Contaminants, including ink, detected in meteorites suggest sample preparation needs improving

The IBeA group of the EHU-University of the Basque Country is proposing new measures to safeguard the purity of extraterrestrial samples. Several contaminants, including traces of ink, originating in the preparation of subsamples, have been identified in Martian meteorites by the EHU’s research group. The finding highlights the importance of stricter protocols to prevent misinterpretations of the composition of these rocks and to ensure the reliability of future studies and Mars sample-return missions. The research is published in the journal Applied Geochemistry.

The study of meteorites is important for planetary science because, among other things, information may be forthcoming about the geochemical composition of the celestial body from which they originated. Since 2014, the EHU’s IBeA group has been working with NASA in this field, thanks to a collaboration agreement with the Johnson Space Center (JSC) through which “they lend us meteorites for various studies,” as the researcher Leire Coloma pointed out. In addition, the research group, which specializes in analytical chemistry and is led by Professor Juan Manuel Madariaga, has its own collection of meteorites.

In the realm of extraterrestrial materials research, the EHU team is involved, among other things, “in analyzing meteorites to determine their chemical and mineralogical composition, and, thus, in furthering progress to determine the composition of Mars or the moon,” said Coloma.

“These rocky fragments arrive on Earth as a mass of rock: when they pass through Earth’s atmosphere, and in the course of various processes, they undergo changes—usually caused by high temperatures and pressures—which generally result in a sort of crust forming on them. This outer layer is therefore altered and means we cannot determine its original mineralogical composition with any certainty.”

So subsamples often need to be prepared in order to study the internal regions of these meteorites. “During this cutting and polishing process, and depending on the technique to be used in the analysis, various tools, equipment, solvents, lubricants and materials are employed; these may contain contaminants that cannot always be completely removed and may prevent accurate characterization.”

“The introduction and use of certain external compounds during sample preparation could lead to incorrect characterization, as it would be unclear whether the minerals detected are the result of contamination or whether they are indeed original components of the meteorites,” explained the IBeA group researcher. In this context, Coloma analyzed several Martian meteorites with the aim of identifying the contaminants introduced during the sample preparation process.

Remedial actions

Raman spectroscopy, one of the techniques used in the laboratory to analyze extraterrestrial samples, was used in the study to detect the residues. The contaminants identified in the samples analyzed fall into two categories: those formed during the sample preparation process (such as diamond fragments used to cut and polish the samples) and those resulting from the handling process (such as blue ink from various sources).

Having cross-checked the identified contaminants against the protocol used during the initial analysis, the IBeA group proposed a series of remedial actions “to reduce or minimize contamination of this type in future samples. This can be achieved by substituting specific solvents or materials used in the process. Through our work, we are aiming to improve the protocols for preparing subsamples for analysis, as it is essential to work in the laboratory in such a way as to avoid introducing any kind of contaminant into the samples.”

Setting up a robust protocol for preparing subsamples is also essential for future sample-return missions, in which the ability to prepare uncontaminated subsamples upon arrival on Earth will be crucial for conducting reliable, accurate scientific research.

Right now, the Perseverance rover of the Mars 2020 mission “is collecting samples from the surface of Mars, which will hopefully reach Earth eventually. The IBeA group is one of the laboratories in the running to receive these return samples from Mars. It is therefore hugely important to have the best possible protocol in place to minimize the introduction of contaminants. Meanwhile, we continue to analyze meteorites to help identify contaminants and improve the process of preparing subsamples,” concluded Coloma.