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McCall's World

Tracked from space to Sudan!

Geoscientist 21.04 May 2011

The Almahata Sitta meteorite #15 in situ on the desert floor during its find on 8 December2008, much as it fell on October 7 earlier that year. Photo: P Jenniskens, SETI Institute.The observed approach of a small asteroid in October 2006 was followed by its recovery in Sudan, where calculations had predicted it would fall. Parties from the University of Khartoum recovered numerous small pieces, including complete fusion-cust coated oriented samples.

The meteorite was essentially an ureilite breccia (a rare achondrite); but there were numerous chondritic inclusions, of H5 and H4 and various EH and EL classes, also a unique chondrite akin to the R chondrites. Thus we not only had the first case of an asteroid observed in space, linked to a material find on the ground (which may now allow correlation of meteorite class to a known asteroid spectral group), but the first observed fall of a brecciated ureilite. The meteorite was named Almahatta Sitta (“Station Six”). All the pieces contained short-lived cosmic isotopes, which mean that they were newly arrived on Earth, so there was no mixing with any earlier meteoritic debris.

This event, in my view, ranks with the Shoemaker-Levy comet strike on Jupiter in importance. An entire issue of Meteoritics and Planetary Science has been devoted to 21 papers on it.

  • Reference: Meteoritcs and Planetary Science 45 (10-11); 1553-1885 with introduction by P Jenniskens and M H Dhaddad 1553-1556.

Young BC Volcanoes pose threat

Mt Baker. USGSCanada is not a country one associates with excitement and certainly not of the volcano kind, but my niece on Vancouver Island sends me BC Magazine, where I was surprised to read that BC possesses 280 ‘young volcanoes’ (active during the last 1.8Ma), 49 of which have erupted in the last 10,000 years. The last major eruption, from Mt Meager, occurred a mere 2400 years ago. Molten flows from Lava Fork in the extreme north flowed into Alaska only 150 yrs ago, and swarms of microseisms near Quesnel, alerted volcanologists three years ago, though nothing happened. One is familiar with the huge Mts Rainier and Baker, twins of Mt St Helens, snowily looming just over the US border. The Pacific ‘ring of fire’ is quite active in the USA and even more active in Alaska to the North, but although BC appears somnolent, its numerous dormant volcanoes could return to activity at any time.
  • Reference: Pynn, L 2010: Sleeping giants: volcanoes are all around us. British Columbia Magazine 52(2); 38-49.

Bounce rock

JMcCThe unusual ‘SNC’ ("snick") meteorites come from a planet rather than an asteroid, and Mars has been the accepted source (though meteorites splashed off Mercury, the only other possible rocky planet source, will have reached Earth, but are unrecognised). Hitherto, however, there has been no correlation between rocks analysed on the Martian surface and SNC meteorites.

However, the rover Opportunity has encountered a rock, named ‘Bounce Rock’, on the surface of Meridiani Planum, taken images with the Panoramic Camera, and obtained spectra with its thermal emission spectrometer. These revealed a Mössbauer spectrum indicating pyroxene-rich mineralogy. Using the alpha-particle X-ray spectrometer, the rock’s bulk chemistry is now also known1. Textural, mineralogical and chemical properties are similar to those of basaltic shergottite (SNC) meteorites which fall to Earth: in particular, Elephant Moraine (EET) 79001 and Queen Alexandra Range (QUE) 94201, from Antarctica. Only chrlorine, iron and titanium exhibit deviations. The iron:manganese and phosphorus concentrations matched.

Bounce Rock is thought to have been ejected by impact from the 19.3km-diameter Bopalu crater, 75km away. This is the first time a match has been found between a rock on the surface of Mars and an SNC meteorite.
  • Reference: 1. Zipfel, J, Schröder, B L, Jolliff, R et al. 2011. Bounce Rock –A shergottite-like basalt encountered at Meridiani Planum, Mars. Meteoritics & Planetary Science 46(1); 1-20.