Juno
Key facts
- What it is
- Large main-belt asteroid
- Size
- About 250 km across
- Discovered
- 1804, by Karl Harding
- Spacecraft
- Not yet visited
- Orbit group
- Main-belt Asteroid
- Average distance from the Sun
- 2.67 au (about 400 million km)
- Time to go round the Sun
- 4.4 years
- Closest and farthest from the Sun
- 1.99 to 3.35 au
- Tilt of its orbit
- 13°
- Spins once every
- 7.2 hours
An au (astronomical unit) is Earth's average distance from the Sun, about 150 million km. Orbit figures are from open tracking data, figures last updated 1 Nov 2026.
Juno was the third asteroid found, discovered by Karl Harding at Lilienthal, near Bremen, in September 1804. It is about 250 kilometres across, much smaller than Ceres, Pallas and Vesta, but still one of the larger bodies in the belt.
Juno is an S-type asteroid, meaning its light shows the fingerprints of stony silicate minerals such as olivine and pyroxene, mixed with some metal. S-types are common in the inner part of the belt, and many ordinary chondrites, the most common meteorites that fall to Earth, are thought to come from bodies of this kind. Juno itself is too large and too far from the escape routes towards Earth to be a major source of meteorites, but studying it helps scientists understand the family of asteroids that the ordinary chondrites belong to.
Its shape is irregular rather than round, and images taken with radio and infrared telescopes show what looks like a large crater on its surface, a scar from a collision. Juno spins once about every seven hours.
Juno is bright enough to see with binoculars or a small telescope when it is well placed, appearing as a faint star that shifts position from night to night. For many years it was listed as a planet, along with Ceres, Pallas and Vesta, until so many new asteroids were found in the 1840s that astronomers began to treat them as a separate class of object.