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Pallasites: The meteorite jewels in the crown

David Bryant (UK) Perhaps unsurprisingly (as a professional dealer in space rocks), I find all meteorites equally fascinating and, in their own way, aesthetically appealing. However, I have to admit, the meteorites known as the Pallasites, with their beautiful structure of olivine fragments suspended in a nickel-iron matrix, are probably the most visually exciting, particularly to the non-specialist. In addition to their undoubted beauty and rarity, Pallasites offer us an intriguing glimpse into the interior of a planet that make them among the most scientifically important of all meteorite types. The name Pallasite is derived from that of the German naturalist, Simon Peter Pallas. Pallas was one of those amazingly observant and gifted polymaths, who seem to have been a lot more abundant during the eighteenth century, as well as lending his name to a whole class of meteorite, an eagle, a warbler, two species of bat, a wild cat and dozens of other plants and animals. In 1772, Pallas obtained a 680kg lump of metal that had been found near Kransnojarsk in Siberia. When it was examined in St Petersburg, it was identified as a new type of stony meteorite. In keeping with tradition, it was named after the location where it was found, but, uniquely, the whole class of meteorites was named for Pallas. There is still some debate about the actual origin of Pallasites. Although some meteorologists contend that the stony-iron structure resulted from a collision between a nickel-iron asteroidal core and a chunk of mantle material … Read More

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Urban micrometeorites: A myth?

Jon Larsen (Norway) Is it possible to find micrometeorites in populated areas? The question has been raised for nearly a century and, despite numerous attempts to find them, the answer up to this day has been a very short “no”. Meanwhile, our knowledge about these amazing stones has gradually increased. There is a continuous evolutionary line in the research on micrometeorites, from the early pioneers, John Murray and Adolf Erik Nordenskiöld in the nineteenth century, to Lucien Rudaux and Harvey H Nininger. With Donald E Brownlee and Michel Maurette in the 1960s, micrometeoritics became real science. During the past two decades, this research has accelerated thanks to, among others, Susan Taylor, who extracted micrometeorites from the water well at the South Pole, Matthew Genge, who figured out the classification, and other splendid researchers, in addition to the space probes that have returned to Earth with dust samples from comets and asteroids. Today, there is a growing literature about micrometeorites, but still the answer to the initial question is “no” and urban micrometeorites have been considered an urban myth. Micrometeorites have been found in the Antarctic, but also, to some extent, in prehistoric sediments, remote deserts and in glaciers – places that are clear of the confusing anthropogenic influence. The wall of contamination has been considered insurmountable. It is therefore with pride and joy that I can report here about a project involving the systematic examination of all sorts of anthropogenic and naturally occurring spherules in an empirical search for micrometeorites … Read More

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Exploding star missing from formation of solar system

Chelsea Leu (USA) A new study, published by University of Chicago researchers challenges, the notion that the force of an exploding star forced the formation of the solar system. In this study, published online in Earth and Planetary Science Letters in November 2012, authors Haolan Tang and Nicolas Dauphas found the radioactive isotope iron 60 – the telltale sign of an exploding star – low in abundance and well mixed in solar system material. As cosmochemists, they look for remnants of stellar explosions in meteorites to help determine the conditions under which the solar system formed. Some remnants are radioactive isotopes, that is, unstable, energetic atoms that decay over time. Scientists in the past decade have found high amounts of the radioactive isotope iron 60 in early solar system materials. “If you have iron 60 in high abundance in the solar system, that’s a ‘smoking gun’ – evidence for the presence of a supernova,” Dauphas, professor in geophysical sciences, told me during a meeting in his office in October 2012. Iron 60 can only originate from a supernova, so scientists have tried to explain this apparent abundance by suggesting that a supernova occurred nearby, spreading the isotope throughout the explosion. However, Tang and Dauphas’ results were different from previous work. They discovered that levels of iron 60 were uniform and low in early solar system material. They arrived at these conclusions by testing meteorite samples. To measure iron 60’s abundance, they looked at the same materials that previous researchers had … Read More

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Lavas from Hawaiian volcano contain fingerprint of planetary formation

Dr Steve Koppes (USA) Hikers visiting the Kilauea Iki crater in Hawaii today walk along a mostly flat surface of sparsely vegetated basalt. It looks like parking lot asphalt, but, in November and December 1959, it emitted the orange glow of newly erupted lava. Now, a precision analysis of lava samples taken from the crater is giving scientists a new tool for reconstructing planetary origins. The results of the analysis, by the University of Chicago’s Nicolas Dauphas and his associates, were published in the 20 June 2008 issue of the journal Science. Fig. 1. Eruption Hill in Kilauea Iki crater on the Big Island of Hawaii. In December 1959, lava spurted 580m feet high from this location. Working with lava samples from the crater, scientists at the University of Chicago and elsewhere have devised a new tool for reconstructing planetary origins. (Photo: Steve Koppes.) The researchers selected Kilauea Iki for their study because scientists have drilled it for samples many times over the years as it cooled. This sequence of samples makes the lava lake a perfect site for studying differentiation – the separation of minerals and elements as magma cools and hardens. In particular, a close examination of iron isotopes – the slight variations the element displays at the subatomic level – can tell planetary scientists more about the formation of crust than they previously thought, according to Dauphas and co-authors, Fang-Zhen Teng of the University of Arkansas and Rosalind T Helz of the US Geological Survey. Dauphas informed … Read More

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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.