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Astronomy 161
An Introduction to Solar System Astronomy
Prof. Scott Gaudi

Lecture 34:

Key Ideas:

Venus is the second planet from the Sun


Surface: mapped using Radar

Venus at a Glance

Orbital Data
Semi-Major Axis: a = 0.723 AU
Orbital Period: 224.7 days
Eccentricity: e = 0.007 (Most circular orbit of the planets)
Inclination: i = 3.39°

Planetary Data
Radius: R = 6052 km (0.949 REarth)
Mass: M = 0.815 MEarth
Rotation: 243.02 days Retrograde!
Axis Tilt: 177.4°, Upside down!

Spacecraft Visits

Mariner & Pioneer satellites (1962)

Venera 7 (1970 - USSR) - first soft landing

Atmospheric Probes:
Pioneer Venus (US: 1978)
Vega 1 & 2 balloon probes (USSR: 1985)

Pioneer Venus Orbiter (US: 1978)
Venera 15 & 16 (USSR: 1983)
Magellan (US: 1990-1994) - most detailed radar mapping
Mars Express (ESA: 2005-present)

The ESA Venus Express spacecraft, is currently in orbit around Venus studying its atmosphere.

Veiled Venus

Venus is completely covered by a thick planet-wide layer of opaque clouds.

First data about the surface came from radar signals bounced off Venus:

Retrograde Rotation

Venus has a slow, retrograde (east-to-west) rotation.

Possible Causes:

Venus' Atmosphere


Surface Pressure: 90 atmospheres

Surface Temperature: uniform 750 K (891 F)

Sulfuric Acid Clouds

The clouds of Venus are not water vapor clouds like on Earth:

Lower atmosphere and surface are clear below the H2SO4 cloud deck.

Runaway Greenhouse Effect

Venus is so hot (750K) because of a runaway greenhouse effect:

The result is that Venus is extremely dry today with very little water!

Venus Unveiled

The surface of Venus has been mapped using imaging radar.

Highest Resolution Map:

The Surface of Venus


Highlands are concentrated into two regions:

These are not ancient highlands like the Moon & Mercury.

Also identified impact craters, volcanoes, and other geological features.

Volcanism & Geologic Activity

Volcanoes are a common terrain feature:

Tectonics, but not plate tectonics:

Impact Craters

Only ~1000 Impact craters are seen on Venus:

Two competing ideas:

Venus & Earth

Volcanic & tectonic repaving:

Tectonic activity is different:

This difference may be related to lack of water in Venus' crust, which makes it more pliable than the Earth's crust.

Atmospheres reflect differing histories:

Why the differences, given that they had the same starting point (volcanic outgassing of CO2 & H2O)?
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