A Bayesian statistical assessment of representative samples for asteroidal or meteoritical material

Abstract

Abstract-Primitive substances in asteroid and meteorite materials represent a record of early solar system evolution. To allow the study of these materials, they must be collected and transferred to the laboratory. Collection during sample return missions requires an assessment of the size of samples needed. Meteorite falls or finds must be subdivided into appropriate subsamples for analysis by successive generations of scientists. It is essential, therefore, to determine a representative mass or volume at which the collected or allocated sample is representative of the whole. For the first time, we have used a Bayesian statistical approach and a selected meteorite sample, Murchison, to identify a recommended smallest sample mass that can be used without interferences from sampling bias. Enhancing background knowledge to inform sample selection and analysis is an effective means of increasing the probability of obtaining a positive scientific outcome. The influence of the subdivision mechanism when preparing samples for distribution has also been examined. Assuming a similar size distribution of fragments to that of the Murchison meteorite, cubes can be similarly representative as fragments, but at orders of magnitude smaller sizes. We find that: (1) at all defined probabilities (90%, 95%, and 99%), nanometer-sized particles (where the axes of a three-dimensional sample are less that a nanometer in length) are never representative of the whole; (2) at the intermediate and highest defined probabilities (95% and 99%), micrometer-sized particles are never representative of the whole; and (3) for micrometer-sized samples, the only sample that is representative of the whole is a cube and then only at a 90% probability. The difference between cubes and fragments becomes less important as sample size increases and any >0.5 mm-sized sample will be representative of the whole with a probability of 99.9%. The results provide guidance for sample return mission planners and curators or advisory boards that must distribute valuable samples for analysis.

Heterogeneity within refractory organic matter from CM2 Carbonaceous Chondrites: Evidence from Raman spectroscopy

“…Meteorite organic matter has been indicated as heterogeneous below the μm scale (Carter and Sephton, 2013;Changela et al, 2018;Le Guillou et al, 2014;Vollmer et al, 2014) and this characteristic should be evident in the Raman response, reflecting differences in the primary constituents available at the time of accretion or formation, or the alteration of the meteorite organic matter. Such heterogeneity might account for the differences observed between the Raman parameters of the current study and those of the previous studies mentioned above.…”

The Albedo of Ryugu: Evidence for a High Organic Abundance, as Inferred from the Hayabusa2 Touchdown Maneuver

“…Thus, future studies should attempt to understand the applicability of different techniques to samples of differing organic abundances and compositions. An increased organic component in Ryugu samples may also mean they become more representative of the whole organic composition at smaller sample sizes (Carter and Sephton, 2013). Such a relationship between organic content and sample representativeness should be investigated to take into account the potential for higher organic contents.…”

Statistics Provide Guidance for Indigenous Organic Carbon Detection on Mars Missions

“…Bayesian statistical approaches (Bayes, 1763;Sivia and Skilling, 2006) have revealed that absolute certainty is unnecessary and in fact is impossible, that the choice of sample has an influence on statistical certainty, and that repeated measurements can change the probability of indigenous organic carbon. The utility of Bayesian statistics on the detection of organic matter in asteroid and meteorite materials has already been demonstrated (Carter and Sephton, 2013). A correct organic detection experiment for Mars will involve treating a series of measurements that have detected organic carbon with incomplete definitiveness as a single large experiment.…”