Mathilde
Key facts
- What it is
- Dark main-belt asteroid
- Size
- About 53 km across (on average)
- Discovered
- 1885, by Johann Palisa
- Spacecraft
- NEAR Shoemaker fly-by, 1997
- Orbit group
- Main-belt Asteroid
- Average distance from the Sun
- 2.65 au (about 400 million km)
- Time to go round the Sun
- 4.3 years
- Closest and farthest from the Sun
- 1.95 to 3.35 au
- Tilt of its orbit
- 6.7°
- Spins once every
- 17.4 days
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.
Mathilde is one of the darkest objects ever photographed by a spacecraft. It reflects only about 4 per cent of the sunlight that falls on it, roughly as much as fresh charcoal. NASA's NEAR Shoemaker spacecraft flew past it on 27 June 1997, on the way to the asteroid Eros, and returned the first close-up images of a dark, carbon-rich C-type asteroid.
The pictures showed a battered body about 53 kilometres across on average, with at least five craters larger than 20 kilometres. Some are so big compared with Mathilde itself that it is a puzzle how it survived the impacts without breaking apart.
The answer seems to lie in its density. The fly-by allowed Mathilde's mass to be measured, and its density came out at only about 1.3 grams per cubic centimetre, less than half that of most stony meteorites. Mathilde must be extremely porous, with perhaps half its volume made of empty space. A body like this can absorb a blow the way a sponge or a sandbag does, compacting under the impact instead of shattering. That probably explains why its craters have sharp rims and why the large impacts did not knock older craters away.
Mathilde also spins very slowly, taking about 17 days to turn once, one of the slowest rotations known.
It was discovered in 1885 by Johann Palisa and is thought to be named after the wife of a French astronomer of the time. Mathilde showed that some asteroids are not solid rocks at all, but loose, fragile bodies, a discovery that matters for understanding how asteroids respond to collisions.