Cutting edge

April 23, 1999

Meteorites are fragments of history that can tell us about the beginnings of life itself

I work at the Natural History Museum, leading a team of seven scientists, including two students, who specialise in the study of meteorites, the pieces of rock and metal that originate mainly in the asteroid belt, and eventually fall to Earth from space.

It would be nice to write that each morning on my way to work I mused upon which frontier of science I would push back that day. But that would be misleading. Scientific research is often tedious and routine. But it can also be unpredictable, and nothing beats the excitement of an interesting or unexpected result from an experiment or analysis.

The purpose of my research is to study the material that is the only remnant we have from the time when the entire solar system formed from a cloud of gas and dust - the pre-solar nebula. From meteorites, we can learn about the processes that occurred as the solar system grew from this collapsing nebula and the timescales of these events. How the solar system formed, and from what starting materials, has a direct bearing on the formation of the Earth and the evolution of life.

Although meteorites are made from the same basic ingredients, each one is different, and full of surprises. Breaking a meteorite open to see the interior is a voyage of discovery. The fresh surface might reveal an unmapped CAI (calcium and aluminium-rich inclusions), a cluster of odd-looking clasts, an unexpected vein of metal. Each feature has to be examined for clues to its origin, its parent body, and back beyond to the formation of all parent bodies.

Over the past few years, my personal research interests have come to encompass our neighbouring planet, Mars. Bombardment of the Martian surface by asteroids has produced craters, and fragments of rock have been ejected into space - several of which have arrived on earth. Although we call Mars the red planet, a result of the iron oxide dust that covers the surface, Martian meteorites are not red, but greenish in colour. The Martian rocks are igneous - they have been formed at high temperatures from a melt, similar in many ways to rocks that come from volcanoes on earth. But some of the Martian rocks have been altered by water flowing across them, just like rocks in a stream-bed on our own planet. Buried within Martian meteorites are tiny clusters of evaporite minerals - the type of salts formed on Earth around rock pools when the tide goes out and sea-water evaporates. The water-lain salts are an intriguing reminder of the bodies of water that once scoured the Martian surface, possibly providing suitable havens for life.

One of the most testing aspects of studying Martian meteorites is the attempts we have made to look at organic compounds within the rocks, trying to disentangle Martian carbon compounds that might be evidence for the building blocks of Martian life, from terrestrial carbon compounds that have contaminated the rocks during their sojourn on Earth. Now I am involved with Beagle 2, an instrument on the planned Mars Express space mission, which will search for past and perhaps present-day life on Mars.

Although meteorites do not fall in Britain often - the last one fell in 1991, new meteorites are being found all the time and sent in to the museum for identification.

And of course, there is always the ultimate excitement for all meteoriticists - that an unusual meteorite might suddenly fall out of the sky and into a preferably nearby but unpopulated field, bringing with it the key to unlock the secrets of the solar system.

Monica Grady, head of petrology and meteoritics, Natural History Museum, London.

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