What is one subtle but important analytical hurdle that Earth-based science must clear when analyzing returned samples?

Answer

Identifying signatures unambiguously Martian and preserved within the rock matrix

A risk exists of terrestrial contamination during the sealing, caching, and return journey; thus, the first task upon arrival will be distinguishing genuinely Martian signatures from anything introduced during the return process.

What is one subtle but important analytical hurdle that Earth-based science must clear when analyzing returned samples?

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