Moon rock study reshapes timeline of ancient lunar impacts

When Apollo 17 astronauts returned with lunar rock sample 76535, they unknowingly carried back a fragment that would continue to puzzle scientists for decades. The rock formed nearly 50 kilometers below the Moon's surface yet shows little evidence of the violent shocks expected from such depths.

Many researchers assumed it was excavated by the colossal impact that created the South Pole-Aitken Basin. But new research led by Lawrence Livermore National Laboratory planetary scientist Evan Bjonnes points to a different origin. Using advanced impact simulations, his team found the Serenitatis Basin impact could have gently lifted the rock to the surface during the later stages of crater formation.

This reinterpretation pushes the Serenitatis event back to about 4.25 billion years ago, roughly 300 million years earlier than previous estimates. That adjustment alters the timeline of lunar impacts and forces a recalibration of how scientists chart the bombardment history of Earth and other inner planets.

"This rock may be small, but it carries a huge story about the Moon's early history. It's like a time capsule from 4.25 billion years ago," Bjonnes said.

By showing that large impacts can raise deep material without shocking it beyond recognition, the study simplifies what had been a complicated explanation involving multiple impacts across the Moon's surface. The results suggest other basins may also be older than currently believed, reshaping how scientists view the early evolution of the solar system.

"By pushing Serenitatis back in time, we're shifting the entire timeline of when big impacts happened across the solar system," Bjonnes said. "That has ripple effects for understanding Earth's early environment too."

The research also highlights the ongoing scientific value of Apollo samples. "It's amazing that more than half a century later, Apollo samples are still revealing brand-new insights," Bjonnes said.

The findings not only refine lunar history but also provide guidance for future exploration. Astronauts investigating major basins may find similar deep-origin rocks on the surface, offering further clues to the Moon's formative years.

Research Report:Evidence for an Early Formation of Serenitatis Basin at 4.25 Ga Shifts Lunar Chronology