The origin of the Moon has been the subject of much scientific debate over the years, but recently we seem to have reached a consensus, Science alert reported.
Millions of years ago, an object the size of Mars collided with Earth, and the debris became the Moon.
The newly formed Moon slowly drifted away from Earth over the following eons. New research, however, offers some surprising nuances to the accepted theory.
According to current theory, the Moon formed about 4.5 billion years ago, shortly after the birth of the Solar System. It began with a massive collision between the early Earth and a Mars-sized protoplanet called Theia.
The impact sent debris into orbit around the Earth, which eventually coalesced to form the Moon.
There is much evidence to support this theory, most notably the composition of the Earth's mantle and lunar rocks.
Most of the debris cloud settles back to Earth, much of it forms the Moon, but some of it is ejected from the Earth-Moon system.
The paper, authored by Stephen Lepp and his team at the University of Nevada, investigates the dynamics of the material ejected from the impact.
Shortly after it was formed, the Moon orbited the Earth at a distance of about 5% of its present value (average distance – 384,400 km), but slowly, due to tidal effects between the Earth and the Moon, drifted away to its current height.
Its surface was mostly molten magma, which gradually cooled and solidified, forming the familiar crust, mantle, and core we see today.
Major eruptions were large heavy impacts on the lunar surface, forming basins and craters, and volcanic activity led to the slow formation of the lunar mantle.
The Moon's orbit around the Earth is slightly elliptical with an eccentricity of 0.0549. It is not a perfect circle and ranges from 364,397 km to 406,731 km from Earth.
The system was not as stable early in the existence of the Earth-Moon system, and particles in the growing Moon had more erratic journeys.
One of the terms that describes evolving orbits is nodal precession (where the orbital intersection points slowly move with the orbit). There are two types, and the first refers to the particles in orbit slowly precessing around the angular momentum vector of the Earth-Moon system.
The other occurs around highly eccentric binary systems when the inclination of the orbiting object is large. The particle moves in the direction of the eccentricity vector of the pair.
Considering the Earth and the orbits of particles in the debris cloud when the Moon began to form, the orbits thus described would be unstable.
The team showed that of all possible particle orbits, those in polar orbits are the most stable. They went further and showed that they existed around the Earth-Moon binary system after the formation of the Moon.
As the distance between the Earth and the Moon slowly increases due to tidal interactions, the region of space in which polar orbits can exist shrinks.
Today, when the Moon is at its current distance from Earth, stable polar orbits do not exist because the Sun-ruled procession of the node predominates.
The team concluded that the presence of material in polar orbits could stimulate the growth of a binary system like the Earth and Moon.
If a significant amount of material had reached a polar orbit, the eccentricity of the Earth-Moon system would increase. | BGNES
