| Object type | Main-belt asteroid, S-type (stony); Flora family member[3] |
|---|---|
| Discovered | July 30, 1916 — Simeis Observatory, Crimea, by Grigory Neujmin[2] |
| Named for | Gaspra, a Black Sea retreat in Crimea[3] |
| Size | ≈ 18.2 × 10.5 × 8.9 km (≈ 12 km mean diameter)[2] |
| Surface area | ≈ 525 km² — about the size of Guam[3] |
| Mass | Unknown — Galileo passed too far away to measure it[3] |
| Rotation period | ≈ 7.04 hours[2] |
| Geometric albedo | ≈ 0.25[2] |
| Distance from Sun | 1.83–2.59 AU (average ≈ 2.21 AU)[2] |
| Orbital period | ≈ 3.3 years[2] |
| Orbital inclination | ≈ 4.1°[2] |
| Surface age | ≈ 20–300 million years (from crater counts)[3] |
| Composition | Olivine-rich for an S-type; olivine to pyroxene ≈ 4:1 to 7:1[3] |
| Spacecraft | Galileo flyby, Oct. 29, 1991 — 1,600 km at ≈ 8 km/s[3] |
Discovery and name
Gaspra was discovered on July 30, 1916, by Russian astronomer Grigory Neujmin at Simeis Observatory in Crimea.[2] He named it after Gaspra, a Black Sea retreat visited by writers such as Gorky and Tolstoy.[3]
Size and shape
Gaspra is an elongated, irregular body about 18 × 10 × 9 km.[2] Its surface area is about 525 km² — about the size of Guam.[3] It rotates once every 7.04 hours.[2]
Because Galileo passed at 1,600 km, Gaspra's weak gravity did not measurably bend the spacecraft's path, so its mass remains unknown.[3]
Galileo: the first close-up of an asteroid
On October 29, 1991, NASA's Galileo spacecraft, en route to Jupiter, flew within 1,600 km of Gaspra at about 8 km/s — making Gaspra the first asteroid ever visited by a spacecraft.[3][1] Galileo returned 57 images, the closest from 5,300 km, with the best showing details about 54 meters across. About 80% of the asteroid was imaged.[3]
Hitting the target was hard: before the encounter, Gaspra's position was known only to within about 200 km. The team developed a pioneering optical navigation campaign, using Galileo's own approach images to pin down where to point the camera.[3]
A young, grooved surface
Gaspra has relatively few large craters. Crater counts suggest its surface is only about 20 to 300 million years old, possibly because it formed in a relatively recent collision.[3] Its surface also shows grooves 100–300 m wide and up to 2.5 km long, likely created by impacts that fractured the underlying rock, and flat areas such as Dunne Regio.[3]
Orbit and family
Gaspra orbits in the inner main belt, between about 1.83 and 2.59 AU from the Sun, once every 3.3 years.[2] It belongs to the Flora family, one of the largest asteroid families with more than 13,000 known members — fragments of a past collision.[4]
Photographing asteroids yourself
Gaspra is too faint for casual viewing, but Galileo's achievement started with something every astrophotographer knows: carefully pointing a camera at a tiny moving target. Brighter asteroids, the Moon and the planets are all within reach of a modest camera setup. Try our astrophotography starter picker.
Read more
Galileo at Gaspra: the first close-up of an asteroid
How a Jupiter-bound spacecraft found a 12-kilometer target with pioneering optical navigation in October 1991.
Read →Ida and Dactyl: Galileo's second asteroid — and the first asteroid moon
Two years after Gaspra, Galileo flew past Ida and found something no one had confirmed before: a moon.
Read →Gaspra and the Flora family: fragments of an ancient collision
What Gaspra's young surface and grooves say about the collision that created thousands of sibling asteroids.
Read →Sources
- Galileo — NASA Science
- Small-Body Database Lookup: 951 Gaspra — NASA JPL Solar System Dynamics
- 951 Gaspra — Wikipedia
- Flora family — Wikipedia
- 243 Ida — Wikipedia
- Dactyl (moon) — Wikipedia
- Planetary Fact Sheet (orbit comparison) — NASA NSSDCA
Figures are rounded; where sources differ we note it. Spotted an error? Tell us.