50 Fun Facts About Asteroid Belt

All the asteroids in the asteroid belt combined have only a few percent of the mass of which body?

The Moon is about thirty times heavier than the entire asteroid belt. Ceres alone holds more than a third of the belt's mass.

On average, roughly how far apart are neighbouring asteroids in the asteroid belt?

About 1 million km of empty space separates one asteroid from the next. Spacecraft cross the belt without having to steer around anything.

The word asteroid, first proposed in 1802, comes from a Greek word with which meaning?

Star-like fitted because even the best telescopes of the day showed the new objects as mere points of light, never as discs.

Ceres, the largest object in the asteroid belt, has held which official classification since 2006?

Dwarf planet is the class Ceres shares with Pluto, and Ceres is the only member that orbits in the inner Solar System.

Which planet's powerful gravity stopped the rocks of the asteroid belt from ever merging into a planet?

Jupiter stirred the young belt so violently that its rocks smashed apart instead of sticking together. Most of the belt's original material was flung out altogether.

Ceres, the first asteroid ever found, was first spotted in 1801 on which holiday?

New Year's Day 1801 was also the first day of the 19th century, so the hunt for asteroids began with the century itself.

Which asteroid, the brightest seen from Earth, can sometimes be glimpsed with the naked eye?

Vesta has an unusually reflective surface, and chips blasted off it by ancient impacts still fall to Earth as meteorites.

Which planet is the asteroid belt's nearest neighbour on the side facing the Sun?

Mars swept up or scattered most of the material that formed near the belt's inner edge, which lies about twice as far from the Sun as Earth.

The asteroid Mr. Spock is a memorial not to the Star Trek character but to which kind of animal?

A cat belonging to the discoverer was the real Mr. Spock, and the committee that approves asteroid names now discourages naming them after pets.

Asteroids numbered 4147 to 4150 are each named after a member of which band?

The Beatles each got one, so Lennon, McCartney, Harrison and Starr sit side by side in the catalogue, and a fifth asteroid honours the band itself.

Ceres, the asteroid belt's largest body, is named after the Roman goddess of what?

Agriculture was her realm, and two years after the discovery a newly found metal was named cerium in the asteroid's honour.

Which NASA spacecraft became the first to orbit two different worlds, both of them in the asteroid belt?

Dawn used fuel-sipping ion engines to circle one giant asteroid for 14 months, then cruised on to orbit Ceres from 2015.

Which spacecraft became the first to cross the asteroid belt, entering it in July 1972?

Pioneer 10 showed the belt was safe to cross, a real worry beforehand. The odds of a probe striking an asteroid are put at under one in a billion.

About three quarters of known asteroids are dark C-type bodies, rich in which element?

Carbon gives these asteroids such dark surfaces that they are harder to detect than other types, so their true share may be even higher.

Early asteroids carry numbers, as in 3 Juno and 5 Astraea; what do those numbers record?

Order of discovery set the numbers because the earliest asteroids were listed as planets and counted off as each one turned up.

Which Italian astronomer discovered Ceres, the first asteroid, from an observatory in Palermo, Sicily?

Giuseppe Piazzi was hunting for a catalogued star when he noticed a nearby point of light shifting from night to night.

In 2014 a space telescope caught Ceres, the asteroid belt's largest body, venting which substance?

Water vapour was a surprise because jets and plumes are the trademark of icy bodies from the outer Solar System, not of asteroids.

In 1891 astronomer Max Wolf sped up the hunt for asteroids by introducing which technique?

Photography showed asteroids as short streaks on long exposures while the stars stayed as dots, and Wolf went on to find 248 of them.

Which planet, found in 1846, broke the Titius–Bode law that had led astronomers to the asteroid belt?

Neptune turned up well inside the orbit the rule predicted, and many astronomers now put the old pattern down to coincidence.

The large main-belt asteroid Kleopatra is famous among astronomers for being shaped like what?

A dog bone has been its nickname since radar revealed two lobes joined by a thick neck, in a body about half as long as the English Channel.

Which astronomer proposed the name asteroids in 1802 for the tiny new objects between the planets?

William Herschel, already famous for finding Uranus, argued the objects deserved a class of their own, though his label took decades to catch on.

Which 24-year-old mathematician worked out the orbit of Ceres so astronomers could find it again in 1801?

Carl Friedrich Gauss invented a new method of computing orbits for the job, and Ceres was found again close to where he said it would be.

Which astronomer wrote in 1596 that an unseen planet must lie where the asteroid belt was later found?

Johannes Kepler thought the space between the fourth and fifth planets was too wide to be empty, two centuries before Ceres was spotted there.

Which asteroid, found by Heinrich Olbers in 1802, was the second ever discovered?

Pallas turned up while Olbers was checking on Ceres, and the newly isolated metal palladium was named in its honour.

Which asteroid, imaged by the Galileo probe in 1993, was the first found to have a satellite of its own?

Ida has a tiny companion called Dactyl, which a mission scientist noticed in the images the probe sent home.

Which asteroid became the first ever visited by a spacecraft when the Galileo probe flew past in 1991?

