WASP-39b
WASP-39b is a hot Saturn-mass exoplanet orbiting the G-type star WASP-39, a Sun-like star with an effective temperature of approximately 5,330 K and a mass of 0.92 solar masses, located about 700 light-years away in the constellation Virgo.[1][2] Discovered in 2011 by the Wide Angle Search for Planets (WASP) project using the transit method, the planet completes an orbit every 4.055 days at a semi-major axis of 0.0483 AU, subjecting it to intense stellar radiation that results in a highly inflated atmosphere.[2][1] With a mass of 0.28 Jupiter masses and a radius of 1.27 Jupiter radii, WASP-39b has a low density of about 0.13 times that of Jupiter, making it one of the most inflated exoplanets known in its mass class.[2][1] Its equilibrium temperature is estimated at around 1,170 K (approximately 900°C), classifying it as a hot gas giant with a puffed-up envelope dominated by hydrogen and helium.[1][2] The planet's close-in orbit and relatively bright host star (J-band magnitude 10.66) have made it an ideal target for detailed characterization using both ground-based and space-based telescopes.[1] WASP-39b gained significant attention through observations by the James Webb Space Telescope (JWST) in 2022, which provided the first unambiguous detection of carbon dioxide in an exoplanet atmosphere via its near-infrared transmission spectrum.[3][4] These JWST data using the NIRSpec PRISM instrument confirmed water vapor (at >10σ), sodium, and carbon dioxide, while later analyses of the same dataset detected sulfur dioxide (from photochemistry) and carbon monoxide, ruled out significant methane, and indicated a clear atmosphere with minimal cloud cover.[5][6][7] The observations suggest a supersolar metallicity (around 10 times solar) and a substellar carbon-to-oxygen ratio (approximately 0.4–0.6), offering key insights into the planet's formation history, likely involving the accretion of icy planetesimals in its natal disk.[8] Prior Hubble and Spitzer observations had already detected water vapor, sodium, and potassium, but JWST's enhanced sensitivity has elevated WASP-39b as a benchmark for studying atmospheric chemistry in hot gas giants.[3]Discovery and nomenclature
Discovery
WASP-39b was discovered by the Wide Angle Search for Planets (WASP) consortium and announced in February 2011.[9] The detection relied on the transit method, which identifies exoplanets by observing periodic dips in stellar brightness as the planet passes in front of its host star.[10] Photometric observations were conducted using the ground-based SuperWASP telescopes, including the SuperWASP-North array on La Palma in the Canary Islands and the SuperWASP-South array in South Africa, spanning data from July 2006 to July 2010.[10] To confirm the planetary nature of the transiting object and measure its mass, follow-up radial velocity measurements were performed using the CORALIE high-resolution spectrograph on the 1.2-meter Euler Telescope at La Silla Observatory in Chile and the SOPHIE high-resolution spectrograph on the 1.93-m telescope at Haute-Provence Observatory in France.[10] These observations, conducted between April and June 2010, detected the star's reflex motion due to the planet's gravitational pull, providing evidence of a Saturn-mass companion.[10] Additional high-precision photometry from the Faulkes Telescope North and the Euler Telescope further refined the transit light curve.[10] The initial findings, including photometric and spectroscopic data, were published in Astronomy & Astrophysics in 2011.[10] Key parameters from the discovery included an orbital period of approximately 4.055 days and a transit depth of about 25 millimagnitudes, suggesting a large planetary radius comparable to Jupiter's.[10] These characteristics marked WASP-39b as a highly inflated gas giant, prompting later detailed atmospheric studies with the James Webb Space Telescope.Nomenclature
WASP-39b is the provisional designation for the exoplanet, following the International Astronomical Union's convention for naming exoplanets after their host star with a lowercase letter suffix indicating the order of discovery, where "b" denotes the first confirmed planet around the star WASP-39.[2] This naming adheres to the Wide Angle Search for Planets (WASP) project's cataloging system, in which host stars receive numerical identifiers based on survey observations, and planets are appended accordingly.[2] In December 2019, during the IAU's centennial NameExoWorlds contest, the exoplanet received the proper name Bocaprins, while its host star was named Malmok; these names, proposed by astronomy enthusiasts from Aruba, honor two scenic beaches on the island—Boca Prins, a secluded white-dune beach in Arikok National Park, and Malmok, known for its sandy shores and historical significance.[11] The contest encouraged global public participation to assign culturally inspired names to selected exoplanetary systems, promoting awareness of astronomy.[11] The host star's designation WASP-39 originates from the WASP survey's internal catalog, and it is cross-identified as 2MASS J14291840-0326403 in the Two Micron All Sky Survey.[12] The WASP-39 system resides in the constellation Virgo.[13] Its distance from Earth is approximately 700 light-years, derived from parallax measurements by the Gaia mission.[12]Host system
Stellar properties of WASP-39
WASP-39 is a G8 main-sequence star, classified as a dwarf slightly cooler and smaller than the Sun. Its effective temperature is measured at 5400 ± 150 K, which places it in the late G spectral type range and contributes to a cooler stellar environment compared to solar conditions.[9] This temperature determination comes from spectroscopic analysis of high-resolution spectra, confirming its position on the main sequence.[9] The star has a mass of 0.93 ± 0.03 solar masses and a radius of 0.895 ± 0.023 solar radii, derived from combined radial velocity and transit modeling.[9] These parameters yield an estimated luminosity of approximately 0.61 solar luminosities, calculated from the effective temperature and radius using the Stefan-Boltzmann relation.[9] Such characteristics indicate a star that is underluminous relative to the Sun, influencing the habitable zone and thermal equilibrium for orbiting bodies. The distance to the system is approximately 700 light-years (214 ± 2 pc), based on Gaia parallax measurements.[12] WASP-39 exhibits an apparent visual magnitude of 12.1, rendering it faint and observable primarily with large ground-based telescopes or space facilities.[9] Its metallicity is solar at [Fe/H] = 0.00 ± 0.07 dex.[12] The age of WASP-39 is estimated at 4-6 billion years using gyrochronology, though isochrone fitting suggests an older value of around 9 billion years, highlighting some discrepancy in age diagnostics.[9] The star displays low activity levels, with no significant Ca II H and K emission or reported stellar flares, consistent with its evolved main-sequence status.[9] These quiet properties facilitate stable observations of its close-in planetary companion.[9]| Parameter | Value | Unit | Reference |
|---|---|---|---|
| Spectral type | G8 | - | Faedi et al. (2011) |
| Effective temperature | 5400 ± 150 | K | Faedi et al. (2011) |
| Mass | 0.93 ± 0.03 | M⊙ | Faedi et al. (2011) |
| Radius | 0.895 ± 0.023 | R⊙ | Faedi et al. (2011) |
| Luminosity | ~0.61 | L⊙ | Derived from Faedi et al. (2011) |
| Apparent visual magnitude | 12.1 | mag | Faedi et al. (2011) |
| Metallicity | 0.00 ± 0.07 | [Fe/H] (dex) | Exoplanet Archive (Hypatia Catalog) |
| Age (gyrochronology) | ~5 (4-6 range) | Gyr | Faedi et al. (2011) |
| Distance | 700 | ly | Exoplanet Archive (Gaia DR3) |