Seventeen years ago, when I returned from the Europa colony, I was asked to give a speech at a middle school assembly. For two hours I talked about recycling. Recycled air, recycled food, recycled water. We throw things away here, but there, everything is recycled.

This kid comes up to me afterwards, a little girl of maybe twelve, and she asks, what’s it like to have less gravity?

I chuckled. It’s lighter, I told her.

No, she said, without a smile. What’s it really like?

I watched her for a few seconds. Her eyes were narrow like she was looking into the sun, and I swear I’ve never seen a kid so intent on knowing something. It was like I had the answers for the most important test she’d ever take.

I didn’t really know what to say. I mean, gravity is gravity. More gravity is heavier, less gravity is lighter. There isn’t much room for elaboration. In the end, I told her that it felt like going downhill on a roller coaster, but that wasn’t true at all. It’s much more peaceful, more still. Everything moves slower up there. Even time.

Now, sometimes I watch the moon and I think, that’s what Europa looks like from a shuttle. I wouldn’t say I miss it, though. I never went back to the colony, and now I’m past the mandatory age limit for space travel. It’s like a roller coaster, I told her. You must be this young to ride this attraction.

I wonder if that little girl ever made it. They say that, in a few decades, everyone on Earth will be recycled.