Muonionalusta

An iron meteorite from Arctic Sweden that fell long before the last ice age – and was carried by glaciers before anyone found it.

Key facts

Type

Iron, IVA (fine octahedrite)

Fell or found

Found

Year

1906 (first discovery)

Country

Sweden

Mass

many masses found in glacial deposits

Official name

Muonionalusta

In the far north of Sweden, close to the Muonio River that forms the border with Finland, lies a landscape of forests, bogs and gravel ridges left behind by the ice sheets of the last ice age. In 1906 the first pieces of an iron meteorite were found there, near the village of Kitkiöjärvi. Since then many more masses have been discovered in the area. The meteorite, called Muonionalusta, has become famous for its beautiful crystal pattern and for having one of the longest histories on Earth of any known meteorite.

A meteorite and the ice

Muonionalusta did not fall recently. Measurements of how long its pieces have been shielded from cosmic rays since landing indicate that it fell to Earth roughly a million years ago. Since then, northern Scandinavia has been covered by great ice sheets several times. The moving ice picked up the meteorite fragments, carried them along and dumped them in deposits of glacial debris called till and in gravel ridges. Many Muonionalusta masses have therefore been found buried in glacial material rather than in a strewn field on the surface. This makes it one of the very few meteorites known to have survived several ice ages, and its time on Earth is one of the longest known for any meteorite.

How could iron survive so long without rusting away? The cold climate, the protection of the surrounding sediments and the meteorite's chemistry seem to have slowed corrosion, although many masses do have a weathered outer layer.

A beautiful pattern

Muonionalusta is an iron meteorite of the IVA group. Like other irons, it is thought to come from the metal core of an asteroid that melted early in the Solar System's history. When a polished slice is etched in a laboratory, it reveals a striking Widmanstätten pattern: thin, interlocking plates of nickel-poor kamacite and nickel-rich taenite crossing at precise angles. In Muonionalusta the plates are narrow, so it is classed as a fine octahedrite. Because it is so attractive, slices of Muonionalusta are widely used for jewellery, watch dials and decorative objects.

Etching uses acids and is professional or adult laboratory work. Children should never cut, heat or put chemicals on any rock they think might be a meteorite.

An ancient clock

Muonionalusta is also important for dating the early Solar System. Scientists have measured lead isotopes in its iron sulphide inclusions and found that the metal crystallised about 4.565 billion years ago, only a couple of million years after the Solar System's first solids formed. That makes it one of the oldest iron meteorites to have been precisely dated. It shows that some asteroids melted, formed metal cores and cooled extremely early in Solar System history.

Hunting in the forest

In recent decades, meteorite hunters have recovered many more masses of Muonionalusta using metal detectors, working in a landscape where the meteorite lies hidden under moss, soil and gravel. Some masses weigh hundreds of kilograms. In Sweden, as elsewhere, laws and landowners' rights must be respected, and significant finds should be reported.

Why it matters

Muonionalusta combines a beautiful iron structure, a remarkably early formation age, and an unusually long stay on Earth. It shows that meteorites can be preserved for very long periods in the right conditions, moved around by glaciers and still recognised. It also reminds us that some meteorites found today fell long before modern humans lived in Europe.

When you see a ring or watch dial with a shimmering silvery lattice, remember that it might have travelled from an asteroid core to the Arctic and then ridden the ice before ending up in your hand.

Did you know?

See more

Muonionalusta in the catalogue