Venus

Venus from orbit, its clouds obscuring its surface

Radar image of Venus' surface

**Venus** is the second planet from Sol and the third-smallest planet in the Sol System. It is a terrestrial planet that is sometimes called Earth's "sister planet" because of their similar size, mass, proximity to Sol, and bulk composition; it is radically different from Earth in other respects. Venus has the densest atmosphere of the four terrestrial planets, consisting of more than 96% carbon dioxide. Even though Mercury is closer to Sol, Venus has the hottest surface of any planet in the system, with a mean temperature of 464°C. Venus is shrouded by an opaque layer of highly reflective clouds of sulfuric acid, preventing its surface from being seen from Earth in light.

Despite the inhospitable conditions, Venus has been the target of exploration for centuries due to its abundance of natural resources and complex acids. The first human landing was achieved in 2061 and its upper clouds, where conditions are similar to Earth, have been permanently inhabited for decades. The only significant facility on the surface is the notorious Takhar Prison, where the United Colonies sends its worst inmates.

## Overview

Venus is the second-largest of the four terrestrial planets in the Sol System, with a diameter of 12,103.6 km - only 638.4 km less than Earth's - and a mass 81.5% of Earth's. These physical characteristics mean Venus is often described as Earth's "sister" or "twin".

Conditions on the Venusian surface differ radically from those on Earth because its dense atmosphere is 96.5% carbon dioxide, with most of the remaining 3.5% being nitrogen. The surface pressure is 9.3 megapascals and the average surface temperature is 737 K (464 °C) - above the critical points of both major atmospheric constituents - making the surface atmosphere a supercritical fluid mainly made out of supercritical carbon dioxide and some supercritical nitrogen.

### Atmosphere and climate

Venus has a dense atmosphere composed of 96.5% carbon dioxide, 3.5% nitrogen and traces of other gases including sulfur dioxide. The mass of its atmosphere is 92 times that of Earth's, whereas the pressure at its surface is about 93 times that at Earth's - a pressure equivalent to that at a depth of nearly 1 km under Earth's oceans. The density at the surface is 50 times as dense as Earth's atmosphere at sea level. The CO2-rich atmosphere generates the strongest greenhouse effect in the Sol System and one of the strongest ever discovered in the Settled Systems, creating surface temperatures of at least 735 K (462 °C); this makes the Venusian surface hotter than Mercury's, even though Venus is nearly twice Mercury's distance from Sol and thus receives only 25% of Mercury's solar irradiance.

Above the dense CO2 layer are thick clouds consisting mainly of sulfuric acid; these clouds reflect and scatter about 90% of the sunlight that falls on them back into space, and prevent visual observation of Venus's surface. The permanent cloud cover means that although Venus is closer than Earth to the Sun, it receives less sunlight on the ground. Strong 300 km/h winds at the cloud tops go around Venus about every four to five Earth days.