Murchison meteorite

The Murchison meteorite is named after the place it fell: Murchison, Victoria, Australia. It is large (over 100 kg) and it was seen falling. It is one of the most studied meteorites, since it belongs to a group of meteorites rich in organic compounds, known as carbonaceous chondrites.

The Murchison meteorite

On 28 September 1969 at about 10:58 am, a bright fireball was seen. It separated into three fragments before disappearing, leaving a cloud of smoke.[1] About 30 seconds later, a tremor was heard. People found fragments over an area larger than 13 km², with fragments up to 7 kg. One, weighing 680 g, broke through a roof and fell in hay.[1] The mass is over 100 kg.

The biochemistry

This type of meteorite is rich in carbon.[2] Murchison contains over 15 amino acids.[3] The amino acids found in the Murchison meteorite can be (and have been) synthesised in laboratory experiments. This was done by the action of electric discharge on a mixture of methane, nitrogen, and water with traces of ammonia.[3]

The amino acids were mostly racemic. This means the chirality of their enantiomers are almost equally left- and right-handed. This suggests they are not caused by terrestrial contamination. A complex mixture of alkanes was isolated as well, similar to that found in the Miller-Urey experiment. Serine and threonine, often earthly contaminants, were absent from the samples.

In 1997 research showed that individual amino-acids from Murchison were enriched in the nitrogen isotope 15N relative to their terrestrial counterparts. This confirmed an extraterrestrial source.[4] The organic materials identified included sugar-like compounds (polyols).[5]

Compound class[6]Concentration (ppm)
Amino acids17-60
Aliphatic hydrocarbons>35
Aromatic hydrocarbons3319
Fullerenes>100
Carboxylic acids>300
Hydrocarboxylic acids15
Purines and pyrimidines1.3
Alcohols11
Sulphonic acids68
Phosphonic acids2

Several lines of evidence show that the inside of well-preserved fragments from Murchison are pristine (not contaminated). A 2010 study identified 14,000 molecular compounds (including 70 amino acids) in a sample of the meteorite.[7][8] There may be 50,000 or more different molecular compositions in the meteorite.[9]

Nucleobases

Measured purine and pyrimidine compounds are in the Murchison meteorite. Carbon isotope ratios for uracil and xanthine show a non-terrestrial origin for these compounds. The results show many organic compounds which are components of life on Earth were already present in the early Solar System. They may have played a role in life's origin.[10]

References
  1. The Meteorite Society database
  2. Planetary science research discoveries: glossary
  3. Nonprotein amino acids from spark discharges and their comparison with the Murchison Meteorite amino acids. Kvenvolden K. et al 1972. Proc. Nat. Acad. Sci. USA 69, 4, 809-811.
  4. Engel, Michael H. & Macko S.A. 1997 (1997). "Isotopic evidence for extraterrestrial non-racemic amino acids in the Murchison meteorite". Nature. 389 (6648): 265–268. Bibcode:1997Natur.389..265E. doi:10.1038/38460. PMID 9305838. S2CID 4411982.{{cite journal}}: CS1 maint: numeric names: authors list (link)
  5. Cooper, George; et al. (2001). "Carbonaceous meteorites as a source of sugar-related organic compounds for the early Earth". Nature. 414 (6866): 879–883. Bibcode:2001Natur.414..879C. doi:10.1038/414879a. PMID 11780054. S2CID 199294.
  6. Pavel, Machalek 2007. "Organic molecules in comets and meteorites and life on Earth. Department of Physics and Astronomy, Johns Hopkins University" (PDF). Retrieved 2008-10-07. {{cite journal}}: Cite journal requires |journal= (help)CS1 maint: numeric names: authors list (link)
  7. Doreen Walton (2010). "Space rock contains organic molecular feast". BBC News. Retrieved 2010-02-15.
  8. Schmitt-Kopplin, Philippe; et al. (2009-12-28). "High molecular diversity of extraterrestrial organic matter in Murchison meteorite revealed 40 years after its fall". PNAS. 107 (7): 2763–2768. Bibcode:2010PNAS..107.2763S. doi:10.1073/pnas.0912157107. PMC 2840304. PMID 20160129.
  9. Matson, John (2010). "Meteorite that fell in 1969 still revealing secrets of the early Solar System". Scientific American. Retrieved 2010-02-15.
  10. Martins, Zita et al 2008 (2008). "Extraterrestrial nucleobases in the Murchison meteorite" (PDF). Earth and Planetary Science Letters. 270 (1–2): 130. arXiv:0806.2286. Bibcode:2008E&PSL.270..130M. doi:10.1016/j.epsl.2008.03.026. S2CID 14309508. Archived from the original (PDF) on 2011-08-10. Retrieved 2008-10-07.{{cite journal}}: CS1 maint: numeric names: authors list (link)
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