The planet closest to Earth is Venus, which orbits the Sun at an average distance of about 41 million kilometers (25 million miles) during its closest approach. Venus is often called Earth's “sister planet” due to its similar size and rocky composition. However, the two planets have significantly different atmospheres and surface conditions. Venus has a thick, toxic atmosphere primarily composed of carbon dioxide, with clouds of sulfuric acid, creating a strong greenhouse effect that leads to extremely high temperatures on its surface, making it inhospitable to life as we know it.