99 Fun Facts About Jupiter

Where does Jupiter rank in distance from the Sun?

Fifth from the Sun, Jupiter is the first planet beyond the asteroid belt, and its gravity sculpts that belt, sweeping clear the empty lanes known as Kirkwood gaps.

Jupiter's mass is equal to roughly how many Earths?

About 300: Jupiter outweighs Earth 318 times and holds more than twice the mass of all the other planets combined, yet the Sun is about a thousand times heavier still.

Roughly how many Earths could fit inside Jupiter?

About 1,000 Earths would fit inside Jupiter, which is 11 times as wide, yet it weighs far less than a thousand Earths because it is made mostly of light gases rather than rock.

How long does Jupiter take to orbit the Sun?

Jupiter takes about 11.9 years to circle the Sun; ancient Chinese astronomers built their cycle of twelve earthly branches on that slow, nearly 12-year march across the sky.

Roughly how long is a day on Jupiter?

A day on Jupiter lasts about 10 hours, the shortest of any planet; the spin is fast enough to bulge the planet, making it about 7% wider at the equator than from pole to pole.

Jupiter's atmosphere is made mostly of which two gases?

Hydrogen and helium are the same two gases that make up the Sun: Jupiter has the ingredients of a star but never grew massive enough to ignite.

What is the Great Red Spot?

The Great Red Spot is a giant anticyclonic storm: unlike a hurricane, it whirls around a centre of high pressure, and astronomers have watched it without a break since the 1870s.

Whose 'Permanent Spot' on Jupiter was long taken for the Great Red Spot?

Cassini found his spot in 1665 and it was followed until 1713; the Great Red Spot enters the record only in 1831, and a 2024 study concluded the two were probably different spots.

In which part of Jupiter does the Great Red Spot sit?

The southern hemisphere holds the spot at about 22 degrees south, penned between an eastward jet stream on its southern edge and a stronger westward one on its northern edge.

What has Jupiter's Great Red Spot been doing for more than a century?

Shrinking: in the late 1800s the spot was about three Earths wide, by 2004 it was half as long, and it has grown rounder as it narrows.

Jupiter's clouds are made mainly of crystals of what?

Jupiter's visible clouds are mostly ammonia crystals, with ammonium hydrosulfide below; the orange and brown streaks come from compounds welling up and changing colour in sunlight.

Why does Jupiter give off more heat than it receives from the Sun?

It is slowly contracting: as Jupiter cools, its own gravity squeezes it and the squeeze heats its interior, a process called the Kelvin–Helmholtz mechanism.

Jupiter's magnetotail stretches out roughly as far as the orbit of which planet?

Saturn's orbit is about where the tail ends: the solar wind stretches Jupiter's magnetic field into a tadpole-shaped tail more than a billion kilometres long.

What exotic material is thought to make up Jupiter's outer mantle and generate its magnetic field?

Fluid metallic hydrogen, formed when pressure strips hydrogen's electrons so it conducts like a liquid metal, makes up much of Jupiter's interior and drives its dynamo.

Jupiter is the only planet whose shared centre of mass with the Sun lies where?

Outside the Sun's surface, by about 7% of its radius: Jupiter is massive enough to make the Sun wobble around that point, the kind of wobble astronomers look for to find planets around other stars.

Where does Jupiter usually rank among the brightest natural objects in the night sky?

Jupiter is usually the third-brightest natural object in the night sky, after the Moon and Venus; only at a favourable opposition can Mars briefly outshine it.

Which Galilean moon orbits farthest from Jupiter?

Callisto is the outermost Galilean moon, orbiting about 1.88 million km from Jupiter, far enough to escape the tidal heating that shapes the inner three; its ancient surface is saturated with craters.

Which four moons were discovered by telescope in 1610?

Io, Europa, Ganymede and Callisto were the first moons seen circling another planet, and the sight of bodies orbiting something other than Earth dealt a blow to the old Earth-centred picture of the heavens.

Which German astronomer, who spotted them independently, gave Jupiter's four big moons the names that stuck?

Simon Marius published the names in 1614, taking up Kepler's idea of calling them after lovers of Zeus; the name their discoverer chose, the Medicean Stars, never caught on.

Which moon of Jupiter is the largest moon in the Solar System, bigger than the planet Mercury?

Ganymede, wider than Mercury, is also the only moon known to make its own magnetic field, which gives it auroras of its own.

Which moon of Jupiter is the most volcanically active body in the Solar System?

