Chapter 8: The Moon Flashcards
What is special about the Moon compared to other objects in the sky?
The only nearby object for which our eyes can ‘resolve features’ of it, meaning its the only object we can see with the naked eye and actually be able to make out it’s features
What have we already learned about the origin of the moon in chapter 6?
- we learned that the moon was created as a result of an impact of earth with a mars-sized planet called Theia
- The collision resulted in a mixing of the two bodies, with Earth getting most of the metal core of the impacting body, leaving the Moon with relatively low density material richer in silicon, aluminum, magnesium and oxygen than in elements like iron and nickel.
- following the collision, the two bodies became ‘solar dance partners’, meaning that there is a gravitational
attraction between the two that dictates the physical properties of their orbital and rotational motion.
What is tidal coupling? What is the result of the tidal coupling of the Moon and Earth?
- Earth’s gravitational influence on the Moon has forced the Moon into exactly the same rotational period and orbital period as Earth; this phenomenon is called tidal coupling.
- The result of the synchronized pattern is that we always see only one hemisphere of the Moon, and the ‘far side’ never rotates into a position of view.
How is the Earth-Moon relationship changing over time in such a way that tidal coupling will be ‘complete’?
- the relationship between Earth and the Moon is constantly changing such that eventually tidal coupling will be complete: not only will one face of the Moon constantly point toward Earth, but one face of Earth will constantly point toward the Moon.
- To accomplish this, Earth’s rotation rate must keep slowing and the distance between Earth and the Moon must keep increasing.
- This will not happen any time soon
has the earth always had only one satellite?
earth has not always had only one satellite: between September, 2006 and June, 2007, a little asteroid (named 2006 RH120) flew so close to Earth it was captured by the planet’s gravity. The little asteroid did about 4 orbits, and then continued on its way
What is a Trojan satellite? How does this compare with the moon, which is a natural satellite?
A Trojan satellite is an object that stays in one position relative to a planet as it follows the same orbit as that planet.
This point at which is stays stationary relative to the planet is called a Legrangian point.
A natural satellite orbits around a planet (such as the Moon orbiting earth) wheras a Trojan satellite doesn’t orbit Earth directly; instead, it shares Earth’s orbit around the Sun but stays in a stable position either ahead of or behind Earth. It “follows” Earth as both orbit the Sun.
Earth has at least 1 Trojan.
How many people have walked on the Moon?
Only 12 people have ever stood on the Moon.
Does the Moon have an atmosphere?
No, the Moon is airless, which is why shadows are sharp and not softened like on Earth.
how did we know the Moon is an airless world (no atmosphere) even before we had any samples of the Moon?
- 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) – therefore gas atoms near its surface escape easily into space
- dramatic and sharp shadows between daylight and darkness, meaning there is no air on the Moon to scatter light and soften shadows.
What other property can we infer about the Moon, knowing that it is an airless world?
an airless world is also a soundless world
What is the side of the Moon that faces Earth called?
It is called the near side.
What are the lighter areas on the Moon’s surface called?
The lighter areas are called the lunar highlands.
What type of rock makes up the lunar highlands?
The lunar highlands are made of a rock called anorthosite.
What are the darker areas on the Moon called?
The darker areas are called maria (the singular is mare).
What fills the maria on the Moon?
The maria are filled with dark, solidified basalt lava from ancient volcanic activity.
How long has the Moon been volcanically inactive?
The Moon has been volcanically dead for about 3 billion years.
How do the craters on the highlands and maria compare?
Both the highlands and maria have craters from asteroid impacts, but the highlands have many more craters than the maria.
What causes craters?
asteroid impacts
Does the Moon have folded mountain ranges like Earth does?
No, the Moon doesn’t have folded mountain ranges. What looks like mountains are actually just heavily cratered areas of the lunar highlands.
What does it mean that the lunar highlands are “saturated with craters”?
It means the highlands are so full of craters that forming a new one would destroy an old one.
What does the saturation of craters on the highlands indicate about the highlands’ age?
It shows that the highlands are very old, as they have accumulated many craters over time, some of them from the early period of our solar system.
What are the relative ages of the highlands vs maria?
the maria are younger than the highlands
What are maria (singluar is mare). What are they made of? What percent of Moon’s surface do they cover?
