When we think about the Moon, we often picture its surface—dusty plains, cratered highlands, and the dark volcanics known as maria. But some of the biggest scientific breakthroughs come not from what we see on the surface, but from what we uncover beneath it. That’s where NASA’s GRAIL mission (Gravity Recovery and Interior Laboratory) transformed our understanding of lunar history.
Looking Beneath the Surface
GRAIL used twin spacecraft flying in tandem to precisely measure variations in the Moon’s gravity field. These small gravitational wiggles reveal density variations underground—essentially giving us an X-ray of the lunar interior. For planetary scientists, it was a goldmine.
Rewriting the Lunar Timeline
But GRAIL didn’t just tell us about structure—it also helped us revisit the chronology of early lunar impacts. Traditionally, we’ve used crater counts to estimate the age of planetary surfaces. But that method has limitations, especially on bodies like the Moon, where surface processes are more complex than they appear.
By correlating gravity anomalies with surface features, we were able to propose new constraints on the timing and sequence of basin-forming impacts, shedding light on how the early Solar System evolved. This matters not only for the Moon, but for Earth too—since many of these impacts occurred during the period when life was just emerging on our planet.
Why It Matters
Understanding the Moon’s interior and impact history isn’t just a theoretical exercise. It informs how we plan lunar surface operations, where we might place landers, how we interpret seismic data, and how we model resource distribution. Subsurface structure influences everything from rover navigation to habitat safety. And on a broader scale, the Moon is a proving ground for studying planetary differentiation, magma oceans, and long-term geological evolution—processes that every rocky planet, including Earth, has undergone.
What’s Next
LunaSCOPE and institutions around the world continue to build upon GRAIL’s legacy by combining its data with topography, seismic modeling, and new orbital datasets to refine our picture of the Moon’s structure. As future NASA missions prepare for sustained surface presence, understanding these hidden layers becomes not just scientifically interesting, but operationally essential.
Further Reading & Resources:
- NASA GRAIL Mission Overview (Evans, 2023)
- Gravity Field of the Moon via GRAIL (Zuber et al., 2013)
- LPI Lunar Impact Cratering
- The fractured Moon: Production and saturation of porosity in the lunar highlands from impact cratering (Soderblom, Evans, et al., 2015)
- Identification of buried lunar impact craters from GRAIL data and implications for the nearside maria (Evans et al., 2016)
- Reexamination of Early Lunar Chronology With GRAIL Data: Terranes, Basins, and Impact Fluxes (Evans et al., 2018)
- Can the Moon’s Center of Mass–Center of Figure Offset Be Explained With a Uniform Primordial Crust? (Jones [w/ Evans] et al., 2025)
