Venus

Second planet from the Sun is Venus... named for the goddess of love and beauty, and seen from earth as the 3rd brightest object in the sky, after the Sun and moon.

In some ways, it's earth sister planet, just a little smaller in diameter.

In temperature, it's rather like the traditional picture of hell!

Through a telescope, Venus is all clouds.

Earlier, there were speculations about plentiful water, swamps and life.

Later we thought the clouds might all be dust...

But now we know they're made of sulphuric acid and carbon dioxide.

In the 1990's the American "Magellan" spacecraft mapped the planet with radar, peering through the clouds to reveal details of the surface for the first time.


Claudia Alexander
U.S. Project Scientist, Rosetta comet mission
Jet Propulsion Laboratory, NASA/Caltech

When the Magellan mission went and did the mapping exercise that it did, it actually brought back the radar evidence that showed that there were just as few craters on the surface of Venus as there was on the surface of the Earth. And what that means is that somehow or other Venus is turning over its surface just like the Earth is, and that's a complete surprise because on Earth we think we know what causes the surface to turn over-there's "continental drift."

The plates that continents sit on move around, and that causes, there's earthquakes as the plates move past one another, and they build mountains and they build islands and so we see evidence around the Earth for what we call plate tectonics...a "continental drift," and we know that that causes the surface to turn over. But on Venus there's nothing like that.

So somehow the surface of Venus is turning over in a way that's completely different from the way the Earth's surface turns over. And so that's very exciting because it means that somehow or other, Venus is continuing to be alive and to be active and to have dynamics...

Revolution

Rotation

Radius

Distance From the Sun

225 Earth days

243 Earth days
The only planet that rotates backwards.

6,051.8 km

108,208,930 km

Mass

Density

Surface Temperature

Moons

4.8690 x 1027 grams

5.24 gm/cm3

Temperatures on Venus can reach 475 C

none

Atmosphere

Craters

Volcanoes

Water

carbon dioxide and nitrogen
Venus has the thickest atmosphere with surface pressures 90 times that of Earth.

While small meteors cannot survive in the dense atmosphere, larger ones have impacted the surface.

There is currently no direct evidence of active volcanoes, but changes in the amount of sulphuric acid in the atmosphere could be evidence that volcanoes are still active.

At one time thought the presence of clouds meant water present.
Now realize they're made of sulfuric acid and carbon dioxide.

A planetary greenhouse effect is caused when gases in the atmosphere drive up surface temperatures by allowing in solar energy, but cutting back its re-emission.

Just as in a greenhouse, the balance between incoming and outgoing heat is critical for living creatures.

It's possible to make things too hot... or too cold.


Chris Chyba
Carl Sagan Chair for the Study of Life in the Universe
SETI Institute & Stanford University

If a planet cools off and stops being able to put carbon dioxide into the atmosphere because volcanism shuts down on that planet, then the planet can't maintain the greenhouse, and that's what went wrong with Mars. There used to be the biggest volcanoes in the solar system but they're all dead now... and now the world is freeze-dried. It's become a kind of barren desert at its surface.

Volcanism on Venus kept putting carbon dioxide into Venus' atmosphere. But what went wrong on Venus is that Venus was so close to the Sun that Venus lost its oceans. The oceans evaporated, they went up into the atmosphere. The sunlight breaks up the water molecules into hydrogen and oxygen, the hydrogen can leak out the top of the atmosphere, and once that happens the water's gone, that's it, end of story.

Once Venus lost its water, it was no longer able to remove the carbon dioxide from its atmosphere, so the greenhouse effect on Venus went haywire in the opposite direction that it went haywire on Mars.

WANT TO LEARN MORE?
Missions:
 • Magellan (1989-1994)
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