Venus

Venus
Name	Venus
Caption	A global view of the cloud-covered surface as imaged by the Magellan spacecraft using radar.
Discovery date	Prehistoric
Discovered by	Unknown
Adjectives	Venusian
Atmosphere composition	~96.5% carbon dioxide, ~3.5% nitrogen

Venus is the second planet from the Sun and is often called Earth's sister planet due to their similar size, mass, and composition. It is the brightest natural object in the night sky after the Moon and has been observed since ancient times. The planet is shrouded in an opaque layer of highly reflective clouds of sulfuric acid, making its surface impossible to see from space in visible light. Extreme surface temperatures and a crushing atmospheric pressure define this hostile world.

Physical characteristics

With a mean radius of approximately 6,052 kilometers, it is only slightly smaller than Earth and has a very similar bulk density, suggesting a comparable internal structure of a metallic iron core, a rocky mantle, and a silicate crust. Unlike Earth, it lacks an intrinsic global magnetic field, which may be due to its extremely slow rotation preventing the dynamo effect in its core. The planet's surface shows evidence of widespread volcanism and is relatively young, with an estimated age of 300-600 million years based on crater counts from missions like Magellan. Its lack of plate tectonics as seen on Earth results in a different method of heat release, likely through periodic, global resurfacing events.

Orbit and rotation

It orbits the Sun at an average distance of about 0.72 astronomical units, completing one revolution every 224.7 Earth days. Its rotation is both exceptionally slow and retrograde, meaning it spins in the opposite direction to most planets in the Solar System; a single sidereal day lasts 243 Earth days, longer than its year. This unusual rotation may be the result of a colossal ancient impact or gravitational interactions with its thick atmosphere. The combination of its orbital period and rotational period creates a solar day on the planet that is approximately 117 Earth days long.

Observation and exploration history

Known since antiquity, it was observed by astronomers like Galileo Galilei, who noted its phases, supporting the heliocentric model of Nicolaus Copernicus. The first successful interplanetary flyby was conducted by NASA's Mariner 2 in 1962, which confirmed the extreme surface temperatures. The Soviet Union achieved the first soft landing with the Venera 7 spacecraft in 1970, which transmitted data from the surface for 23 minutes. Subsequent missions, including the Venera program landers and the Pioneer Venus project, provided detailed data on the atmosphere and surface. The most comprehensive global radar mapping was performed by the Magellan orbiter in the early 1990s.

Atmosphere and climate

The atmosphere is overwhelmingly composed of carbon dioxide with clouds of sulfuric acid, creating the strongest greenhouse effect in the Solar System. This traps immense heat, leading to a mean surface temperature of about 737 Kelvin, hot enough to melt lead. The atmospheric pressure at the surface is 92 times that of Earth's, equivalent to the pressure found nearly a kilometer underwater in Earth's oceans. High-altitude winds in the cloud tops race around the planet at speeds exceeding 300 kilometers per hour in a phenomenon known as super-rotation, while surface winds are very slow. The dense atmosphere also causes a scattering of light that gives the sky a perpetual orange-yellow hue.

Geological features

The surface is dominated by vast volcanic plains covering about 80% of the terrain, punctuated by two major highland continents, Ishtar Terra in the north and Aphrodite Terra near the equator. Ishtar Terra contains Maxwell Montes, the highest mountain, which is taller than Mount Everest. Evidence of extensive volcanism is seen in thousands of volcanoes, including large shield volcanoes like Sif Mons and pancake domes. Other notable features include coronae, which are large, ring-like structures created by upwelling mantle material, and tessera, which are highly deformed, rugged regions that may be the oldest surviving crust. Impact craters are relatively few and uniformly distributed, indicating a globally young surface.

In culture

As the morning and evening star, it has been a significant celestial object in the mythology and astronomy of many cultures, often associated with deities of love and war, such as the Roman goddess Aphrodite and the Mesopotamian Inanna. It features prominently in literature, from the epic of Gilgamesh to modern science fiction like C. S. Lewis's *Perelandra*. The planet has been a central subject in discussions about extraterrestrial life and the anthropic principle, especially before the space age when its cloud cover led to speculation about a tropical, Earth-like world. Its hostile environment has made it a common setting for stories about human exploration and survival against extreme odds.

Category:Planets of the Solar System Category:Terrestrial planets