HAT-P-8b
A hot Jupiter with a mass and radius 50% greater than Jupiter's.
HAT-P-8b is a gas giant planet about 720 light-years away in Pegasus, circling the star GSC 02757-01152. It was detected via the transit method on December 5, 2008, and is the 11th planet found by the HATNet Project. This hot Jupiter has a mass and radius each 1.5 times that of Jupiter. Because it transits, the orbital inclination is known, so the mass is precise. The planet orbits extremely close to its star—roughly 20 times closer than Earth is to the Sun, and about eight times closer than Mercury—making its surface temperature around a thousand kelvins. Its year lasts just 3 days, 1 hour, 49 minutes, and 54 seconds, compared to Earth’s sidereal year of 365 days, 6 hours, 9 minutes, and 10 seconds. A 2012 study using the Rossiter–McLaughlin effect found the planet’s orbit is mildly misaligned with the star’s rotation axis, with a misalignment of -17°.
Quick Facts
- Discoverer
- HATNet Project
- Discovered
- December 5, 2008
- Discovery Method
- Transit
- Apsis
- astron
- Semimajor
- 0.04496 · 0.00046 · 0.00045 AU
- Period
- 3.0763458 · 0.0000024 d
- Inclination
- 87.51.9 · 0.9
- Star
- GSC 02757-01152
Facts from the source article.
Lore & Background
HAT-P-8b was discovered by transit on December 5, 2008, and is the 11th planet discovered by the HATNet Project. The planet's mass is known exactly because its orbital inclination is known, a typical advantage for transiting planets. It orbits its star at a distance roughly 20 times smaller than Earth's distance from the Sun, placing it about 8 times closer to its star than Mercury is to the Sun. This close orbit results in an extremely high surface temperature, on the order of a thousand kelvins, and a very short year lasting only 3 days, 1 hour, 49 minutes, and 54 seconds. A study in 2012 using the Rossiter–McLaughlin effect determined that the planet's orbit is mildly misaligned with the rotational axis of its star, with a misalignment of -17°.
Reader's Guide
HAT-P-8b is notable as a hot Jupiter with well-determined physical parameters due to its transiting nature. Its mass and radius, each 50% greater than Jupiter's, place it among the inflated gas giants whose large size relative to mass challenges models of planetary structure and atmospheric heating. The precise orbital period and distance, combined with the known stellar properties, allow for detailed characterization of its atmosphere and thermal properties. The measured orbital misalignment of -17° from the star's rotational axis, determined via the Rossiter–McLaughlin effect, provides insight into the system's dynamical history, suggesting that the planet may have migrated inward through interactions with a protoplanetary disk or other bodies. As one of the earlier discoveries by the HATNet Project, HAT-P-8b contributes to the statistical understanding of hot Jupiter occurrence and orbital architectures around Sun-like stars. Its extreme proximity to its star and high temperature make it a valuable target for atmospheric studies, including potential detection of molecular species and thermal emission.
More in Transiting Exoplanets, Part 5 1-24
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