Kapoeta

A howardite that fell in South Sudan in 1942 – a piece of the battered surface of the asteroid Vesta.

Key facts

Type

Achondrite (howardite, HED group)

Fell or found

Fell (witnessed)

Year

1942 (5 April)

Country

South Sudan

Mass

about 11 kg

Official name

Kapoeta

On 5 April 1942, a single stone weighing about 11 kilograms fell near the town of Kapoeta, in what is now South Sudan. It was collected and sent for study, and it soon became one of the most important meteorites of its type. Kapoeta is a howardite, and it offers a remarkable view of the surface of one of the largest asteroids in the Solar System.

What is a howardite?

Howardites are named after the English chemist Edward Charles Howard, who in 1802 helped prove that meteorites come from space. They belong to a family of meteorites called the HED meteorites: howardites, eucrites and diogenites. Eucrites are basalts, rocks formed from lava on or near the surface of their parent body. Diogenites are made mostly of the mineral orthopyroxene and formed deeper down, as crystals settled in cooling magma. Howardites are breccias, rocks made of broken fragments cemented together, that contain a mixture of eucrite and diogenite material.

The HED meteorites share very similar oxygen isotopes, the different forms of oxygen atoms, which shows that they come from the same parent body. For decades scientists have linked them with the asteroid Vesta, one of the largest bodies in the asteroid belt, because Vesta reflects light in the same way as these rocks.

A piece of Vesta's soil

Kapoeta is a special kind of howardite called a regolith breccia. Regolith is the layer of broken rock and dust covering the surface of airless bodies such as the Moon and asteroids, constantly churned by small impacts. Kapoeta contains gases implanted by the solar wind, a stream of particles flowing out from the Sun. Those gases can only be absorbed by grains lying exposed on the very surface of an airless body. Their presence shows that much of Kapoeta was once part of Vesta's surface layer.

Under a microscope its fragments range from coarse crystals of pyroxene to fine dust welded together, a texture that records the constant churning of Vesta's surface by small impacts. Kapoeta also contains dark fragments of carbonaceous chondrite material, debris from other asteroids that collided with Vesta. These fragments are like foreign pebbles mixed into Vesta's soil.

Confirmed by a spacecraft

In 2011 and 2012, NASA's Dawn spacecraft orbited Vesta and studied its surface in detail. Its instruments found that the surface is covered with a mixture of eucrite-like and diogenite-like material, just as expected from the HED meteorites. Dawn also detected dark material on Vesta, consistent with the carbonaceous debris seen in meteorites like Kapoeta. It saw an enormous impact basin near Vesta's south pole, called Rheasilvia, which is thought to have blasted out much of the material that eventually became the HED meteorites. Telescopes have also found a family of small asteroids, called vestoids, with the same surface composition as Vesta. They are fragments knocked off by impacts, and some lie on paths leading towards orbits that can deliver meteorites to Earth.

Why it matters

Kapoeta is one of the best samples of an asteroid's surface available on Earth. It allows scientists to study how impacts mix and grind up rocks on airless bodies, and how material from other asteroids is added to the mixture. It also helped confirm that meteorites in our collections can be traced back to specific worlds seen by spacecraft. Specimens are held in research collections around the world.

Kapoeta is especially fitting for this website, which shares its name with this family of meteorites. Every howardite is a fragment of Vesta's battered skin, built from the debris of countless impacts over billions of years. Holding one is the closest most of us will come to scooping up a handful of soil from another world.

Did you know?

See more

Kapoeta in the catalogue