The planet known for having a very thick atmosphere is Venus. Venus has a dense atmosphere composed primarily of carbon dioxide, with clouds of sulfuric acid, making it the most toxic atmosphere in the solar system. This thick layer traps heat, resulting in surface temperatures soaring to about 900 degrees Fahrenheit (475 degrees Celsius), even hotter than Mercury, despite being farther from the Sun. The atmospheric pressure on Venus is also about 92 times that of Earth, comparable to being nearly a mile underwater. These extreme conditions create a hostile environment, making it challenging for exploration and potential human habitation.