A recent study published in Nature suggests that the moon may be over 100 million years older than previously estimated. For decades, scientists believed the moon formed around 4.35 billion years ago after a Mars-sized object collided with early Earth. However, new findings propose an earlier formation- approximately 4.51 billion years ago with a significant "re-melting" event occurring later.
This re-melting happened as the moon drifted away from Earth, influenced by the planet's gravitational pull, which caused extreme heating and altered its surface. Lead author Francis Nimmo, a professor at the University of California, Santa Cruz, explained that this heating likely reset the lunar rocks' "clocks," obscuring the moon's true age.
"The moon rocks don't reveal when the moon was formed, but rather when this later heating event occurred," Nimmo stated.
For decades, scientists have debated the moon's age. The Apollo samples pointed to a younger moon, but other researchers questioned this timeline, arguing that the solar system likely lacked the large celestial objects needed for such a collision 4.35 billion years ago. Nimmo's findings align with the view that the moon formed earlier, helping resolve this long-standing debate.
The study also offers new insights into the age of lunar minerals like zircon, found in Apollo samples. Previously thought to have formed during the moon's creation, their much older age- about 4.5 billion years- has puzzled researchers. Nimmo's team attributes this to a process called "tidal heating," where Earth's gravity stretches and squeezes the moon's orbit, causing it to heat up dramatically.
Similar tidal heating effects are seen between Jupiter and its moons. For instance, Jupiter's moon Io experiences enough gravitational stress to heat its interior and generate magma.
Upcoming lunar missions, such as China's Chang'e 6 and NASA's Artemis program, may shed further light on the moon's history. Carsten Munker, a scientist from the University of Cologne who was not involved in the study, praised the research for bridging the gap between opposing theories on the moon's age.
"This study was written by researchers who once argued for a younger moon, but now they agree on an older age," Munker noted, adding that refining the timeline of these early solar system events is critical to understanding planetary formation.
While the difference between 4.35 billion and 4.51 billion years may seem minor, it is significant for unravelling the chaotic early days of the solar system. "The solar system evolved rapidly. Within tens of millions of years, the celestial bodies we know today took shape," Munker explained. "Pinpointing these early events is crucial to understanding the formation of the Earth-moon system and our cosmic neighbourhood."
