The tilt of the Moon's orbit has been attributed to the influence of a second Earth satellite.

According to the most widely accepted hypothesis, the Moon is the result of a collision between Earth and a hypothetical planet named after the heroine of ancient myths, Theia, who was the mother of the Moon goddess Selene. It is believed that this planet was about the size of Mars and was completely shattered upon impact. Many fragments from this collision either fell to Earth or drifted into interplanetary space, but some formed a ring around our planet, which eventually coalesced to create the Moon.

The issue with this scenario is that the original ring of debris should have been located in the plane of Earth's equator; thus, the Moon would have initially moved in that plane as well. This is a general principle: the protoplanetary disk where worlds are born, the accretion disk of a black hole, and even the galactic disk—all tend to align in the equatorial plane of their central object. This applies to planetary satellites as well. A good example is the largest moons of Jupiter: Io, Europa, Ganymede, and Callisto. They continue to orbit close to the equatorial plane of the gas giant.

Meanwhile, the Moon's orbit today, four and a half billion years after its formation, is tilted relative to Earth's equator by 18-28 degrees, accounting for oscillations. Astronomers, through calculations, look back into the distant past and see that this tilt was originally about 10 degrees, which is still significant. According to scientists, this can only occur if something intervened in the relationship between Earth and the Moon.

Previously, there was a theory suggesting that numerous planetesimals—small bodies in Earth's vicinity—could have had an impact. Recently, astrophysicist Wenshuai Liu from Henan Normal University in China proposed an unexpected hypothesis: he suspects that Earth initially had two natural satellites.

This implies three potential scenarios for the subsequent events: either the two moons merged into one to form the current Moon, or one of them drifted away, or it collided with Earth. The researcher calculated the parameters of the lunar orbit in all three scenarios and presented his findings in a paper available on the preprint server arXiv.

For the scenario involving the merging of two moons, the scientist assumed that together they would have had a mass slightly greater than that of the current Moon. According to his calculations, it would have been positioned approximately 50,000 kilometers from Earth with an orbital tilt of 15.5 degrees relative to the planet's equator.

In the other two scenarios, a significant tilt occurs if one moon had the mass of the current Moon, while the other, along with the planet, equaled the mass of today's Earth. Simulations of the dynamics of the remaining satellite's interaction with Earth indicated that over the next 40,000 years, the Moon would have drifted to about 64,000 kilometers, while its orbital tilt relative to the planet's equator would have decreased to 12 degrees. The astrophysicist emphasized that all this creates more plausible initial conditions for achieving the modern parameters of the lunar orbit.