Astronomers have long been puzzled about the exact timeline of how the Moon came to be. The prevailing theory is that a Mars-sized object named Theia collided with Earth in the early Solar System, ejecting material into orbit that eventually formed into the Moon. However, determining the precise timing of this cataclysmic event has proven to be a challenge.

Recently, at the 55th annual Lunar and Planetary Science Conference (LPSC 55) in Texas, researchers proposed a new timeline that places the giant impact earlier than previously thought. According to their estimates, the collision occurred just 50 million years after the formation of the Solar System.

Pinpointing the exact age of the Moon’s formation is complicated due to conflicting evidence from various sources. One line of evidence comes from studying planetary orbits, which suggest that the collision likely happened within the first 100 million years of the Solar System’s existence. Any later than this, and the orbits of the inner planets would have been disrupted, impacting the stability of Jupiter’s trojan asteroids.

Based on these orbital observations, the best estimate for the impact falls between 37-62 million years after the Solar System’s formation. Researchers believe that the Moon would have solidified from a molten state into a solid surface within about 10 million years post-impact.

However, geological evidence seems to contradict this timeline, with the earliest known moon rocks dating back to around 208 million years. Similarly, rocks on Earth appear to have formed a crust at approximately 218 million years.

Another dating method involving the decay of Hafnium into Tungsten suggests an early formation of the Moon’s core around 50 million years after the Solar System’s birth.

The challenge lies in reconciling all these different pieces of evidence into a coherent explanation for lunar formation. At LPSC 55, researchers presented a scenario that attempts to do just that. They propose an early collision around 50 million years, followed by a cooling period lasting 10 million years. Subsequently, the Moon went through a phase of reheating before finally cooling again around the 200-million-year mark.

This reheating phase is believed to have been caused by tidal forces as the Moon’s orbit stabilizes around Earth. The theory suggests that the Moon’s inclination and eccentricity increased post-impact, leading to tidal processes that liquified the Moon. Similar processes can be observed on other moons in the Solar System.

The cooling process was likely prolonged by secondary impacts from leftover material hitting the Moon over millions of years. Additionally, new evidence in the form of Rubidium-Strontium decay measurements supports the early collision date of around 50 million years.

This research, conducted by Steven J. Desch of Arizona State University and A. P. Jackson of Towson University, offers a compelling narrative for the formation of the Moon and highlights the complexities involved in unraveling the mysteries of our celestial companion.