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Earth Has A Second Moon: Cruithne With A Horseshoe Orbit

How many satellites does the Earth have? Most of us would mention the moon and only the moon. However, truth is we might be having more than one satellite. Back in 1997, it was discovered that another heavenly body known as 3753 Cruithne practically orbits around the Earth. It is an asteroid orbiting the sun in a quasi-orbital satellite, that is, it does not have an elliptical orbit, but it has a horseshoe-shaped one.


Photo credits: Cruithne’s wacky orbit around the sun. YouTube, CC BY-SA

What is a horseshoe orbit?

A horseshoe orbit is a type of co-orbital motion involving a smaller orbiting heavenly body and a larger one. Cruithne, also referred as the second moon of the Earth, orbits the sun in a bean shape orbit. The Earth sometimes repels it when it gets closer to it. Cruithne then travels around the sun, ultimately meeting the Earth from the other side. As it approaches the Earth from the other side, it turns again and moves away yet again.


Horseshoe orbit movement

Horseshoe orbits are common in our universe. Saturn has a number of moons that orbit around it in this fashion.

The swinging movement of Cruithne even brings it close to Venus and Mars.
It orbits the sun around one time a year. However, it takes 800 years for it to bring the ring shape orbit to completion.

What is Cruithne like?

Our ‘second moon’ is about 5 km across.

Unfortunately, we do not know much about it. Images of it have remained blurry. Sending out human or machine explorers to document it would be much of a challenge, according to experts.

Possibility of Cruithne hitting the Earth

A similar event might have occurred in the past, at the end of the Cretaceous period. If Cruithne does strike us, it would cause a massive extinction of the Earth’s species. Thankfully, experts believe that despite the vague possibility, it is otherwise highly unlikely for such a collision to occur. The point where it has been forecast to be at its closest to us is around 2,750 years away.

Furthermore, Cruithne might potentially come in very close proximity with Venus in 8 000 years. This might send it further away from us, preventing it from harming us.

Other flying objects acting as ‘moons’

Many other quasi-orbital satellites in the form of lumps of rocks have been detected by astronomers.


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