Chp 10: Venus

Question 1

Why is it hard for us to view Venus’ surface?

Answer 1

The problem is that we are looking not at a solid surface, but at the top of a layer of cloud which never clears.

Question 2

What are our 3 main sources of information about Venus?

Answer 2

Magellan (USA), USSR missions, Venus Express (Europe)

Question 3

Why does Venus rotate clockwise (opposite to most other planets)?

Answer 3

Venus was rotating in a clockwise direction (called retrograde motion) very slowly
-it’s likely all planets rotated in the same sense originally, and got knocked about by large impacts toward the end of their growth period.

Question 4

Which is longer, a year or a day on Venus?

Answer 4

Days are longer, On Venus, one rotation on its axis takes the equivalent of 243 Earth days and the planet’s orbit around the Sun takes the equivalent of 225 Earth days.

Question 5

What is the composition of the cloud layer? (Venus)

Answer 5

-Venus is completely covered with a thick blanket of clouds (consisting primarily of droplets of liquid/solid sulfur and droplets of sulfuric acid) that hides its surface from view

Question 6

What is the greenhouse effect?

Answer 6

Any greenhouse effect begins with incoming short wavelength light energy from the Sun warming a planet’s surface, but ends up with a surface or near-surface growth of heat because of the inability of the long wavelength infrared energy to escape a CO2-rich atmosphere and get back out to space.

Question 7

How does the greenhouse effect differ on Venus and Earth?

Answer 7

-Venus has a runaway greenhouse effect.
-Without an ozone layer to protect the Venusian
atmosphere from ultraviolet radiation, the atmospheric water was broken up and much of the hydrogen was lost to space.
-The released oxygen presumably formed oxides in the soil.
-runaway greenhouse effect has made the
surface deadly dry.
-Earth avoided this runaway greenhouse effect because it was farther from the Sun and cooler.
-it could form and preserve liquid-water oceans to absorb the carbon dioxide, which left a nitrogen atmosphere that was relatively transparent in some parts of the infrared wavelength range.

Question 8

Of the 3 closest planets to the Sun (Mercury, Venus, Earth), which is the hottest?

Answer 8

Venus is the hottest, then Mercury, lastly Earth

Question 9

Has there ever been water on Venus? What is the evidence? What happened to it?

Answer 9

Yes, Venus Express detected OH (the other breakdown product of the water molecule) in the Venus atmosphere

• the only other planet (so far) to have detectable OH in the atmosphere is Earth. These discoveries can only mean that Venus once had an abundance of liquid water that since broke down to atomic form.
• Without an ozone layer to protect the Venusian atmosphere from ultraviolet radiation, the surface of Venus warmed, any oceans that did exist evaporated

Question 10

Earth and Venus have similar amounts of carbon – so why doesn’t Earth have the same runaway greenhouse effect as Venus?

Answer 10

Earth avoided this runaway greenhouse effect because it was farther from the Sun and cooler.
-it could form and preserve liquid-water oceans to absorb the carbon dioxide, which left a nitrogen atmosphere that was relatively transparent in some parts of the infrared wavelength range.

Question 11

Why are there fewer impact craters (and fewer small craters) on Venus compared to Moon and Mercury?

Answer 11

This is a result of the planet’s dense atmosphere -the small objects just burn up through friction with the atmosphere.

Question 12

What is the evidence that the surface of Venus is young?

Answer 12

• crater counts give an important estimate for the relative age of the surface of a Solar System body – unless the surface has been renewed at some point.
• Venus has fewer craters of any size relative to Moon, Mercury and Mars, and those we see appear to be young, radar images show them to be rough, suggesting they’ve not had time to erode much.
• there has to have been some sort of global resurfacing about 500 million years ago (i.e., planet-wide volcanic eruptions!).

Question 13

What volcanic features exist on the surface of Venus?

Answer 13

• coronae:They are thought to be formed by mantle plumes that bring magma right up under the crust, and then partially subside
• caldera:a deep volcanic crater, possibly the result of one of the coronae blowing its top
• ‘pancake volcanoes’, thought to be formed by quite viscous magma, flattened by the high atmospheric pressure. (viscous: high resistance to flow; opposite of fluid)

Question 14

What causes a global volcanic event? What is the evidence that this has occurred?

