Venus — second planet from the Sun and Earth’s closest planetary neighbor — is a world of extremes: similar in size and bulk to Earth but utterly different in surface conditions, atmosphere, and geological character.

Basic facts

Mean distance from Sun: ~0.72 AU (≈108 million km).

Radius: ~6,051 km (about 95% of Earth’s).

Mass: ~0.82 Earth masses.

Average density: ~5.24 g/cm³.

Orbital period (Venus year): ~224.7 Earth days.

Rotation period (sidereal day): ~−243 Earth days (retrograde — rotates opposite most planets).

Solar day (sunrise to sunrise): ~116.8 Earth days.

Moons: none.

Atmosphere and climate

Composition: ~96–97% carbon dioxide (CO2), ~3–4% nitrogen (N2), with trace amounts of sulfur dioxide (SO2), water vapor (H2O) in ppm, and other trace gases.

Pressure: surface pressure ≈ 92 bar (about 92 times Earth's sea-level pressure) — equivalent to being roughly 900 m underwater on Earth.

Temperature: mean surface temperature ≈ 735 K (≈462 °C / 864 °F) — hot enough to melt lead and permanently too hot for liquid water.

Greenhouse effect: extreme runaway greenhouse — thick CO2 atmosphere traps solar heat efficiently; clouds of sulfuric acid high in the atmosphere reflect sunlight but also contribute to atmospheric heat trapping.

Clouds: dense, highly reflective cloud deck composed mainly of concentrated sulfuric acid droplets (H2SO4). The clouds extend roughly from ~45 km to 70 km altitude and create a bright, featureless glare in visible light.

Atmospheric dynamics: super-rotation — upper atmosphere circulates much faster than the planet’s surface rotation, with winds of several hundred km/h; complex vertical structure with temperature inversions and a strong zonal (east–west) flow.

Surface and geology

Visibility: surface invisible in optical wavelengths from space because of the thick clouds; radar and infrared observations reveal terrain.

Topography: varied — broad volcanic plains, large shield volcanoes, extensive lava flows, highlands (Ishtar Terra and Aphrodite Terra), steep-sided tesserae (heavily deformed highland terrains).

Volcanoes: numerous; Maxwell Montes and large volcanic rises and coronae are common. Many features indicate extensive volcanism; some evidence suggests volcanic activity may have occurred in the geologically recent past (hundreds of thousands to millions of years), but active volcanism today remains under investigation.

Tectonics: no Earth-like plate tectonics observed. Deformation appears to be dominated by mantle upwellings, crustal shortening in highlands, and localized rifting and tessera formation.

Impact craters: relatively scarce and uniformly distributed, indicating a resurfacing event(s) that erased older craters. Crater sizes and densities imply a geologically young surface (roughly several hundred million years since major resurfacing).

Surface chemistry: basaltic rocks are expected; surface weathering occurs under high temperature and pressure with a different set of mineralogical reactions than on Earth.

Magnetic field and interior

Intrinsic magnetic field: Venus lacks a strong, global intrinsic magnetic field like Earth’s. Measurements show only a weak, induced magnetosphere produced by interaction of the ionosphere with the solar wind.

Core and interior: likely iron-rich and at least partially molten, but slow retrograde rotation and other factors may prevent a sustained dynamo that would generate a strong magnetic field. Interior structure inferred from density, moment of inertia, and seismic analogs suggests crust, mantle, and core similar in proportion to Earth.

Observational history and exploration

Visibility from Earth: bright object in the sky (the third-brightest object after the Sun and Moon) because of its highly reflective clouds; shows phases like the Moon when viewed through a telescope.

Historical significance: associated with mythology in many cultures; known since prehistoric times. Early telescopic observations were limited by clouds; misinterpretations (e.g., imagined vegetation or canals) existed before space-age data.

Spacecraft exploration: visited by many probes from several nations. Early flybys and orbiters (Mariner 2, Venera series, Pioneer Venus) established basic properties. The Soviet Venera landers were the first to return images and direct surface data (mid- to late-1970s and early 1980s) but survived only for minutes to hours because of harsh conditions. Later missions (Magellan) used radar to map the surface in detail; ESA’s Venus Express and Japan’s Akatsuki studied the atmosphere and dynamics. Planned and recent missions (NASA, ESA, and others) aim to study atmospheric chemistry, potential volcanic activity, and surface/interior processes.

Surface missions: Venera landers and the Vega probes provided the only direct surface measurements and images to date. Survived from a few minutes up to about two hours.

Unique and notable features

Retrograde rotation: Venus spins opposite to most planets; the cause is debated (giant impacts, tidal interactions, or atmospheric tides).

Day length vs. year length: a Venusian sidereal day (~243 Earth days) is longer than its year (~224.7 Earth days). Because of retrograde rotation, the Sun would appear to rise in the west and set in the east.

Cloud-top habitability zone: while the surface is inhospitable, some proposals have suggested that Venus’ upper cloud decks (around 50–60 km altitude) have temperate temperatures and pressures (Earth-like), spurring speculative ideas about aerial habitats or the remote possibility of microbial life in aerosols — though harsh acidic chemistry and UV radiation pose major challenges.

Runaway greenhouse as a cautionary example: Venus is often cited in climate science as a cautionary extreme of greenhouse warming when large amounts of CO2 remain in the atmosphere and oceans evaporate.

Open questions and active research areas

Current volcanic activity: is Venus still volcanically active today? Orbital and spectral data suggest possibly recent eruptions; upcoming missions will aim to confirm.

Atmospheric evolution: how did Venus lose water and evolve into a CO2-dominated atmosphere? Quantifying the timing and mechanisms of water loss (hydrodynamic escape, photodissociation, and hydrogen escape to space) is key.

Lack of magnetic field: detailed interior models and measurements are needed to understand core state and heat transport history.

Surface age and resurfacing processes: what caused large-scale resurfacing and when did it happen? Better constraints on crater retention ages and volcanic history are sought.

Why Venus matters

Comparative planetology: Venus is Earth’s sister in size and composition but diverged drastically. Studying it helps constrain planetary formation, atmospheric evolution, and climate extremes.

Climate lessons: Venus provides a natural laboratory for greenhouse physics on planetary scales and helps refine models of atmospheric feedbacks and habitability thresholds.

Exploration challenge: the high temperatures, pressures, and corrosive atmosphere push engineering limits — developing technology for long-lived landers, high-altitude platforms, and advanced remote sensing is scientifically and technically valuable.