Author's personal copy Chemie der Erde 68 (2008) 1–29 INVITED REVIEW The significance of meteorite density and porosity G.J. Consolmagno a,Ã , D.T. Britt b , R.J. Macke b a Specola Vaticana, V-00120 Vatican City State, Holy See (Vatican City State) b Department of Physics, University of Central Florida, Orlando, FL 32816-2385, USA Received 3 December 2007; accepted 15 January 2008 Abstract Non-destructive, non-contaminating, and relatively simple procedures can be used to measure the bulk density, grain density, and porosity of meteorites. Most stony meteorites show a relatively narrow range of densities, but differences within this range can be useful indicators of the abundance and oxidation state of iron and the presence or absence of volatiles. Typically, ordinary chondrites have a porosity of just under 10%, while most carbonaceous chondrites (with notable exceptions) are more than 20% porous. Such measurements provide important clues to the nature of the physical processes that formed and evolved both the meteorites themselves and their parent bodies. When compared with the densities of small solar system bodies, one can deduce the nature of asteroid and comet interiors, which in turn reflect the accretional and collisional environment of the early solar system. r 2008 Elsevier GmbH. All rights reserved. Keywords: Asteroids; Density; Meteorites; Porosity; Solar nebula; Trans-Neptunian objects 1. The study of meteorite density and porosity 1.1. Introduction On Earth, a geologist can take samples in situ, recognizing the stratigraphic relationship between neighboring samples, and then measure the chemical and physical properties of those samples in the lab. For studying the solar system, an analog of a stratigraphic sequence can be found in the compositions and orbital locations of small solar system bodies, which represent the relatively unprocessed material from which the major planets were formed. There are two major sources of information on the compositional diversity of the small bodies of the solar system: remote information from telescopic observations of asteroid, comet, and Trans-Neptunian object (TNO) mineralogy, and direct samples of meteorites that have fallen from the asteroid belt onto Earth, and into our labs. The 44 compositional types, subtypes, and meta- morphic grades of meteorites represent an invaluable resource of ‘‘free’’ geological material from asteroids that sample their mineralogy, geochemistry, and small- scale structure as well as textural and isotopic evidence of their origin and evolution. Their chemical study has been going on with a remarkable intensity since the Apollo era, coinciding with the development of highly precise devices such as scanning electron microscopes (SEMs)/microprobes and mass spectrometers, which have allowed ever finer measurements of chemical and isotopic compositions to be made at ever higher resolution on ever tinier samples. But until recently, the measurement of the physical properties of these samples has not been pursued with the same vigor. Here ARTICLE IN PRESS www.elsevier.de/chemer 0009-2819/$ - see front matter r 2008 Elsevier GmbH. All rights reserved. doi:10.1016/j.chemer.2008.01.003 Ã Corresponding author. Tel.: +39 06 6988 5266; fax: +39 06 6988 4671. E-mail address: gjc@specola.va (G.J. Consolmagno).