What do the Moon’s newly studied Dewar region and McGetchin crater reveal about its ancient magnetic field and present-day impact geology, including how researchers identified the buried volcanic rock and estimated the field’s strength 4.2 billion years ago, why that evidence mat

The Dewar region offers evidence that the Moon had an internally generated magnetic field about 4.2 billion years ago; McGetchin shows how a single recent impact can alter lunar ground far beyond the hole it makes. The first finding probes the Moon’s early interior, while the second gives researchers a rare, dated example of impact geology in action. 12

• Dewar’s buried rock: Researchers compared orbital gravity and magnetic measurements over this far-side region rather than relying on a returned rock sample. They interpret the matching anomalies as a buried, magnetized volcanic rock body whose recorded magnetism supports an ancient lunar dynamo. The 4.2-billion-year age and inferred field strength are model-based estimates, not direct measurements of a field that still exists. The available evidence here does not establish a reliable numerical strength estimate. 34

• Why it matters: Apollo samples have yielded conflicting accounts of how strong and long-lived that field was. A large, buried source provides an independent line of evidence that a field existed, without by itself settling whether it was continuous or occasionally strong. Further measurements—and, ultimately, well-dated samples from the far side—could test the rock’s identity, age, and magnetization. 356

• McGetchin’s discovery: The impact occurred between April 11 and May 22, 2024. During a routine check of Lunar Reconnaissance Orbiter imagery in 2025, Robert Wagner noticed a bright patch with a dark halo; comparison with earlier images revealed a new crater about 222 meters wide and 43 meters deep—the largest newly formed crater identified in the solar system. The bright patch is expelled material, not the crater itself. 278

• What the cold spot adds: Thermal observations show disturbed ground around the crater is unusually cold, extending the impact’s detectable effects beyond its visible excavation. That makes McGetchin a valuable test of how an impact loosens or redistributes insulating lunar soil. Continued imaging and temperature measurements can show how that disturbed surface changes, while the ejecta and crater offer a fresh target for studying material brought up from below. The precise cause and persistence of the cold spot remain questions to test, not settled properties of all lunar soil. 29