Venus is almost Earth’s twin in size - and utterly unlike it in every other way. A crushing carbon-dioxide atmosphere traps the Sun’s heat so effectively that its surface stays hot enough to melt lead, day and night, pole to pole.
It spins backwards - on Venus, the Sun rises in the west.
One rotation takes 243 Earth days, longer than its year.
Surface pressure is ~92× Earth’s - like being 900 m underwater.
The greenhouse effect, at full power
Sunlight gets in, but heat cannot get back out through Venus’s thick CO₂ atmosphere. The result: 464 °C everywhere. Venus is the Solar System’s warning about what a runaway greenhouse effect can do.
Physical characteristics
Diameter
12,104 km
Mass
4.870e+24 kg
Surface gravity
8.9 m/s²
Density
5.24 g/cm³
Rotation period
-5,832.5 h (retrograde)
Axial tilt
177.4°
Mean temperature
464 °C
Geometric albedo
0.69
Known moons
0
Atmosphere and composition
Atmosphere
96.5% CO₂ and 3.5% N₂ beneath sulfuric-acid clouds; surface pressure is a crushing 92 bar.
Composition
An iron core and rocky silicate mantle beneath a basaltic crust repaved by volcanism.
Interior structure
Iron coremodelled
Probably similar to Earth’s; whether any of it is solid is unknown.
Rocky mantlemodelled
Hot silicate rock; sluggish convection may drive the volcanism.
Basalt crustmodelled
No plate tectonics - the whole surface seems to renew in rare global episodes.
How we know: No seismometer has survived on Venus, so its interior is inferred from its Earth-like size and density. The absence of a magnetic field hints its core stirs differently than Earth’s.
The first spacecraft to visit Mercury, and the first ever to use one planet’s gravity (Venus) to slingshot to another. Its three flybys in 1974-75 mapped about 45% of Mercury’s surface.
MagellanNASA · Orbiter · 1989–1994 · completed
Magellan used radar to see through Venus’ permanent clouds, mapping 98% of the surface and revealing a young volcanic world with remarkably few impact craters. It burned up in the atmosphere it studied in 1994.