Gaspra
Key facts
- What it is
- Main-belt asteroid
- Size
- About 18 km long
- Discovered
- 1916, by Grigory Neujmin
- Spacecraft
- Galileo fly-by, 1991
- Orbit group
- Main-belt Asteroid
- Average distance from the Sun
- 2.21 au (about 330 million km)
- Time to go round the Sun
- 3.3 years
- Closest and farthest from the Sun
- 1.83 to 2.59 au
- Tilt of its orbit
- 4.1°
- Spins once every
- 7 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.
Gaspra was the first asteroid ever seen close up. On 29 October 1991 NASA's Galileo spacecraft, travelling to Jupiter, passed within about 1,600 kilometres of it and sent back the first detailed pictures of an asteroid's surface. Until then asteroids had been little more than points of light.
The images showed an irregular, angular body about 18 kilometres long, shaped rather like a lumpy potato. Gaspra is an S-type asteroid, made of stony silicate minerals mixed with metal, the same broad kind of material as the ordinary chondrite meteorites.
Scientists were surprised by how few large craters it had. Small craters cover its surface, but big ones are rare. Because craters build up steadily over time, this suggested that Gaspra's surface is young by asteroid standards, perhaps only a few hundred million years old. The likely reason is that Gaspra itself is a fragment from a larger asteroid that was broken apart in a collision, so its present surface was created when it was chipped off. Faint grooves on the surface may be cracks from that violent birth.
Gaspra was discovered in 1916 by the Russian astronomer Grigory Neujmin and is named after a spa resort on the Crimean coast. It orbits in the inner part of the belt, among a group of asteroids called the Flora family.
The Galileo fly-by proved that spacecraft could find and photograph small, fast-moving targets in the asteroid belt. Every later asteroid mission builds on what was learned at Gaspra.