Study Suggests Earth Had Several Hidden Moons Billions of Years Ago

The Earth-Moon system as we know it was formed approximately 4.5 billion years ago when a protoplanet named Theia collided with the young Earth, which was only about 100 million years old at the time. This colossal impact expelled a vast amount of debris. Some of this debris returned to Earth, while the remainder coalesced to form our Moon. Over the years, scientists have intensely studied this event and its repercussions, even identifying potential remnants of Theia within Earth’s mantle. Some researchers suggest that the Moon may have formed in just a few hours.

Recent research from the University of Nevada proposes that the aftermath of the Theia collision may have produced not just one Moon, but multiple moons. These findings, available on the non-peer-reviewed preprint server arXiv, indicate that various small moons—termed polar moons or circumbinary particles—existed temporarily. According to the scientists, these moons could exist because the newly formed Moon was much closer to Earth at the time. Initially, the Moon was about 238,900 miles away on average, only five percent of its current distance from Earth.

The study explains, “Circumbinary orbits that are polar or highly inclined to the Earth-Moon orbit are subject to two competing effects: nodal precession about the Earth-Moon eccentricity vector and Kozai-Lidov oscillations of eccentricity and inclination driven by the Sun.”

The researchers found that, while stable polar orbits do not exist around the current Earth-Moon distance, they were stable right after the Moon’s formation when a significant amount of debris surrounded the system.

Nodal precession refers to the slow change in a body’s orbital parameters around the angular momentum vector. Kozai-Lidov oscillations describe the variations in eccentricity and inclination in a binary system due to a distant third body. Factoring in these dynamics, the study concluded that polar region particles were the most stable, closely related to the Moon’s initial proximity to Earth. As time passed, the Moon began to move away from Earth due to tidal forces.

The study posits, “If a significant mass of material ended up on polar or librating orbits, then the eccentricity of the Earth-Moon binary could have been increased as a result of its interaction.”

This new theory provides valuable insights into the formation of the Earth-Moon system and could aid scientists in understanding exoplanets beyond our solar system.