With no gravitational force to work against, your body not only doesn't need the same amount of muscle and bone, it starts breaking them down. As on Earth, so in space: use it or lose it. And exercise may not solve the problem.

I can't think that leaving Earth once is enough.

The solar system should be viewed as our backyard, not as some sequence of destinations that we do one at a time.

This universe knows about me and my crops.

Luckily, there are some rocks left over from our earliest days, asteroids formed during our solar system's birth. Occasionally, some of them drop in on Earth, and when they do, they're called meteorites.

Part of knowing how to think is knowing how the laws of nature shape the world around us. Without that knowledge, without that capacity to think, you can easily become a victim of people who seek to take advantage of you.

Give a kid a book, and you change the world. In a way, even the universe.