Venus (planet)

Venus (planet)
NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of · Public domain · source
Name	Venus
Caption	Cloud-covered disk of Venus
Discoverer	Ancient observers
Discovered	Prehistory
Mean radius km	6051.8
Mass kg	4.867e24
Density kg m3	5243
Gravity ms2	8.87
Escape velocity kms	10.36
Rotation period	243.025 Earth days (retrograde)
Orbital period	224.701 Earth days
Semi major axis AU	0.723332
Eccentricity	0.0068
Inclination deg	3.3947
Satellites	None

Venus (planet) Venus is the second planet from the Sun and one of the four terrestrial planets in the Solar System. It is similar in size and composition to Earth yet distinguished by a dense carbon dioxide atmosphere, extreme surface temperatures, and a slow retrograde rotation. Venus has been observed since antiquity and remains a primary target for planetary science, comparative planetology, and study of planetary atmospheres.

Overview

Venus is classified as an inner planet of the Solar System and a terrestrial world alongside Mercury, Earth, and Mars. It is often called Earth's "sister planet" due to comparable radius and mass, but differs markedly in atmospheric composition and surface conditions. Venus appears as the Morning Star or Evening Star from Earth and figures prominently in the observational records of civilizations such as the Babylonian Empire, Maya civilization, and Ancient Greeks.

Physical characteristics

Venus has a mean radius of about 6,051.8 km and a mass of 4.867×10^24 kg, yielding a mean density similar to Earth and indicating a silicate mantle and metallic core. The planet's surface gravity is approximately 0.904 g, and its internal structure is inferred from geodesy and comparative modeling used in studies by agencies such as NASA, European Space Agency, and Roscosmos. Venus lacks a significant intrinsic magnetic field comparable to Earth's magnetic field; measurements from missions including Pioneer Venus and Magellan constrain core properties and dynamo theories.

Atmosphere and climate

Venus's atmosphere is dominated by carbon dioxide with clouds of sulfuric acid, producing a surface pressure about 92 times that of Earth at sea level. A powerful greenhouse effect raises mean surface temperatures to roughly 735 K (462 °C), hotter than the surface of Mercury despite greater distance from the Sun. The atmosphere exhibits super-rotation, with upper clouds circulating much faster than the planet's rotation; this phenomenon has been studied by missions such as Venera program, Venus Express, Akatsuki, and instruments aboard Mariner 10. Trace gases like sulfur dioxide and transient phenomena observed by Pioneer Venus and Venus Express inform models of volcanic outgassing and atmospheric chemistry.

Geology and surface features

Radar mapping by Magellan and altimetry from Magellan and Venera landers revealed a surface dominated by volcanic plains, large shield volcanoes, vast coronae, tessera terrain, and few impact craters, implying geologically young resurfacing. Prominent features include highland regions such as Ishtar Terra with Maxwell Montes and Aphrodite Terra, as cataloged in planetary nomenclature overseen by the International Astronomical Union. Models of Venusian tectonics propose stagnant-lid convection rather than plate tectonics as on Earth, with episodic lithospheric overturns hypothesized in work by researchers at institutions like Caltech and Smithsonian Institution.

Orbit and rotation

Venus orbits the Sun at an average distance of about 0.723 AU with a nearly circular orbit (eccentricity ~0.0068) and an orbital period of ~224.7 Earth days. Its axial tilt is small (~177.4° when accounting for retrograde rotation), producing negligible seasonal insolation variations relative to Earth. Venus rotates slowly and retrograde, completing one sidereal rotation in about 243.0 Earth days, resulting in a solar day of about 116.8 Earth days. Synodic periods between Venus and Earth underlie historical phenomena observed by astronomers such as Galileo Galilei and charted in records by the Babylonian Empire.

Observation and exploration

Venus has been the subject of terrestrial observations since antiquity and of robotic exploration since the early space age. Key missions include the Venera program (USSR), which achieved the first successful landings and surface measurements; Mariner 2 (NASA), the first successful flyby; Magellan (NASA), high-resolution radar mapping; Venus Express (ESA), long-duration atmospheric studies; and Akatsuki (spacecraft) (JAXA), focused on cloud dynamics and atmospheric phenomena. Recent and planned missions—such as proposals by NASA (e.g., VERITAS, DAVINCI+), ESA studies, and concepts from Roscosmos and private companies—aim to resolve questions about past habitability, volcanic activity, and atmospheric evolution. Ground-based and space-based observations using facilities like the Hubble Space Telescope, ALMA, and large observatories augment mission data.

Cultural significance and mythology

Venus has profound cultural importance across many societies. In Roman mythology it is associated with the goddess Venus, while the Ancient Greeks identified it with Aphrodite. The planet figures in the calendrical and astronomical systems of the Maya civilization and the Babylonian Empire, and it appears in works by Ptolemy and Claudius Ptolemaeus's corpus. In art and literature, Venus inspired creations from Sandro Botticelli's "The Birth of Venus" to Renaissance and modern poetry; it features in science fiction by authors like H. G. Wells and Isaac Asimov and in speculative studies at institutions such as SETI Institute.

Category:Terrestrial planets