Io, with over 400 active volcanoes, is the most volcanically active body in the Solar System; tidal flexing by Jupiter and the neighbouring Galilean moons heats its interior.

NASA launched a spacecraft in 2024 to study the hidden ocean of which moon of Jupiter?

Europa's ocean, sealed under an icy shell, may hold twice as much water as all of Earth's seas; Europa Clipper will fly past the moon 49 times to judge whether it could support life.

Jupiter's three inner large moons circle it in a locked 4:2:1 rhythm, which is an example of what?

An orbital resonance: the innermost moon circles Jupiter four times and the next one twice for each orbit of the third, a pattern called a Laplace resonance, and the repeated tugs keep their interiors warm.

Which moon of Jupiter, found by Edward Barnard in 1892, was the last discovered by eye through a telescope?

Amalthea, spotted by Edward Emerson Barnard in 1892, was the last moon found by an astronomer looking through an eyepiece; every one since has turned up in photographs or digital images.

What are Jupiter's faint rings mostly made of?

Jupiter's rings are mostly fine dust, unlike Saturn's icy rings; the main ring is thought to be debris knocked off the small moons Adrastea and Metis by meteoroid impacts.

Which spacecraft discovered Jupiter's rings, in 1979?

Voyager 1 discovered Jupiter's faint ring system in March 1979, photographing it in a long exposure as the probe looked back toward the Sun; Voyager 2 confirmed it that July.

Which was the first spacecraft to fly past Jupiter, in 1973?

Pioneer 10 flew past in December 1973 through radiation stronger than predicted, which triggered false commands and cost some pictures; its readings helped engineers harden the probes that followed.

How did NASA dispose of its first Jupiter orbiter in 2003, to avoid contaminating a moon?

Plunged it into Jupiter: after eight years in orbit, Galileo was deliberately burned up in the planet's atmosphere to protect one of its own discoveries, a possible ocean under a moon's icy crust.

For roughly how long did the 1995 atmospheric entry probe transmit from inside Jupiter's atmosphere?

About an hour: the probe parachuted into the clouds in December 1995 and sent data for 58 minutes before the rising heat and pressure silenced it.

NASA's Juno spacecraft arrived at Jupiter on which US holiday in 2016?

July 4, Independence Day, was still the date in the United States when Juno arrived in 2016: after a five-year flight it fired its main engine for 35 minutes to let Jupiter's gravity capture it.

What did Juno find at each of Jupiter's poles?

Cyclone clusters: eight ring a central one at the north pole and a smaller group circles another at the south; each tries to drift poleward, but the cyclone in the middle pushes it back.

Which comet, torn into fragments, crashed into Jupiter in July 1994?

Comet Shoemaker–Levy 9 struck in more than 20 pieces, the first collision between Solar System bodies ever watched as it happened, and left dark scars that Jupiter's winds took months to erase.

Why had the comet that hit Jupiter in 1994 already broken into a chain of pieces?

Jupiter's gravity tore it apart: on a close pass in July 1992, tidal forces pulled the comet into more than 20 fragments, which circled the planet for two years before they struck.

Jupiter has been called the Solar System's what, because of how many impacts it absorbs?

Jupiter has been called the Solar System's vacuum cleaner: its gravity draws in far more asteroid and comet impacts than Earth receives, though whether it shields the inner planets is debated.

Asteroids sharing Jupiter's orbit at its Lagrange points are known as what?

Jupiter's Trojans, grouped in a Greek camp ahead of the planet and a Trojan camp behind, are leftovers from the early Solar System; NASA launched the Lucy probe in 2021 to fly past several of them.

Timing the eclipses of Jupiter's moons in the 1670s allowed Ole Rømer to estimate what?

Ole Rømer estimated the speed of light in 1676 after noticing that eclipses of Jupiter's innermost big moon ran late when Earth was farthest away: the delay was the extra time the light took to cross the gap.

Which Babylonian god did the planet Jupiter represent?

Marduk, chief god of Babylon, lent the planet his name, and Babylonian astronomers tracked it with care: their records show them finding its position from the area under a graph of its speed against time.

Which day of the week is named after Jupiter in French, Spanish and Italian?

Thursday: the Romans called it Iovis dies, Jupiter's day, which became jeudi, jueves and giovedì; English swapped in Thor, the god the Germanic peoples matched with Jupiter.

Hindu astrologers named the planet after Brihaspati and call it Guru, meaning what?

