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The Imilac meteorite: a gem as old as the solar system
At 4.5 billion years old, the Imilac meteorite dates back to the beginning of our solar system.
Dr Caroline Smith, Head of Earth Sciences Collections at the Museum, sheds light on the secrets the sparkling rock holds about the formation of our own planet.
This extraterrestrial piece is part of an ancient pallasite meteorite. It is a slice from one of the world's largest specimens of its kind.
It's thought to have been part of a much larger meteor that weighed up to 1,000 kilogrammes and exploded over the Atacama Desert in northern Chile, possibly in the fourteenth century.
Following the explosion, fragments of various sizes were scattered across a vast area of barren desert.
Not only is the meteorite beautiful, it contains information about our own planet's early history, from the very beginning of the solar system.
And at over 4.5 billion years old, it is the oldest specimen displayed in the Museum's Hintze Hall.
Molten asteroids
Pallasite meteorites like the Imilac formed in the asteroid belt, located between Mars and Jupiter. They are made up of minerals and metal, remnant materials from the first few million years of the solar system.
They formed inside asteroids at a time when planets were only just coming together.
If we cut our Earth in half, we would also see an iron and nickel core in the middle
Caroline says, 'This type of meteorite is made from iron, nickel metal and a mineral called olivine. This is a green-yellow iron - magnesium silicate - and it is really beautiful when the light shines through it.
'It formed when large bodies of rock, which we call planetesimals, were melting and crashing into each other.'
A pattern emerges
In this molten state, the heavier iron and nickel in the planetesimal sunk to the centre and formed a core. The lighter rocks rose to the upper layers, which together are called a mantle.
The traditional view is that pallasite meteorites are from where the planetesimal's core and mantle meet.
Caroline says, 'Recent studies have suggested that collisions played an important role in the formation of pallasites too. During the bustling, crowded early solar system, hit-and-run collisions could have completely disrupted the planetesimal, mixing the core and mantle materials together.'
After billions of years in the asteroid belt, other impacts fragmented the pallasite parent body, creating the meteorites that end up on Earth today.
A snapshot of our planet's formation
Rocky planets like Earth formed in the same way as those early planetesimals, but on a much larger scale. Pallasites can therefore be useful in finding out about Earth's geology.
Caroline says, ‘If we cut our Earth in half, we would also see an iron and nickel core in the middle. Around that would be the rocky mantle, and above that you would get the solid crust which is what we walk around on.
'We haven't been able to drill down into the Earth's core, but geologists, seismologists and other scientists can use pallasites as analogues for the composition and structure of our own Earth and get a good idea about its interior.'
Magnesium silicate glitters when light shines through it
Imilac on display
The Museum meteorite collection contains more than 5,000 registered samples, representing about 2,000 different meteorites (there are often multiple samples from the same meteorite).
There are 117 fragments of pallasites, representing 29 different pallasite meteorites.
Imilac alone represents 22 registered pieces in the Museum.
Unlike many other types of meteorite, this slice of Imilac is an exceptionally striking specimen. When light is shone through it, the green-yellow olivine crystals sparkle like gems.
Caroline says, 'Imilac is stunning, but it was also chosen because many meteorite examples can deteriorate in Earth's atmospheric conditions. Imilac is a very stable meteorite, so even though it'll be on display, it will still be accessible for research purposes.'
The Museum's world-renowned meteorite collection is used by both scientists based at the Museum and visiting specialists.
Caroline and her team are also working with the European Space Agency and the European Commission to advise them on curating solar system materials collected during current and upcoming space missions.
See the meteorite slice in Hintze Hall.
