Venus

## Atmosphere

### **Composition**

* Carbon Dioxide (96%)
* Nitrogen (3%)
* Other gases (1%)

## General Information

Venus is the second planet from the Sun. It is a rocky planet with the densest atmosphere of any rocky body in the Solar System, as well as the only one with a mass and size comparable to its orbital neighbor Earth. It is always visible in the sky near the Sun. This also applies to Mercury, but Venus stands out more since it is the third brightest object in the sky after the Sun and the Moon, appearing brighter than any fixed star or other star-like classical planet.

Venus has an exceptionally thick carbon dioxide atmosphere and a weak induced magnetosphere, which together with the planet's widespread sulfuric acid cloud cover provide an intense greenhouse effect. This causes the air to become a supercritical fluid at the surface, where it has a mean temperature of 737 Kelvin and a crushing pressure 92 times that of Earth at sea level. At cloudy altitudes of 50 km above the surface, however, the radiation, temperature, and pressure are all very similar to those at Earth's surface. Venus' cloud layers have been shown to offer conditions that may be favorable for life, and recent studies have found suggestive but unconvincing evidence of life on the planet.

Venus may have formerly had enough liquid surface water to support oceans, but eventually runaway greenhouse effects evaporated whatever water remained, and the solar wind carried it into space. Venus is believed to be made up of a core, mantle, and crust. The crust is supposed to be active in volcanism, which releases heat from within the planet and shapes its surface through huge resurfacing rather than plate tectonics. In the Solar System, Venus is one of only two planets without a moon.

Strong currents and atmospheric drag have caused Venus's rotation to slow down and turn retrograde, or against its orbital orientation. A Venusian year is slightly less than two Venusian days long due to this rotation and the fact that it takes Venus 224.7 Earth days to complete one orbit around the Sun, making it the longest solar day length in the Solar System at 117 Earth days. With synodic periods of 1.6 years, Venus and Earth's orbits are the closest of any two planets in the Solar System.

### Properties

Having a rocky composition similar to Earth, Venus is one of the four terrestrial planets in the Solar System. Venus is only 638.4 km smaller than Earth in diameter, and its mass is 81.5% that of Earth. Venus has a dense atmosphere that is composed primarily of carbon dioxide (96.5%), with nitrogen making up the majority of the remaining 3.5%. As a result, conditions there are very different from those on Earth.  The average surface temperature is 737 Kelvin, while the surface pressure is 9.3 megapascals.

Venus has a dense atmosphere made up of 96.5% carbon dioxide and 3.5% nitrogen. These gases are present at the planet's surface as supercritical fluids with a density of 6.5% for water and traces of other gases, such as sulfur dioxide. Its atmosphere is 92 times heavier than Earth's, but at its surface, the pressure is roughly 93 times greater—that is, it is similar to the pressure found nearly 1 km (5 8 mi) below Earth's oceans. At the surface, the density is 65 kg/m3 (4.1 lb/cu ft), which is 50 times more dense than the Earth's atmosphere at 293 Kelvin at sea level, or 6.5% of the density of water.

#### Water

Research has revealed that there might have been significant amounts of liquid water on Venus' surface billions of years ago, and that the planet's atmosphere might have resembled that of the early Earth. The initial water and the present atmosphere evaporated after 600 million to several billion years due to solar force from the Sun's increasing luminosity and potentially significant volcanic resurfacing. As soon as a certain amount of greenhouse gasses, including water, were introduced to the atmosphere, a runaway greenhouse effect resulted.

#### Life

The possibility that life exists in Venus's upper cloud layers, 50 km above the surface, where the atmospheric conditions are the most Earth-like in the Solar System, with temperatures ranging between 303 and 353 Kelvin, pressure and radiation levels roughly equal to those at Earth's surface, but with acidic clouds and carbon dioxide air—has been discussed despite the fact that the surface conditions on Venus are no longer hospitable to any Earth-like life that may have formed prior to this event.

#### Clouds

Thick clouds of mostly sulfuric acid, which is created by the chemical reaction of sulfur dioxide and water to produce sulfuric acid hydrate, are seen above the thick layer of CO2. Furthermore, the clouds contain about 1% ferric chloride. Phosphoric anhydride, aluminum chloride, and ferric sulfate are further potential components of the cloud particles. Particle size distributions and compositions vary among clouds at different elevations. Similar to dense cloud cover on Earth, these clouds reflect over 70% of sunlight that strikes them back into space . Because they cover the entire planet, they make it impossible to see Venus's surface.

#### Volcanoes

Smooth, volcanic plains covering about 80% of Venus's surface are made up of 10% smooth or lobate plains and 70% plains with wrinkle ridges. The remainder of its surface area is composed of two highland "continents," one located in the planet's northern hemisphere and the other just south of the equator. The northern continent, around the size of Australia, is named Ishtar Terra after the Babylonian goddess of love, Ishtar. Ishtar Terra is home to Venus's highest mountain, Maxwell Montes. Peak elevation on Venus is 11 km above mean surface elevation.