Teacher is the meaning of guru, and Brihaspati is the teacher of the gods; the Sanskrit word's literal sense is 'heavy' or 'weighty', which happens to suit the most massive planet.

The old adjective 'jovial', from Jupiter's astrological influence, has come to mean what?

Merry is the sense 'jovial' took from astrology, which held that people born under Jupiter were cheerful; the same belief gave English 'saturnine' for the gloomy temper of those born under Saturn.

The name Jupiter comes from a Proto-Indo-European compound meaning what?

Father Sky-God is the sense of the ancient compound *Dyēu-pəter, which began as a form of address, the way the god was called on in prayer; the Greeks' 'Zeu pater' comes from the same phrase.

What is the identifying weapon of the Roman god Jupiter?

Jupiter's weapon is the thunderbolt, often shown clutched in the talons of his sacred eagle, the bird that became the standard of the Roman legions.

The ancient Greeks knew the planet as Phaethon, meaning what?

Shining one is what Phaethon means, from a Greek verb 'to shine'; by the fourth century BC the Greeks had tied the planet to Zeus instead, and the Romans in turn named it for their own chief god.

Which spacecraft used a Jupiter gravity assist in 2007 on its way to Pluto?

New Horizons swung past Jupiter on 28 February 2007, and the planet's gravity flung it onward fast enough to cut about three years from its journey to Pluto.

Why does Jupiter have almost no seasons?

Its axis is barely tilted: Jupiter leans only about 3 degrees, so it spins almost upright and neither hemisphere ever tips far toward the Sun.

NASA's Juno probe is named for Jupiter's wife, who in myth managed to do what?

See through his veil of clouds: in the story NASA tells, Jupiter hid his mischief behind clouds and Juno peered through them, just as the probe looks beneath the planet's cloud tops.

Which European Space Agency probe, launched in 2023, is on its way to study Jupiter's icy moons?

Juice, the Jupiter Icy Moons Explorer, is due at Jupiter in 2031 and is then meant to settle around one of its big moons, which would make it the first spacecraft to orbit a moon other than our own.

Heinrich Schwabe, whose 1831 notes begin the Great Red Spot's record, discovered which cycle?

The sunspot cycle: Schwabe, an apothecary turned astronomer, counted sunspots for 17 years before noticing that their numbers rose and fell about every ten years.

In 1955 the astronomers Burke and Franklin discovered that Jupiter gives off bursts of what?

Radio waves: the bursts kept time with the planet's spin, which gave a more precise length for Jupiter's day and the first evidence that it has a magnetic field.

Which toy company made the aluminium figurines riding to Jupiter aboard NASA's Juno spacecraft?

Lego cast its minifigures of Galileo, the god Jupiter and the goddess Juno in aluminium rather than plastic so they could endure the extremes of spaceflight.

Jupiter, the heavyweight of the Solar System, is nearly two and a half times as massive as what?

All the other planets combined would still weigh less than half as much as Jupiter, yet the Sun is roughly a thousand times heavier again.

In which 1968 science-fiction film does the spaceship Discovery One carry its crew towards Jupiter?

2001: A Space Odyssey sends Discovery One after a signal that a monolith found on the Moon beamed towards Jupiter, a purpose Dave Bowman learns only from a prerecorded video.

Which composer's final symphony, No. 41 in C major, is nicknamed the Jupiter?

Mozart's last and longest symphony probably owes its nickname to the impresario Johann Peter Salomon, who had settled in London.

In Gustav Holst's orchestral suite The Planets, Jupiter is subtitled the Bringer of what?

Jollity came from astrology, not myth: Holst said the suite was suggested by the planets' astrological significance and had no connection with the classical gods.

Galileo's 1610 discovery of moons circling Jupiter dealt a blow to which ancient picture of the cosmos?

The Earth-centred universe of Ptolemy had everything circling our own world, so moons plainly orbiting another planet were very hard to explain away.

Which bird, sacred to the Roman god Jupiter, became one of the commonest symbols of Rome's army?

The eagle outranked every other bird when Roman priests read omens from their flight, and it appears on Greek and Roman coins as the god's emblem.

On a clear night, what is the least you need to see Jupiter's four largest moons from Earth?

Ordinary binoculars will pick them out, and a small telescope adds the dark cloud belts that stripe the planet.

Which of these records is Jupiter believed to hold among the Solar System's planets?

The oldest planet is the current best estimate for Jupiter, thought to have formed just one million years after the Sun and roughly 50 million years before Earth.

Unlike every earlier spacecraft sent to Jupiter, NASA's Juno probe gets its electricity from what?

