WASP-13b
A low-density, inflated hot Jupiter orbiting a sunlike star.
Cruinlagh, originally designated WASP-13b, is a planet that orbits the sunlike star Gloas (WASP-13) in the Lynx constellation. Discovered in 2008, it was confirmed through radial velocity measurements from the SOPHIE and FIES spectrographs, following initial transit detections by the SuperWASP-North program between 2006 and 2007. The discovery was reported in the journal *Astronomy and Astrophysics* on May 19, 2009, with the paper received on April 7 of that year.
The planet has a mass of 0.477 times that of Jupiter and a radius 1.389 times Jupiter’s, making it less than half as massive but nearly 40% larger. This low density—the fifth-lowest among known exoplanets at the time of a 2011 study—may stem from a low-mass core or the complete absence of one. Cruinlagh orbits its star every 4.35298 days at a distance of 0.05362 AU (about 5% of the Earth-Sun distance), with an orbital inclination of 86.9°, meaning it passes nearly edge-on as seen from Earth.
The host star, Gloas, is a G-type star with a mass 1.09 times the Sun’s, a radius 1.559 times the Sun’s, and a density 0.288 times the Sun’s. Its effective temperature is 5826 K, slightly warmer than the Sun, and its iron content is roughly solar ([Fe/H] ≈ 0). With an apparent magnitude of 10.42, it is invisible to the naked eye. Follow-up observations between 2009 and 2011, using the Liverpool Telescope’s RISE camera, refined the planet’s mass, radius, density, and age, and also detected a limb darkening effect that could affect future atmospheric studies. The planet’s name was changed in 2019 to Cruinlagh, and the star to Gloas, chosen by Isle of Man schoolchildren from the Manx words for “to orbit” and “to shine,” respectively.
Quick Facts
- Discoverer
- Skillen et al. (SuperWASP)
- Discovered
- April 1, 2008
- Discovery Method
- Transit
- Apsis
- astron
- Semimajor
- 0.05379 0.00059 · 0.00077 AU
- Period
- 4.353011 (± 1.3e-05) d
- Inclination
- 85.64 (± 0.24)
- Star
- WASP-13
- Single Temperature
- 1356 K
Facts from the source article.
Lore & Background
WASP-13b was identified as a potential transiting object from 3329 images of its host star taken by the SuperWASP-North program between November 2006 and April 2007. Photometric follow-up on February 16, 2008, using the James Gregory Telescope in Scotland, produced a light curve, though the last twenty of 1047 exposures were discarded due to cloud cover. Radial velocity measurements from the SOPHIE spectrograph at Haute-Provence Observatory and spectral data from the FIES spectrograph at the Nordic Optical Telescope confirmed the planet's mass and its planetary nature. The discovery was reported in a journal on April 7, 2009.
The planet orbits its star at about 5% of the Earth–Sun distance every 4.35 days. Its low mass relative to its size may be due to a low-mass core or the absence of a core entirely. A 2011 study re-examined the planet's parameters using the RISE camera on the Liverpool Telescope, observing two partial and two full transits, and refined its mass, radius, density, and age while accounting for limb darkening. That study ranked Cruinlagh as the fifth-lowest-density exoplanet known at the time, behind Kepler-7b, WASP-17b, TrES-4b, and CoRoT-5b.
In 2019, the International Astronomical Union assigned the name Cruinlagh, a Manx word meaning 'to orbit', chosen by school children from the Isle of Man. The host star was named Gloas, meaning 'to shine'.
Reader's Guide
WASP-13b is significant as an example of an inflated hot Jupiter, a class of exoplanets whose anomalously large radii challenge standard planetary formation and evolution models. Its low density—among the lowest known at the time of its 2011 reanalysis—makes it a key object for studying the mechanisms that cause planetary inflation, such as internal heating or a missing massive core. The planet's discovery and follow-up observations illustrate the collaborative process of wide-field transit surveys (SuperWASP) combined with ground-based photometric and radial velocity confirmation. The 2011 study that re-constrained its parameters also highlighted the presence of limb darkening, a factor that must be accounted for in future atmospheric studies. The planet's naming by school children from the Isle of Man adds a cultural dimension to its legacy, linking astronomical discovery with local heritage. As one of the lowest-density exoplanets, Cruinlagh continues to serve as a benchmark for understanding the diversity of planetary compositions and the physics of close-in gas giants.
Did You Know?
- WASP-13b has a mass of 0.477 Jupiter masses but a radius of 1.389 Jupiter radii, making it less dense than Jupiter.
- The name Cruinlagh is a Manx word meaning 'to orbit', chosen by Isle of Man school children in 2019.
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