Why is the moon so big compared to the earth?

L'une des spécificités de la Lune est d'être particulièrement grosse par rapport à la Terre. © Studio-FI, Adobe Stock

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In the solar system, the earth has many specialties. One of them has a relatively large moon. Our moon actually reaches 1% Mass Of the earth. An exceptional size for a satellite. Everything else Moons Of the solar system, including the moons Giant planetsIn fact, less than one tenth of their planet’s mass, except for saron, is 12% by mass. Pluto. What could have allowed this uniqueness?

As a reminder, the moon was created A huge impact between a planetary body and ancient Earth. To scientists, this collision is certainly one of the explanations for the Moon’s exceptional size compared to Earth. However, this does not explain everything. This is because large conflicts of this type were regimental at the beginning of the formation of the solar system. Still the moons of Mars, Thursday, Saturn, Uranus And Neptune Are relatively small. It should be noted that Mercury And Venus is not a natural satellite.

Smaller planets form larger moons

The diversity of moons we see in our solar system is actually the result of the diversity of processes that lead to their formation. Because not everything is the result of conflict. Jupiter or Titan’s moons, like Saturn’s moon, are suppressed from a single disk by most natural satellites. Thing Remains following the formation of their own planet. The moons of Mars (Phobos and Timos)As well as Neptune Moon (Triton), Even if this hypothesis is discussed, would actually be rock bodies captured by the gravitational pull of these two planets. Our Moon and Saron will only come from the debris of major impacts with protoplanetary bodies.

In an article published in Nature CommunicationsThe team of scientists observed the formation of moons after such an impact, thank you Numerical simulation. In particular, they studied the collision of the bodies of the planets and the impact of various parameters such as their respective masses.

Researchers have shown that only during a major impact Rock planets Glacier planets less than six times the mass of Earth and less than the mass of an Earth can form relatively large moons.

Controlling factor: The amount of gas in the trash can

In their simulations, scientists designed several types of collisions: between two rock protoplanets or between two. Ice moons. These two types of planets differ in their composition. Rock planets have a center Iron And one Code Silicate, whereas icy planets are composed mainly of silicate core and mantle water ice. Simulations show that in each of the two cases, the conflict creates one Cloud Particulate matter and GasIt then condenses to form a new body, the moon.

However, the values ​​of the colliding masses play an important role in the final result. Appears to be (also called) rocky planets Will tell) Is six times heavier than Earth, and the moons resulting from the collision are relatively small. This also applies to ice planets that are once heavier than Earth. Values ​​below these masses will only lead to the formation of relatively large moons, at least a few percent of the mass of the mother planet. One of the factors controlling the formation of large moons is the amount of vapor (in Silicate Or water) depending on the type of planet) is on the garbage disk.

In fact, a disk made up mainly of gas does not lead to the formation of the Moon. For very large planets, debris falls quickly onto the planet before it forms the moon. In contrast, for smaller planets, such as Earth, less gas allows different objects to orbit around each other, eventually leading to the formation of a larger moon (simulation below).

Simulation of the formation of a large moon. © AGU, YouTube

These results help to understand the evolution of the Earth-Moon pair and to provide research avenues for the detection of potential “exomons” around planets with masses close to Earth.

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