A child astronaut takes an imaginary trip to Mercury, learns about the harsh conditions on the rocky planet, and decides that Earth is a good home after all. Includes solar system diagram, Mercury vs. Earth fact chart, and glossary.A child astronaut takes an imaginary trip to Mercury, learns about the harsh conditions on the rocky planet, and decides that Earth is a good home after all. Includes solar system diagram, Mercury vs. Earth fact chart, and glossary.