The lowlands of the Moon –
The maria are areas of ancient lava flows with only a few centimetres of loose dust on their surfaces, and they cover 17% of the Moon’s surface.
How deep is the loose dust that covers the maria?
The maria are covered by only a few centimeters of loose dust.
Did the lava that created the maria form high peaks?
No, the lava was too fluid to form high peaks.
What are sinuous rilles, and where are they found?
How were some sinuous rilles formed?
Sinuous rilles are long, winding channels often found near the edges of the maria, formed by flowing lava.
In some cases, such a channel may have had a roof of solid rock, forming a lava tube. When the lava drained away, meteoroid impacts collapsed the roof to form a sinuous rille.
How does the appearance of the far side of the Moon differ from the near side?
The far side has almost no maria and is much more heavily cratered by asteroid impacts
Which side is the near side of the moon and which is the far side
the near side is on the right - smoother and more maria
the far side is the left - heavily cratered and hardly any maria
What information can we learn from the craters of a planet?
The number and distribution of craters can tell us about the age and history of the surface, the nature of its surface material, and even aspects of its internal structure
- the more impact craters a surface has, the older that surface must be because it has been around for longer to experience more impacts
define meteoroid
define asteroid
meteoroid: sand size to 100m in diameter
asteroid: 100m to 1000km in diameter
What does the number of impact craters on a surface indicate about its age?
The more impact craters a surface has, the older it is, because it indicates a longer exposure to potential impacts.
How can scientists use crater counts to estimate the age of a surface?
By estimating the rate of crater production and counting the total number of craters, scientists can calculate the relative age of the surface. (it can not give us an age in years but we can compare which surfaces are older vs younger)
What can even a small telescope reveal about the Moon?
A small telescope can reveal many craters on the Moon’s surface.
How often do objects a few tens of meters in diameter likely strike the Moon?
Are large impacts common on the Moon today?
Objects a few tens of meters in diameter probably strike the Moon every 50 years or so.]
large impacts are quite rare today, and most of the craters we see were formed during the Solar System’s youth.
When was the first ‘real-time’ small meteoroid impact observed on the Moon?
The first real-time observation of a small meteoroid impact on the Moon was in 1999. we continue to see small events like that but no large impacts.
What is the mass of the moon?
7.4 x 10^22 kg
this is around the same mass that was accumulated by earth during Late Heavy Bombardment
Why do meteotoids and asteroids typically strike planets at 10 km per second or faster?
Because of the combination of orbital speed and planetary gravity, meteoroids (and asteroids) typically strike planets at 10 or more kilometres per second.
Why do smaller meteoroids often fail to form craters on planets like Earth?
The atmosphere can slow down or destroy smaller meteoroids before they reach the surface.
What types of energy are created when a meteoroid or asteroid impacts a surface?
The impact converts kinetic energy into:
* thermal energy (heat)
* acoustic energy (sound)
* and mechanical energy (rock fracturing and ejection).
What is a shockwave, and how does it affect the rock during an impact?
A shockwave is a zone of highly compressed energy that compresses and deforms the rock, making it act almost like a fluid around the impact site.
What happens to the rock layers below the surface during an impact?
How is the rim of a crater formed?
upon penetrating the surface, this shockwave ‘explodes’ or releases energy below surface, any rock layers that may initially have been flat are heaved upward and outward, bent back, and folded back over surrounding rock
The rim around the crater is built partly from this up-thrust rock and partly from excavated debris dumped around the edge. (excavated debris refers to material that is thrown out or removed from the ground during the formation of a crater. When a meteoroid or asteroid impacts the surface, the force of the collision is so powerful that it breaks apart and ejects pieces of the surface material outward. This debris is then scattered around the crater and contributes to building the raised rim or edge of the crater.)
Explain 5 steps in crater formation and draw a diagram of the formed crater
1. Impact of meteorite: A meteorite strikes the surface at high speed. The initial contact generates a shock wave that starts to compress the surface material.
2. Beginning of shock wave: The shock wave from the impact begins to travel downwards and outwards. The subsurface layers start to react to the shock, beginning the deformation process.
