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Venus Astronomical symbol of Venus
Venus
Names
Adjective Venusian or (rarely) Cytherean, Venerean
Orbit
Reference date J2000
Longest distance from the Sun 108,942,109 km
0.728 231 28 AU
Shortest distance from the Sun 107,476,259 km
0.718 432 70 AU
Longest distance from the center of its orbital path
("semi-major axis")
108,208,930 km
0.723 332 AU
How long it takes to complete an orbit 224.700 69 day
0.615 197 0 yr
1.92 Venus solar day
How long an orbit seems to take
(from the central body)
583.92 days
Average speed 35.02 km/s
Angle above the reference plane
("inclination")
3.394 71° to Ecliptic
3.86° to Sun’s equator
2.19° to Invariable plane
Natural things which orbit it None
Size and other qualities
Average radius 6,051.8 ± 1.0 km
0.949 9 Earths
Surface area 4.60×108 km²
0.902 Earths
Volume 9.38×1011 km³
0.857 Earths
Mass 4.868 5×1024 kg
0.815 Earths
Average density 5.204 g/cm³
Surface gravity 8.87 m/s2
0.904 g
Escape velocity 10.46 km/s
Turning speed 6.52 km/h (1.81 m/s)
Angle at which it turns
(in relation to its orbit)
177.3°
Angle above the celestial equator
("declination")
67.16°
How much light it reflects 0.65 (geometric) or 0.75 (bond)
Surface temp. Min. Avg. Max.
Kelvin 735 K
Celsius 461.85 °C
Seeming brightness
("apparent magnitude")
up to -4.6 (crescent)
-3.8 (full)
Atmosphere
Pressure 93 bar (9.3 MPa)
Make-up ~96.5% Carbon dioxide
~3.5% Nitrogen
0.015% Sulfur dioxide
0.007% Argon
0.002% Water vapor
0.001 7% Carbon monoxide
0.001 2% Helium
0.000 7% Neon
trace Carbonyl sulfide
trace Hydrogen chloride
trace Hydrogen fluoride

Venus is the second planet from the sun. It is a terrestrial planet because it has a solid, rocky surface like other planets in the inner solar system. Astronomers have known Venus for thousands of years. The ancient Romans named it after their goddess Venus. Venus is the brightest object in the night sky except for the Moon. It is sometimes called the morning star or the evening star as at some elongations it is easily seen just before the sun comes up in the morning and, at other elongations, just after the sun goes down in the evening. Venus comes closer to the Earth than any other planet does.

Venus is sometimes called the sister planet of Earth as they are quite similar in size and gravity. In other ways the planets are very different. Venus' atmosphere (air) is mostly carbon dioxide with clouds of sulphuric acid. Sulphuric acid is a chemical that is very poisonous to humans.

Venus was the first planet to have its motions plotted across the sky, as early as the second millennium BC and spins very slowly on its axis, it spins in the opposite direction to the other planets. A day on Venus is equal to 117 days on Earth.

As the planet with the closest approach to Earth, Venus has been a prime target for early interplanetary exploration. Venus's thick clouds render observation of its surface impossible in visible light, and the first detailed maps did not emerge until 1991. Plans have been proposed for rovers or more complex missions.

Physical Properties

Venus globe
Radar view of the surface of Venus (Magellan spacecraft)

Venus is a terrestrial planet so, like the Earth, its surface is made of rock. Venus is much hotter than Earth. All the carbon dioxide in the atmosphere acts like a blanket, trapping heat from the Sun. This effect is called the greenhouse effect and it is very strong on Venus. This makes the surface of Venus the hottest of any planet's surface in the Solar System with an estimated average temperature of 480 °C (896.0 °F). This is hot enough to melt lead or zinc. 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.

Geography

The Venusian surface was a subject of guesswork until some of its secrets were revealed by planetary science in the 20th century. Venera landers in 1975 and 1982 returned images of a surface covered in sediment and relatively angular rocks. The surface was mapped in detail by Magellan in 1990–91. The ground shows evidence of extensive volcanism, and the sulfur in the atmosphere may indicate that there have been recent eruptions.

Venus2 mag big
The Magellan spacecraft was able to produce this image of the planet's surface. Red, in this false-color map, represents mountains, while blue represents valleys. The large yellow/red area in the north is Ishtar Terra featuring Maxwell Montes, the largest mountain on Venus

Venus has no oceans because it is much too hot for water. Venus' surface is a dry desert. Because of the clouds, only radar can map the surface. It is about 80% smooth, rocky plains, made mostly of basalt. Two higher areas called continents make up the north and south of the planet. The north is called Ishtar Terra (about the size of Australia) and the south is called Aphrodite Terra (roughly the size of South America). They are named after the Babylonian and Greek goddesses of love.