Solar panels gather so little energy that far out that Juno needed the largest solar wings ever deployed on a planetary probe at the time it launched.

Which Greek god did the Romans regard as the equivalent of their chief god Jupiter?

Zeus lent Jupiter his stories wholesale: Latin writers and Roman artists retold the Greek myths and reused the imagery under the Roman name.

Hoping for a patron, Galileo first named Jupiter's four big moons after which powerful Italian family?

The Medici brothers were honoured with the 'Medicean Stars', and the flattery helped Galileo win a post as the family's chief mathematician and philosopher.

In which short 1610 treatise did Galileo announce that he had found moons circling Jupiter?

The Starry Messenger, known in Latin as Sidereus Nuncius, was the first published scientific work based on observations made through a telescope.

Galileo proposed using the eclipses of Jupiter's moons as a celestial clock to help navigators find what?

Longitude could be worked out by timing the eclipses, a trick too fiddly on a moving ship but practical on land, where it was later used to re-map France.

In the Greek-influenced Roman tradition, Jupiter was the brother of which two gods?

Neptune and Pluto, rulers of the sea and the underworld, are the Roman equivalents of Poseidon and Hades, and the brotherhood itself was borrowed from Greek tradition.

On which hill in ancient Rome did the great Temple of Jupiter Optimus Maximus stand?

The Capitoline held the most important temple in ancient Rome, traditionally dedicated in 509 BC, the year the Republic replaced the kings.

Which goddess shared Jupiter's greatest temple in Rome with Jupiter and Juno, each in a separate chamber?

Minerva, Jupiter's daughter and the goddess of wisdom, had the chamber on the right, with Juno on the left and Jupiter in the middle.

The Romans worshipped Jupiter under the title Optimus Maximus, a Latin phrase meaning what?

Best and greatest was a title with political weight: Rome's consuls swore their oath of office in Jupiter's name.

Which day of each Roman month, later made infamous by Julius Caesar's murder, was sacred to Jupiter?

The Ides fell at the midpoint of the month, with a full moon, and belonged to Jupiter because heavenly light then shone both day and night.

What name do astronomers give to the alignment in which Earth sits roughly in line between the Sun and Jupiter?

Opposition brings Jupiter roughly as close to Earth as it gets, so it looks larger and brighter and stays up almost all night, rising around sunset.

Jupiter's dark cloud bands are called belts; what are the lighter bands between them known as?

Zones are colder than the belts and mark gas that is welling up, while the darker belts mark gas that is sinking.

Jupiter rotates faster than any other planet in the Solar System, which makes it visibly bulge where?

Around its equator Jupiter is about 7% wider than it is from pole to pole, a squashed shape that an amateur telescope can show.

Which feature, found on Earth and Mars, does Jupiter lack, its atmosphere merging smoothly into the interior below?

A solid surface never arrives, so scientists treat the level where the pressure matches Earth's sea-level air as Jupiter's 'surface' and measure heights from there.

Jupiter is the largest member of which class of planet, a group that leaves out Uranus and Neptune?

Gas giants once meant all four big outer planets, but since the 1970s Uranus and Neptune have increasingly been classed apart as ice giants.

Jupiter would need roughly 13 times its present mass to fuse deuterium and count as what?

A brown dwarf is still not a true star: Jupiter would have to be about 75 times more massive to ignite like the Sun.

Which invisible structure around Jupiter would look larger than the full Moon in our sky if human eyes could see it?

Its magnetosphere is, by volume, the largest known continuous structure in the Solar System after the heliosphere, the Sun's own magnetic bubble.

Which glowing displays shine permanently around Jupiter's poles?

Auroras on Jupiter never switch off, and they have been observed in infrared, visible, ultraviolet and X-ray wavelengths.

What nickname is given to the slushy, ice-coated hailstones thought to fall deep into Jupiter's atmosphere?

Mushballs form in the same violent storms as 'shallow lightning', flashes the Juno mission found coming from clouds unusually high in the atmosphere.

What nickname is given to the patch of strangely shaped magnetic field found near the equator of Jupiter?

The Great Blue Spot may be Jupiter's rough equivalent of Earth's South Atlantic Anomaly, and it shows signs of shifting over the years.

What did measurements by NASA's Juno probe suggest about the heavy-element core at the centre of Jupiter?

It is large and diffuse, blending into the mantle above and reaching 30 to 50 per cent of the way out from the centre.

