TERRESTRIAL PLANETS

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saturnbutton1.JPG (21728 bytes)Moon

saturnbutton1.JPG (21728 bytes)Moon - Surface

saturnbutton1.JPG (21728 bytes)Moon - Interior

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saturnbutton1.JPG (21728 bytes)Moon Questions

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Q1.  In considering the origin of the Moon, why is unlikely that Earth captured the Moon as it passed us? Answer

Q2.  How does the impact theory for the origin of the Moon explain general properties of the Moon? Answer

Q3.  How does the co-accretion (or double planet) theory suggest the Moon formed? What are the major deficiencies of this theory for the origin of the Moon? Answer

Q4.  Describe how the Moon formed according to the currently accepted theory. How does it explain the properties of the Moon? Answer

Q5.  Explain the concept of resonance. Answer

 

 

 

 

 




















saturnbutton1.JPG (21728 bytes)Moon - Interior Questions

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Q1.  Why do we believe that the core of the Moon is very small? Answer

 

 

 

 




















 

 

saturnbutton1.JPG (21728 bytes)Moon - Surface Questions

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Q1.  How do we know that most of the Moon’s craters formed very early in its history? Answer

Q2.  What formed the dark regions on the face of the Moon? Other than being darker, how are they different in appearance from the lighter regions? Answer

Q3.  Describe the events which occur during the formation of a medium sized crater. Answer

Q4.  How can we determine the relative age of different parts of the Moon from Earth-based observations alone? Answer

Q5.  Why are all the maria on the side of the Moon that faces Earth? Answer

Q6.  Describe the processes which occur during the formation of a crater. Why do some craters have flat-bottomed floors? Answer

Q7.  Describe the properties of the material found on the surface of the Moon. What role have meteorites played in determining these properties? Answer

Q8.  How is the age of a rock determined? Explain the reasoning behind your procedure. Answer

Q9.  How is a central mountain peak formed in a crater? Answer

Q10.  How do we know the maria are much younger than the highlands on the Moon? Answer

Q11.  How can a resonance affect the motion of an object? Describe a resonance in the solar system, and describe how the motion has been altered. Answer

Q12.  Why is the front side of the Moon different in appearance from the back side? Answer

Q13.  Describe the sequence of events when a large meteor collides with the Moon to create a crater. Answer

Q14.  Why is the surface of the Moon covered by a thick layer of powdery dust? Answer

 

 

 

 




















 

 

 

saturnbutton1.JPG (21728 bytes)Moon Answers

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A1.  The Moon is so large relative to the Earth that it would be very difficult for Earth's gravity to capture it as it moves past us. This is analogous to a human being trying to catch a bowling ball.

A2.  If a large object impacted on Earth and splattered debris into Earth orbit to form the Moon, most of the impactor's core would fall to the center of Earth, leaving the Moon with a very small core. Most of the volatile metals (like gold and silver) would be vaporized, leaving the Moon deficient in those elements.

A3.  The co-accretion theory suggests the Moon formed as a separate object in close association with the forming Earth. That is, they formed at the same time and at the same distance from the sun. This theory fails to explain why the Moon’s core is so much smaller than Earth’s. It also fails to explain the more subtle differences in the chemical composition at the surface, for example, the deficiency on the Moon of volatile metals like gold and lead.

A4.  The currently accepted theory for the formation of the Moon suggests that a Mars-sized body collided with Earth. Some of the material of the colliding body and the surface of Earth were blasted into orbit around Earth, and later collected together to form the Moon. Most of the core material of the impactor would fall to the center of Earth, producing a very small core for the Moon. Most of the volatile metals would be evaporated by the impact and lost.

A5.  Resonance occurs when a small force is applied at the same point in a cycle of motion. For example, a child kicks in the air at the back of each swing on a playground swing. This small force gradually increases the amplitude of the swing to a large effect.

 

 

 

 




















 

saturnbutton1.JPG (21728 bytes)Moon - Interior Answers

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A1.  The average density of the Moon is only barely larger than the average density of a typical rock. Since material in a core should be significantly denser than rock, the core of the Moon cannot be very large or the overall density would be larger.

