Earth may have 'stolen' its Moon, new research suggests
The unique mass ratio between Earth and its single moon has long intrigued scientists, as it differs from other planets in our solar system that either have multiple moons or none at all. The prevailing theory suggests that the Moon is either a "child" or "sibling" of Earth, originating from the same material in our solar system. However, recent research by astronomers Darren Williams and Michael Zugger of Pennsylvania State University, challenges this idea.
Earth's 'adopted' child?
Williams and Zugger propose that the Moon could be an "adopted" child of Earth, born elsewhere in the solar system and later drawn in by Earth's gravitational pull. Their research indicates that terrestrial planets like Earth can gravitationally capture moons, a potential explanation for our current Earth-Moon system. This theory challenges the widely accepted Giant Impact Hypothesis, which suggests that a large object collided with Earth, creating debris that eventually formed into our planet and its moon.
Binary capture: A new perspective on Moon's origin
The astronomers introduced the concept of binary capture, where two gravitationally bound bodies pass a third body. The third body then captures one member of the pair, separating them and keeping the captured body in its orbit. This scenario has been observed in our solar system with Neptune's moon Triton, which orbits Neptune in a direction opposite to that of its other moons and at a different angle.
Moon's orbit
Williams and Zugger noted that our Moon's orbit around Earth is not as neatly aligned with the equator, as one might expect from a debris cloud origin. Their mathematical modeling suggests that an object the size of the Moon could have been captured by a body the size of Earth. The researchers' calculations indicate that Earth could have captured an even larger object, potentially the size of Mercury or Mars, although such an orbit would not have been stable.
Moon's receding rate aligns with new theory
The researchers found that an object the size of our Moon could have initially been in an elliptical orbit that gradually became more circular over time. This object would then start to drift away at a rate similar to the current receding rate of our Moon, which is approximately 3.8cm per year. However, they acknowledge that other properties like mineral and isotope similarities between Earth and its moon are more consistent with a closer relationship than their capture scenario suggests.