NASA's Juno probe looped back in 2013 for a gravity boost from which planet before heading out to Jupiter?

Earth gave Juno its slingshot two years after launch, a speed boost that set the probe on course for its arrival in 2016.

The electronics of NASA's Juno probe sit inside a vault of which metal to survive Jupiter's radiation?

Titanium walls a centimetre thick cut the radiation reaching Juno's electronics by a factor of 800.

NASA's Juno spacecraft circles Jupiter in which kind of orbit, unlike the earlier Galileo orbiter's equatorial path?

Polar orbits let Juno pass over both poles while dodging the worst of the radiation belts, so its total dose is lower than the Galileo orbiter's was.

Which solar probe swung past Jupiter in 1992 to fling itself into an orbit over the Sun's poles?

Ulysses used Jupiter's gravity to tilt its path about 80 degrees out of the plane of the planets; it was originally named Odysseus for its long, indirect route.

Which NASA spacecraft, named after a famous fossil, launched in 2021 to tour asteroids that share Jupiter's orbit?

Lucy takes its name from the Lucy hominin fossils because its targets may preserve the 'fossils of planet formation' from the early Solar System.

Which space shuttle carried the Jupiter-bound Galileo spacecraft into Earth orbit in October 1989?

Atlantis set Galileo on a roundabout road: the craft took just over six years, helped by planetary flybys, to reach Jupiter in December 1995.

What failed to open on NASA's Galileo spacecraft during its journey to Jupiter?

Its main antenna never deployed, so Galileo sent its findings home through a small low-gain antenna at far slower bit rates.

On its way to Jupiter, the Galileo spacecraft found Dactyl, the first confirmed moon of which asteroid?

Ida was only the second asteroid ever visited by a spacecraft, and its tiny companion, about 1.4 kilometres across, turned up in the images Galileo sent back.

The 2009 impact that left a Pacific-sized scar on Jupiter was first spotted by an amateur astronomer in which country?

Australia's Anthony Wesley caught the dark mark from his home observatory in New South Wales, before anyone had identified the object that struck the planet.

In the 'jumping-Jupiter' scenario, the young Jupiter's wandering may have flung what out of the Solar System entirely?

An extra giant planet may have been cast out as the migrating Jupiter disturbed its neighbours' orbits, leaving only the four giants seen today.

In Western astrology, Jupiter is the traditional ruling planet of Sagittarius and which other zodiac sign?

Pisces has since gained a second, 'modern' ruling planet, which is why astrologers describe Jupiter as its traditional one.

Which British hymn is sung to a tune Holst adapted from his Jupiter movement?

I Vow to Thee, My Country borrowed the stately theme from the middle of the movement in 1921, fitted to a patriotic poem by Cecil Spring Rice.

In Chinese, Japanese, Korean and Vietnamese, Jupiter's name links it to which of the Five Elements?

Wood supplies the planet's East Asian name, the 'wood star', one of the five planet names taken from the Chinese Five Elements.

What do astronomers call the meeting of Jupiter and its ringed neighbour in the sky roughly every 20 years?

A great conjunction as tight as December 2020's is rare: the two planets have come within a sixth of a degree of each other only four times since the year 1200.

By long-standing convention, the moons of Jupiter are named after which figures connected with the god?

His lovers and descendants supply the names: lovers and favourites came first, and descendants were added to the pool in 2004.

Gaps in the asteroid belt cleared by Jupiter are named after which American astronomer, who noticed them in 1866?

Daniel Kirkwood also worked out why the gaps exist: an asteroid there would keep falling into step with Jupiter's own trips around the Sun.

Which hypothesis has the young Jupiter drifting towards the Sun, then reversing like a sailing boat changing course?

The grand tack would have cut off the disc of planet-building rubble at about Earth's distance from the Sun, limiting the material left to form Mars.

Which Chinese astronomer may have glimpsed a moon of Jupiter with the unaided eye in the 4th century BC?

Gan De recorded a small star 'in alliance' with the planet, a note the historian Xi Zezong read as a sighting made some 2,000 years before the telescope.

Rome's flamen Dialis, the high priest of Jupiter, lived under taboos and could not ride or even touch which animal?

A horse was only one of the taboos: the priest was also barred from swearing an oath and from sleeping away from his own bed for three nights running.

Astronomers use the mass of Jupiter as a convenient unit for weighing which kind of distant object?

Exoplanets are routinely weighed in Jupiter masses: one well-studied world, HD 209458 b, comes in at 0.69 of a Jupiter.