Venus

Venus is the second planet from the Sun. It is about the same size and mass as Earth, but it has no liquid water. Its atmosphere is much thicker and denser than that of any other rocky body in the Solar System. The atmosphere is made mostly of carbon dioxide, and a thick cloud layer of sulfuric acid covers the whole planet. At the surface, the air reaches about 464 °C (867 °F), which makes Venus the hottest planet in the solar system. The pressure there is 92 times greater than Earth's pressure at sea level. This turns the lowest layer of the atmosphere into a supercritical fluid. From Earth, Venus looks like a star-like point of light. It appears brighter than any other natural point of light in the sky. It can be seen as either the brightest "morning star" or "evening star." In Old English, it was also given the poetic name Ēarendel, meaning "ray of light," along with two earlier epithets.

Venus orbits closer to the Sun than Earth does. The orbits of the two planets bring them near each other in synodic periods of 1.6 years. During this time, Venus comes closer to Earth than any other planet does. In interplanetary spaceflight from Earth, Venus is often used as a stopping point for gravity assists. These offer a cheaper route that helps spacecraft save fuel. Venus has no moons. It spins very slowly in a retrograde direction around its axis. This happens because of competing forces of solar tidal locking and the uneven heating of Venus's massive atmosphere. As a result, a Venusian day is 116.75 Earth days long, which is about half of a Venusian solar year. A Venusian solar year is 224.7 Earth days long.

Venus has a weak magnetosphere. Because it lacks an internal dynamo, its magnetosphere is caused by the solar wind interacting with the atmosphere. Inside, Venus has a core, a mantle, and a crust. Internal heat escapes through active volcanism, which causes resurfacing, instead of plate tectonics. Venus may once have had liquid water on its surface and a habitable environment. Then a runaway greenhouse effect evaporated any water and changed Venus into its present state. The cloud layer has conditions that are the most similar to Earth's in the Solar System. These conditions have been identified as possibly favourable for life on Venus. Possible biomarkers were found in 2020. This sparked new research and missions to Venus.

People all over the world have observed Venus throughout history, and it has become especially important in many cultures. With telescopes, the phases of Venus became easy to see. By 1613, these phases were presented as clear evidence against the geocentric model, which was the main idea at the time. They also supported the heliocentric model. In 1961, Venera 1 became the first spacecraft to visit Venus when it flew past the planet. This was the first interplanetary spaceflight. The first data from Venus were sent back during the second interplanetary mission, Mariner 2, in 1962. In 1967, Venera 4 reached Venus as the first interplanetary impactor. It was followed by the lander Venera 7 in 1970. In 1974, Mariner 10 captured the first images of Venus during its gravity assist on the way to Mercury. As of 2025, Solar Orbiter is on its way to fly by Venus in 2026. The next mission planned to launch to Venus is the Venus Life Finder, which is also scheduled for 2026.

For the deity, see Venus (mythology). For other uses, see Venus (disambiguation).

Physical characteristics

Venus is shown to scale with other planetary-mass objects in the Inner Solar System. From left: Mercury, Venus, Earth, the Moon, Mars, and Ceres.

Venus is one of the four terrestrial planets in the Solar System. This means it is a rocky world, like Earth. It is very similar to Earth in size and weight, so people often call it Earth's "sister" or "twin." Venus is nearly perfectly round because it spins slowly. It is a little smaller than Earth. It is the third-smallest planet in the Solar System.

Conditions on Venus are very different from Earth. Its thick atmosphere is mostly carbon dioxide, with most of the rest being nitrogen. This creates a strong greenhouse effect. The effect makes the surface extremely hot. The air near the surface is also very heavy and thick.

Atmosphere and climate

Main article: Atmosphere of Venus

Further information: Extraterrestrial sky § Venus

Venus has a very thick atmosphere. It is mostly made of carbon dioxide. The air at the surface is about 93 times as heavy as Earth's air. This thick air traps so much heat that the surface is hotter than Mercury, even though Venus is farther from the Sun. Scientists such as Carl Sagan have studied Venus to learn about climate change on Earth. Thick clouds of sulphuric acid cover the whole planet. They reflect most of the sunlight, so very little light reaches the ground. The atmosphere also moves much faster than the planet turns. Strong winds blow at the cloud tops at about 300 km/h (185 mph). This is called super-rotation.

