Nakhla

The 1911 Egyptian fall that gave its name to a whole family of Martian meteorites – and a story about a very unlucky dog.

Key facts

Type

Martian meteorite (nakhlite)

Fell or found

Fell (witnessed)

Year

1911 (28 June)

Country

Egypt

Mass

about 10 kg, in some 40 stones

Official name

Nakhla

On the morning of 28 June 1911, villagers near El Nakhla el Baharia, in the Abu Hommos district east of Alexandria in northern Egypt, heard explosions and saw a column of white smoke in the sky. Stones began to fall over the fields. Around 40 were collected, ranging from a few tens of grams to nearly two kilograms, with a total mass of about 10 kilograms. They looked ordinary enough at first: greenish grey inside, with a glossy black crust. Yet Nakhla would turn out to be one of the most scientifically important meteorites ever to fall.

The legend of the dog

A farmer from the nearby village of Denshal reported that one of the stones had struck and killed a dog, leaving it, in his words, like ashes. The story has been repeated many times, and Nakhla is sometimes called the meteorite that killed a dog. No remains were ever found and nobody was able to confirm the report, so it is best treated as an intriguing but unverified tale.

From Egypt to Mars

For decades Nakhla was simply regarded as an unusual achondrite, a stony meteorite that had melted and crystallised like a volcanic rock. Its youthful age puzzled scientists. Most achondrites crystallised about 4.5 billion years ago, shortly after the Solar System formed, but Nakhla crystallised from molten rock only about 1.3 billion years ago. Small asteroids should have cooled and stopped volcanic activity long before then, so where could such a young volcanic rock have come from?

In the late 1970s and early 1980s the answer emerged. Nakhla was grouped with two other unusual meteorites, Shergotty and Chassigny, into the so-called SNC meteorites. Then gases trapped inside a related Antarctic meteorite were found to match, almost exactly, the Martian atmosphere measured by NASA's Viking landers in 1976. The conclusion was remarkable: these meteorites had been knocked off Mars by asteroid impacts. Nakhla became the type specimen, the official reference example, of the nakhlites, one of the main groups of Martian meteorites.

A rock shaped by Martian water

Nakhla is made mainly of green crystals of the mineral augite, a type of pyroxene, along with olivine, set in a fine-grained matrix. It formed in a thick lava flow or shallow intrusion, where crystals settled out of the cooling melt. Its olivine crystals are crossed by thin veins of reddish-brown iddingsite, a mixture of clays, iron oxides and salts. Studies show that these were formed on Mars by liquid water flowing through the rock, long after it crystallised. Nakhla therefore preserves direct evidence that water was active below the Martian surface relatively recently in the planet's history.

Like other Martian meteorites, Nakhla was launched into space by an impact. Measurements of the effects of cosmic rays show that it spent around 11 million years travelling through space before falling in Egypt. All the known nakhlites, now dozens of stones, seem to have been ejected by the same impact, which suggests they come from one area of Mars.

Why it matters

Nakhla is one of only a few Martian meteorites seen to fall, which means it reached scientists quickly with little contamination from Earth. It is one of the most studied rocks from another planet, examined for its minerals, its water-formed salts and clays, and its organic carbon. Specimens are held by museums including the Natural History Museum in London and the Egyptian Geological Museum in Cairo, and new instruments are still revealing fresh details in samples collected more than a century ago.

It is a powerful reminder that a handful of dark stones collected by farmers in 1911 contained a message from another world, waiting decades for science to be able to read it.

Did you know?

See more

Nakhla in the catalogue