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Celebrating the Ashdon Meteorite

Michael E Howgate One hundred years ago, a grapefruit-sized lump of rock ended its four and a half billion year long journey through space by crashing into a field in northwest Essex. To be more precise, at 1pm on Friday, 9 March 1923, Frederick Pratt, a thatcher and farm labourer, heard what he described as a loud “sissing” noise, and a couple of seconds later saw: a projectile fell about ten or fifteen yards from him, causing the earth to spout up like water” (News report in The Times newspaper, 7 June 1923). Three days later and suitably equipped, he went back to the spot with a friend and they dug up the ‘Ashdon’ meteorite. Being a sensible chap, he knocked a piece off, presumably to check that it was not just a common flint he had unearthed, and then took it to the local police station. The Saffron Walden bobbies were not interested, so he took it home to Wendens Ambo. Here, he showed it to his vicar, the Reverend Francis W Berry who, being an alumnus of Trinity College Cambridge, showed much more interest. Berry recognised the importance of Pratt’s find and purchased it from him, so that he could donate it to the Mineralogical Department of the British Museum (Natural History). The keeper of mineralogy, Dr. George T Prior, a noted expert on meteorites visited the site three months later with both Frederick Pratt and the Rev. Berry in attendance. (Prior’s description of the Ashdon meteorite appeared … Read More

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Meteorites: ‘rocks’ from space

Dr Vic Pearson (UK) Every year, thousands of tonnes of dust and rock penetrate the Earth’s atmosphere. The fiery passage of these objects produces the familiar ‘shooting star’ phenomenon, known as meteors. Much is destroyed during this descent, but some material is delivered to the Earth’s surface, either as meteorites or micrometeorites (the latter being typically less than 1mm). However, only 1% of the surviving material is large enough for identification and recovery, making meteorites and micrometeorites much sought after, both scientifically and commercially. Fig. 1. Meteors, or shooting stars, are a regular sight in our skies. Not all survive atmospheric entry but produce spectacular fireballs. (Image courtesy of A. Danielson.) Naturally, bombardment by extraterrestrial materials has been ongoing throughout Earth’s history. The early Solar System would have been a turbulent time and the young Earth was subject to much greater amounts of extraterrestrial infall than today. Our geological record contains many impact craters, and fossilised meteorites have been found in Ordovician sediments in Sweden (Schmitz et al., 2001), thought to be the result of the catastrophic break-up of an asteroid 470 million years ago. Today, it is accepted that the majority of meteorites are fragments of asteroids broken off during collisions with other extraterrestrial objects, perturbed from their orbits by the gravitational effects of Jupiter. The origins of micrometeorites are less well constrained and evidence abounds for both cometary and asteroidal origins. Types of meteorites Meteorites are generally classified as either falls or finds. Falls are those that are … Read More

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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.