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The mystery of Earth’s second moon

Lona Middleton
Staff Writer
lkemp@lhup.edu

 

wikimedia.org

We all know the Earth has one moon. We are so sure of this that we simply call it “moon” rather than the name it was given by the Greek or Roman names, Selene or Luna, respectively. What if I told you that assumption was wrong? We have another moon and its name is 3753 Cruithne or just Cruithne for short. It’s true. It was detected way back in 1997 and has a rather unusual orbit.
Cruithne has what is called a horseshoe orbit and so doesn’t have the pretty elliptical orbit our moon does. It makes a strange and messy ring around the Earth in a pattern that looks a lot like some kid drew it with a Spirograph. It takes only a year to orbit the sun while slipping into both Venus’s and Mar’s territory. Cruithne takes 800 years though to complete its rather odd orbit around us.

morguefiles.com

morguefiles.com

So now you know we have a second moon but it is nothing like the familiar one we see every night. It is only a little over 3 miles in diameter and the gravity is so weak that a good jog could launch you into space from its surface.  The sad thing about this odd orbital satellite is that it won’t be ours forever. It will eventually get so close to Venus, in about 8,000 years, that it the planets gravity will fling it out of our orbit and off into the rest of space.
That will be the end of our second moon but don’t despair. It turns out that Earth may have many more odd orbiting satellites in the future. We have in the past. They latch on to our gravity and orbit in a multitude of strange patterns before eventually leaving us and heading off somewhere else, perhaps to another celestial body to orbit.

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