Mercury is the smallest and innermost planet in the solar system, known for its extreme temperatures, lack of atmosphere, and rapid orbit around the Sun. Articles are a unique way for readers to learn about the world around them. In addition to building reading comprehension skills and increasing vocabulary, articles can be used for writing and research. Each Planet is broken into 6 single-page sections: Introduction, What is it Made of?, By the Numbers, Neighbors, Amazing Facts, and Words to Know.