Which planet has a thick atmosphere primarily composed of carbon dioxide?

The planet known for having a thick atmosphere primarily composed of carbon dioxide is Venus. This dense atmosphere is about 96.5% carbon dioxide, with clouds of sulfuric acid, making it one of the most inhospitable environments in our solar system. The immense atmospheric pressure on Venus is about 92 times that of Earth at sea level, contributing to extreme greenhouse effects that keep surface temperatures extremely high, averaging around 465 degrees Celsius (869 degrees Fahrenheit).

Understanding Venus's atmospheric composition is crucial because it plays a significant role in the planet's geology and climate. This contrasts with Earth, which has a balanced atmosphere composed primarily of nitrogen and oxygen, Mercury, which has a very thin atmosphere with negligible carbon dioxide, and Mars, which has a thin atmosphere that contains only about 95% carbon dioxide but lacks the dense, pressurized conditions found on Venus.