 

 

 




















 

 

saturnbutton1.JPG (21728 bytes)Moon - Surface Answers

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A1.  By comparing the density of craters (for example, number of craters per million square miles) on different parts of the Moon’s surface with the ages of the rocks found in those regions, we can determine that most of the craters formed very early in the history of the Moon.

A2.  The dark regions on the Moon are lava flows from the early history of the Moon. They have far fewer craters than other regions on the Moon, because the lava covered the earlier craters.

A3.  The energy of motion of the impactor is released on contact in an explosion which destroys the impactor and excavates a crater about 10 times bigger than the original object. The material expelled from the crater is hurled upward, and then falls back to the surface to form a raised ejecta blanket surrounding the new crater. Bedrock under and around the crater is shattered, and the rock closest to the crater may even be melted by the energy released in the explosion.

A4.  The older a region is, the greater the number of craters it will have. Relative ages can be determined by just counting the number of craters in a given area.

A5.  Maria formed as lava oozed to the surface through cracks formed in the crust of the Moon by giant impacts. Because of Earth’s gravitational attraction, the crust is thinner on the side of the Moon which faces Earth. With a thinner crust it was more likely that cracks produced during an impact would reach down to the mantle where molten material was present.

A6.  When an object strikes the surface of a planet, it is moving so rapidly that the force of the collision causes it to explode. The energy of this explosion blows a great deal of material up into the sky — both the impactor and some of the surface material. Shock waves from the explosion also shatter the rock under and around the new crater, and push the surrounding material into a raised rim around the crater. The material blasted out of the crater falls back to the surface to form an ejecta blanket around the crater. In some cases enough of this material falls back into the crater to give it a flat bottom as it partially fills in the new crater.

A7.  The surface material on the Moon is composed of ordinary rock broken into a fine powder or dust. The rocks on the surface of the Moon were ground down by the countless impacts of tiny meteorites.

A8.  The age of a rock can be determined by measuring the amount of a radioactive substance in the rock compared to the amount of its decay product in the rock. This ratio tells us how many half lives (the length of time required for half of the radioactive substance to decay) have occurred since the rock formed. Laboratory measurements of the half life then allow us to find the age of the rock in years.

A9.  When a large meteorite impacts another body, the energy of motion of the impactor causes an explosion which excavates a crater far larger than the original body. When the extra weight of the material from the crater is removed, the remaining crust rebounds by springing upward. If this rebound is frozen in place as the crust re-cools, the central peak will remain.

A10.  The relative age of any solid planetary surface can be determined from the relative density of craters on the surface. The highlands have many more craters per unit area than do the maria. That means that the surface is much older, which has allowed the number of craters to build up over a longer time interval.

A11.  A resonance occurs when a small force acted repeated at the same point in the cycle of motion of an object. Even though the force is very small, its effect accumulates over time to produce a noticeable change in the motion of the object. The force of Earth acting on the "heavy" side of the Moon has slowly pulled that side to always face Earth as the Moon orbits Earth. The action of the sun on Mercury has produced a similar result there, except that Mercury rotates three times for every two orbits around the sun.

A12.  When the Moon was forming, its interior was pulled slightly off center because of the strong pull of gravity of Earth. As a result, the crust on the side which faces Earth is thinner than the crust on the back side. That made it easier for giant impacts on our side of the Moon to crack the early crust so that maria could be formed. There also appear to be more giant impacts on our side of the Moon, perhaps as a result of the gravitational focusing of incoming material by Earth.

A13.  Because of the violence of the impact, the meteor explodes on impact. This explosion blasts out a crater about 10 times larger than the original meteor. This explosion also pushes surrounding surface layers upward, producing a raised rim around the new crater. Powerful shockwaves travel downward into the crust of the Moon, shattering the rocks under the impact. The heat generated by the impact may melt the rocks left in the crater. Material blasted out of the crater falls back to the surface to form an ejecta blanket around the new crater.

A14.  ince the Moon has no atmosphere, even the tiniest meteor strikes the surface at high speed. These tiny specks of rock create tiny craters in the surface material of the Moon and chip off tiny flakes of material. The accumulation of these flakes over billions of years is the regolith or dust found on the surface of the Moon.