The planet has few impact craters, demonstrating that the surface is relatively young, approximately 300–600 million years old. Venus has some unique surface features in addition to the impact craters, mountains, and valleys commonly found on rocky planets. Among these are flat-topped volcanic features called "farra", which look somewhat like pancakes. These features are volcanic in origin.

Atmosphere

AtmosphereofVenus
Pie chart of the atmosphere of Venus. Second pie chart is an expanded version of the trace elements that don't fit into the first one

Venus' atmosphere is mostly carbon dioxide and nitrogen gas with clouds of sulphuric acid. Because the atmosphere is so thick or dense the pressure is very high. The pressure is 92 times the pressure on Earth, or roughly the pressure found 900 m (3,000 ft) underwater on Earth - enough to crush many things.

Venus is by far the hottest planet in the Solar System, with a mean surface temperature of 735 K (462 °C; 863 °F), even though Mercury is closer to the Sun. Venus is shrouded by an opaque layer of highly reflective clouds of sulfuric acid, preventing its surface from being seen from space in visible light. The only way scientists are able to see it is by using infrared and ultraviolet cameras and radar. Venus Express discovered, in 2011, that an ozone layer exists high in the atmosphere of Venus.

Venuspioneeruv
Cloud structure in the Venusian atmosphere

Studies have suggested that billions of years ago Venus's atmosphere was much more like Earth's than it is now, and that there may have been substantial quantities of liquid water on the surface, but after a period of 600 million to several billion years, a runaway greenhouse effect was caused by the evaporation of that original water, which generated a critical level of greenhouse gases in its atmosphere. Although the surface conditions on Venus are no longer hospitable to any Earth-like life that may have formed before this event, there is speculation on the possibility that life exists in the upper cloud layers of Venus, but the environment is acidic.

Thermal inertia and the transfer of heat by winds in the lower atmosphere mean that the temperature of Venus's surface does not vary much between the night and day sides, despite Venus's extremely slow rotation. Winds at the surface are slow, moving at a few kilometres per hour, but because of the high density of the atmosphere at the surface, they exert a significant amount of force against obstructions, and transport dust and small stones across the surface. This alone would make it difficult for a human to walk through, even if the heat, pressure, and lack of oxygen were not a problem.

Magnetic field and core

Venera-4 model in museum
Venera-4 model

In 1967, Venera 4 found Venus's magnetic field to be much weaker than that of Earth. This magnetic field is created by an interaction between the ionosphere and the solar wind, rather than by an internal dynamo as in the Earth's core. Venus's small induced magnetosphere provides protection to the atmosphere against cosmic radiation.

The weak magnetosphere around Venus means that the solar wind is interacting directly with its outer atmosphere. Atmospheric erosion by the solar wind probably led to the loss of most of Venus's water during the first billion years after it formed.

Orbit and rotation

VenusDonMiguel
The planet Venus, shown here rotating in a clockwise motion

Venus orbits the Sun at an average distance of about 0.72 AU (108 million km; 67 million mi), and completes an orbit every 224.7 days. Although all planetary orbits are elliptical, Venus's orbit is the closest to circular. When Venus lies between Earth and the Sun in inferior conjunction, it makes the closest approach to Earth of any planet at an average distance of 41 million km (25 million mi). The planet reaches inferior conjunction every 584 days, on average.

All the planets in the Solar System orbit the Sun in a anticlockwise direction as viewed from above Earth's north pole. Most planets also rotate on their axes in an anti-clockwise direction, but Venus rotates clockwise in retrograde rotation — it has the slowest rotation of any planet. Because its rotation is so slow, Venus is very close to spherical. Venus's rotation has slowed down in the 16 years between the Magellan spacecraft and Venus Express visits.

From Venus to Venus Transit (7302572892)
Artist's conception of the view of the Sun from under the clouds of Venus

To an observer on the surface of Venus, the Sun would rise in the west and set in the east, although Venus's opaque clouds prevent observing the Sun from the planet's surface.

Venus may have formed from the solar nebula with a different rotation period, reaching its current state because of chaotic spin changes caused by planetary and tidal effects on its dense atmosphere, a change that would have occurred over the course of billions of years.

Venus has no natural satellites. It has several trojan asteroids. An explanation for the lack of satellites is the effect of strong solar tides, which can destabilize large satellites orbiting the inner terrestrial planets.

Observation

La Luna y Venus al amanecer desde Popayán
The Moon and Venus at sunrise

To the naked eye, Venus appears as a white point of light brighter than any other planet or star (apart from the Sun). The planet is bright enough to be seen in a clear midday sky and is more easily visible when the Sun is low on the horizon or setting.

Venus "overtakes" Earth every 584 days as it orbits the Sun. As it does so, it changes from the "Evening Star", visible after sunset, to the "Morning Star", visible before sunrise. Venus is hard to miss when it is at its brightest. As the brightest point-like object in the sky, Venus is a commonly misreported as a "unidentified flying object".

