By Tim Lambert
The Discovery of the Asteroids
The asteroids are small heavenly bodies, almost all of which orbit between Mars and Jupiter. The first asteroid to be discovered was Ceres. It was discovered by Giuseppe Piazzi in 1801. He named it after the Greek goddess of Agriculture. In 1802 Wilhelm Olbers discovered a second tiny heavenly body. He named it Pallas after Pallas Athene, the Greek goddess of wisdom. Soon, other asteroids were discovered. In 1804 Karl Ludwig Harding discovered Juno. Wilhelm Olbers discovered Vesta in 1807. Vesta is the brightest asteroid in the sky.
In 1845 Karl Ludwig Hencke discovered a fifth asteroid, which he called Astraea. By the end of the 19th century hundreds of asteroids had been discovered. By the end of the 20th century over 100,000 were known. Today, more than 1 million asteroids are known. (After 1891 photography was used to discover asteroids).
In 1802, William Herschel coined the term asteroids, derived from Greek words meaning star-like.
In 1993, the Galileo spacecraft discovered that the asteroid Ida has a small moon. We now know that many asteroids have tiny moons orbiting them. Some asteroids have two or more moons orbiting them.
In 1906, Max Wolf discovered Achilles, an asteroid sharing Jupiter’s orbit. More such asteroids were discovered, some orbiting ahead of Jupiter and some after. They are known as Trojan asteroids. Since 1990 Trojan asteroids have been discovered in the same orbit as other planets, Mars, Uranus, Neptune and Earth.
Though most asteroids orbit between Mars and Jupiter, some have orbits that bring them closer to the Sun than Mars. Asteroids that come close to Earth are called Near-Earth Asteroids (NEOs).
A Near-Earth Asteroid called Icarus goes closer to the Sun for part of its orbit. In 1960, Arthur C Clarke wrote a story about a man in a spaceship who crashes on Icarus. It was called Summertime on Icarus. In 1968, Icarus became the first asteroid to be observed by radar.
Spacecraft to Asteroids
Many spacecraft have been sent on missions to the Asteroids. In 1991 the Galileo spacecraft became the first to fly past an asteroid. It flew past an asteroid called Gaspra. Then, in 1993, it flew past Ida.
In 2000, the NEAR spacecraft orbited the asteroid Eros. The next year, 2001, it landed on Eros. In 2011, the Dawn spacecraft orbited and explored Vesta. It then explored Ceres.
The Psyche spacecraft was launched in 2023 on a mission to explore an asteroid called Psyche. It’s expected to arrive in 2029. The Lucy spacecraft was launched in 2021. It is expected to reach the Jupiter Trojan asteroid Eurybates in 2027. At the moment, several more missions to the Asteroids are planned.
In 2006, the International Astronomical Union reclassified Ceres, the largest asteroid, as a dwarf planet.
Ceres
Last revised 2026