60 Fun Facts About Asteroids

Most known asteroids orbit in the main belt between which two planets?

The belt lies roughly 2 to 4 astronomical units from the Sun.

Which astronomer coined the word asteroid, from Greek for 'star-like'?

Early asteroids showed no disc in telescopes, so they looked like stars that moved.

What was the first asteroid to be discovered, on 1 January 1801?

It was announced as a new planet and is now classed as the belt's only dwarf planet.

Giuseppe Piazzi, who found the first asteroid, was a priest of which religious order?

He was also a mathematician and ran the observatory at Palermo.

Piazzi's original two-part name for his discovery honoured the goddess of agriculture and whom?

The goddess's oldest temple stood in Sicily, which made her a doubly local choice.

Roughly how large is the largest object in the belt?

That is about a quarter of the Moon's diameter.

The combined mass of all asteroids is only about what fraction of the Moon's mass?

About 60 per cent of that sits in just four bodies.

Asteroids are broadly classified as C (carbonaceous), S (silicaceous) and which other class?

C stands for carbonaceous and S for silicaceous.

What is the key feature that makes an object a comet rather than an asteroid?

Some objects sit on a continuum, and dormant comets can end up looking just like asteroids.

Any object smaller than what size is traditionally called a meteoroid rather than an asteroid?

Above that, a rocky body that is not a planet or comet counts as an asteroid.

Approximately how many asteroids are known?

On average they are about a million kilometres apart, so the belt is mostly empty space.

How far apart, on average, are the objects in the asteroid belt?

Spacecraft cross the belt routinely without any risk of collision.

Which asteroid is the brightest visible from Earth, sometimes faintly visible to the naked eye?

It reaches magnitude 5.1 and is thought to be the second most massive asteroid.

Which German astronomer discovered the second asteroid in 1802 and the fourth in 1807?

Like the first, his 1802 find was at first considered a planet.

Which asteroid is the third largest in the Solar System by volume and mass?

It gives its name to the Pallas family of asteroids.

Which spacecraft, launched in 2007, orbited two different protoplanets of the asteroid belt in turn?

It entered orbit around the first in July 2011 and left for the second in late 2012.

The brightest of the dwarf planet's mysterious bright spots lies in the middle of which crater?

The central spot is named Cerealia Facula, and the group to its east Vinalia Faculae.

Which spacecraft took the first close-up image of an asteroid, 951 Gaspra, in 1991?

Two years later, en route to Jupiter, it also imaged 243 Ida and its moon.

What is the name of the small moon of asteroid 243 Ida, discovered in probe images from 1993?

Mission member Ann Harch spotted it in the returned pictures.

Which spacecraft made the first landing on an asteroid, touching down on Eros in 2001?

It was renamed after planetary scientist Eugene Shoemaker following its 1996 launch.

Which asteroid was the target of the first sample-return mission, Japan's Hayabusa?

Its low density suggests it is a rubble pile of boulders rather than a solid body.

Hayabusa2 returned samples of which asteroid to Earth on 5 December 2020?

The samples contained uracil, one of the four components of RNA, and vitamin B3.

NASA's OSIRIS-REx collected a sample from which asteroid in October 2020?

The capsule parachuted back to Earth on 24 September 2023.

In which US state did the OSIRIS-REx sample capsule land in September 2023?

Distribution and analysis of the material to laboratories worldwide followed.

NASA's DART spacecraft deliberately crashed into which asteroid moonlet in September 2022?

Neither it nor its parent body posed any threat; the pair simply made an ideal test target.

By how much did the DART impact shorten the moonlet's orbit around its parent asteroid?

The result vastly exceeded the pre-defined success threshold of 73 seconds.

Which Italian CubeSat photographed the DART impact?

ESA's Hera mission, launched in 2024, will survey the aftermath in detail.

Which asteroid briefly had a 2.7% chance of hitting Earth on Friday 13 April 2029, per early 2004 estimates?

It will instead pass about 31,600 km above the surface, closer than geostationary satellites.

The name of the asteroid feared in 2004 is the Greek form of which Egyptian deity?

A serpent of chaos was a fitting namesake for a supposed doomsday rock.

What is the highest rating any asteroid has ever received on the Torino impact hazard scale?

The 2029 near-miss asteroid held it for four days in late 2004; 2024 YR4 reached 3 in early 2025.

The Torino scale runs from 0 to what maximum value?

It combines collision probability with the kinetic energy of the possible impact.

An Earth-orbit-crossing object is defined as potentially hazardous if it is larger than what?

The Spaceguard sky-scanning effort has been hunting for such objects since 1998.

