About 40 light-years from Earth, seven planets orbit a small, dim, red sun. TRAPPIST-1e, the fourth planet from the star, is in the habitable zone, meaning liquid water could exist on its surface. The six other Earth-size planets are so close that they would loom like moons in its red-tinged sky. Imagine what the other planets would look like from TRAPPIST-1e! What hues would appear under a red sun?