP-18 b compared to Earth?
WASP-18 b has 13.90 times the radius of Earth and about 3,242 times its mass.
How long is a year on WASP-18 b?
One orbit around WASP-18 takes 0.9 Earth days — short enough that 388 of its years would fit into one Earth year.
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