Astronomy 100 -- Terrestrial Planets

MERCURY
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Basic Properties of Mercury
1) How big is it?
A) Diameter = 1/2 Earth diameter.
B) Mass = 1/20 Earth mass.

2) How old it it?

4.6 billion years

3) Where is it?

0.4 A.U. from the Sun.
3.5 light-minutes from the Sun.

4) What's it doing?

Rotation Period = 59 days.
Revolution Period = 88 days.

3 rotation periods = 2 revolution periods!
Look here at Fix Figure 10-03.

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CHARACTERISTICS OF MERCURY

Densest Planet


Core-Mantle-Crust structure
Very large iron core (origin from early impact?)
An interior model: Fix Figure 10-13.

Atmosphere -- none to speak of.


Due to lack of atmosphere, wide range of surface temperatures.
In the sunlight, very hot ==> 500° Centigrade.
In the dark, very cold ==> -200° Centigrade.

Surface is very old. No plate tectonics.

Heavily cratered, with some regions resurfaced just after formation.
Are there explosive volcanic eruptions? Check it out!

Surprise! Water ice in both polar region craters!


Probably from comets.

VENUS
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Basic Properties of Venus

1) How big is it?
A) Diameter is about 1 Earth diameter (just a little smaller).
B) Mass is about 1 Earth mass (just a little smaller).

2) How old it it?

4.6 billion years

3) Where is it?

0.7 A.U. from the Sun.
6 light-minutes from the Sun.

4) What's it doing?

Rotation Period = 243 days in retrograde.
Sun rises in the west and sets in the east.
Why so different?
Revolution Period = 226 days.
Look here at Fix Figure 10-16.

CHARACTERISTICS OF VENUS

• Core-Mantle-Crust structure
  No magnetic field (lack of molten core or slow rotation)

• Atmosphere -- Thick, hot atmosphere mostly carbon dioxide.
  Surface temperature = 500°C = 900°F = 750 K.
  Atmospheric pressure = 100 times Earth's (all due to CO₂)
  Clouds of sulfuric acid.

• Lots of geologic activity, though no plate tectonics.
  Unique geologic features: arachnoids, coronae, and pancake domes.
  Large impact craters, no small ones, on surface.
  Two "continents" -- Ishtar and Aphrodite.
  Lots of volcanos!! More than 1600 major ones.
  These are shield volcanos (like Hawaii, not like Mt. St. Helens).
  No eruptions have been observed.

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VENUS' HOT ATMOSPHERE:
THE GREENHOUSE EFFECT

What is the "Greenhouse Effect?
Carbon dioxide and water vapor, along with several other gases, are known as "GREENHOUSE GASES". Visible and ultraviolet light from the Sun is absorbed by the surface of the planet. This energy is reradiated as infra-red light, which is absorbed by the greenhouse gases, heating up the atmosphere. These gases act like the glass plates of the greenhouse or the windows of a car which let the sunlight in, but prevent the IR radiation from escaping. This then heats of the air in the greenhouse or the car.

Fix Figure 8-25

The atmospheres of Venus and Earth have similar amounts of nitrogen.

Venus' CO₂ is in the atmosphere.
Earth's CO₂ removed by liquid water and Life.

What is the concern for the Earth?

The small amount of CO₂ in the atmosphere causes a warming of the Earth of between 20° and 25° Centigrade. Will more CO₂ cause more warming?

"Can Man Effect the Atmosphere?"

• Increase in CO₂ in the atmosphere.
  1) Fossil fuel burning.
  2) Destruction of rain forests.
• More heat being input.
  Ozone layer destroyed by CFCs means more ultra-violet light will reach the surface.
• Warmer atmosphere leads to melting icecaps and higher sea levels.
  Also, more water vapor in the atmosphere which will lead to more heating.

  Will increased cloud cover help?

What's "In the Bank"?

CFCs take about 40 years to reach the ozone layer.
Ocean levels expected to rise 1 to 5 feet.
Higher sea level ==> Drastic weather changes.

• How delicate is the balance?
  Can a "Runaway Greenhouse" occur?
  Warm ocean ==> more water vapor and CO₂ in atmosphere ==> more heat ==> more evaporation and less CO₂ dissolved in ocean ==> thicker atmosphere holding more heat ==> warmer ocean ==>

  Gaia Theory ==> Earth is a self-regulating organism and will correct itself.
  Just ask the dinosaurs!

MARS

An Extensive Page On Mars

Basic Properties of Mars

1) How big is it?
A) Diameter is about 1/2 Earth diameter.
B) Mass is about 1/10 Earth mass.

2) How old it it?

4.6 billion years

3) Where is it?

1.5 A.U. from the Sun.
12 light-minutes from the Sun.

4) What's it doing?

Rotation Period = 24 hours, very similar to an Earth day.
Revolution Period = 687 days (about 2 years).

5) Two Moons: Phobos (diameter = 22 km). A great close-up of Phobos

Deimos (diameter = 13 km).


6) Red color -- Most likely due to iron oxide (rust).

This red dust in the atmosphere produces a red sky and blue sunsets!

CHARACTERISTICS OF MARS

• Core-Mantle-Crust structure. The Martian Interior.
  
  The iron core is relatively small.
  Very weak magnetic field (iron core may be solid)
  Very little seismic activity (completely solid interior?)

• Extreme surface geologic features, though no plate tectonics.
  Very large shield volcanos.
  Olympus Mons: the largest mountain in the Solar System.
  500 km in diameter, 24 km high.
  3-D Olympus Mons. Be sure to use your red-blue glasses!
  Very large canyons -- Valles Marineris (as long as the US)
  These features are very large with respect to the size of Mars itself.

• Atmosphere -- very thin atmosphere
  Composition is 95% carbon dioxide, 5% nitrogen and argon.
  Atmospheric pressure = 1/100 times Earth's
  Surface temperature (Warmest = 0° C, Coldest = -100° C)
  Clouds (fog) of water vapor.

• Strong evidence for water flow (liquid water) on the surface.
  Two possible scenarios
  1) Lots of rain (early warm atmosphere)
  2) Volcanic eruptions and meteor impacts melt permafrost
  (always thin atmosphere).
  Which of these cases is true is important for whether life could have evolved on this planet.
  Where is the water now?
  1) Evaporated (gone from the planet)
  2) Permafrost (frozen just below the surface)

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Is There Life on Mars?

Viking I and II Landers. Panorama I. Panorama II.

"No one" waved back.
Five experiments with "hard-to-explain" results.
"Bizarre chemistry?"
--- some results have never been reproduced in labs on Earth.

Fossils in Mars meteorites? Maybe. Maybe not.

[How Martian meteorites get to Earth]

There are "bizarre" forms on the Earth.
100,000 year old spores will come to life.
Organisms in deep caves eat rocks!
So, there is hope for finding life on Mars.