Here's why:

* Composition: Venus's atmosphere is primarily composed of carbon dioxide (96.5%) with nitrogen making up most of the rest (3.5%). This dense composition contributes significantly to its weight.

* Pressure: The atmospheric pressure at the surface of Venus is about 92 times that of Earth's, equivalent to being about 900 meters (3,000 feet) below the surface of the ocean on Earth.

* Density: Venus's atmosphere is incredibly dense, making it extremely difficult for sunlight to penetrate to the surface.

* Runaway Greenhouse Effect: The thick atmosphere traps heat from the sun, resulting in surface temperatures exceeding 460°C (860°F), making it the hottest planet in our solar system.

While other gas giants like Jupiter and Saturn have much larger atmospheres by volume, Venus's atmosphere is the densest and most oppressive in our solar system.