Estherville

In 1879 a meteorite half metal and half stone crashed onto the Iowa prairie – a rare mesosiderite, still a puzzle to scientists.

Key facts

Type

Stony-iron, mesosiderite

Fell or found

Fell (witnessed)

Year

1879 (10 May)

Country

United States (Iowa)

Mass

more than 300 kg in total

Official name

Estherville

On the afternoon of 10 May 1879, people in north-western Iowa heard tremendous explosions and saw a fireball streak across the sky. Near the small town of Estherville, several large masses and many smaller fragments fell onto the prairie. The largest buried itself several metres deep in the ground, leaving a hole that soon filled with water. When it was dug out, it weighed about 200 kilograms. Other large pieces and many small fragments were found nearby, bringing the total to more than 300 kilograms.

A rare stony-iron

Estherville is a mesosiderite, a rare kind of stony-iron meteorite. Mesosiderites are made of roughly equal amounts of metal and rock, but they are very different from the other stony-iron meteorites, the pallasites. In pallasites, crystals of olivine sit in a continuous framework of metal. In mesosiderites, the metal and the rock are mixed together in an irregular breccia, a rock made of broken fragments cemented together, and the rocky part is made mostly of pyroxene and plagioclase feldspar, similar to basaltic and related rocks.

The name 'mesosiderite' comes from Greek words meaning 'half iron'.

A cosmic puzzle

Mesosiderites are one of the great puzzles of meteorite science. Their rocky parts resemble the basalts and pyroxene-rich rocks of the HED meteorites, which are thought to come from the crust of a melted asteroid like Vesta. Their metal resembles material from the core of a melted asteroid. Yet in a melted asteroid, the core lies deep in the centre and the crust at the surface, so how did the two become mixed?

The leading explanation is that mesosiderites formed in a violent collision. Molten metal from the core of one asteroid may have been mixed with the crust of another body, or with the shattered crust of the same body, during a massive impact. The mixture then cooled extraordinarily slowly, perhaps buried deep within a large body. Measurements of how fast the metal cooled suggest some of the slowest cooling rates known for any meteorite. Scientists are still debating the details.

Pieces scattered by curiosity

The Estherville fall attracted enormous public interest, and newspapers across the United States reported it. Local residents collected fragments, and the large masses were dug out and sold. Pieces travelled to museums in the United States and Europe, where scientists studied them. Thousands of small fragments, many only pea-sized, were found scattered across the fields, and some were found long after the fall. Many were picked up by children and farmers in the years that followed.

Under the microscope, the rocky parts reveal fragments of pyroxene-rich and basaltic rock, much like those in howardites. Many of the small fragments were rounded metal nodules that had broken free from the stony material, while the larger masses were mixtures of metal and stone.

Why it matters

Estherville is one of only a handful of mesosiderites ever seen to fall, so it provides fresh samples of a rare and puzzling type of meteorite. Studying it helps scientists understand how asteroids collided and mixed in the early Solar System, and how core and crustal material could be brought together in a single rock. It is also one of the largest meteorite falls in the history of the United States.

The town of Estherville is proud of its meteorite, and specimens have been displayed locally. The story reminds us how a single afternoon can make a small town famous around the world.

As always, if you think you have found a meteorite, check the laws where you live, ask the landowner's permission, and contact a museum or university. Never try to cut, heat or put chemicals on a suspected meteorite.

Did you know?

See more

Estherville in the catalogue