Jupiter
Jupiter formed just one million years after the Sun, roughly 50 million years before Earth came into existence. Current models suggest this massive planet began its life at or beyond the snow line, a distance from the early Sun where temperatures were cold enough for volatiles like water to condense into solids. The proto-planet first grew as a solid core before accumulating its gaseous atmosphere. As it gained mass, Jupiter reached 20 times the weight of Earth, with half that mass composed of silicates and ices. Once the growing planet exceeded 50 Earth masses, it carved a gap in the solar nebula. This process took between three and four million years to complete.
The Grand Tack hypothesis proposes that Jupiter initially formed about five astronomical units from the Sun. As the young planet accreted more mass, interactions with the gas disk and orbital resonances from Saturn caused it to migrate inward. This migration disrupted the orbits of several super-Earths closer to the Sun, causing them to collide destructively. Saturn later migrated inward faster than Jupiter until they became captured in a 3:2 mean motion resonance near 3.5 astronomical units. This event reversed their direction, sending both planets outward to their current locations over a period of three to six million years. The final migration of Jupiter occurred over several hundred thousand years, allowing inner planets including Earth to form from the remaining rubble.
Jupiter's atmosphere consists of 76% hydrogen and 24% helium by mass, with trace amounts of carbon, oxygen, sulfur, neon, ammonia, water vapor, phosphine, and hydrocarbons. The outermost layer contains crystals of frozen ammonia floating above cloud layers located in the tropopause region. These clouds form bands at different latitudes known as tropical regions, subdivided into lighter-hued zones and darker belts. Wind speeds reaching 600 kilometers per hour are common within these zonal jet streams.
The Great Red Spot stands as a persistent anticyclonic storm located 22 degrees south of the equator. First observed in 1831, though possibly seen as early as 1665, this storm rotates counterclockwise every six days. Its maximum altitude reaches about 200 kilometers above surrounding cloud tops. Initial observations in the late 1800s showed the spot spanning approximately 40,000 kilometers across. By October 2021, Juno measured its depth at around 350 kilometers. The storm has significantly decreased in size since discovery, shrinking by roughly one kilometer per year. In April 2017, scientists discovered a Great Cold Spot in Jupiter's thermosphere measuring 20,000 kilometers across and 100 degrees cooler than surrounding material.
Jupiter possesses an outer mantle of fluid metallic hydrogen extending outward to about 80% of the planet's radius. A diffuse inner core mixes with this mantle, spanning 30 to 50% of the planet's radius and containing heavy elements totaling seven to twenty-five times Earth's mass. This mixing process likely arose during formation or resulted from an impact by a planet ten times Earth's mass a few million years after Jupiter formed. At depths where pressure exceeds 1.3 megapascals, hydrogen enters a supercritical fluid state without distinct liquid or gas phases.
The magnetic field generated by eddy currents within the fluid metallic hydrogen core is the strongest in the Solar System. Its dipole moment reaches 4.2 times 10^27 tesla cubic meters, tilted 10.31 degrees relative to the rotation pole. Surface magnetic field strength varies between 4.2 and 14 gauss. At approximately 75 Jupiter radii from the planet, solar wind interaction creates a bow shock. The magnetosphere extends outward until nearly reaching Saturn's orbit. Volcanoes on Io emit sulfur dioxide forming a gas torus along its orbital path. Ionized particles create a plasma sheet co-rotating with the planet, generating radio emissions detectable from Earth at frequencies between 0.6 and 30 megahertz.
Jupiter hosts 97 known natural satellites, with only 16 exceeding 10 kilometers in diameter. The four largest moons, Io, Europa, Ganymede, and Callisto, orbit within the magnetosphere and remain visible through common binoculars. Ganymede stands as the largest of these four, measuring 5,262 kilometers across and surpassing Mercury in size. These Galilean moons form a Laplace resonance where for every four orbits Io completes, Europa makes exactly two and Ganymede one. This gravitational pattern distorts their orbits into elliptical shapes while tidal flexing generates internal heat.
