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The Jupiter Portal


Astronomical symbol of Jupiter

Voyager 1 Image of Jupiter's Great Red Spot in False Color.jpg
Voyager 1 Jupiter Io Europa.jpg

Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with a mass slightly less than one-thousandth of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn, Uranus and Neptune. Together, these four planets are sometimes referred to as the Jovian or outer planets. The planet was known by astronomers of ancient times and was associated with the mythology and religious beliefs of many cultures. The Romans named the planet after the Roman god Jupiter. When viewed from Earth, Jupiter can reach an apparent magnitude of −2.94, making it on average the third-brightest object in the night sky after the Moon and Venus. (Mars can briefly match Jupiter's brightness at certain points in its orbit.)

Jupiter voy1.jpg

Jupiter is primarily composed of hydrogen with a quarter of its mass being helium; it may also have a rocky core of heavier elements. Because of its rapid rotation, Jupiter's shape is that of an oblate spheroid (it possesses a slight but noticeable bulge around the equator). The outer atmosphere is visibly segregated into several bands at different latitudes, resulting in turbulence and storms along their interacting boundaries. A prominent result is the Great Red Spot, a giant storm that is known to have existed since at least the 17th century when it was first seen by telescope. Surrounding the planet is a faint planetary ring system and a powerful magnetosphere. There are also at least 63 moons, including the four large moons called the Galilean moons that were first discovered by Galileo Galilei in 1610. Ganymede, the largest of these moons, has a diameter greater than that of the planet Mercury. Jupiter has been explored on several occasions by robotic spacecraft, most notably during the early Pioneer and Voyager flyby missions and later by the Galileo orbiter. The most recent probe to visit Jupiter was the Pluto-bound New Horizons spacecraft in late February 2007. The probe used the gravity from Jupiter to increase its speed. Future targets for exploration in the Jovian system include the possible ice-covered liquid ocean on the moon Europa.

Selected article

Image of Metis taken by the Galileo spacecraft
Metis (/ˈmts/ MEE-təs; Greek: Μήτις, translit. lang), also known as Jupiter XVI, is the innermost moon of Jupiter. It was discovered in 1979 in images taken by Voyager 1, and was named in 1983 after the first wife of Zeus, Metis. Additional observations made between early 1996 and September 2003 by the Galileo spacecraft allowed the surface of the moon to be imaged.

Metis is tidally locked to Jupiter, which led to a high asymmetry in the shape of the moon, with one of the diameters being almost twice as large as the smallest one. It is also one of the three moons in the Solar System known to orbit its planet in less than the length of that planet's day, the other two being Jupiter's Adrastea and Mars's Phobos. It orbits within the main ring of Jupiter, and is thought to be a major contributor of material to the rings.

Selected biography

Carl Sagan
Carl Edward Sagan /ˈsɡən/ (November 9, 1934 – December 20, 1996) was an American astronomer, astrophysicist, cosmologist, author and science popularizer and science communicator in the space and natural sciences. During his lifetime, he published more than 600 scientific papers and popular articles and was author, co-author, or editor of more than 20 books. In his works, he advocated skeptical inquiry and the scientific method. He pioneered exobiology and promoted the Search for Extra-Terrestrial Intelligence (SETI).

Sagan became world-famous for his popular science books and for the award-winning 1980 television series Cosmos: A Personal Voyage, which he narrated and co-wrote. A book to accompany the program was also published. Sagan also wrote the novel Contact, the basis for the 1997 film of the same name.


Jupiter Atmosphere ˑ Exploration (Voyager 2) ˑ Rings

Major Moons ˑ Io ˑ Europa ˑ Ganymede ˑ Callisto

Astronomers: Galileo Galilei ˑ Gan De ˑ Gerard Kuiper ˑ Giovanni Domenico Cassini

See Also: Formation and evolution of the Solar System ˑ Gas Giant ˑ Nebular hypothesis

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Italicized articles are on dwarf planets or minor moons.



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