NEXT STEPS IN EXPLORING THE LUNAR MANTLE

The Apollo program was instrumental in shaping our idea of the lunar mantle, but many questions remain unanswered. For example, the narrow aperture of the Apollo passive seismic experiment did not allow the lower mantle and core to be imaged with the fidelity needed to look at heterogeneity, layering, and to define mineralogy. With the recognition of meteorites from the Moon in 1983 (ALHA81005, GRL 10, Issue 9), there are now more than 330 named stones with >25 of these being basaltic allowing a snapshot of the mantle source from which they were extracted. However, we do not know the exact location on the lunar surface where any of these originated. While the Apollo samples have some context, none were collected from in situ bedrock. So what are the next steps for exploring the lunar mantle?

Orbital missions in the 1990s and this century have now given us an unprecedented new view of the lunar surface that will allow targeted surface exploration to answer remaining and new questions about the interior of the Moon. These datasets can be used to target sampling the oldest and youngest basalts (from crater counts), as well as sampling the compositions not represented in the current collections. Maybe the most important issue is that a Lunar Geophysical Network (LGN) is a named mission in NASA’s decadal survey for the New Frontiers program and will be proposed in the next call for proposals. This network will be long-lived and global in nature and the data returned will significantly enhance data from the recent GRAIL mission.

The longevity of the 3 LGN nodes will allow others to be added thus allowing the International Lunar Network concept to finally be realized. Addition of nodes is possible through international partnerships, and with the Commercial Lunar Payload Services call from NASA there could be other ways to supplement the LGN. Such a network is also important for human exploration because shallow moonquakes have magnitudes >5 and could threaten any long-term surface assets.

The current US space policy coupled with strong international interest in the Moon affords an opportunity to explore the lunar mantle in more sophisticated ways thanks to the data from Apollo and subsequent orbital missions. The presentation will present rationale for site selection of the LGN and sample return to further our knowledge of the lunar mantle.