EpistellarJovian Type

Hot, dark gas giants with temperatures between 900 Kelvin and 1400 Kelvin

Image from Steve Bowers
Millennium, a hot epistellar Jovian world with unusual spiral rings caused by a recent encounter with a large comet. The dark clouds on this world are composed of alkali metals
Jovian Class planets that, through planetary migration in the early accretion disk, have settled into circular orbits of 0.7 to 0.2 AU from their primary, with orbital periods of usually only a few days. They are tidally locked and often glow an incandescent orange. Also called 51 Pegasi-Type Planets or Sudarsky class IV worlds. There area large number of subtypes. These worlds have varying masses, from microjovian to superjovian size.

The temperatures of these worlds range from 900 to 1400 Kelvin. At these temperatures, alkali metals vaporize, and most commonly sodium condensates fill the atmosphere, darkening it to a grayish-brown. Sometimes titanium and vanadium clouds predominate. The typical albedo would be 0.03. Likely tidal locking does not allow for the formation of cloud banding. As with HyperThermalJovian worlds, lesser-massed EpistellarJovians may experience atmospheric loss due to the high temperatures and strong stellar winds, in some extreme cases leading to the formation of a very faint comet-like tail, and possibly even the eventual desiccation of the world into a Chthonian planet. This atmospheric loss would also form a tenuous envelope of bluish gas about the planet. Example Millenium
HD 189733 b - Blueglass
Image from Steve Bowers
Blueglass - a tidally-locked epistellar jovian planet, is hot enough at the epistellar point to produce blue-gray silicate clouds
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Development Notes
Text by John M. Dollan in his Planet Classification List
Initially published on 24 October 2001.