SPACE is the vast, seemingly infinite expanse that exists beyond the Earth's atmosphere. It contains all celestial bodies, including stars, planets, moons, and galaxies. The universe is constantly expanding, and space is a near-perfect vacuum, meaning it has very low pressure and density. In space, there is no air, which is why sound cannot travel. The temperature can vary widely, from extremely hot near stars to extremely cold in the void. Astronomers study space using telescopes and spacecraft to learn more about its mysteries, including the formation of the universe and the potential for life on other planets like Mars.