Moon contamination may complicate study of ancient ice

A JGR Planets paper reports that simulations show more than half of methane released by lunar landers can end up in permanently shadowed regions, and the median transport time from pole to pole was about 32 Earth days.

A new study in JGR Planets models how methane from lunar lander exhaust can spread across the Moon and collect in permanently shadowed regions (PSRs). The authors, Francisca Paiva and Silvio Sinibaldi of ESA's planetary protection office, examined whether that methane could contaminate ice thought to be ancient and informative about prebiotic chemistry. Their simulations tracked methane released during lander descent, including scenarios for landers such as ESA's proposed Argonaut. They found significant transport of methane into PSRs and across hemispheres in a matter of weeks to months. Key findings: - The simulation showed that more than 50% of methane released during descent eventually resided in permanently shadowed regions. - For a south-pole landing the model indicated about 42% of methane deposited in south PSRs and about 12% reaching north PSRs, showing cross-hemisphere transport. - The median modeled travel time from the south pole to the north pole was about 32 Earth days; the simulation ran for seven lunar days (roughly seven Earth months). - Very low temperatures in PSRs (down to double-digit kelvin) and adsorption to cold surface materials make PSRs likely long-term collectors of volatile organics. - Lunar ice is relatively porous and is affected by micrometeoroid "gardening," which can mix surface material deeper into ice and complicate efforts to distinguish modern contamination from ancient deposits. - The authors note that current COSPAR guidance (including category IIb requirements to list organics on missions targeting PSRs) may not fully prevent contamination of these study sites. Summary: The reported results indicate methane released by landers could introduce modern organics into PSRs and confound future chemical studies of otherwise ancient lunar ices. The authors argue planetary protection guidance should be reconsidered for missions approaching PSRs; timing and any specific policy response are undetermined at this time.