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14.8: Venus

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"Venus favors the bold". — Ovid, a Roman poet.

Our nearest planetary neighbor, Venus, was named after the Roman goddess of love because it appeared as the brightest and most beautiful star in the skies. Most of the planet's features are named for real or mythological women.

Venus

Venus’ thick clouds reflect sunlight well, so Venus is very bright. When it is visible, Venus is the brightest object in the sky besides the Sun and the Moon. Because the orbit of Venus is inside Earth’s orbit, Venus always appears close to the Sun. When Venus rises just before the Sun rises, the bright object is called the morning star. When it sets just after the Sun sets, it is the evening star.

Of the planets, Venus is most similar to Earth in size and density. Venus is also our nearest neighbor. The planet’s interior structure is similar to Earth’s, with a large iron core and a silicate mantle ( Figure below ). But the resemblance between the two inner planets ends there.

Find out more about Venus at the following link: http://www.nasa.gov/worldbook/venus_worldbook.html .

Venus’s interior is similar to Earth’s.

Motion

Venus rotates in a direction opposite the other planets and opposite to the direction it orbits the Sun. This rotation is extremely slow, only one turn every 243 Earth days. This is longer than a year on Venus — it takes Venus only 224 days to orbit the Sun.

Extreme Atmosphere

Venus is covered by a thick layer of clouds, as shown in pictures of Venus taken at ultraviolet wavelengths ( Figure below ).

This ultraviolet image from the Pioneer Venus Orbiter shows thick layers of clouds in the atmosphere of Venus.

Venus' clouds are not made of water vapor like Earth’s clouds. Clouds on Venus are made mostly of carbon dioxide with a bit of sulfur dioxide. They also contain corrosive sulfuric acid. Because carbon dioxide is a greenhouse gas, the atmosphere traps heat from the Sun and creates a powerful greenhouse effect. Even though Venus is further from the Sun than Mercury, the greenhouse effect makes Venus the hottest planet. Temperatures at the surface reach 465 o C (860 o F). That’s hot enough to melt lead.

The atmosphere of Venus is full of acid, its pressure is crushing, and the enormous amount of carbon dioxide causes runaway greenhouse effect (4d) : http://www.youtube.com/watch?v=HqFVxWfVtoo (2:05).

The atmosphere of Venus is so thick that the atmospheric pressure on the planet’s surface is 90 times greater than the atmospheric pressure on Earth’s surface. The dense atmosphere totally obscures the surface of Venus, even from spacecraft orbiting the planet.

Venus’s Surface

Since spacecraft cannot see through the thick atmosphere, radar is used to map Venus’ surface. Many features found on the surface are similar to Earth and yet are very different. Figure below shows a topographical map of Venus produced by the Magellan probe using radar.

This false color image of Venus was made from radar data collected by the Magellan probe between 1990 and 1994. What features can you identify?

Orbiting spacecraft have used radar to reveal mountains, valleys, and canyons. Most of the surface has large areas of volcanoes surrounded by plains of lava. In fact, Venus has many more volcanoes than any other planet in the solar system, and some of those volcanoes are very large.

Most of the volcanoes are no longer active, but scientists have found evidence that there is some active volcanism ( Figure below ). Think about what you know about the geology of Earth and what produces volcanoes. What does the presence of volcanoes suggest about the geology of Venus? What evidence would you look for to find the causes of volcanism on Venus?

This image of the Maat Mons volcano with lava beds in the foreground was generated by a computer from radar data. The reddish-orange color is close to what scientists think the color of sunlight would look like on the surface of Venus.

Venus also has very few impact craters compared with Mercury and the Moon. What is the significance of this? Earth has fewer impact craters than Mercury and the Moon, too. Is this for the same reason that Venus has fewer impact craters?

It’s difficult for scientists to figure out the geological history of Venus. The environment is too harsh for a rover to go there. It is even more difficult for students to figure out the geological history of a distant planet based on the information given here. Still, we can piece together a few things.

On Earth, volcanism is generated because the planet’s interior is hot. Much of the volcanic activity is caused by plate tectonic activity. But on Venus, there is no evidence of plate boundaries and volcanic features do not line up the way they do at plate boundaries.

Because the density of impact craters can be used to determine how old a planet’s surface is, the small number of impact craters means that Venus’ surface is young. Scientists think that there is frequent, planet-wide resurfacing of Venus with volcanism taking place in many locations. The cause is heat that builds up below the surface, which has no escape until finally it destroys the crust and results in volcanoes.

Summary

  • Venus has a very thick, carbon dioxide-rich atmosphere, so the planet has a very strong greenhouse effect.
  • The surface of Venus has very few impact craters, so it must be very young. This suggests that the planet experiences volcanism and has a hot interior.
  • Venus has a lot of volcanoes, including some very large ones.

Practice

Use this resource to answer the questions that follow.

http://www.youtube.com/watch?v=NjXt4CtH_9o

1. How long is a day on Venus?

2. How is Venus similar to Earth?

3. Describe Venus' atmospheric composition.

4. What is the average temperature of Venus?

5. What is the rain on Venus?

6. How bright does Venus look to us?

7. Describe the conditions on Venus' surface.

8. What is Sif Mons?

9. How would a probe last on Venus?

10. What country successfully landed probes on Venus?

Want to know more about Venus? See https://www.windows2universe.org/venus/venus.html .

Review

1. Under what conditions is a planet subject to such a large greenhouse effect?

2. Why does the number of impact craters on the surface of a planet indicate the conditions found in the interior?

3. Why does Venus always appear to be near the Sun when viewed from Earth?

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Date Created:

Feb 24, 2012

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Sep 23, 2014
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