The Chicxulub crater, from the impact that ended the dinosaurs, is buried under which peninsula?

It is about 200 km across and about a kilometre beneath younger sediments.

Roughly how big was the asteroid that made the Chicxulub crater 66 million years ago?

The impact is now widely accepted as the primary cause of the extinction of 75 per cent of species.

Which rare element did the Alvarez team find concentrated at the Cretaceous–Paleogene boundary?

Father-and-son team Luis and Walter Alvarez proposed the impact theory in the late 1970s.

The geophysicists who found the Chicxulub crater in the late 1970s were prospecting for what?

Glen Penfield could not prove it was a crater at the time and gave up; a ring of cenotes later confirmed it.

The Chelyabinsk meteor exploded over Russia in which year?

About 1,491 people sought medical treatment, nearly all hurt by glass from windows blown in by the shock wave.

Why did the Chelyabinsk object approach undetected?

It exploded about 30 km up; the injuries came minutes later when the shock wave arrived.

The Tunguska event flattened Siberian forest on 30 June of which year?

The explosion was between 3 and 50 megatons TNT equivalent.

Asteroid Day is held every 30 June on the anniversary of which event?

Cofounders in 2014 included Stephen Hawking and Queen guitarist-astrophysicist Brian May; the UN adopted it in 2016.

Jupiter's trojan asteroids cluster around which two Lagrange points?

They sit 60 degrees ahead of and behind the planet in its orbit.

What was the first Jupiter trojan discovered, found by Max Wolf in 1906?

The trojans are named for heroes of the Trojan War, with Greek and Trojan camps at each point.

NASA's Lucy mission to the trojans is named after a famous what?

The trojans may be 'fossils of planet formation'; the fossil itself was named after 'Lucy in the Sky with Diamonds'.

Who spotted the asteroid belt gaps in 1866 and explained them by resonance with Jupiter?

The gaps that bear his name mark orbits where Jupiter's pull sweeps asteroids away.

Which asteroid, target of a 2023 NASA mission, was thought to be a protoplanet's metal core?

Observations reported in 2020 cast doubt on the core idea, which the spacecraft aims to settle.

Which asteroid is the fourth largest in the main belt, with a mean diameter of about 433 km?

It holds about 3 per cent of the belt's total mass.

Which Chinese mission launched in May 2025 to sample the near-Earth asteroid Kamoʻoalewa?

It will also visit the active asteroid 311P/PanSTARRS.

How many asteroids is NASA's Lucy spacecraft tasked with studying?

Two are main-belt bodies and eight are Jupiter trojans.

Which company released the classic arcade game Asteroids in 1979?

It became Atari's best-selling arcade game with over 70,000 units.

The belt's dwarf planet is not a full planet because it fails which part of the IAU definition?

It shares its orbit with thousands of asteroids and holds only about 40 per cent of the belt's mass.

Eros, the first near-Earth asteroid visited by a spacecraft, was discovered in which year?

Carl Gustav Witt in Berlin and Auguste Charlois in Nice found it on the same night.

What process makes asteroids grow darker and redder as they age?

Most of the colour change happens in the first hundred thousand years, which limits how well spectra can date an asteroid.

Which technique did Max Wolf pioneer in 1891 that dramatically sped up asteroid discovery?

Asteroids showed up as short streaks on long-exposure plates; Wolf alone found 248, starting with 323 Brucia.

ESA's Hera spacecraft, launched in October 2024, is designed to study the aftermath of which event?

It will measure the crater and the momentum transferred to judge how efficient the deflection was.

The Titius–Bode law predicted a missing planet at roughly what distance from the Sun?

Herschel's discovery of Uranus near the predicted spot beyond Saturn gave the now-discredited formula a boost.

Which class of near-Earth asteroids has orbits lying entirely inside Earth's orbit?

Also called Apoheles, their aphelion is smaller than Earth's perihelion distance of 0.983 AU.

What is the name of the extended mission sending NASA's Bennu sample-return probe on to Apophis?

The spacecraft delivered its Bennu sample to Earth in September 2023 before heading on.

On which asteroid was surface water ice confirmed in 2009 using NASA's Infrared Telescope Facility?

Its whole surface appears ice-covered; water vapour on Ceres followed in a 2014 ESA detection.

How many Saturn V rockets did the 1967 'Project Icarus' plan propose launching at an asteroid?

The plan for deflecting 1566 Icarus was drawn up before the Saturn V had even flown.

Which object, found in 1979 and seen sprouting a tail in 1996, was the first known active asteroid?

It was given the cometary designation 133P/Elst-Pizarro after Eric Elst and Guido Pizarro spotted the tail.