WASP-8b
A hot Jupiter with a retrograde orbit and higher density than Jupiter.
WASP-8b is a hot Jupiter exoplanet located 294 light-years away in the constellation of Sculptor, making it closer to Earth than many other planetary systems of its kind. It orbits the star WASP-8A, which resembles the Sun and is part of a binary system with a red dwarf companion (WASP-8B) that has half the Sun's mass and lies 4.5 arcseconds away. The planet and its star were announced on 1 April 2008 by Dr. Don Pollacco of Queen's University Belfast at the RAS National Astronomy Meeting (NAM 2008), as part of the SuperWASP batch from -6b to -15b.
The planet circles its star at an average distance of 0.08 AU, completing one orbit in just over 8.1 days. This is somewhat farther from its star than other hot Jupiters, but its orbit has a relatively high eccentricity of 0.3. At periastron, it comes as close to its star as those similar planets do. A particularly striking feature is its orbit-spin angle relative to the star, which indicates that WASP-8b moves in a retrograde direction—opposite to the star's rotation.
WASP-8b has a mass about 2.2 times that of Jupiter and a radius slightly larger, placing it in the hot Jupiter class. Its density is greater than Jupiter's, which is unusual for a gas giant orbiting so close to its star. The planet is extremely hot, with a measured dayside temperature of 1552 K, significantly higher than its equilibrium temperature of 947 K.
Quick Facts
- Discoverer
- Cameron et al. (SuperWASP)
- Discovered
- April 1, 2008
- Discovery Method
- Transit
- Eccentricity
- 0.3057 · 0.0046
- Star
- WASP-8
Facts from the source article.
Lore & Background
WASP-8b was discovered as part of the SuperWASP batch -6b to -15b and announced on 1 April 2008 by Dr. Don Pollacco of Queen's University Belfast at the RAS National Astronomy Meeting (NAM 2008). The planet orbits its Sun-like star at an average distance of 0.08 AU, completing a year in slightly more than 8.1 days. Its orbit has a relatively high eccentricity of 0.3, bringing it at periastron as close to its star as other hot Jupiters. The planet's orbit-spin angle implies it orbits retrograde to the spin of WASP-8A.
The planet has a mass about 2.2 times and a radius slightly bigger than that of Jupiter, making it denser than Jupiter. Its measured dayside temperature is 1552 K, hotter than its equilibrium temperature of 947 K. The star WASP-8A forms a binary system with a red dwarf star (WASP-8B) of half the Sun's mass, located 4.5 arcseconds away. The system is 294 light-years from Earth.
Reader's Guide
WASP-8b is significant as one of the early hot Jupiters discovered by the SuperWASP survey, announced alongside planets WASP-6b through WASP-15b. Its retrograde orbit stands out as an extreme orbital characteristic, challenging standard models of planetary formation and migration that typically assume prograde alignment. The planet's higher density compared to Jupiter, despite being a close-orbiting gas giant, also distinguishes it from many similar exoplanets. The system's relative proximity to Earth at 294 light-years makes it more accessible for follow-up studies than many other exoplanet host systems. The binary nature of the star system, with a red dwarf companion, adds further context for understanding the planet's formation environment. The measured dayside temperature exceeding the equilibrium temperature indicates additional heating mechanisms, possibly from tidal forces due to its eccentric orbit. These features make WASP-8b a valuable case study for planetary atmospheres, orbital dynamics, and the diversity of hot Jupiter systems.
Did You Know?
- WASP-8b orbits retrograde to the spin of its parent star.
- Its orbit has an eccentricity of 0.3, bringing it closer to its star at periastron.
- The planet is denser than Jupiter despite being a hot Jupiter.
More in Transiting Exoplanets, Part 4 1-24
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