Bacubirito

A long, heavy iron from the mountains of north-western Mexico, now displayed at a science centre in Culiacán.

Key facts

Type

Iron, ungrouped

Fell or found

Found

Year

1863 (first reported)

Country

Mexico (Sinaloa)

Mass

about 20 tonnes (estimated)

Official name

Bacubirito

In the hills of the state of Sinaloa in north-western Mexico, near the village of Bacubirito, lay a giant iron meteorite partly buried in the ground. It was reported to the outside world in the 1860s, and it soon became famous as one of the largest meteorites known. Today it is displayed in the city of Culiacán, the capital of Sinaloa, where visitors can walk around it and marvel at its size.

A long iron

Bacubirito is unusual in shape as well as size. It is long and somewhat flattened, more than 4 metres in length, which makes it one of the longest meteorites known. Its mass is usually estimated at around 20 tonnes, although as with many giant irons, it has never been weighed precisely. It ranks among the heaviest meteorites ever found, and it is the largest known in Mexico.

At the start of the 20th century, the American naturalist and dealer Henry Ward visited the site and had the meteorite excavated and photographed, bringing it wider attention. Photographs of people standing beside the excavated mass helped to spread its fame around the world. It remained near Bacubirito for decades before being moved, in 1959, to Culiacán. Since then it has become a symbol of the region and is now part of a science centre, where it introduces visitors to meteorites and the Solar System.

What it is made of

Bacubirito is an iron meteorite, made largely of iron-nickel metal. Most iron meteorites can be assigned to one of a small number of chemical groups, which scientists believe come from the cores of a limited number of parent asteroids. Bacubirito's chemistry does not match any of the established groups, so it is classified as ungrouped. That means it probably comes from a parent body that is otherwise not represented, or only poorly represented, in our meteorite collections.

Like other irons, Bacubirito formed when metal separated from rock inside an asteroid that had melted, sinking to form a core. The metal then cooled extremely slowly. When a slice of such metal is polished and etched in the laboratory, it typically reveals a pattern of interlocking metal crystals, the Widmanstätten pattern, that records this slow cooling over millions of years.

No crater

Like Hoba in Namibia, Bacubirito was found without an obvious crater. It probably fell long ago, and any small crater it created has been worn away or filled in by erosion and sediments. Its surface has been weathered by long exposure to air and water, giving it a rough, brownish crust. Its sheer length surprises many visitors, who expect meteorites to be small and round.

Why it matters

Bacubirito is important both scientifically and culturally. As an ungrouped iron, it adds to our knowledge of the variety of metal-rich bodies that once existed in the early Solar System. Every new chemical group or ungrouped iron suggests the existence of another parent asteroid that melted and formed a core.

As a public treasure, it inspires curiosity in thousands of visitors each year. Displays like this are a reminder that meteorites are part of our shared natural heritage, and that the largest ones are best kept where everyone can see and learn from them.

If you visit, think about the journey Bacubirito has made: from the core of a vanished asteroid, through millions of years in space, to a fiery plunge through Earth's atmosphere, a long rest in the Sinaloan hills, and finally a place in a modern science centre.

As always, if you think you have found a meteorite, check local laws and talk to a museum or university. Large finds in particular may be protected as national heritage.

Did you know?

See more

Bacubirito in the catalogue