Venus is Earth's closest planetary neighbor and is often called Earth's "sister" or "twin" planet. It has similar size, mass, and composition to Earth, though its dense carbon dioxide atmosphere makes the surface extremely hot and inhospitable. Venus likely had oceans in the past that evaporated due to a runaway greenhouse effect. It has volcanoes and mountains, but no magnetic field or moon. Venus rotates in the opposite direction of Earth, so the sun would appear to rise in the west and set in the east.