50 Fun Facts About Jupiter

Where does Jupiter rank in distance from the Sun?

It is the first of the giant planets beyond the asteroid belt.

Jupiter's mass is roughly how many times that of Earth?

That is nearly 2.5 times the mass of all the other planets combined, yet still less than a thousandth of the Sun.

Jupiter's diameter is about how many times Earth's?

It is also about a tenth the diameter of the Sun.

How long does Jupiter take to orbit the Sun?

The Chinese built their twelve-year cycle of earthly branches on this near-12-year orbit.

Roughly how long is a day on Jupiter?

It is the fastest-spinning planet, which flattens it into an oblate spheroid 7% wider at the equator.

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

About 76% hydrogen and 24% helium by mass, close to the primordial mix of the solar nebula.

What is the Great Red Spot?

It rotates anticlockwise about once every six days and rises some 8 km above the surrounding cloud tops.

Since when has the Great Red Spot been continuously observed?

Robert Hooke and Cassini may have seen it in the 1660s, though that identification is disputed.

How does the Great Red Spot compare in size with our own planet?

It has shrunk a lot: it was about 41,000 km across in the late 1800s and about 16,500 km by 2015.

Roughly how wide was the Great Red Spot in the late 1800s, before it began shrinking?

By 2015 it was down to about 16,500 by 10,940 km and losing roughly 930 km of length a year.

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

The orange and brown streaks come from compounds welling up and changing colour in sunlight.

Jupiter radiates more heat than it receives from the Sun. Which mechanism drives this?

The planet is still slowly shrinking, by about a millimetre a year.

Which planet has the strongest magnetic field in the Solar System?

Its magnetosphere stretches downwind almost to the orbit of Saturn.

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

Under enormous pressure hydrogen becomes an electrical conductor, like a liquid metal.

Jupiter is the only planet whose barycentre with the Sun lies where?

The common centre of mass sits about 7% of a solar radius above the Sun's surface.

Jupiter is usually which brightest object in Earth's night sky?

At opposition Mars can occasionally outshine it.

How many known moons does Jupiter have (as of the article)?

Only 16 of them are larger than 10 km across; most are captured asteroids.

Which four moons were discovered by telescope in 1610?

Simon Marius spotted them a day later and it was his names, taken from Zeus's lovers, that stuck.

Who gave the four big moons the names that stuck, taken from Zeus's lovers?

Galileo had called them the Medicean Stars after his patrons.

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

It is also the only moon known to generate its own magnetic field.

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

Over 400 active volcanoes are driven by tidal heating as Jupiter, Europa and Ganymede pull it about.

Which icy moon of Jupiter is a prime target in the search for life because of its subsurface ocean?

Hubble has detected water-vapour plumes, and NASA's Europa Clipper is on its way to investigate.

The three inner Galilean moons orbit in a 4:2:1 pattern known as what?

Each moon gets an extra tug at the same point every orbit, keeping their orbits slightly elliptical and their interiors warm.

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

Everything since has been found on photographs or by spacecraft.

Jupiter has faint rings. Unlike Saturn's, what are they mostly made of?

The main ring is thought to be debris knocked off the small moons Adrastea and Metis.

Which spacecraft discovered Jupiter's rings, in 1979?

They also confirmed the Great Red Spot rotates anticlockwise.

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

It later became the first probe to leave the inner Solar System entirely.

Which was the first spacecraft to orbit Jupiter, arriving in December 1995?

It stayed more than seven years and dropped a probe into the atmosphere, despite a jammed main antenna.

The 1995 atmospheric entry probe recorded winds of more than what speed before it was destroyed?

It parachuted through 150 km of atmosphere and found temperatures above 300 °C.

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

It sent back the first-ever images of Jupiter's north pole and found clusters of polar cyclones.

Juno found a group of how many cyclones around Jupiter's north pole?

A central storm ringed by eight others; the south pole has a similar arrangement.

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

It was the first collision between Solar System bodies ever watched directly.

Why had the 1994 impactor comet broken into a chain of pieces before it hit the planet?

It had passed inside Jupiter's Roche limit and was already orbiting the planet when discovered.

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

It takes about 200 times more asteroid and comet hits than Earth, though whether it protects us is debated.

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

They are split into Greek and Trojan 'camps' named for heroes of the Iliad; the first found was 588 Achilles.

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

The eclipses ran about 17 minutes late when Jupiter was on the far side of the Sun.

Which Babylonian god did the planet Jupiter represent?

The Babylonians used its 12-year circuit of the sky to lay out the constellations of their zodiac.

Chinese, Japanese, Korean and Vietnamese names for Jupiter mean which of the Five Elements' 'star'?

In China it was also the 'year star', because it hops one zodiac constellation each year.

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

Brihaspati is the religious teacher of the gods in Vedic tradition.

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

Astronomers use 'Jovian' instead; 'zenography' borrows from Zeus.

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

Dyeu-pater is the same root that gives Greek Zeus pater and Sanskrit Dyaus Pita.

What is the identifying weapon of the Roman god Jupiter?

His sacred bird was the eagle, which became the standard of the Roman legions.

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

Its modern Greek name is Dias, from Zeus.

Who discovered the characteristic bands of Jupiter's atmosphere, in 1639?

He was a Neapolitan optician testing a telescope of his own making.

Jupiter has been visited by how many robotic probes since 1973, according to the article?

Seven flybys and two dedicated orbiters, with two more on the way.

Jupiter's orbital period is roughly what fraction of Saturn's, forming a near-resonance?

That near 5:2 relationship shaped the early migration of both planets.

A 'Great Cold Spot' was discovered in 2017 in which region of Jupiter?

It is about 24,000 km across and was found via infrared light from the trihydrogen cation.

By roughly how much does Jupiter shrink each year as it contracts under the Kelvin-Helmholtz mechanism?

At its formation the planet was hotter and roughly twice its present diameter.

Which pharmacist made the earliest known detailed drawing of the Great Red Spot, in 1831?

Hooke may have glimpsed the spot in 1664 and Cassini in 1665, though those sightings are disputed.

In 1955 Burke and Franklin found Jupiter emitting radio bursts at what frequency?

The bursts kept time with the planet's rotation, giving astronomers a more precise value for its spin.