Long ago, Venus may have had liquid water on its surface. Later, the water evaporated as the Sun grew brighter. Lightning has been hard to confirm. The Venera probes first detected possible bursts, and Venus Express later clearly found signs of lightning. High, cool mountain peaks such as Maxwell Montes are the coolest places on the planet. In 1995, the Magellan spacecraft photographed a bright substance on the highest peaks. It is called "Venus snow" and looks a little like snow on Earth. Scientists have also found an ozone layer and a huge swirling area of air at the south pole. In 2019, astronomers noticed that the amount of sunlight absorbed by the atmosphere rises and falls in a pattern that follows the Sun's sunspot cycle.

Orbit and rotation

Main article: Orbit of Venus

Venus orbits the Sun at an average distance of about 0.72 AU (108 million km; 67 million mi). It takes about 224.7 days to go around the Sun once. Its orbits are almost circular, though they were once much more stretched out.

Venus spins in the opposite direction from most planets, including Earth. It spins clockwise, while it travels around the Sun the other way. One day on Venus, measured by one full spin, lasts about 243 Earth days. That is longer than its year of 224.7 days. Because of this slow, backward spin, the Sun would rise in the west and set in the east for someone standing on Venus. Thick clouds, however, block the view of the Sun. Venus has no moons, but it does have some trojan asteroids that travel along with it.

Earth and Venus have a near orbital resonance of 13:8. This means Earth goes around the Sun eight times for every 13 trips Venus makes. Because of this, Venus comes closest to Earth about every 584 days. At its closest, it is about 41 million km (25 million mi) away. That is closer than any other planet gets to Earth. Mercury, however, is more often the closest planet to Earth. Scientists have also used Venus as a stopping point for gravity assist trips. This helps spacecraft travel to places such as Mercury, the Sun, and Mars more easily.

Observability

To the naked eye, Venus looks like a white point of light. At its brightest, it has an apparent magnitude of −4.92. This makes it brighter than any other planet or star except the Sun. Venus is bright enough to be seen in daylight, and it is easiest to spot when the Sun is low in the sky. As an inferior planet, it always stays within about 47° of the Sun. Every 584 days, Venus "overtakes" Earth as it orbits the Sun. It changes from the "Evening Star" to the "Morning Star." Because it is the brightest point of light in the sky, people often mistake it for an "unidentified flying object." Venus can also appear more than 8° north or south of the ecliptic, farther than any other planet or the Moon. Sometimes the Moon blocks the view of Venus for people in certain parts of the Earth. This happens about twice a year on average.

Main article: Phases of Venus

As Venus orbits the Sun, it shows phases like those of the Moon when seen through a telescope. It looks like a small, full disc when it is on the far side of the Sun. It looks like a thin crescent when it passes between Earth and the Sun. Its largest size and "new phase" happen at inferior conjunction. Venus is easily seen in a clear daytime sky when it is bright enough and far enough from the Sun, though most people do not know to look for it. Edmund Halley calculated its maximum naked eye brightness in 1716. French emperor Napoleon Bonaparte once saw it in daylight at a reception in Luxembourg. It was also seen during the inauguration of American president Abraham Lincoln in Washington, D.C., on 4 March 1865.

Main article: Transit of Venus

A transit of Venus happens when Venus passes in front of the Sun during inferior conjunction. Most inferior conjunctions do not produce a transit, because Venus's orbit is slightly tilted. Transits happen in a pattern that repeats every synodic period of about 1.6 years, forming cycles of 243 years. Transits were important because they helped astronomers measure the astronomical unit, and so the size of the Solar System. Jeremiah Horrocks made the first known observation of a transit in 1639, after the transit in 1631 of Mercury. Only seven transits have been observed so far, since Johannes Kepler calculated them in 1621. Captain Cook sailed to Tahiti in 1768 to record the third observed transit. This later led to the exploration of the east coast of Australia. The most recent transits took place on 8 June 2004 and 5–6 June 2012. The ones before them were in December 1874 and December 1882. The next transits will occur in December 2117 and December 2125.

A long-standing mystery is the so-called ashen light, a faint glow on the dark side of Venus when it is a crescent. The first claimed sighting was in 1643, but the glow has never been reliably confirmed. Some observers think it may come from electrical activity in the Venusian atmosphere. Others think it could be an illusion caused by looking at a bright, crescent-shaped object.

