Scientific research in meteoritics includes the collection, identification, and classification of meteorites and the analysis of samples taken from them in a laboratory. Typical analyses include investigation of the minerals that make up the meteorite, their relative locations, orientations, and chemical compositions; analysis of isotope ratios; and radiometric dating. These techniques are used to determine the age, formation process, and subsequent history of the material forming the meteorite. This provides information on the history of the Solar System, how it formed and evolved, and the process of planet formation.
History of investigation
Before the documentation of L'Aigle it was generally believed that meteorites were a type of superstition and those who claimed to see them fall from space were lying.
In 1960 John Reynolds discovered that some meteorites have an excess of 129Xe, a result of the presence of 129I in the solar nebula.[5]
Methods of investigation
Mineralogy
The presence or absence of certain minerals is indicative of physical and chemical processes. Impacts on the parent body are recorded by impact-breccias and high-pressure mineral phases (e.g. coesite, akimotoite, majorite, ringwoodite, stishovite, wadsleyite).[6][7][8]Water bearing minerals, and samples of liquid water (e.g., Zag, Monahans) are an indicator for hydrothermal activity on the parent body (e.g. clay minerals).[9]
Radiometric dating
Radiometric methods can be used to date different stages of the history of a meteorite. Condensation from the solar nebula is recorded by calcium–aluminium-rich inclusions and chondrules. These can be dated by using radionuclides that were present in the solar nebula (e.g. 26Al/26Mg, 53Mn/53Cr, U/Pb, 129I/129Xe). After the condensed material accretes to planetesimals of sufficient size melting and differentiation take place. These processes can be dated with the U/Pb, 87Rb/87Sr,[10]147Sm/143Nd and 176Lu/176Hf methods.[11] Metallic core formation and cooling can be dated by applying the 187Re/187Os method to iron meteorites.[12][13] Large scale impact events or even the destruction of the parent body can be dated using the 39Ar/40Ar method and the 244Pu fission track method.[14] After breakup of the parent body meteoroids are exposed to cosmic radiation. The length of this exposure can be dated using the 3H/3He method, 22Na/21Ne, 81Kr/83Kr.[15][16] After impact on earth (or any other planet with sufficient cosmic ray shielding) cosmogenic radionuclides decay and can be used to date the time since the meteorite fell. Methods to date this terrestrial exposure are 36Cl, 14C, 81Kr.[17]
^A meteorite is a solid rock which has landed on Earth after originating in space. It should not be confused with a meteor (a shooting star, caused by an incoming object burning up in the Earth's atmosphere) or a meteoroid (a small body orbiting within the Solar System).
When the Journal of the Meteoritical Society and the Institute of Meteoritics of the University of New Mexico first appeared in 1953, it quoted the then accepted definition of meteoritics as the science of meteorites and meteors, but it went on to explain that meteorites at the time included what are now called meteoroids: Meteoritics may be defined independently of meteorites and meteors, however, as that branch of astronomy that is concerned with the study of the solid matter that comes to the Earth from space; of the solid bodies of subplanetary mass that lie beyond the Earth; and of the phenomena that are associated with such matter or such bodies.[1]
^ abLeonard, Frederick C. (1953). "Introducing meteoritics: The Journal of the Meteoritical Society and the Institute of Meteoritics of the University of New Mexico". Meteoritics. 1 (1): 1–4. Bibcode:1953Metic...1....1L. doi:10.1111/j.1945-5100.1953.tb01299.x.
^Hutchison, R.; Alexander, C.M.O.; barber, D.J. (30 June 1987). "The Semarkona meteorite: First recorded occurrence of smectite in an ordinary chondrite, and its implications". Geochimica et Cosmochimica Acta. 51 (7): 1875–1882. Bibcode:1987GeCoA..51.1875H. doi:10.1016/0016-7037(87)90178-5.
^Birck, J.L.; Allègre, C. J. (28 February 1978). "Chronology and chemical history of the parent body of basaltic achondrites studied by the 87Rb-87Sr method". Earth and Planetary Science Letters. 39 (1): 37–51. Bibcode:1978E&PSL..39...37B. doi:10.1016/0012-821X(78)90139-5.
^Bouvier, Audrey; Vervoort, Jeffrey D.; Patchett, P. Jonathan (31 July 2008). "The Lu–Hf and Sm–Nd isotopic composition of CHUR: Constraints from unequilibrated chondrites and implications for the bulk composition of terrestrial planets". Earth and Planetary Science Letters. 273 (1–2): 48–57. Bibcode:2008E&PSL.273...48B. doi:10.1016/j.epsl.2008.06.010.
^Bogard, D.D; Garrison, D.H; Jordan, auJ.L; Mittlefehldt, D (31 August 1990). "39Ar-40Ar dating of mesosiderites: Evidence for major parent body disruption < 4 Ga ago". Geochimica et Cosmochimica Acta. 54 (9): 2549–2564. Bibcode:1990GeCoA..54.2549B. doi:10.1016/0016-7037(90)90241-C.
^Eugster, O (31 May 1988). "Cosmic-ray production rates for 3He, 21Ne, 38Ar, 83Kr, and 126Xe in chondrites based on 81Kr-Kr exposure ages". Geochimica et Cosmochimica Acta. 52 (6): 1649–1662. Bibcode:1988GeCoA..52.1649E. doi:10.1016/0016-7037(88)90233-5.
^Nishiizumi, K.; Regnier, S.; Marti, K. (1 October 1980). "Cosmic ray exposure ages of chondrites, pre-irradiation and constancy of cosmic ray flux in the past". Earth and Planetary Science Letters. 50 (1): 156–170. Bibcode:1980E&PSL..50..156N. doi:10.1016/0012-821X(80)90126-0.
G. J. H. McCall, ed. (2006). The history of meteoritics and key meteorite collections : fireballs, falls and finds. London: Geological Society. ISBN978-1862391949.
