* Runaway Greenhouse Effect: Venus has a thick atmosphere composed primarily of carbon dioxide (CO2). This dense CO2 atmosphere acts like a giant blanket, trapping heat from the sun. The heat gets trapped and keeps building up, leading to a "runaway greenhouse effect." This effect makes Venus's surface temperature incredibly hot, reaching around 867°F (464°C).
* Mercury's Thin Atmosphere: Mercury, on the other hand, has a very thin atmosphere. This means there's little to no insulation to trap heat. While Mercury receives a lot of solar energy because of its proximity to the sun, most of that energy radiates back into space without being trapped.
* Day-Night Temperature Fluctuations: Due to its slow rotation, Mercury experiences extreme temperature differences between its day and night sides. While the sun-facing side can reach over 800°F (427°C), the night side can drop to -290°F (-179°C).
In short: It's not just distance from the sun that determines a planet's temperature, but also the composition of its atmosphere. Venus's thick, carbon dioxide-rich atmosphere traps heat and leads to a runaway greenhouse effect, making it the hottest planet in our solar system.