Transits

2012 Transit of Venus from SF
2012 Transit of Venus

Venus can sometimes be seen passing between the sun and earth. Venus looks like a black dot when seen through a special telescope. Transits appear in pairs, the latest was June 8, 2004 and June 5–6, 2012. The transit could be watched live from many online outlets or observed locally with the right equipment and conditions.

The previous pair of transits occurred in December 1874 and December 1882; the following pair will occur in December 2117 and December 2125. The oldest film known is the 1874 Passage de Venus, showing the 1874 Venus transit of the sun.

Historically, transits of Venus were important, because they allowed astronomers to determine the size of the astronomical unit (used to measure distances within our Solar System), and hence the size of the Solar System as shown by Horrocks in 1639. Captain Cook's exploration of the east coast of Australia came after he had sailed to Tahiti in 1768 to observe a transit of Venus.

Ground-based research

Percival Lowell observing Venus from the Lowell Observatory in 1914
Percival Lowell observing Venus from the Lowell Observatory in 1914

Little was discovered about Venus until the 20th century. Its almost featureless disc gave no hint what its surface might be like, and it was only with the development of spectroscopic, radar and ultraviolet observations that more of its secrets were revealed. The first ultraviolet observations were carried out in the 1920s, when Frank E. Ross found that ultraviolet photographs revealed considerable detail that was absent in visible and infrared radiation. He suggested this was due to a dense, yellow lower atmosphere with high cirrus clouds above it.

Spectroscopic observations in the 1900s gave the first clues about the Venusian rotation. Vesto Slipher tried to measure the Doppler shift of light from Venus, but found he could not detect any rotation. He concluded the planet must have a much longer rotation period than had previously been thought. Later work in the 1950s showed the rotation was retrograde. Radar observations of Venus were first carried out in the 1960s, and provided the first measurements of the rotation period.

Radar observations in the 1970s revealed details of the Venusian surface for the first time. Pulses of radio waves were beamed at the planet using the radio telescope at Arecibo Observatory, and the echoes revealed two highly reflective regions, designated the Alpha and Beta regions. The observations also revealed a bright region attributed to mountains, which was called Maxwell Montes.

Exploration

Venera 1 (a) (Memorial Museum of Astronautics)
Model of Venera 1 - Memorial Museum of Astronautics Moscow

The first robotic space probe mission to Venus, and the first to any planet, began with the Soviet Venera program in 1961. The United States' exploration of Venus had its first success with the Mariner 2 mission on 14 December 1962, becoming the world's first successful interplanetary mission, passing 34,833 km (21,644 mi) above the surface of Venus, and gathering data on the planet's atmosphere.

On 18 October 1967, the Soviet Venera 4 successfully entered the atmosphere and deployed science experiments. Venera 4 showed the surface temperature was hotter than Mariner 2 had calculated, at almost 500 °C (932 °F), determined that the atmosphere is 95% carbon dioxide (CO2), and discovered that Venus's atmosphere was considerably denser than Venera 4's designers had anticipated. The joint Venera 4Mariner 5 data were analysed by a combined Soviet–American science team over the following year, in an early example of space cooperation.

Mariner 5 plaque
Mariner 5 plaque

Venera 7, the first space probe to land on Venus, was destroyed by the hostile conditions on Venus after only 23 minutes. In 1974, Mariner 10 swung by Venus on its way to Mercury and took ultraviolet photographs of the clouds, revealing the extraordinarily high wind speeds in the Venusian atmosphere.

In 1975, the Soviet Venera 9 and 10 landers transmitted the first images from the surface of Venus, which were in black and white. In 1982 the first colour images of the surface were obtained with the Soviet Venera 13 and 14 landers.

NASA obtained additional data in 1978 with the Pioneer Venus project that consisted of two separate missions: Pioneer Venus Orbiter and Pioneer Venus Multiprobe. The successful Soviet Venera program came to a close in October 1983, when Venera 15 and 16 were placed in orbit to conduct detailed mapping of 25% of Venus's terrain.

Several other Venus flybys took place in the 1980s and 1990s that increased the understanding of Venus, including Vega 1 (1985), Vega 2 (1985), Galileo (1990), Magellan (1994), Cassini–Huygens (1998), and MESSENGER (2006).

Then, Venus Express by the European Space Agency (ESA) entered orbit around Venus in April 2006. Equipped with seven scientific instruments, Venus Express provided unprecedented long-term observation of Venus's atmosphere. ESA concluded that mission in December 2014.

Venus Express in orbit (crop)
Artist's view of Venus Express in orbit

As of 2016, Japan's Akatsuki is in a highly elliptical orbit around Venus since 7 December 2015, and there are several probing proposals under study by Roscosmos, NASA, and India's ISRO.

In 2016, NASA announced that it was planning a rover, the Automaton Rover for Extreme Environments, designed to survive for an extended time in Venus's environmental conditions. It would be controlled by a mechanical computer and driven by wind power.

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