Astronomers describe that the present-day tilt of the Moon is likely a result of collision-free encounters of the early Moon with small planetary bodies in the inner Solar System.
We still don’t know exactly how the Moon formed, but the generally accepted hypothesis is that it formed from debris ejected by the impact of a planet-sized object with the early Earth. However, if this were the case, the Moon should have an inclination of around 50° – whereas the present-day value is of approximately 5°. The discrepancy is huge, but now, Kaveh Pahlevan and Alessandro Morbidelli believe they have finally solved this problem.
They ran a series of simulations and found that a few millions of years after the Moon was formed, the new Earth-Moon system was highly changeable, and had optimal conditions for the ‘excitation’ of the lunar orbit through gravitational encounters. In other words, in that time, the Moon’s (and to a much lesser extent, the Earth’s) tilt was affected by gravitational interactions with other planetary bodies.
The authors suggest that while it’s not certain, there’s quite a high chance that these interactions were responsible for changing the Moon’s tilt to the angle we see today.
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