Venus is the second planet from the Sun and is one of the four terrestrial planets in the Solar System. It orbits the Sun at an average distance of about 108.2 million kilometers (67.2 million miles) and completes one orbit approximately every 224.7 Earth days. Venus is similar to Earth in overall size, mass, and composition, which is why it is often described as Earth’s “sister planet.” Venus has a mean diameter of about 12,104 kilometers (7,521 miles), making it slightly smaller than Earth, and it possesses a dense atmosphere and a solid rocky surface.
The atmosphere of Venus is composed primarily of carbon dioxide, with smaller amounts of nitrogen and trace gases. Thick clouds of sulfuric acid completely cover the planet, preventing direct observation of the surface in visible light from space. The atmospheric pressure at the surface is about 92 times that of Earth's sea-level pressure, equivalent to the pressure found nearly 900 meters (about 3,000 feet) underwater on Earth. Venus also experiences an extreme greenhouse effect because its dense carbon dioxide atmosphere traps heat very efficiently. As a result, the average surface temperature is approximately 465°C (869°F), making Venus the hottest planet in the Solar System, even hotter than Mercury, despite Mercury being closer to the Sun.
Venus rotates very slowly and in a retrograde direction, meaning it spins opposite to the direction of its orbit around the Sun. One rotation of Venus takes about 243 Earth days, which is longer than its orbital period. Consequently, a Venusian day, defined by its rotation relative to the stars, is longer than a Venusian year. The planet has no known natural moons and no known planetary ring system.
Formation
Venus formed approximately 4.6 billion years ago through accretion in the protoplanetary disk of gas and dust surrounding the young Sun, similar to other terrestrial planets. Dust grains collided and stuck together, forming planetesimals that grew into planetary embryos and eventually the planet via gravitational accumulation. Conditions involved a relatively hot inner solar system region, with Venus accreting from similar materials as Earth but closer to the Sun. No strong evidence supports formation via giant collision or capture, the standard nebular accretion model applies, though details of volatile delivery and exact timing remain models.
Early Evolution
After formation, Venus underwent differentiation, developing a metallic core, silicate mantle, and crust as heavier materials sank. It experienced the Late Heavy Bombardment, impacts, and cooling. Early Venus likely had oceans and a more temperate atmosphere, but a runaway greenhouse effect, driven by increasing solar luminosity, volcanic outgassing of \(CO_2\), and water vapor feedback, led to evaporation of surface water and atmospheric thickening. Models suggest possible plate tectonics or mobile lid regimes early on, transitioning to stagnant lid. Surface resurfacing occurred 300–700 million years ago. Uncertainties persist regarding the duration of habitability and exact triggers for the greenhouse runaway.
Origin and Evolution of life
No evidence of life on Venus exists today; its surface is a hostile 460–475 \(^\circ C\) inferno with crushing pressure and sulfuric acid clouds. Past habitability is debated: some models indicate liquid water and temperate conditions for up to 3 billion years early in history, potentially allowing life to arise (e.g., via prebiotic chemistry in oceans). Phosphine detections in clouds sparked interest in possible aerial microbial life, but this remains unconfirmed and controversial. Conditions preventing life include extreme heat, lack of liquid water on the surface, and atmospheric chemistry; future cloud habitability is speculative.
Future Trajectory
Venus's orbit is stable in the short term, with slow retrograde rotation. Over billions of years, as the Sun evolves into a red giant (~5 billion years from now), its expanding outer layers are predicted to engulf Mercury and Venus due to their proximity, vaporizing or destroying them. Orbital changes from solar mass loss may widen paths slightly, but Venus is too close to survive. No significant habitability shifts are expected before then, as the planet remains in a runaway greenhouse state. Long-term fate ties to stellar evolution.
Composition and Structure
Venus has a composition similar to Earth's: an iron-nickel core (2,900–3,500 km radius, likely partially liquid), silicate mantle, and thin basaltic crust (40 km average, up to 65 km). No global magnetic field is detected, possibly due to slow rotation or core dynamics. The surface features thousands of volcanoes, coronae, tesserae, and vast lava plains; a global resurfacing event 300–700 Ma reset the crater record. The atmosphere is 96.5% \(CO_2\), 3.5% \(N_2\), with sulfuric acid clouds, surface pressure 92–93 bar, and temperature 465 \(^\circ C\) due to the extreme greenhouse effect.
