In all our searching of the universe, we’ve never seen another moon like ours. It's big, it's weird, it's played a huge role in shaping our planet. But how did we get it? Every possible story points to cataclysm.

This is the second episode of our new four-part series, Lost Worlds.

For more, go to http://vox.com/unexplainable

It’s a great place to view show transcripts and read more about the topics on our show.

Also, email us! unexplainable@vox.com

We read every email.

Support Unexplainable by making a financial contribution to Vox! bit.ly/givepodcasts

Learn more about your ad choices. Visit podcastchoices.com/adchoices

Effectively Wild Episode 620: 2015 Season Preview Series: Chicago White Sox