Compositional differences between meteorites and near-Earth asteroids

Abstract

Understanding the nature and origin of the asteroid population in Earth's vicinity (near-Earth asteroids, and its subset of potentially hazardous asteroids) is a matter of both scientific interest and practical importance. It is generally expected that the compositions of the asteroids that are most likely to hit Earth should reflect those of the most common meteorites. Here we report that most near-Earth asteroids (including the potentially hazardous subset) have spectral properties quantitatively similar to the class of meteorites known as LL chondrites. The prominent Flora family in the inner part of the asteroid belt shares the same spectral properties, suggesting that it is a dominant source of near-Earth asteroids. The observed similarity of near-Earth asteroids to LL chondrites is, however, surprising, as this meteorite class is relatively rare ( approximately 8 per cent of all meteorite falls). One possible explanation is the role of a size-dependent process, such as the Yarkovsky effect, in transporting material from the main belt.

Surface composition and taxonomic classification of a group of near-Earth and Mars-crossing asteroids

“…Thus, establishing links between the spectral properties of NEAs and those measured in the laboratory for meteorite samples is fundamental to determine their possible parent bodies (Burbine et al, 2002;Binzel et al, 2002). Recent studies show that about 2/3 of the observed NEAs have surface compositions consistent with LL chondrites, which represent only about 10% of the ordinary chondrites falls (Vernazza et al, 2008;de León et al, 2010;Dunn et al, 2013). These results contradict the general assumption that the spectral characteristics of the most common type of NEAs should be consistent with those of the most common meteorites to fall on Earth.…”

“…This degree of thermal metamorphism indicates that the parent body where Itokawa originated must have had a diameter larger than 20 km, necessary to reach temperatures of ∼ 800 o C that can explain the range of petrologic types observed among the Itokawa particles . LL ordinary chondrites have been linked to the Flora family (Vernazza et al, 2008), which is located in the inner part of the main belt near the ν 6 secular resonance. Although the derived silicate compositions of 241662 (2000 KO44) and19764 (2000 NF5) are consistent with that of LL ordinary chondrites, we noticed that their olivine abundances (66%) are lower than the ranges found by Vernazza et al (2008) for LL chondrites (70-85%), and members of the Flora family (76-82%).…”

“…LL ordinary chondrites have been linked to the Flora family (Vernazza et al, 2008), which is located in the inner part of the main belt near the ν 6 secular resonance. Although the derived silicate compositions of 241662 (2000 KO44) and19764 (2000 NF5) are consistent with that of LL ordinary chondrites, we noticed that their olivine abundances (66%) are lower than the ranges found by Vernazza et al (2008) for LL chondrites (70-85%), and members of the Flora family (76-82%). However, this discrepancy could be explained by the fact that Vernazza et al (2008) used a radiative transfer model (Shkuratov et al, 1999) to calculate the ol/(ol + px) ratios, while we used empirical spectral calibrations derived from the analysis of ordinary chondrites.…”

Spectral properties of the largest asteroids associated with Taurid Complex

“…Experiments in the laboratory with meteorite samples found that reflectance spectra are darker and bluer for coarser grain sizes, supporting their hypothesis. Vernazza et al (2008) made a histogram of the ol ol+px ratios of 57 ordinary chondrites. This histogram has a peak around 0.65 which corresponds to OC-L meteorites that are in contrast with a similar histogram of 38 NEAs belonging to the S-complex, which has a peak around 0.8.…”

Re-assessing the ordinary chondrites paradox

“…Based on the position of the 1 and 2a µm bands and on the band area ratio, and using calibrations derived from laboratory measurements of meteorites, the authors conclude that 25% of their sample were compatible with the OC mineralogy. Vernazza et al (2007) use a sample of 150 spectra of S-complex asteroids from 0.4 to 2.5 µm (but with the visible and NIR portions obtained at different occasions) to investigate this issue. The authors use Shkuratov et al (1999) radiative transfer model, the Brunetto et al (2006) space weathering model, and optical constants derived from the work of Lucey (1998) in their analysis.…”