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Meteorites and tektites

David Bryant (UK) The Solar System formed around five billion years ago from a cloud of dust and debris orbiting the Sun. By a process of accretion and remelting by electrical discharges within the dust cloud, this material condensed into spherical particles called chondrules. By collision, the chondrules fused together to form larger and larger planetesimals and these aggregated to form asteroids and the planets themselves. All the rocky planets (that is, Mercury, Venus, Earth and Mars), together with many of their satellites, show evidence of the collisions that formed them. Debris from the original formation of the Solar System is still abundant. Many tonnes fall onto the Earth every year as meteorites – perhaps as much as 300 tonnes each day. These can be broadly classified into the three types discussed below. (1) Stony meteorites (a) Chondrites are debris from the original condensation of the Solar System and are undifferentiated. That is, the various elements of the original solar cloud are all present. For this reason, they are attracted to a magnet because of the nickel-iron they contain (within more massive bodies, like asteroids and planets, the heavy elements migrated inwards to form a core). Chondrites are classified using an alphanumeric system that refers to the abundance and size of their chondrules (on a scale of 3 to 6, with 3 meaning there are abundant chondrules present and 6 meaning there are indistinct or sparse chondrules) and their iron content (referred to as either ‘L’ for low or ‘H’ … Read More

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Meteorites: A primer

Dr Kendal Martyn Meteorites have long held fascination for me – that is, they aren’t from this planet. Added “glamour” has come from recent suggestions that at least one meteorite impact on earth could be responsible for mass-extinction events, the largest “smoking gun” in evolutionary selection. Also, meteorites are the … Read More

Book review: The Tunguska Mystery, by Vladimir Rubtsov and Edward Ashpol

It appears that I was naive to assume the Tunguska explosion of 1908 had been adequately explained. It was a meteorite or, more probably, a comet that exploded above a remote area of Siberia. Wrong! This fascinating book shows that we still await an adequate scientific explanation and the jury is still out on what precisely the object was.