Every so often (including this past week), a story comes out about “Earth’s second moon,” an asteroid that got snagged by our planet’s orbit.  But this is apparently more complicated than it sounds at first.

The concept itself seems like it would be pretty straightforward. Asteroids get picked up by planets all the time. Some theories speculate that this is where the moons of Mars came from.

This isn’t the first time that an asteroid has hung around near Earth, but as you can see from this screen capture from my research for this post, calling those asteroids moons hasn’t always been universally accepted — not even by the same news outlets.

Written on the very same day, too. But not by the same person. I checked.

I’m not an astrophysicist, so I’ll stick to the basics for both of our sakes

  • Occasionally, asteroids get caught in weird, distant orbits around the Earth
  • These asteroids are so far away from the Earth that the sun pulls their orbits into weird shapes
  • Eventually (based on all the examples I found), these asteroids leave Earth behind and continue on their way to wherever it is that asteroids go

According to Paul Chodas, manager of NASA’s Center for Near-Earth Object Studies  (by way of CNN): “Our calculations indicate 2016 HO3 has been a stable quasi-satellite of Earth for almost a century, and it will continue to follow this pattern as Earth’s companion for centuries to come.” So don’t expect to be able to go outside tonight and see an asteroid rising and setting next to the moon. It’s been there since before World War II, and we’re just talking about it now, so it’s probably pretty hard to spot, even with a telescope.

Even though the news of the latest “second moon” has come out within the past week, stories of other, similar moons have come out periodically for years. I’ve included what seem to be the most helpful links below:

This video is super helpful: http://www.bbc.com/earth/story/20160615-earth-probably-has-more-than-one-moon-a-lot-of-the-time

http://gizmodo.com/earths-new-quasi-moon-will-stick-around-for-centuries-1782082812

http://www.smithsonianmag.com/smart-news/bet-you-didnt-know-about-earths-second-moon-180954455/

http://www.cnn.com/2016/06/16/us/nasa-asteroid-circles-earth/

Photograph of moon used for cover photo source: Wikimedia Commons

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