A faint planetary ring system surrounds Jupiter, composed mainly of dust rather than ice like Saturn's rings. Three main segments include an inner halo torus, a relatively bright main ring, and an outer gossamer ring. The main ring likely originates from material ejected by satellites Adrastea and Metis. Additional components of the dusty gossamer ring come from moons Thebe and Amalthea. Evidence suggests a fourth ring may consist of collisional debris from Amalthea strung along its orbit. The age of this ring system remains unknown but possibly dates back to Jupiter's formation.
Babylonian astronomers recorded observations of Jupiter during the seventh and eighth centuries before Christ. Ancient Chinese observers knew the planet as the wood star, establishing a cycle of twelve earthly branches based on its approximate eleven-year revolution around the Sun. By the fourth century BC, these observations evolved into the Chinese zodiac associating each year with a Tai Sui star controlling the region opposite Jupiter's position. The historian Xi Zezong claimed that Gan De reported seeing a small star in alliance with the planet, potentially indicating a moon sighting nearly two millennia before Galileo.
In 1610, Italian polymath Galileo Galilei discovered four largest moons using a telescope, marking the first telescopic observation of moons other than Earth's. Just one day later, Simon Marius independently found these same moons though he did not publish until 1614. Marius's names for Io, Europa, Ganymede, and Callisto eventually prevailed. During autumn 1639, Neapolitan optician Francesco Fontana tested a 22-palm telescope discovering characteristic atmospheric bands. Giovanni Cassini used new instruments in the 1660s to observe spots and estimate rotation periods. In 1892, E.E. Barnard observed Amalthea at Lick Observatory, the last planetary moon discovered visually through a telescope.
Automated spacecraft have visited Jupiter since the 3rd of December 1973 when Pioneer 10 passed within 130,000 kilometers. Six years later Voyager missions vastly improved understanding of Galilean moons while discovering Jupiter's rings. The Galileo mission became the first orbiter reaching the planet on the 7th of December 1995. It remained in orbit for over seven years conducting multiple flybys before deliberately crashing into Jupiter on the 21st of September 2003 to avoid contaminating Europa. A titanium atmospheric probe released from Galileo entered Jupiter's atmosphere on July 1995 collecting data for 57.6 minutes before destruction.
NASA's Juno mission arrived at Jupiter on the 4th of July 2016 studying the planet from a polar orbit. The spacecraft completed twelve orbits before its budgeted plan ended in July 2018. Operations extended until September 2025 with four lunar flybys including Ganymede, Europa, and two Io encounters. Future plans include ESA's Jupiter Icy Moon Explorer launched the 14th of April 2023 and NASA's Europa Clipper launched the 14th of October 2024. Chinese National Space Administration proposes Tianwen-4 targeting an orbiter around 2035.
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Common questions
When did Jupiter form relative to the Sun and Earth?
Jupiter formed just one million years after the Sun, roughly 50 million years before Earth came into existence. Current models suggest this massive planet began its life at or beyond the snow line where temperatures were cold enough for volatiles like water to condense into solids.
What is the composition of Jupiter's atmosphere by mass?
Jupiter's atmosphere consists of 76% hydrogen and 24% helium by mass with trace amounts of carbon oxygen sulfur neon ammonia water vapor phosphine and hydrocarbons. The outermost layer contains crystals of frozen ammonia floating above cloud layers located in the tropopause region.
How large and deep is the Great Red Spot storm on Jupiter?
The Great Red Spot stands as a persistent anticyclonic storm located 22 degrees south of the equator that rotates counterclockwise every six days. Its maximum altitude reaches about 200 kilometers above surrounding cloud tops while Juno measured its depth at around 350 kilometers by October 2021.
Which spacecraft visited Jupiter first and when did it arrive?
Automated spacecraft have visited Jupiter since the 3rd of December 1973 when Pioneer 10 passed within 130,000 kilometers. Six years later Voyager missions vastly improved understanding of Galilean moons while discovering Jupiter's rings.
Who discovered the four largest moons of Jupiter and when?
In 1610 Italian polymath Galileo Galilei discovered four largest moons using a telescope marking the first telescopic observation of moons other than Earth's. Just one day later Simon Marius independently found these same moons though he did not publish until 1614.