Tech UPTechnologyCould Earth have more than one moon?

Could Earth have more than one moon?

The moon, not a moon, but THE moon. Because we assume that the Earth only has one moon, although this is not the case. Not always, I mean. Earth has had more moons in the past , but before we talk about them, let’s give some context.

If we look at the rest of the inner planets in the solar system, it seems that the Earth has an excess of moons. Mercury and Venus do not have and Mars has two, although everything indicates that they are asteroids captured from the neighboring asteroid belt. Earth’s moon is certainly not a captured asteroid, it’s too big and massive for that. Therefore it seems that the Earth would be the only one of this quartet of planets with a minimally “natural” satellite.

Of course the satellites of all the planets are natural, nobody has built them, although some are more natural than others. You see, we know of 3 possible mechanisms by which a planet can get a moon . From most to least natural, they would be the following. First, from the protoplanetary disk , the disk of gas and dust that surrounds a star when it is forming and from which planets form, smaller bodies can form that end up orbiting those planets . This would have formed the largest satellites of Jupiter, Saturn or Uranus. I am talking about satellites like Ganymede, Titan or Oberon.

Another option is what we believe happened on Earth. Millions of years after the planet forms, a collision with another body with a similar orbit takes place. From the collision large amounts of material are ejected that ends up forming a satellite or falling to the planet. This is how we think the Moon was formed. This mechanism could also explain the formation of the moons of Mars, although there is not much evidence to support this idea. The last option involves gravitational capture by a wandering asteroid . This is how (most likely) Mars got its only two moons, Phobos and Deimos, and how Neptune got its largest moon, Triton, which was probably a captured dwarf planet.

We could therefore say that the most natural way to get a satellite is from the same material that ended up forming the planet it orbits, secondly creating the satellite from the expulsion of part of the planetary material after a collision and, finally , capturing an object that was created elsewhere in the solar system. So if Earth were to get a new satellite it would have to be by gravitational capture. The second option would technically still be possible, but you’ll agree that it doesn’t make much sense to consider it.

Well, could the Earth get to capture an asteroid or comet, getting a new moon? Yes, it could, and probably has done so hundreds of times throughout its history . Probably because it’s only been a few decades since we’ve had the ability to detect these moons, which are usually asteroids a few meters in diameter. And yet in that time we have detected at least 2 new moons around the Earth. Given the size and timing of these satellites, it is difficult to make definitive and questionable discoveries. It is hard but not impossible.

On September 14, 2006, an object about 3 meters in diameter that appeared to orbit the Earth was detected . At first it was thought that it could be part of a rocket used during one of the Apollo missions three decades earlier. This was not entirely a whim of its discoverers, since the object J002E3, discovered in 2002, is currently believed to correspond to the third stage of the Saturn V rocket used in the Apollo 12 mission. Well, the object discovered in 2006 ended up being a rock and was named the 2006 RH120 . This object orbited the Earth for 11 months between 2006 and 2007 until a close approach with the moon projected it back to the heliocentric orbit from which it had left, thereby becoming a second Earth moon for almost an entire year.

In 2020, another similar object was discovered, called 2020 CD3 , which was orbiting the Earth from the beginning of 2017 until May 2020 , when it returned to its orbit around the Sun. The main impediment to the existence of a second satellite around the Earth is precisely our first satellite, the Moon, which due to its great mass (relative to the Earth), is capable of perturbing the orbits of these objects, making them unstable .

However, one need only look at Pluto to see that perhaps a second moon is not too much to ask. Pluto has 5 moons in total, although one of them, Charon, accounts for more than 99.99% of the mass of the five moons together. Charon is so massive that Pluto is often considered to be more of a double planet, Pluto-Charon. But despite that, the other 4 moons have stable orbits around this double system. This indicates that something similar on Earth would, in principle, be possible, although most likely the orbit of that second moon would have to be beyond the lunar orbit itself, at least twice as far away. Now we just have to hope that we win the lunar lottery and that, in the future, the Earth gets a second permanent satellite.

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