MacroJovians are primarily defined by their mass, which ranges from 7.6 to 13.0 that of Jupiter. This upper number is the theoretical lower range which separates gas giant from brown dwarfs.
These are the most massive of planets, although like the SuperJovians, their sizes are not much greater than that of Jupiter. However, this great mass also means that most of the accretion disk material will have gone into the construction of the planet, leaving it highly unlikely that any other Jovians will share the system. Even terrestrial worlds may be small and unimposing, if they are even present at all. Many MacroJovians, early in their history, tend to form in elliptical orbits, their manner and placement of formation more akin to that of a star than a planet. This of course means that most other planets that do initially form will be gravitationally ejected out of the system very early on.
These worlds are so massive that many of their atmospheric characteristics have begun to resemble that of brown dwarfs. Some of the most massive examples may even experience flare activity of a sort, spurred on by high internal temperatures and their massive magnetic fields.
The moons of these worlds can be very large indeed, and what the star system lacks for other planets, it more than makes up for with the presence of quite often numerous major moons.
A MacroJovian planet (image use courtesy of Don Edwards).
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