Chp 8: Moon Flashcards
What is tidal coupling?
-Ever since the stabilization of the Moon after the big collision, Earth’s gravitational influence on its much smaller neighbour has forced the Moon into exactly the same rotational period and orbital period as Earth; this phenomenon is called tidal coupling.
What is a Trojan satellite
(a Trojan is an object that has the same orbit as another body, but doesn’t collide with that body because it’s located in a particular point on the orbit – called a Legrangian point - where it can remain stable and not collide with the other body)
Has Earth ever had more than one satellite?
yes
- Before visiting the Moon how did we know:
a. That the Moon had no atmosphere?
- our understanding of gravity tells us that a world as small as the Moon must have a low escape velocity (the initial velocity any object needs to escape gravity), and gas atoms near its surface escape easily into space.
- we can see dramatic and sharp shadows between daylight and darkness, meaning there is no air on the Moon to scatter light and soften shadows. Clearly, the Moon is an airless (and therefore soundless) world.
Explain how studying impact craters can tell us about the age of the Moon.
Relative ages
- The surface there is saturated with craters, meaning that it would be impossible to form one new crater without destroying the equivalent of one old crater.
- the highlands are old regions where we see craters from early in the history of the Solar System.
What is the maria? Why does it only occur on the near side of the Moon?
- darker areas of the moon is called maria
- The dark material filling the maria is actually dark, solidified basalt lava from earlier periods of lunar volcanism.
- far side’s crust is thicker, therefore has less maria
Are you more likely to see small craters form on the Moon or Earth? Why?
Moon, If the planet has an atmosphere (like Earth), smaller meteoroids may be destroyed in that atmosphere or slowed so much they do not make craters. The Moon, of course, has no atmosphere, so we see craters of all sizes.
If the same size meteorite were to hit the Earth and Moon, which would form the bigger crater?
- Moon, that factor must be larger (perhaps 50 times) because there is no atmosphere to slow objects.
- For Earth impacts, we use a ‘rule of thumb’ that says a crater will be roughly 15-20 times the size of the impactor.
What are the general steps of crater formation?
The kinetic energy of high speed impacts is converted upon impact into thermal, acoustic and mechanical energy; the latter fractures, distorts and ejects rock from the impact site (i.e., it makes a crater!)
What is crater saturation?
a point of saturation: when every new crater obliterates an old one
Why are all Moon rocks igneous rocks?
they formed by the cooling and solidification of molten rock (because surely the surface must have been a ‘magma ocean’ following its assembly out of the ‘impact’ debris ring surrounding Earth)
Why aren’t sedimentary rocks found on the Moon?
The Moon has only weak gravity and no water or atmosphere.
What is the regolith and how is it formed?
Both the highlands and the lowlands of the Moon are covered by a layer of powdered rock and crushed fragments called the regolith.
-About 1 percent of the regolith is meteorite fragments, and the rest is composed of the smashed remains of Moon rocks that have been ground down by the constant blasting by meteoroids.
Is there seismic activity on the Moon?
The Moon is seismically much quieter than Earth - about 100 million times less.
What is the geological history of the Moon?
Stage 1: molten state, As the Moon cooled, denser materials sank to form a small core, and low-density minerals ‘floated’ to the top to form a low-density crust. In this way the Moon differentiated into core, mantle, and crust
Stage 2: period of cratering that began as soon as the crust solidified, Late Heavy Bombardment at the end of planet building.
Stage 3: Such intense cratering led to lava flooding. Although the Moon cooled rapidly after its formation, some process (probably radioactive decay) heated material deep in the crust, and part of that material melted.
Stage 4: This was a final period of slow evolution. most surface changes during this period have been produced by the more or less constant bombardment by small meteoroids. The overall terrain on the Moon is almost fixed.
