Lecture #13 Thursday, Feb. 15

Guest Lecturer: Prof. Sherrill

Handouts:

Notes:

In The News:

· NEAR Collision with Eros. The Spacecraft landed at 3:07 pm on Monday. Preliminary results: the last photo was taken from 120 m above the surface. Here is the second to last image.

Today:

  1. Review
  2. The Earth (continued)
  3. The Moon

 

  1. The Earth (continued)
    1. Review of the structure of the Earth.
    2. Plate Tectonics
      1. Continents, which are made of less dense material, float on the mantel and drift over time.
      2. Convection helps drive the motion.
    3. The Earth's Atmosphere
      1. The Earth's atmosphere is relatively thin, and is about 100 km thick.
      2. It is made of mostly nitrogen (71%) and oxygen (21%). Oxygen comes as a waste product of photosynthesis and nitrogen from decaying plant and animal material.
      3. There are also small amounts of water vapor, methane and CO2. These are greenhouse gasses. The carbon-dioxide causes a greenhouse effect on the Earth that raises the average temperature from -21 C to 14 C.
      4. The Ozone layer prevents harmful ultraviolet light from reaching the surface.
      5. The Earth can keep its atmosphere because of its high escape velocity of 11.2 km/s and that the average speed of air molecules is well below this value.
    4. Earth’s Magnetic Field
      1. Earth is like a big magnet with a magnetic field that extends far out into space.
      2. Metal liquid core and rapid spin are needed for a strong magnetic field.
      3. The Aurora (Northern Lights) are the result of the Earth’s magnetic field.
    5. Life on Earth
      1. Life on Earth began almost as soon as it was possible around 3.8 billion years ago.
      2. The one thing essential for life on Earth is liquid water.
      3. Multi-celled organisms did not develop until about 1 billion years ago.
      4. From time to time there are mass extinctions. These may be caused by collisions with large meteorites. The extinction of the dinosaurs is thought to have been caused by a collision 65 million years ago.
        1. Half of species died at about the same time
        2. A worldwide layer of sediment has been found dating to the same time.
        3. A candidate is the Chicxulub meteor crater in Mexico. Other craters. Damage
        4. The meteor that killed the dinosaurs was thought to be 6 miles wide.
  1.  The Moon
    1.  Basic Properties
      1.  Density 3.3 g/cm3
      2.  Gravity 1/6th that of Earth ( The moon has 1/80th the mass and about 1/4 the radius)
      3.  No Atmosphere because the escape velocity is only 2.4 km/s. DEMOS
      4. Rotational period of 27.3 days. This means the Moon always keeps the same face toward the Earth. The reason is that Moon is tidally locked to the Earth.
      5. Surface temperature ranges from -250 F to +250 F.
    2. Exploration of the Moon
      1.  Luna Program (Soviet)
        1.  Luna 3 mapped the far side of the Moon in 1959.
        2.  Luna 9 landed on the Moon in 1966.
      2.  Apollo Program send and landed men on the moon from 1968 to 1972. See table 8.2 for details.
        1. Age of rock returned showed the Moon is the same age as the Earth; 4.5 billion years old.
        2. Seismic stations showed the Moon has a cold, solid interior
        3. The Moon does not have a magnetic field. This also indicates no liquid core.
      3. Clementine took detailed pictures of the Moon and showed hints for polar ice caps.
      4. Lunar Prospector (NASA) confirmed ice on the Moon (6 billion tons). Also found that the Moon has a very small iron core.
    3.  The Lunar Surface (picture) (southpole)
      1. Comprised of highlands (older areas over 4 billion years old), many impact craters, and Maria (Latin for sea). The Maria are younger (3.3 to 3.8 billion years old).
      2. The highlands are very heavily cratered.
      3. The maria were formed latter by large impacts where molten material flowed out to make the relatively smooth areas.
      4. The fine-grained sand all over the surface of the Moon is from shattered rocks.
    4. Craters on the Moon
      1. Cratering process
      2. Using Crater Counts to date planets
        1. See figure 8.16
        2. After about 4 billion years ago most of the heavy bombardment stopped.
        3. Very heavily cratered areas in the solar system must be older than 4 billion years.
        4. The Maria must be younger than 4 billion years (rocks returned from them confirm this to be true).
    5. The origin of the Moon - various theories
      1.  fission hypothesis (The Moon broke off the early Earth) - not accepted
        1. material should have fallen back to Earth
        2. the moon should have been in the Earth’s equatorial plane; it is in the ecliptic plane
        3. the hole for the Pacific ocean was formed by continental drift
      2. sister hypothesis (Earth and Moon formed together) – not accepted because it does not explain why the Moon lacks iron.
      3. giant impact theory - most accepted
        1. the Earth suffered a giant impact in its early stages of formation, while the surface was still molten, with a body perhaps the size of Mars.
        2. can explain the chemical composition due to the intense heat generated in the collision.
        3. it could explain the gold and platinum in the surface layers of the Earth.
      4. capture hypothesis (Earth’s gravity captured a stray object) - not very likely because you need a third body to carry away kinetic energy.