Read the paragraph from the section "Health Problems In Space." Putting your body in space has many dangers. You are exposed to many things in space. It means limited food and exercise. It means different sleep cycles. It could lead to many other problems we do not know about yet. Scientists say it's important to understand the effects space travel has on the body. It will be even more important for longer trips, like going to Mars.

What is the main idea of the paragraph?