This spot is a great storm two and a half times the diameter of the Earth that has lasted for over 300 years and shows no signs of ever lessening or ending. Jupiter is remarkable in that it emits almost twice as much heat as it receives from the Sun. This may be heat left over from its formation. There is a strong greenhouse effect which keeps the temperature of the upper atmosphere at about 120-130 Kelvin at both equator and pole, even on the dark side of the planet. Jupiter consists mainly of hydrogen, with a much smaller amount of helium.
Heavier elements are present in combination with hydrogen.
Jupiter has at least 14 moons. In 1979 the Voyager 1 spacecraft found that Jupiter has a faint ring of particles at a distance of about 130,000 Km from the Planets center, orbiting every 7 hours. Saturn is most known for its bright ring system. Second only to Jupiter in size among the planets, Saturn has an equatorial diameter of 74,000 miles. Like Jupiter it is composed mostly of gas and wrapped in dense clouds.