The planet with the most extensive and thick atmosphere is Venus. Its atmosphere is composed primarily of carbon dioxide, with clouds of sulfuric acid, making it incredibly dense and harsh. The atmospheric pressure on Venus is about 92 times that of Earth, which is equivalent to being nearly a kilometer underwater. This thickness contributes to an extreme greenhouse effect, resulting in surface temperatures that can reach around 900 degrees Fahrenheit (475 degrees Celsius). The unique atmospheric conditions lead to a constant, shroud-like appearance of the planet, obscuring its surface and making it one of the most inhospitable environments in the solar system.