Cryojovian Type worlds

Cold , mostly cloudless gas giants in the outer parts of a planetary system

Hackenbush
Image from Steve Bowers
Hackenbush, a cold, cloudless cryojovian in the outer parts of the Pen-y-Ghent system
These worlds do not have upper level clouds because it is too cold for condensates to form, although some latitudes may have methane clouds, reflecting local warm climes. The result is also a Jovian world that can have a variety of blue hues, although atmospheric haze could mute the color. These worlds are also unique in that they are composed of a larger amount of rock and ice, with large cores and a less massive Jovian atmosphere than typical gas giants.

In the outer regions of a young solar system planets form more slowly, and these worlds rarely accrue enough mass to become hydrogen-helium giants. This means that many gas giants in the Neptunian class are cryojovian in nature (sometimes called ice giants or cryoneptunians, to distinguish them from warm and hot Neptunian sized planets in the inner regions of a planetary system). An example is Hackenbush in the Penyghent system. Sometimes, however, large gas giants form in the outer regions of planetary systems from core collapse, in a similar fashion to a companion star; these objects are in fact failed stars, and if massive enough will undergo fusion of deuterium and become brown dwarfs.
 
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Development Notes
Text by John M. Dollan and Steve Bowers

Initially published on 31 December 2007.