1. Astronomy 04 The Solar System
Test 2 on Chapters 7-11 will be this Wed 5/21.
Review will be tomorrow.
Astronomy 04 The Solar System
Chapter 20:
“Planet Earth”

2. Four Stages of Planetary Formation:
Condensation
Accretion
Planetesimals
Protoplanet

3. Four Stages of Planetary Development:
Differentiation
Cratering
Flooding
Surface Evolution

4. Differentiation
Early in Earth’s history when it was still totally molten, materials separated according to density.
Metals such as iron (Fe) and nickel (Ni) sank to the center while light rocky materials like silicates (Si) floated to the surface.

5. Cratering
After Earth had cooled and a crust had formed, a heavy bombardment of planetesimals and meteorites blasted its surface forming craters.

6. Flooding
Molten lava flowed through cracks in Earth’s crust produced by planetesimal impacts.
Huge amounts of vapor in the atmosphere condensed and torrential rains fell, drained off the continents and formed the first oceans.

7. Slow Surface Evolution
Air and water erosion along with shifting continental plates constantly changed the appearance of Earth over the last 3.5 billion years.

8. Earth is a unique planet in many ways:
Life exists on Earth surface.
Earth has large amounts of liquid water on its surface.
Earth has oxygen in its atmosphere.

9. Earth is a unique planet in many ways:
Earth surface is constantly being renewed through the process of Plate Tectonics.

10. Earth’s magnetic field protects it from the solar wind.
The rotation of Earth’s highly-conductive iron nickel core generate the magnetic field in a process called the dynamo effect.

11. Chapter 20: “Planet Earth”
Earth’s magnetic field protects it from the solar wind.

13. The surface where the solar wind is first deflected by Earth’s magnetic field is called the bow shock.
The cavity in the solar wind generated by Earth’s magnetic field is called the magnetosphere.

14. High energy particles from the solar wind trapped within the magnetosphere produce the Van Allen belts.

15. The magnetic field of Earth acts with the solar wind to produce the colorful aurora.

16. The crust of Earth is broken up into huge pieces called plates.
The theory that deals with the origin and motion of these plates is called plate tectonics.

17. The huge cracks in Earth’s crust that separate plates are called faults.
Here we see the famous San Andreas fault which runs just to our west through the Santa Cruz Mountains.

19. The plates consist of the crust and the uppermost layers of Earth’s mantle which together form the lithosphere.
At the bottom of the lithosphere – 100 km down – we find the mantle,
The mantle, although solid, is highly elastic. The plates “float” and move on the mantle.

20. Plates are formed along regions called “midocean rifts” where lava wells up from below.
Near the rifts, Earth’s crust is pulling apart at the rate of 2-4 cm per year.

21. In other places, sections of the crust are pushed below the continents into subduction zones. This process builds mountains and volcanoes.

22. Rocks that form near the the midcoean rifts are solidified lava called basalts.

23. One of the marks of plate tectonics is folded mountain chains.
Crustal plates can also split apart to open new seas. The first sign of such splitting is a long, straight, deep depression called a rift valley.

24. About 250 million years ago all continents belonged to a single land mass called Pangea.
Gradually the plates drifted apart from each other forming the land masses we know today.

25. The first atmosphere of Earth called the primeval atmosphere consisted of hydrogen, helium, methane and ammonia.
A secondary atmosphere was formed as Earth cooled through the process of outgassing. It consisted of carbon dioxide and water vapor.
When plant life appeared on Earth, carbon dioxide was oxygen was produced through the process of photosynthesis.

26. Oxygen reacted with sunlight to produce ozone gas which shielded Earth from lethal short wavelength radiation from the Sun and set the stage for the appearance of animal and human life.

27. Today, humans are releasing large amounts of greenhouse gases into the atmosphere which may be resulting in global warming.
This warming is due to the greenhouse effect.

28. The Solar System Chapter 21.1: “The Moon”
Astronomy 04
The Solar System Chapter 21.1:
“The Moon”
Please pick up your Test 2 Scantron on front table
if you haven’t already.

29. The diameter of the Moon is 3476 km (2160 miles) with a mean distance from the Earth of 384,000 km (239, 000 miles).
The distance of the Moon from Earth varies from about …
220,000 to 260,000 miles.
The Moon has a gravity 1/6 that of Earth.
The Moon has no atmosphere.

30. The combination of the Moon's lower mass and its smaller radius means that its surface gravity is 1/6 the Earth's surface gravity.
Walking on the Moon is much different from walking on the Earth, as is falling on the Moon.

31. The Moon/Earth mass ratio is 1/80.
The Moon is made mostly of rock with little metallic material.
The average density of the Moon is 3.37 g/cm3 which is consistent with basaltic silicates and not consistent with a large iron (Fe)/nickel (Ni) core like the Earth.
This relates to the Giant Impact Theory of the Moon’s formation.

