Object 14: WASP-103

Podcast release date: 10 February 2020

Right ascension: 16:37:15.6


Epoch: ICRS

Constellation: Serpens

Corresponding Earth location: Approximately 1740 km south of the tip of Baja California

WASP-103 is a star located in the constellation Serpens at a distance of about 2869 light years (880 pc) [1,2]. It's a relatively ordinary yellow-white star that fuses hydrogen into helium in its core like the Sun [3]. However, it is one of many stars that was targeted in a survey with the acronym WASP. WASP stands for Winning And Score Predictor, and it's used to estimate the score in cricket games with a limited number of overs [4]. It also stands for the Washington State Patrol, the state law enforcement agency in Washington. In astronomy, WASP stands for the Wide Angle Search for Planets.

The WASP consortium (where consortium is a formal name for a collaborative research group) was established in the year 2000 to survey the sky for stars with exoplanets [5]. Out of the multiple techniques available for doing this, the consortium decided to search for transits, which is the slight dimming in light from a star that is expected when a planet passes in front of that star. Instead of relying on existing instruments on existing telescopes, the consortium built two of their own instruments for detecting these transits. Both instruments are called SuperWASP; one is located at the Observatorio del Roque de los Muchachos on the island of La Palma on the Canary Islands, and the other is located at the Sutherland Station of the South African Astronomical Observatory [5]. Each of these instruments consist of a robotic mount with up to to eight cameras attached to the mount. Each camera consists of an astronomical digital sensor called a charge-coupled device or CCD with a telephoto lens attached. These cameras have a very wide field of view. Every 40 minutes, the instrument can make images of the entire sky, so they can detect sudden changes in star brightness rather well as long as the stars that they are looking at are relatively bright.

At this point, you would probably guess that the object for this episode, which is WASP-103, was found to have an exoplanet orbiting it, and you would be right. The planet has the unexciting designation WASP-103b. It was initially detected by the WASP survey in observations from 2010, 2011, and 2012 [3]. Follow-up observations in 2013 with another robotic telescope called TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope) confirmed the presence of the planet [3], and additional subsequent observations with several more instruments on several more telescopes helped to constrain the characteristics of the planets, although these instruments and telescopes did not have acronyms nearly as clever as SuperWASP [3,6,7].

The planet WASP-103b is a gas giant with a mass 1.47 times the mass of Jupiter and a diameter of roughly 1.6 times the diameter of Jupiter [7]. Gas giants are very commonly detected in exoplanet surveys, so this isn't too surprising. However, the planet appears to orbit its star at a distance of 0.0198 AU (where 1 AU is the distance from the Earth to the Sun) [7]. This is extremely close. WASP-103b also orbits its host star once every 22 hours, which is insanely fast [7]. Keep in mind that Mercury, the planet closest to our Sun, orbits at a distance of about 0.39 AU and completes an orbit once every 88 Earth days. WASP-103b is extreme compared to any object in our Solar System.

Because WASP-103b is so close to its star, it gets extremely hot. The estimated temperature on the daytime side of the planet is about 2630 degrees Celsius [7]. This has potentially caused the planet to expand and to lower the density of the planet in a way that is very similar to how air expands and decreases in pressure in a hot air balloon [3]. The planet may also be tidally distorted by the gravitational forces of the star in a way that is more severe than the way that astronomers have distorted words to create clever acronyms [3]. This could have a couple of different effects. First, it is possible that the star could be tidally stripping gas from the gas giant. Second, it is likely that the tidal effects are causing the orbit of WASP-103b to decay, which means that the planet could be slowly spiralling into the star.

WASP-103b is one of very few Jupiter-sized exoplanets that have been found orbiting extremely close to their host stars [3]. This class of exoplanets are called hot Jupiters. Many, if not all, of the exoplanets are expected to be falling inwards into their host stars just like WASP-103b. The WASP survey should be particularly sensitive to large exoplanets with very short orbital periods, but they seem to have detected very few [3,8]. WASP-103b is therefore a rare but very good example of a planet close to being destroyed by its host star.


[1] Gaia Collaboration et al., The Gaia mission, 2016, Astronomy & Astrophysics, 595, A1

[2] Gaia Collaboration et al., Gaia Data Release 2. Summary of the contents and survey properties, 2018, Astronomy & Astrophysics, 616, A1

[3] Gillon, M. et al., WASP-103 b: a new planet at the edge of tidal disruption, 2014, Astronomy & Astrophysics, 562, L3

[4] Brooker, S. and Hogan, S., A Method for Inferring Batting Conditions in ODI Cricket from Historical Data, 2011, University of Canterbury Research Repository

[5] Pollacco, D. L. et al., The WASP Project and the SuperWASP Cameras, 2006, Publications of the Astronomical Society of the Pacific, 118, 1407

[6] Southworth, John et al., High-precision photometry by telescope defocusing - VII. The ultrashort period planet WASP-103, 2015, Monthly Notices of the Royal Astronomical Society, 447, 711

[7] Delrez, L. et al., High-precision multiwavelength eclipse photometry of the ultra-hot gas giant exoplanet WASP-103 b, 2018, Monthly Notices of the Royal Astronomical Society, 474, 2334

[8] Hellier, Coel et al., Seven transiting hot Jupiters from WASP-South, Euler and TRAPPIST: WASP-47b, WASP-55b, WASP-61b, WASP-62b, WASP-63b, WASP-66b and WASP-67b, 2012, Monthly Notices of the Royal Astronomical Society, 426, 739


Podcast and Website: George J. Bendo

Music: Immersion by Sascha Ende

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