A new theory from scientists at the University of California suggests that Venus might have once had a moon that was eventually pulled into the planet itself. According to a study published in The Astrophysical Journal, any natural satellite orbiting Venus would have slowly spiraled inward and eventually collided with the planet due to Venus's extremely slow rotation. Astrophysicist Stephen Krane explained that computer models showed that moons of various sizes would have met the same fate, crashing into Venus within a relatively short time frame—likely within the first billion years of the planet's existence, which dates back about 4.5 billion years. Previously, scientists believed that Venus either never had a moon or that any moon it may have had was destroyed by a massive collision with another celestial object. Unlike Earth, which rotates once every 24 hours, Venus takes 243 Earth days to complete a full rotation. This slow rotation means that Venus lacks the gravitational forces that push Earth’s moon away. In fact, Earth’s moon is slowly moving away from our planet at a rate of about 4 centimeters (1.6 inches) per year, as measured by laser reflectors left on the Moon during the Apollo 11 mission. Venus is similar in size and structure to Earth but is slightly smaller and has a thick, toxic atmosphere that creates a runaway greenhouse effect. This has led to surface temperatures as high as 880 degrees Fahrenheit (471 degrees Celsius), making it the hottest planet in the solar system. Although there is no direct evidence that Venus once had a moon, scientists consider it unlikely that Venus avoided the kinds of collisions that are thought to have formed Earth’s moon. To learn more about Venus, two upcoming NASA missions—DAVINCI+ and VERITAS—are set to launch in the late 2020s or early 2030s. These missions will study Venus’s atmosphere and geological features, aiming to uncover more about the planet’s history and its potential past as a mooned world.