33. The lunar surface is a grey-tan color with a low albedo of 0.07

34. General Properties of the Moon
The Moon has 1/80th mass of Earth and 1/6th the gravity – not enough gravity to retain an atmosphere.
Any gases expelled or outgassed during the Moon’s early history have escaped.
Luna 3 was a Russian spacecraft which returned first photos of Moon’s far side in 1959 and Luna 9 first spacecraft to land on Moon in 1966.
It was the U.S. Apollo Program which used 9 spacecraft during the period to put 12 astronauts on the Moon’s surface.

35. The U.S. Apollo Program accomplished three major objects for lunar science:
It collected 837 lbs of moon rock which was returned to Earth.
It deployed ALSEP (Apollo Lunar Surface Experiments Packages)
The Apollo Command Module which orbited Moon photographed and analyzed the lunar surface.
  Today no nation has the technical ability to return to the Moon. It would take a ten year committed effort to do so.

39. Moon’s surface is covered with fine-grained soil or dust
a few cm deep.

40. The Moon has a cold solid interior and little seismic activity.
The Moon is geologically dead and has experienced little change over the last 3.5 billion years.

41. The Moon also lacks a magnetic field which would be generated by motions in liquid metallic core.
Moon rock has been dated from 3.3 to 4.4 billion years. The oldest earth rock is dated to 3.8 billion years.

42. Chapter 21.1: “The Moon”
Please pick up your Test 2 Scantron on front table
if you haven’t already.

43. The Major Surface Features:
Maria,
Highlands
Craters
Rays
Impact Basins
Mountains
Rilles (Valleys)

44. The dark areas are called maria or seas.
The Moon’s surface shows light rough cratered areas and dark relatively smooth areas with fewer craters.
The dark areas are called maria or seas.

45. Maria Maria cover 17% of Moon’s surface and are much less cratered.
They consist of volcanic plains and impact basins. They are
composed of basaltic rocks dated to 3.8 billion years.

46. Maria:
Dark-colored regions which turn out to be smooth plains of basaltic lava.
They are the remnants of large impact events that cracked the crust and allowed the lava from the mantle to flow upward and erase early cratering.
Note that the impacts must have occurred after the initial phase of cratering.

47. The Moon – Part 2
Highlands:
The lighter colored, heavily cratered regions are called the lunar highlands.
The bare, chaotic terrain indicates that these regions are primordial and one would expect the oldest rocks in these regions.

48. Lunar Highlands
The lunar highlands are the oldest geologically. They date
to 4.4 billion years and are composed of anorthosites
(silicate rocks). The lunar highlands are heavily cratered.

50. Normal, round craters are due to impacts from objects up to a couple thousand meters.
Object larger (asteroids) will typically crack the crust and form impact basins.

52. Lunar mountains have low rounded profiles and are the result of early impacts.

53. Mare Oriental: The Moon’s Largest Impact Basin
The Moon – Part 2

54. Geological History of the Moon:
The weight of the evidence is that the Moon was active geologically in its early history, but the general evidence suggests that the Moon has been essentially dead geologically for more than 3 billion years.
Based on that evidence, we believe the chronology of Lunar geology was as follows:
The Moon was formed about 4.5 billion years. The surface was subjected continuously to an intense meteor bombardment associated with debris left over from the formation of the Solar System.
As the intense meteor bombardment associated with debris left over from the formation of the Solar System continued, most of the craters that we now see on the surface of the Moon were formed.

55. The largest meteoroids punctured the Moon’s crust and lava poured out from inside the Moon producing the Moon’s mare and impact basins.
The regions that were not covered by the lava flows are the present Highlands; thus, they are heavily cratered, and formed from different rocks than the seas.
The volcanism stopped about 3.1 billion years ago: the Moon has been largely dead geologically since then except for the occasional meteor impact or small moonquake, and micro-meteorite erosion of the surface.

56. Erosion is slow on a world without an atmosphere and is caused by:
1) slumping (gravity)
2) other impacts
3) temperature changes
4) moonquakes
The result is that young craters have sharp edges (usually less than 200 million years old) and old craters are rounded, smoother (with ages of order a billion years old).

57. Current crater-formation-rate can be estimated from the number of craters and the number of potential projectiles present in the Solar System today.
It indicates a crater of 1 km is formed every 200,000 years.
A 10 km crater is formed every few million years.
A 100 km crater every billion years.
Both this and radioactive dating of moon indicates age of 4.5 billion years.

58. Origin of the Moon
The Fission Theory suggests the Moon broke off from Earth. But this is Impossible physically. It cannot be modeled by computer. If this were then case then why are Earth and the Moon such different compositions?
The Capture Theory proposes the Moon formed elsewhere but was captured by Earth’s gravity. But this is highly improbable mechanically.

59. Origin of the Moon
The Sister Theory suggests the Moon formed together with but independent of Earth.
The Giant Impact Theory suggests the Moon formed when a giant planetesimal struck Earth and threw material off into space.