Answer 14

-Venus, lacking any sign of plate tectonics, could build up tremendous heat and, like a gigantic pressure cooker periodically ‘boil over’ into volcanic eruptions that resurface the whole planet.
-The theory is that sometime between 300-500 million years ago, the whole planet was resurfaced by basaltic lava flows; they erupted for thousands to millions of years.
-The crater-counting techniques suggest the surface of the planet is no older than about 500
million years.

Question 15

Why do rocks erode faster on Earth than on Venus?

Answer 15

Rocks may be much stronger on Venus simply because they have zero water content. On Earth, volcanic rocks contain several percent water

Question 16

What causes erosion on Venus?

Answer 16

by wind

Question 17

What causes the weak magnetic field on Venus (how does this differ from the cause of the magnetic field on Earth)?

Answer 17

• Venus’s magnetic field doesn’t come from the interior of the planet; the solar wind and the atoms/molecules of the upper atmosphere creates a very weak magnetosphere that drapes itself over the planet and stretches out behind the night-side in a long tail
• Earth’s magnetic field is generated by the speed differential between an inner solid metal core and an outer liquid metal core.

Question 18

What is the proposed geological history of Venus – how does this compare to the stages of formation of the other rocky planets you have read about so far?

Answer 18

The small number of craters on the surface of Venus hints that the entire crust has been replaced within the last half-billion years or so. This may have occurred in a planet-wide overturning as the old crust broke up and sank, and lava flows created a new crust. This could happen periodically on Venus, or the planet may have had a geologic history more like Earth’s, until a single resurfacing not too long ago.
Other planets (Earth, the Moon, and Mercury):
1. Differentiation (separation of material according to density)
2. Cratering (a period of violent impacts)
3. Flooding (not by water but by lava flows)
4. Slow surface evolution

Question 19

What are the arguments for and against Venus having a partially liquid core?

Answer 19

• If Venus has no such zonation (i.e., if the core is completely liquid metal), there should not be a magnetic field.
• Similarly, if Venus does indeed have solid-liquid cores but no difference in rotation speed of the two, there should not be a magnetic field.

Question 20

Why is there no active plate tectonics on Venus?

Answer 20

• the crust is very dry and is consequently about 12% less dense than Earth’s crust. This low-density crust is more buoyant than Earth’s crust and thus resists being push/pulled into the interior.
• Also, the crust is so hot that it is halfway to the melting point of rock. Such hot rock is not very stiff, so it cannot form the rigid plates typical of plate tectonics on Earth.

Question 21

How does the composition of the atmosphere affect the climate? (Venus)

Answer 21

• Carbon dioxide is pretty transparent to in-coming light energy, but fairly opaque to out-going infrared energy
• the wavelengths of radiated energy that CO2 does allow to escape back into space from a planet surface are exactly blocked by water and sulfur dioxide

Question 22

Explain the ‘Runaway Greenhouse Effect’

Answer 22

A runaway greenhouse effect occurs when a planet’s atmosphere contains a more than sufficient amount of greenhouse gas to block thermal radiation from the planet, preventing the planet from cooling and from having liquid water on its surface.

Question 23

Flattened volcanic domes seen on Venus are called ____________ volcanoes

Answer 23

pancake

Question 24

Which is bigger, Venus or Earth?

Answer 24

Earth is slightly bigger

Question 25

Concentric fractures surrounding dome structures on Venus’ surface are called

Answer 25

coronae

Question 26

Venus’ clouds consist primarily of

Answer 26

Sulphur

Question 27

(T/F) Venus exhibits large cyclonic storms at its poles.

Answer 27

True

Question 28

The surface of Venus is approximately

Answer 28

500 million years old

Question 29

What is the main component of the atmosphere? (Venus)

Answer 29

-Below the sulphuric acid layer, the thick atmosphere is composed mainly of carbon dioxide (96.5%), 3.5% nitrogen, 0.1% to 0.4% water vapour, 130 ppm (parts per million; 100 ppm is equivalent to 0.01%) sulfur dioxide, and 60 ppm of free oxygen