Jupiter is a gas giant composed mainly of hydrogen and helium. Increasing pressure inward changes hydrogen's physical state, so the visible cloud tops are not a solid surface on which a spacecraft could land. Deep electrically conducting material, internal motion and rotation contribute to its strong planetary magnetic field.[ref]
Jupiter Facts by National Aeronautics and Space Administration. Structure, Surface and Magnetosphere: composition, conducting hydrogen and the absence of a true solid surface
Its atmosphere is a laboratory for rotating-fluid dynamics: bands and persistent storms reveal motions above an interior that cannot be directly imaged. Gravity and magnetic measurements constrain deeper structure, while emerging thermal radiation probes the cooling energy budget. The category hot Jupiter compares an exoplanet with this giant-planet scale while allowing a very different irradiation environment.
The Great Red Spot is a large atmospheric vortex in Jupiter's southern hemisphere. Its counterclockwise circulation corresponds to a high-pressure system in the rotating-fluid interpretation.[ref]
The Great Red Spot: An Ancient Storm in Jupiter's Atmosphere by National Aeronautics and Space Administration. NASA description: counterclockwise circulation in the southern hemisphere indicates high pressure
A mass unit based on Jupiter, conventionally written ; numerical calculations must state the adopted value or gravitational parameter.
