How the moon was made l New Simulation

Our only satellite, the Moon, known to us by many names such as Luna, and Selene, has fascinated us for all of our existence. We have looked up at it and wondered about its influence on us. And we have also thought long and hard about how it came to be.

We now understand our Moon’s origin story.

The Moon and its structure

The moon orbits the Earth at an average distance of 384,400 km (238,900 mi), which is about 30 times the diameter of Earth. Ever since it has been captured by Earth’s gravity, it has been tidally locked, causing the same side of the Moon to always face Earth. The tidal locking means that the lunar day and the lunar month are the same length, at 29.5 Earth days. Our Moon also affects the Earth’s tides (along with the Sun).

It is 1.2% the mass of the Earth, with a diameter of 3,474 km (2,159 mi). This is approximately one-quarter of Earth’s. It is the largest most massive satellite in relation to its parent planet in the solar system. Overall, it is the fifth largest and most massive moon and is larger and more massive than all the known dwarf planets.

The Moon has a surface gravity of one sixth of the Earth, approximately half of Mars. After Jupiter’s moon Io, our Moon’s surface gravity is the second highest among all the moons of the solar system. Boasting a differentiated and terrestrial body, it has no significant hydrosphere, atmosphere, or magnetic field.

An astronaut jumping on the Moon, illustrating that the gravitational pull of the Moon is approximately 1/6 of Earth’s. The jumping height is limited by the EVA space suit’s weight on the Moon of about 13.6 kg (30 lb) and by the suit’s pressurization resisting the bending of the suit, as needed for jumping. NASA

The lunar surface is covered in dust and mountains and impact craters can be seen all over it, in addition to ray-like streaks. Plains of cooled magma called maria (seas) are also visible on the near side (side facing us). The maria were formed when molten lava flowed into ancient impact basins.

Moon’s internal structure: solid inner core (iron-metallic), molten outer core, hardened mantle and crust. The crust on the Moon’s near side permanently facing Earth is thinner, featuring larger areas flooded by material of the once molten mantle forming today’s lunar mare. CC BY (WIKIPEDIA)

This brightest celestial object in our night sky is always illuminated by the light from the Sun (except during a lunar eclipse, when it passes through Earth’s shadow). From Earth about 59% of the lunar surface is visible over time due to cyclical shifts in perspective (libration), making parts of the far side of the Moon visible.

Our fascination with the Moon

As mentioned before, humans have always been fascinated with this bright object in the night sky. It has been a source of inspiration and knowledge. It has been crucial to increasing our understanding of the cosmos, natural science, time-keeping and space-flight, but has also played a huge part in our mythologies, religion, art and poetry.

The Night Sky By Van Gogh (Wikipedia)

Sumerian Cylinder Seal of King Ur mom-Nammu (Wikipedia)

We first made physical contact with it on September 13, 1959, when the first human-made object to reach an extraterrestrial body, the Soviet Union’s Luna 2 impactor, arrived on the Moon. And then on July 20, 1969, humans for the first time landed on the Moon(or any extraterrestrial body), at Mare Tranquillitatis with the lander Eagle of the United States’ Apollo 11 mission.

Since then we have continued to explore our only satellite first with crewed missions and then robotically. Scientists have also been wondering about how it actually formed.

How the moon formed

Billions of years ago our planet, in the first throes of its birth was a completely different world. The theory goes that the Moon formed billion years ago, not long after Earth’s formation, from the debris thrown out by a giant impact between Earth and a Mars-sized body call Theia.

But how exactly this formation took place has remained a puzzle for decades. Most theories claim the Moon formed out of the debris of this collision, coalescing in orbit over months or years.

But now we have a new theory and a new simulation that posits that: “the Moon may have formed immediately, in a matter of hours, when material from the Earth and Theia was launched directly into orbit after the impact”.

“This opens up a whole new range of possible starting places for the Moon’s evolution,” said Jacob Kegerreis, a postdoctoral researcher at NASA’s Ames Research Center in California’s Silicon Valley, and lead author of the paper on these results published in The Astrophysical Journal Letters. “We went into this project not knowing exactly what the outcomes of these high-resolution simulations would be. So, on top of the big eye-opener that standard resolutions can give you misleading answers, it was extra exciting that the new results could include a tantalisingly Moon-like satellite in orbit.”

One thing scientists have always wondered about is why the composition of the Moon is so similar to that of Earth, which they have been able to do by analysing the composition of lunar material based on its isotopic signature, a chemical clue to how and where an object was created. This lunar material has been available ever since astronauts have brought back samples from the Moon.

According to NASA: “The lunar samples scientists have been able to study in labs show very similar isotopic signatures to rocks from Earth, unlike rocks from Mars or elsewhere in the solar system. This makes it likely that much of the material that makes up the Moon originally came from Earth.”

Previous theories posited that Theia sprayed out into orbit and mixed with a very small amount of material from Earth. This would be less likely because of the strong similarities we see in the composition of the two bodies, unless Theia was also isotopically similar to Earth.

According to NASA: “There have been other theories proposed to explain these similarities in composition, such as the synestia model – where the Moon is formed inside a swirl of vaporized rock from the collision – but these arguably struggle to explain the Moon’s current orbit.”

The new simulation puts forward a different theory, where the Moon may have formed immediately, in a matter of hours, when material from the Earth and Theia was launched directly into orbit after the impact.

According to a statement: “This faster, single-stage formation theory offers a cleaner and more elegant explanation for both these outstanding issues. It could also give new ways to find answers for other unsolved mysteries. This scenario can put the Moon into a wide orbit with an interior that isn’t fully molten, potentially explaining properties like the Moon’s tilted orbit and thin crust – making it one of the most enticing explanations for the Moon’s origins yet.”

Extremely detailed simulations were used in this new research, operating at the “highest resolution of any simulation run to study the Moon’s origins or other giant impacts. This extra computational power showed that lower-resolution simulations can miss out on important aspects of these kinds of collisions, allowing researchers to see new behaviors emerge in a way previous studies just couldn’t see.”

“The more we learn about how the Moon came to be, the more we discover about the evolution of our own Earth,” said Vincent Eke, a researcher at Durham University and a co-author on the paper. “Their histories are intertwined – and could be echoed in the stories of other planets changed by similar or very different collisions.”

See the computer simulation in this video by the researchers:

Sources: NASA Statement, and Full Study

Saima Baig

I am a Chartered Environmentalist from the Royal Society for the Environment, UK and co-owner of DoLocal Digital Marketing Agency Ltd, with a Master of Environmental Management from Yale University, an MBA in Finance, and a Bachelor of Science in Physics and Mathematics. I am passionate about science, history and environment and love to create content on these topics.