The Challenge of Icy Sample Return Begins With Artemis

Abstract Throughout the Solar System, volatiles are found as solid ices. Returning ices to Earth for scientific analysis is critical to understanding the formation of a Solar System that bears life. This challenge begins with the Artemis missions to the lunar south polar region, where the coldest lunar regolith is enriched in H 2 O and other ices—systems with complex phase equilibria. Ignoring solution chemistry results in erroneous conclusions that—if allowed to guide Artemis sampling, transport, and curation planning—would result in irreparable damage to returned samples. Here we use the H 2 O‐NH 3 binary as a model for more complex ices. At 1 bar, H 2 O‐rich ices undergo peritectic melting at or below −95°C, changing the textural record of the ice and generating a liquid with >30% NH 3 . At lunar surface pressures, sublimation of NH 3 —and sample damage—begins at least 100 C° lower, increasing the challenge of icy sample return.