Gaspra was a bonus target, since the probe was only passing through the belt on its long cruise to the outer Solar System.

Which name is given to the nearly empty lanes in the asteroid belt, swept clear by a giant planet's gravity?

Kirkwood gaps mark orbits where an asteroid would circle the Sun in step with the giant planet, so its repeated tugs pull the asteroid away.

Fine dust from colliding asteroids helps to create which faint glow seen in dark skies after dusk?

Zodiacal light is sunlight bouncing off dust spread along the plane of the planets, though the asteroid belt supplies a tenth of that dust at most.

Many mid-sized asteroids are not solid rock but loose heaps held together by gravity, known as what?

Rubble piles form when the fragments of a shattered asteroid drift back together, leaving large empty voids between the chunks inside.

Asteroids are rocky leftovers from the formation of the Solar System, roughly how long ago?

4.6 billion years of collisions have ground the belt down, yet most of its largest bodies are survivors from the era when the planets formed.

If Earth were shrunk to the size of a nickel, Ceres would be about as big as which of these?

A poppy seed is the right scale because Ceres is only about a thirteenth as wide as Earth, even though it is by far the biggest thing in the belt.

Seven asteroids are named after the astronauts lost in 2003 aboard which Space Shuttle?

Columbia's seven astronauts each have an asteroid of their own, a rare sombre entry in a catalogue full of playful names.

Ceres spins almost perfectly upright, tilted only about four degrees, so it never has which of these?

Seasons need a tilted axis, and Ceres also spins quickly, with a full day there lasting only about nine hours.

Which organisation has the final say on the names that discoverers propose for newly numbered asteroids?

International Astronomical Union rules are loose, which is why an asteroid can carry the name of a rock musician such as Frank Zappa.

Which metal-rich asteroid, possibly a shattered world's exposed core, did NASA send a probe towards in 2023?

Psyche gave its name to the probe as well, and at about 220 km across it is the heaviest known asteroid of its metallic type.

Which NASA spacecraft flew past the main-belt asteroids Dinkinesh in 2023 and Donaldjohanson in 2025?

Lucy takes its name from a famous fossil skeleton, and Donaldjohanson honours the scientist who found that fossil.

What are the asteroids called that share a giant planet's orbit, well beyond the asteroid belt's outer edge?

Trojans are named after heroes of the Trojan War and travel in two swarms, one ahead of the planet and one behind, and may rival the main belt in number.

In 1918 Kiyotsugu Hirayama showed that many asteroids travel in groups with matching orbits, called what?

Families are the scattered wreckage of a single parent asteroid smashed in a collision, and about a third of the belt's asteroids belong to one.

The bright spots that puzzled scientists in Ceres's Occator crater turned out to be made of what?

Salt deposits mark the places where brine from a reservoir deep inside Ceres has seeped up to the surface.

The discoverer of Ceres suspected a planet in 1801 but cautiously announced his find as which kind of object?

A comet was the safe label, though he confided that its slow, steady motion made him suspect it was something better.

Which nickname did the 24 astronomers take who set out around 1800 to find a planet where the asteroid belt lies?

The Celestial Police split the sky into 24 zones, one per member, yet Ceres was spotted by an astronomer who had not yet received his invitation.

Ahuna Mons, the largest mountain on Ceres, is thought to be which unusual kind of landform?

An ice volcano, or cryovolcano, erupts chilled mud instead of molten rock, and this one is the closest to the Sun found so far.

The old astronomical symbol for Ceres, still used by astrologers, is a stylised drawing of which tool?

A sickle was one of the goddess's classical emblems, and two astronomers apparently suggested it independently the year after the discovery.

Which name from Greek myth was given to the shattered planet once imagined as the source of the asteroid belt?

Phaeton was the youth who crashed the Sun god's chariot, an apt name for a wrecked world, though the belt holds far too little material to have been a planet.

Which force, named after a civil engineer, lets radiated heat slowly shift the orbits of asteroid belt bodies?

The Yarkovsky effect is a tiny push that adds up over time, and it is the main way small asteroids drift into the belt's unstable zones.

Which European probe flew past the asteroids Šteins and Lutetia on the way to its main target?

Rosetta gave astronomers their first close look at Lutetia, which was then the largest asteroid any spacecraft had visited.

The main-belt asteroid that NASA's Stardust probe flew past in 2002 is named after which famous diarist?

Anne Frank's asteroid, discovered in 1942, served as a practice target before the probe's main encounter.

Asteroid number 9007, discovered in 1983, was fittingly named after which fictional character?

James Bond earned the honour because the asteroid's catalogue number ends in 007, the secret agent's famous code number.

Which hypothesis, named after a sailing manoeuvre, has a giant planet swerving through the young asteroid belt?

The Grand Tack has the planet drifting towards the Sun and then reversing like a yacht changing course, scattering asteroids and leaving the belt with little mass.

Which NASA probe flew past the dark main-belt asteroid Mathilde in 1997 on its way to orbit Eros?

NEAR Shoemaker found Mathilde as dark as fresh asphalt and so light for its size that it is probably loosely packed inside.