Shergotty

The 1865 fall in India that gave its name to the most common family of Martian meteorites.

Key facts

Type

Martian meteorite (basaltic shergottite)

Fell or found

Fell (witnessed)

Year

1865 (25 August)

Country

India (Bihar)

Mass

about 5 kg

Official name

Shergotty

On the morning of 25 August 1865, a stone fell near the town of Sherghati, in the Gaya district of what is now the state of Bihar in India. It weighed about 5 kilograms and was collected and sent for study. The town's name, spelled Shergotty in the records of the time, was given to the meteorite. More than a century later, Shergotty would lend its name to the most common family of meteorites from Mars: the shergottites.

A volcanic rock from space

Shergotty is a basaltic shergottite, a volcanic rock similar to the basalts that form from lava on Earth. It is made mainly of the mineral pyroxene, together with a glassy material called maskelynite. Maskelynite was first described in Shergotty. It forms when the mineral plagioclase feldspar is struck by an intense shock wave and turned into glass without fully melting. Its presence shows that Shergotty experienced enormous pressures, almost certainly during the impact that blasted it off Mars.

The pyroxene crystals in Shergotty are elongated and arranged in a way that suggests they grew and settled in a flowing magma, perhaps in a lava flow or a shallow intrusion beneath the surface. Under a microscope, many pyroxene crystals are zoned, with their chemistry changing from core to rim as the surrounding magma evolved.

A young age

Shergotty crystallised only about 165 to 180 million years ago, when dinosaurs were alive on Earth. Most meteorites are around 4.5 billion years old, because their parent asteroids stopped being geologically active very early. For a rock to have formed from molten lava so recently, its parent body must have been large enough to stay hot inside for billions of years. That clue, along with others, pointed scientists towards Mars.

Becoming a Martian meteorite

In the 1970s and early 1980s, scientists recognised that Shergotty, Nakhla and Chassigny shared unusual features, and they began calling them the SNC meteorites. Then gases trapped in shock-melted glass in a related shergottite from Antarctica were found to match the Martian atmosphere measured by NASA's Viking landers. The SNC meteorites were recognised as pieces of Mars. Shergotty became the type specimen for the shergottites, the largest group of Martian meteorites. Most Martian meteorites known today are shergottites, mostly found in hot deserts and Antarctica.

Shergottites come in several varieties. Basaltic shergottites like Shergotty and Zagami resemble lavas. Olivine-phyric shergottites contain large olivine crystals in a finer groundmass, and other types are rich in olivine and pyroxene that accumulated as crystals settled. Their ages vary, but many are relatively young, a few hundred million years old or less.

From India to the world

Shergotty was one of the earliest meteorites from India to be studied in detail. Specimens are held in collections in India and around the world, and the meteorite has been examined repeatedly as new techniques became available, from microscopes to modern mass spectrometers. Its chemistry and minerals have been compared with data from spacecraft and rovers studying the Martian surface.

Why it matters

Shergotty is one of the cornerstones of Martian meteorite science. It defines the most common group of Martian meteorites, it was the first meteorite in which maskelynite was described, and it is one of only a handful of Martian meteorites seen to fall. It helps scientists understand how Martian magmas formed and evolved, how Martian rocks respond to giant impacts, and how a rock can be thrown off one planet and land on another.

It is also a reminder that important meteorites can come from anywhere. A stone that fell in Bihar in 1865 turned out to be one of our best samples of a planet that humans have yet to visit.

Did you know?

See more

Shergotty in the catalogue