PES 105        Fall 2001 General Astronomy I

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Lecture Notes:

Venus

text: , Chapter 8: Section 8.3

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Introduction and General Properties

Here is a good link for information about the Venus: http://seds.lpl.arizona.edu/billa/tnp/venus.html

Here is a good link for more information, photos and movies about Venus: http://www.solarviews.com/eng/venus.htm

Here is a link with pictures of Venus: http://antwrp.gsfc.nasa.gov/apod/index/Venus.html

Venus is always fairly close to the Sun.

often the morning or evening star

albedo = 0.76 . . . . highest of all planets

covered by clouds

density = 5.3 g/cm³ . . . similar to Earth

size: similar to Earth

closest planet to Earth

=> Venus might be like Earth ?

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Motions

orbit:

orbital period = 225 days

rotation:

• rotation period = 243 days
  • siderial "day" is longer than a "year"
  • (solar day = 117 days)
• rotates "backwards"

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Interior

observe NO magnetic field and very slow rotation

Even with slow rotation we expect at least a small field unless:

1. core is not molten - (Why not ?)
2. Venus is undergoing a field reversal !!
3. model is wrong

Venus is differentiated => was molten at some time

continental drift ?

no strong evidence - but some local cracking and motion

volcanoes ?

• definitely active within last 10 million years
• many dormant volcanoes
• gasses in atmosphere from volcanoes
• suspect that Venus may still be active
• Volcanoes of Venus are described at this link: http://www.solarviews.com/eng/venvolc.htm

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Surface

covered by clouds

use radar mapping from Earth and from spacecraft

Observe:

• rolling plains (90 %)
  • contain some impact craters and volcanoes
• highlands (10%)
  • tall mountains and valleys
  • two "continents"

Overall - quite flat

This is demonstated in Figure 8.11 [Link to Figure 8.11]

This link has an animation showing elevations in false color: http://www.solarviews.com/cap/venus/vidven2.htm

Erosion - some erosion from wind

Surface age - about 400 million years

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Atmosphere

very dense

Composition:

• carbon dioxide - 96 %
  • strong greenhouse effect traps heat
  • surface temperature about 750 K
    • hotter than Mercury !!
• nitrogen - 4 %
  • from volcanoes ?
• almost no oxygen
  • no life

dense atmosphere leads to high surface pressures (about 100 x Earth)

lightning observed in atmosphere [Galileo spacecraft, 1991]

Ciculation

very slow rotation

so convection should dominate

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History

4.5 billion years ago	planetisimals combine
	planet is molten - differentiation occurs
	hydrogen and carbon monoxide atmosphere
4 billion years ago	crust cools
	craters form from impacts
	hydrogen gas escaped
	water in atmosphere breaks up into hydrogen (escapes) and oxygen (reacts with rocks)
. . . Something happens to cause backwards rotation . . .	Collision with a planetisimal ?
since then	slow evolution and cooling
1/2 billion years ago	major volcanic activity
	lava covers old craters

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