Observation and exploration history

Main article: Observations and explorations of Venus

Venus is bright enough to be seen without aid in Earth's sky. It is the third brightest object in the sky, after the Sun and the Moon. It is one of the classical planets, which people have known about since ancient times. Some ancient cultures thought the morning and evening stars were two separate stars. However, a cylinder seal from the Jemdet Nasr period and the Venus tablet of Ammisaduqa from the First Babylonian dynasty show that the ancient Sumerians already knew they were the same object. Later, Galileo Galilei used his telescope and saw that Venus showed phases. This showed that Venus orbits the Sun. It supported Copernicus's heliocentric model and went against Ptolemy's geocentric model. The atmosphere of Venus was discovered in 1761. Little more was learned until the 20th century. In the 1920s, Frank E. Ross used ultraviolet photographs to show more detail in the clouds.

In 1961, the robotic space probe Venera 1 was the first attempt at an interplanetary spaceflight to Venus, but it lost contact on the way. The first successful interplanetary mission was Mariner 2. It passed Venus in 1962 and collected information about its atmosphere. In 1967, Venera 4 found that the surface was hotter than expected and that the atmosphere was 95% carbon dioxide (CO₂). On 15 December 1970, Venera 7 became the first spacecraft to soft land on another planet. In 1974, Mariner 10 used a gravity assist for the first time to change its path toward Mercury. In the 1970s, radar observations from the Arecibo Observatory revealed details of the surface for the first time. In 2006, Venus Express, the first Venus mission led by the European Space Agency, entered orbit around the planet. Today, no probes are active at Venus. However, several missions are being developed or planned, including the Venus Life Finder, which is expected to launch no earlier than summer 2026. Venus has also been considered as a stopping point for crewed missions to Mars. Scientists have proposed floating cities in the planet's atmosphere. The conditions there are more like Earth's surface than those on the planet's surface.

Possibility of life

Main article: Life on Venus

Venus's surface is no longer suitable for any Earth-like life that might have formed there long ago. Some people think life may exist in the upper cloud layers, about 50 km above the surface. There, conditions are the most like Earth's in the Solar System. Some scientists have also suggested that extremophile microorganisms might live in the cooler, acidic upper parts of the Venusian atmosphere. In 1967, Carl Sagan and Harold J. Morowitz wrote in a Nature article that tiny objects seen in Venus's clouds might be organisms similar to Earth's bacteria. Interest in life on the surface dropped a lot after the early 1960s, when it became clear that conditions there were extreme.

Water, carbon dioxide, and sunlight, which are needed for photosynthesis, are plentiful near the clouds. In August 2019, astronomers led by Yeon Joo Lee reported changes in the planet's albedo and light absorbance. These changes could be caused by unknown substances, possibly tiny living things high in the atmosphere. In September 2020, scientists saw a possible sign of an absorption line of phosphine, a gas that is not known to be made by any known process on Venus. This led to talk that life might exist there now. Later research, however, linked that signal to sulphur dioxide instead. Because the surface is so harsh, Venus is in planetary protection category two, the second lowest. This means there is only a remote chance that spacecraft could bring interplanetary contamination that would affect investigations.

In culture

Venus is one of the most noticeable objects in the night sky. Many cultures have seen it as special, and it appears in mythology, astrology and fiction. Several hymns praise Inanna as the goddess of the planet Venus. In some myths, her movements may match the movements of Venus in the sky. The planet seems to set in the West and then rise again in the East. Long ago, the Ancient Egyptians and Greeks named the morning and evening stars. Later, the Greek names were recognized as one object, "the star of Venus." The English name comes from the ancient Romans, who named Venus after their goddess of love, Aphrodite. In Chinese and other East Asian languages, the planet is called "metal star." The Maya thought Venus was the most important object in the sky after the Sun and Moon.

Many poets, including Homer, Sappho and William Wordsworth, wrote about the star and its light. In science fiction, the thick clouds of Venus let writers imagine what its surface was like. The Venus symbol is a circle with a small cross beneath it. It has ancient Greek origins and is used as the astronomical symbol for Venus. It also became a gender symbol for female.