Venus is the hottest planet in our solar system, even though it is farther from the Sun than Mercury, the closest planet. Venus has a surface temperature of about 900 degrees Fahrenheit (480 degrees Celsius), which is significantly hotter than Mercury's highest surface temperature of around 800 F (430 C). This difference in temperature is due to the composition of Venus’s atmosphere and how it interacts with sunlight. Mercury has almost no atmosphere, so sunlight hits its surface directly, heating the rocks to extremely high temperatures during the day. However, without an atmosphere to trap that heat, Mercury quickly loses its warmth once the Sun sets, causing large temperature swings between day and night. In contrast, Venus has a dense atmosphere that is about 90 times thicker than Earth's and is mostly made of carbon dioxide. This thick atmosphere acts like a blanket, trapping heat so effectively that Venus's surface temperature remains almost constant, regardless of where the Sun is in the sky. The thick atmosphere of Venus also reflects most of the sunlight that reaches it. About 3% of the sunlight passes through the thick clouds and reaches the surface. If Venus’s atmosphere and clouds were removed, the planet would actually be cooler than Mercury, as it would receive only about 29% of the sunlight Mercury gets. This highlights how the atmosphere plays a crucial role in Venus’s extreme heat. Venus's dense atmosphere did not form all at once, and scientists are still studying how it developed. Evidence suggests that past and present volcanic and tectonic activity on Venus have contributed to the buildup of greenhouse gases in its atmosphere. Today, Venus is considered to be in a "post-runaway greenhouse" state, where the extreme heat is a self-sustaining process. The heat is locked in by the atmosphere itself, which traps infrared radiation, making it difficult for the planet to cool down.