Venus

Venus is the second planet from the Sun. Similar in size and mass to Earth, Venus has no liquid water, and its atmosphere is far thicker and denser than that of any other rocky body in the Solar System. The atmosphere is composed mostly of carbon dioxide and has a thick cloud layer of sulfuric acid that spans the whole planet. At the mean surface level, the atmosphere reaches a temperature of 737 K (464 °C; 867 °F) and a pressure 92 times greater than Earth's at sea level, turning the lowest layer of the atmosphere into a supercritical fluid. From Earth, Venus is visible as a star-like point of light, appearing brighter than any other natural point of light in the sky, as either the brightest "morning star" or "evening star".

Venus orbits closer to the Sun than the Earth does. The orbits of Venus and Earth make the two planets approach each other in synodic periods of 1.6 years. In the course of this, Venus comes closer to Earth than any other planet. In interplanetary spaceflight from Earth, Venus is frequently used as a waypoint for gravity assists, offering a faster and more economical route. Venus has no moons and a very slow retrograde rotation about its axis, a result of competing forces of solar tidal locking and differential heating of Venus's massive atmosphere. As a result, a Venusian day is 116.75 Earth days long, about half a Venusian solar year, which is 224.7 Earth days long.

Venus has a weak magnetosphere; lacking an internal dynamo, it is induced by the solar wind interacting with the atmosphere. Internally, Venus has a core, a mantle, and a crust. Internal heat escapes through active volcanism, resulting in resurfacing, instead of plate tectonics. Venus may have had liquid surface water early in its history with a habitable environment, before a runaway greenhouse effect evaporated any water and turned Venus into its present state. There are atmospheric conditions at cloud layer altitudes that are the most similar ones to Earth in the Solar System and have been identified as possibly favourable for life on Venus, with potential biomarkers found in 2020, spurring new research and missions to Venus.

Throughout history humans across the globe have observed Venus and it has acquired particular importance in many cultures. With telescopes, the phases of Venus became discernible and, by 1613, were presented as decisive evidence disproving the then-dominant geocentric model and supporting the heliocentric model. Venus was visited for the first time in 1961 by Venera 1, which flew past the planet, achieving the first interplanetary spaceflight. The first data from Venus were returned during the second interplanetary mission, Mariner 2, in 1962. In 1967, the first interplanetary impactor, Venera 4, reached Venus, followed by the lander Venera 7 in 1970. As of 2025, Solar Orbiter is on its way to fly-by Venus in 2026, and the next mission planned to launch to Venus is the Venus Life Finder, scheduled for 2026 as well.