Volcanic activity appears to have altered a large portion of Venus' surface. Venus boasts 167 huge volcanoes that span more than 100 km in diameter, making it home to several times the number of volcanoes as Earth. The Big Island of Hawaii is the only volcanic complex of its magnitude on Earth. While the surface of Venus is thought to be 300–600 million years old, the oceanic crust of Earth is continuously recycled by subduction along tectonic plate borders, with an average age of roughly 100 million years.

#### Craters

Venus has a uniform distribution of about a thousand impact craters on its surface. A variety of degrading states are visible in the craters of other cratered bodies, like the Moon and Earth. Degradation on Earth is brought on by wind and rain erosion, whereas on the Moon it is caused by consecutive impacts. Approximately 85% of Venus's craters are in perfect shape. The quantity and excellent preservation of the craters suggest that the planet experienced a worldwide resurfacing event between 300 and 600 million years ago, which was succeeded by a decline in volcanism. Venus is assumed to be unable to support a process that keeps its crust moving continuously, in contrast to Earth.

#### Magnetic Field

Venus's magnetic field was discovered by Venera 4 in 1967 to be significantly less than Earth's. Unlike the Earth's core, which is powered by an internal dynamo, this magnetic field is created by an interaction between the ionosphere and the solar wind. Venus's modest induced magnetosphere, which reaches heights of 54 to 48 km Earth-like, offers very little shielding to the atmosphere from solar and cosmic radiation.

Given that Venus is roughly the same size as Earth and was predicted to have a dynamo at its center, the absence of an intrinsic magnetic field on the planet was unexpected. Three things are needed for a dynamo to function: convection, rotation, and a conducting liquid.

#### Orbit

Every 224.7 days, Venus completes one orbit of the Sun, covering an average distance of roughly 0.72 AU (108 million km; 67 million mi). With an eccentricity of less than 0.01, Venus's orbit is now the closest to being circular among all planetary orbits, despite the fact that they are all elliptical. The eccentricity of the Venus orbit may have been far higher in the past, reaching values as high as 0.31 and potentially influencing the early evolution of the climate, according to simulations of the early solar system orbital dynamics.

### History

Venus is one of the star-like classical planets that human societies have known and identified throughout history because it is bright enough in the Earth's sky to be seen without the need for assistance. Venus is the third brightest object in the sky, behind the Sun and the Moon. Some cultures did not recognize Venus as a single entity, believing it to be two separate stars on each horizon: the morning and evening star. This was because Venus appears to move discontinuously, disappearing for many days at a time due to its proximity to the sun and then reappearing on the other horizon.

Still, the Venus tablet of Ammisaduqa from the First Babylonian dynasty and a cylinder seal from the Jemdet Nasr period suggest that the Sumerians were aware that the morning and evening stars were one and the same celestial phenomenon as well.

Early in the 17th century, Italian physicist Galileo Galilei utilized a telescope to see the planet for the first time and discovered that it had phases similar to the Moon, ranging from crescent to gibbous to full and vice versa. Venus appears as a half-lit phase when it is farthest from the Sun in the sky, and as a crescent or full phase when it is closest to the Sun. This was one of the earliest findings to blatantly defy the Ptolemaic geocentric theory, which held that the Solar System was concentric and centered on Earth. This was only possible if Venus orbited the Sun.

Russian polymath Mikhail Lomonosov made the discovery of Venus' atmosphere in 1761. German astronomer Johann Schröter made the first observation of Venus's atmosphere in 1790. Schröter discovered that the cusps stretched across more than 180° when the planet was a slender crescent.

Frank E. Ross conducted the first ultraviolet observations in the 1920s after discovering that ultraviolet images could capture a significant amount of detail that visible and infrared light could not. He proposed that high cirrus clouds atop a dense, yellow lower atmosphere were the cause of this.

When the robotic space probe Venera 1 of the Soviet Venera program flew to Venus in 1961, humanity accomplished its first interplanetary mission, even though it lost touch en route.

Thus, the United States' Mariner program's Mariner 2 mission to Venus, which passed on December 14, 1962, at 34,833 kilometers above the planet's surface and collected data on the planet's atmosphere, was the first successful interplanetary mission.

Furthermore, the first radar observations of Venus were conducted in the 1960s, yielding the first accurate determinations of the rotation period.

Launched in 1966, Venera 3 was the first probe and lander by humans to reach and strike a celestial world other than the Moon. However, due to its crash into Venus, the probe was unable to return any data. Before making contact with Venus, Venera 4 was launched in 1967 and carried out successful research experiments in the planet's atmosphere. Venus's atmosphere was found to be significantly denser than what Venera 4's designers had anticipated, and the surface temperature was shown to be nearly 500 °C higher than what Mariner 2 had projected. Additionally, Venera 4 revealed that the atmosphere contained 95% carbon dioxide.

The first black-and-white photographs from Venus' surface were transmitted in 1975 by the Soviet Venera 9 and 10 landers. With NASA's Pioneer Venus project, which involved the Pioneer Venus Multiprobe and Pioneer Venus Orbiter, two independent missions that orbited Venus from 1978 to 1992, more data were collected. The Soviet Venera 13 and 14 landers were used in 1982 to capture the first color photos of the surface. Following the successful Soviet Venera program's conclusion in 1984, when Venera 15 and 16 operated in orbit between 1983 and 1984, thoroughly mapping 25% of Venus's landscape.