3. Compression wave: The compression wave intensifies as it moves through the subsurface, causing the material to compress and fracture. The surrounding rock begins to crack and move, setting the stage for the crater’s formation.
4. Ejecta: The shock wave reaches a critical point where it pushes outwards strongly, throwing up debris and material from the surface. This ejected material, known as ejecta, starts to form a curtain of debris around the impact site.
5. Crater formation: The area below the impact collapses into a bowl shape, forming the actual crater.
Features of crater:
Ejecta blanket: The debris thrown out during the impact settles around the new crater.
Overturned crater rim: The edges of the crater where the ground has been pushed up and folded back due to the impact.
Fracture system: Cracks and faults that appear in and around the crater due to the intense stress and deformation caused by the impact.
Crater: The final, bowl-shaped depression.
How do scientists use crater size frequency distribution (CSFD) to estimate the age of celestial surfaces like the Moon’s
Scientists plot the number of craters against their sizes on a graph that typically forms a straight line due to more small impactors than large ones, causing more smaller craters.
As a surface ages and collects impacts, this line shifts upward, indicating more craters.
**Crater saturation **occurs when new impacts start obliterating old craters, which helps identify very old surfaces. This method, enhanced with age data from lunar samples, allows scientists to calculate the relative ages of different Moon regions by observing their positions on the cratering curve.
The term “cumulative” refers to the fact that for each point on the x-axis (crater diameter), the y-axis value represents the total number of craters per square kilometer that are equal to or larger than that diameter.
In logarithmic plots, the downward trend does not actually indicate a reduction in the cumulative total. Instead, it shows that the rate of increase in the number of craters is decreasing as crater size increases. This is because larger craters are rarer than smaller ones. The line trends downward due to the logarithmic scaling of both axes, emphasizing the rapid drop-off in frequency as crater size increases.
What is represented in this image?
this is a cumulative crater size frequency distribution
How have scientists built a geological time scale for the moon?
By carefully counting craters on the surface different regions of the Moon and figuring out relative ages
Pre-Nectarian Period
Age: More than 3.92 billion years ago.
This period includes the formation of the Moon and is characterized by intense bombardment by meteorites, leading to numerous impact basins. The craters from this era are the oldest and have been heavily modified by subsequent impacts.
Nectarian Period
Age: About 3.92 to 3.85 billion years ago.
Named after the Nectaris Basin, this period features the creation of several large basins. The surface still bears signs of the heavy bombardment phase.
Imbrian Period
Age: 3.85 to about 3.16 billion years ago.
Early Imbrian: Characterized by the formation of the Imbrian and Orientale basins.
Late Imbrian: Known for extensive volcanic activity that led to the formation of mare basalts, which are large, dark, basaltic plains formed from ancient volcanic eruptions.
Eratosthenian Period
Age: About 3.2 to 1.1 billion years ago.
This period is marked by fewer basalt flows and the formation of newer craters with faint rays—ejecta that appears as light streaks emanating from craters.
Copernican Period
Age: 1.1 billion years ago to present.
Characterized by the most recent craters that have bright rays, indicating they are younger and have not been weathered or darkened by space weathering. This period is named after the prominent crater Copernicus.
What does this graph illustrate?
illustrates the relationship between crater density and the age of lunar surfaces
graph starts from the right at 0 (present time) and goes to the left, the negative numbers meaning that it goes back in time.
The downward trend in crater density over time reflects a decrease in the rate at which impacts occurred.
What is this image
the Luna 9 spacecraft, the first ever spacecraft to soft land on another planetary body, launched by the Soviets
What are mare basalts, and how old are they?
Mare basalts are dense, dark rocks formed from volcanic activity in the lunar maria, aged between about 3.1 and 3.8 billion years.
What is represented in this image
(a) cross sections of the moon based on analysis of seismograms (c) collected by Apollo seismometers (b)
What is this image?
Lunar maria
Draw a diagram of moon crustal thickness variation and the proportions of its layers
What is the largest impact basin in the Solar System, and where is it located?
The Aitken Basin, located near the Moon’s south pole, is the largest impact basin in the Solar System. It is about 2,500 kilometers in diameter and 13 kilometers deep.
