Joe McCall reports on an important conference on those starry messengers, the meteorites... and other stuff
Geoscientist 17.9 September2007
“In Nature’s infinite book of secrecy, a little I can read”
Shakespeare
The Meteoritical Society held its latest meeting, MetSoc69, at ETH in Zurich. Nowadays, research in these areas is largely a matter of remote sensing, hence largely instrumental and of ever increasing diversity and accuracy. However the deductions drawn about the asteroids and planets are to a degree, inevitably more speculative than they might have been in days gone by. The meeting however displayed the amazing range of this fascinating field, from which I have selected a few highlights.
Yorkshire terror
In 2005 a rare pallasite stony-iron was discovered in Yorkshire
1 (Figure 1). was unusually sulphur rich, the high troilite content adding to our knowledge of core formation in the pallasite parent body. The metal-rich regions are consistent with the view of Scott
2 that pallasites formed by injection of metallic liquid into dunite, composed largely of olivine.
Meteorites and asteroids
A major concern in meteoritic research is to match the various types of meteorite to visible asteroids. One method is to work from petrological, mineralogical and other instrumental studies in the laboratory and so build up a picture of the asteroidal parent body - which may not now exist.
A second, quite different approach is to use cameras and reliable observer reports to define the orbital characteristics of fireballs from which meteoroids are recovered – and hence to find the source of the particular meteorite type. Until quite recently only three or four such orbits had been determined but a fall of an L6 type ordinary chondrite in January 2000(Villalbeto de la Peña, Spain - Figures 2, 3) became the ninth such case
4. All nine orbits determined indicate a source in the Main Asteroid Belt and the meteorites include both chondrites and achondrites. Phil Bland of Imperial College and associates
5 have set up a camera network and search-and-recovery parties on the Nullarbor Plain, Western Australia and already have defined one fireball orbit, though without recovering any material (it may have been of very small mass).
Gaffey
6 recounted how asteroid spectral studies had been initiated in the early 1970s to identify specific parent bodies of meteorites, in order to place the compositional, temporal and genetic data from meteorite studies into a spatial context within the early solar system. Naively, it was then supposed that asteroid-meteorite linkages would quickly reveal themselves. The identification of 4-Vesta as the likely parent body of the HED (howardite, eucrite, diogenite) achondrite differentiated meteorites encouraged this belief. However, the failure to identify other matches, and of several proposed matches under close scrutiny, have squashed this unfounded optimism. Three decades later only four likely parent bodies have been identified – for HEDs, H-chondrites, IIE irons and aubrite achondrites. Advances in meteoritic science have since revealed that the early models that ruled our thinking in those days were over simplistic.
Shot stars
In 2003 Birger Schmitz described the find of fossil L-Chondrite meteorites embedded in Middle Ordovician (~ 470 Ma) limestones in southern Sweden
7. The flux of meteorites to Earth was two orders higher then than now, a fact attributed to a collision of parent bodies somewhere in space. Schmitz updated the story
8 , reporting on the discovery of extraterrestrial chromite [with higher TiO
2, Cr/(Cr+Al) and a narrow range of V
2O
5] in the limestone. This has also been recognised in the resurge deposits of the Lockne impact structure in Central Sweden, with which this event is now coupled.