Week 7
Why Does the Moon Have Craters?
Embedded Files
Learning Intentions
Learning Intentions
I have developed scientific inquiry and data collection skills
I have investigated the principles of density and diameter of projectiles their role in impact dynamics - specifically the formation of craters during collisions.
I have continued to develop research skills, specifically focussing on analyzing geographical, historical, and socio-economic factors of the use of science.
Tasks
Tasks
Investigation Skills
Prac report: Investigating Craters
Literacy & research
Alternative Criteria D Research Assessment (Formative): Time Zones in China
Knowledge and understanding
Why does the Moon have craters?
Why does the Moon have craters?
An asteroid or meteor is more likely to hit Earth because Earth is a lot bigger than the Moon, giving a meteoroid more area to hit! But we can see many thousands of craters on the Moon and we only know of about 180 on Earth! Why is that?
The truth is both the Earth and the Moon have been hit many, many times throughout their long 4.5 billion year history.
This view of the Moon's cratered North and South Pole was seen by NASA's Clementine spacecraft in 1996. Credit: NASA/JPL/USGS
Where did all of Earth's craters go?
Where did all of Earth's craters go?
The main difference between the two is that Earth has processes that can erase almost all evidence of past impacts. The Moon does not. Pretty much any tiny dent made on the Moon’s surface is going to stay there.
Three processes help Earth keep its surface crater free. The first is called erosion. Earth has weather, water, and plants. These act together to break apart and wear down the ground. Eventually erosion can break a crater down to virtually nothing.
Footprints from Apollo 11 1969 - still visible
The Moon has almost no erosion because it has no atmosphere. That means it has no wind, it has no weather, and it certainly has no plants. Almost nothing can remove marks on its surface once they are made. The dusty footsteps of astronauts who once walked on the Moon are still there today, and they aren’t going anywhere anytime soon.
The second thing is something called tectonics. Tectonics are processes that cause our planet’s surface to form new rocks, get rid of old rocks, and shift around over millions of years.
Because of tectonics, the surface of Earth is recycled many times throughout its long history. As a result, very few rocks on Earth are as old as the rocks on the Moon. The Moon has not had tectonics for billions of years. That’s a lot more time for craters to form and stay put.
The third thing is volcanism. Volcanic flows can cover up impact craters. This is a major way impact craters get covered up elsewhere in our solar system, but it is less important than the recycling of crust here on Earth. The Moon once had large volcanic flows way in the past that did cover up many of the bigger earlier impacts, but it has been without volcanism for around three billion years.
Lunar Craters
Lunar Craters
It appears as a bright spot in the southern highlands with rays of bright material that stretch across much of the nearside.
Tycho's prominence is not due to its size. At 53 miles (85 kilometres) in diameter, it is just one among thousands similarly-sized craters.
What really makes Tycho stand out is its relative youth. It formed recently enough that its beautiful rays, material ejected during the impact event, are still visible as bright streaks. All craters start out looking like this after they form, but their rays gradually fade away as they sit on the surface, exposed to the space environment which over time darkens them until they fade into the background.
How old is Tycho? Because the impact event scattered material to such great distances, it's thought that some of the samples at the Apollo 17 landing site originated at the Tycho impact site. These samples are impact melt glass, and radiometric age dating tells us that they formed 108 million years ago.
So if these samples are truly from Tycho, the crater formed 108 million years ago as well. This may still seem old, but compared to the 3.9 billion-year age for many large lunar craters, Tycho is the new kid on the block. Directly sampling material from within the crater would help us learn more about not just when Tycho formed, but the ages of terrains on other planets throughout the solar system.
Planetary surfaces are dated by counting the number of craters on the surface, and comparing that number to the number of craters that formed on a surface for which we know the age by actually sampling the rocks. The problem is, there aren't that many places for which we've sampled the rocks, and confirming the age of Tycho would help date younger surfaces, which are not well sampled.
Tycho is also of great scientific interest because it is so well preserved, it is a great place to study the mechanics of how an impact crater forms. Tycho's central peak is thought to be material that has rebounded back up after being compressed in the impact, and though it's a peak now, it originated at greater depth than any other portion of the crater. The floor of the crater is covered in impact melt, rocks that were heated to such high temperatures during the impact event that they turned to liquid, and flowed across the floor. In the image below, impact melt flowed downhill and pooled, where it cooled.
Water on the Moon
Water on the Moon
LCROSS mapping of the lunar south pole showing Cabeus and Shackleton craters, which have beenfound to contain ice.
There is water on the Moon—lots of it. Permanently-shadowed craters at both poles have been trapping and accumulating ice for billions of years, research has shown. These cold traps contain at least 600 million tons of ice according to research done over the last few years.
Concentrated stores of ice on the Moon could revolutionize space travel. Lunar ice could be mined and split into its component elements hydrogen and oxygen to make rocket fuel, then brought to low Earth orbit and sold. An orbiting filling station could spur a wave of space travel because spaceships wouldn’t have to bring all the fuel they need from Earth. Considering that it costs about $10,000 to put one kilogram of payload into low earth orbit, there is a huge incentive to set up a mining camp on the Moon to tap these vast deposits of water to create a sustainable expansion into space.
The lunar poles are unique because they have craters that never get a drop of sunlight, making them super cold. Shackleton crater, named after the famous Antarctic explorer Ernest Shackleton, is one that has been studied in detail. Situated at the Moon’s south pole, the interior of Shackleton crater is in permanent shadow. Also, the rim of this crater is in constant sunlight, making it an ideal location as a lunar outpost. Sunlight on the rim could provide energy for solar panels which in turn could provide the energy needed to harvest the water in the crater, and NASA is planning on setting up an outpost there by 2020. NASA’s Lunar Reconnaissance Orbiter (LRO) probed this impact crater with radar back in 2009. Shackleton crater was a good candidate because it is so massive—4.2 km deep and 21 km across, making it one of the deepest crater on the Moon. By analyzing the reflections off Shackleton crater, researchers discovered that is contains radar-transparent material which is consistent with ice.
Several other Moon missions have corroborated the existence of water on the Moon. In 2008, India’s Chandrayaan-1 spacecraft found evidence of water molecules on the lunar surface by deploying an impact probe onto the surface of the moon and then flying through the cloud of debris it kicked up.
Chandrayaan-1 also mapped the moon with radar from 2008 to 2009 and found that the polar regions contained ice within the depths of permanently-shadowed craters. In 2009, the Lunar Crater Observation and Sensing Satellite (LCROSS) also discovered water and ice kicked up after an impact probe smashed into the Cabeus crater near the Moon’s south pole.
Chandrayaan-3 is the third Indian lunar exploration mission.It consists of a lander named Vikram and a rover named Pragyan, similar to those of the Chandrayaan-2 mission.
Chandrayaan-3 was launched on 14 July 2023. The spacecraft entered lunar orbit on 5 August, and the lander touched down in the lunar south pole region on 23 August 2023 at 12:32 UTC, making India the fourth country to successfully land on the Moon, and the first to do so near the lunar south pole.
Investigation skills
PRAC: Investigating craters
PRAC: Investigating craters
Literacy & research
Alternative Criteria D Research Assessment (Formative): Time Zones in China
Alternative Criteria D Research Assessment (Formative): Time Zones in China
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