This topic submitted by Sarah Mack, Christopher Berg, Nora Hoxha, Jennifer Harman ( Macksa@muohio.edu, bergcs@muohio.edu, Hoxha@muohio.edu, ) on 10/10/03 .

Natural Systems 1 Syllabus---Western Program---Miami University

Impact craters on the Moon
Researchers: Sarah Mack, Nora Hoxha, Christopher Berg, Jennifer Harman

Introduction
Mankind has always felt the need to explore and conquer the unknown; matter of fact, there is even the old clichŽ- curiosity killed the cat. However, this cat is not dead- yet. Numerous efforts have been made to explore the Universe, perhaps the most intriguing body of mass known, and we are still left asking how? why? and what? In particular, the Moon has been subject to observation for as long as humans have had the brain capacity to do so. Before extensive telescope observation and the visit to the Moon in 1969, people believed that the Moon was capable of sustaining life and was home to many living organisms. The Greeks were the first to understand Earths sole satellite, the Moon, at a significant level, but it would not be until 1610, when Galileo peered into his looking glass, that it was determined that the little dark areas on the Moons surface were highlands and valleys (7). We now know that those deep cavities were created by billions of years of meteors impacting the surface.
Knowing that numerous amounts of meteors, asteroids, and comets have crashed into the Moon over billions of years, we became intrigued as to why there are so few craters on the Earth. Also, the recent scientific discovery of an asteroid with the possibility of hitting the earth, 2003 QQ47, sparked an interest in the probability of a collision. Similarly, it was once suggested that a large impact event caused the extinction of nearly 50% of all living species, mainly the dinosaurs, over 65 million years ago. And evidence has been found that a large asteroid did strike the Earth at that time, creating a crater known as Chicxulub off the coast of MexicoÕs Yucatan Peninsula (10). So, in theory, if 2003 QQ47 does strike the Earth, history may be repeated.
We then wondered if the position of the Earth has had an affect on the outcome of impact craters on the Moon. Our hypothesis is that since there is no atmosphere on the Moon to protect it from getting hit by meteors or other potential impactors, the Earth acts as a shield to protect the side of the Moon closest to the Earth, while the far-side is unprotected. Therefore, we predict that there are more impact caters on the far-side of the Moon and less on the near-side. Through satellite images, surface observation, and statistical analysis research, we will explore precisely how much our Earth protects its only satellite from meteors and asteroids.

Background Information
To gather background information for our project, we researched many topics relating to the Moon. A basic understanding of the Moon and its interaction with the Earth is important if we want to be able to accurately conduct our research.
The MoonÕs diameter is 27% of the diameter of the Earth, or about 3,476 km. Its mass is 1/81st that of the Earth, in other words, it would take 81 moons to equal the mass of the Earth (8). It is important to reflect upon these measurements, because the Earth would then provide a lot of protection for the Moon.
Liberation is a rocking movement of the Moon. Due to liberation, on Earth we always view the same 59% of the MoonÕs surface (8). The MoonÕs gravitational attraction to the Earth is stronger on the near-side and weaker on the far-side (12). Additionally, due to this gravitational interaction between the Earth and the Moon, the Moon is locked in phase with its orbit so the same side always faces the Earth (12). The side of the Moon that always faces the Earth is respectively called the near-side of the Moon. Therefore, the far-side of the Moon always faces away from the Earth.
When one observes the Moon, he or she would notice many dark spots. Each dark spot is called a mare (pl. maria). Early astronomers believed that maria were actually once great seas, but they are now just plains on the Moon. Scientific observations have also concluded that most maria are found on the near-side of the Moon, while the far-side has very few, which scientists do not yet understand (8).
A meteorite crater is a depression that results from an impact of a meteorite with any planetary body (1). Most of the craters found on the Moon are circular, with the exception of two that scientists still do not know how they were formed (8). Data collected from satellites and spacecrafts indicate that roughly 3,000,000,000,000 craters with diameters of one meter or greater exist on the Moon's surface (2).In fact, 80% of the Moon's surface has been resurfaced by meteorite, most of which is on the far-side (4). Earth is thought to have had similar collisions with meteors, but because of plate tectonics many of these craters are no longer visible (6). The chances were downsized, but the idea was put into our minds, and we realized that Earth has a delicate balance and an asteroid could have catastrophic affects.
The size, mass, speed, and angle of a falling object determine the size, shape, and complexity of the impact (8). Simple analysis tells us that a small, slow moving object will leave a smaller crater than would a large, fast moving object. Some very large craters can even cause additional craters to result from the original impact (8).
Most meteors strike the Moon at an impact speed of generally 20 km per second, thus resulting in an impact crater 10 to 20 times larger than the size of the impact object (9).
There are two major types of craters: simple impact and complex impact. Simple impact craters are bowl-shaped and smooth. Complex craters often have one or more peaks in the middle of the crater and appear more rigid than simple craters. The diameter of a simple crater is generally less than 15 km, while complex craters have diameters between 20 and 175 km (8). The diameter at which craters become complex depends on the surface gravity of the planet: The greater the gravity, the smaller the diameter that will produce a complex structure. On Earth, this transition diameter is 2Ð4 km; on the Moon, at one-sixth Earth's gravity, the transition diameter is 15Ð20 km. A third type of crater is called an impact basin. There are only 40 impact basins on the Moon, characterized by diameters over 300 km. Additionally, most impact basins are located on the far side of the Moon (8). Interestingly, observations have also revealed that the deepest basin found on the Moon, the Aitken basin, is located on the nearside, while the highest regions of the Moon are found on the far side (12).
King Crater, located on the far-side of the Moon is 77 km in diameter and more than 5 km deep (9). Copernicus Crater, one of the youngest craters believed to have formed around 1 billion years ago is, located on the near-side and is 93 km in diameter. Both King and Copernicus are complex craters; however, the central peak at King is much larger than Copernicus.
This first picture is of the craters found on the near side of the Moon. The second picture is of the far-side of the Moon (11.)

Astronomers have done a lot of investigation and research on the formation of the impact craters on the moon. Impact craters are the remains of the collisions of an asteroids, comets, and meteorite on the moon. The best place to compare and study the craters on the moon was looking and studying impact crater on our own planet, the Earth. According to the studies and research the size and the depth and the form of the craters varies due to the speed, size, and the mass of the meteors, asteroids, comets, and other space junk that hits the moon. Also the angle from where the meteors hit the moon result different types of craters. The small and simple craters are caused by small and slow objects that have a low energy impact. The very large and heavy object can sometimes cause a secondary cratering that is a smaller crater or series of craters formed into the big crater as ejected material falls back to the ground. Comets and asteroids that hit the Moon at such a high speed of 20 kilometers per second will result a crater that is 10 to 20 times larger in diameter then the impacting object. The largest crater that can be seen on the Moon is called Bailly or the 'fields of ruin.' It covers an area of about 26,000 square miles, about the size of West Virginia, and over three times the size of Wales. The crater print will not erode since there is no wind or water on the Moon, and it should take at least 10 million years to fade away.

There are different types of the impact craters on the moon, the complex and the simple types.

The simple type impact craters have a bowl-shaped form, and it is mostly surrounded with smooth walls. This type of crater has a diameter less the 9 miles or 15 kilometers and their depth is about 20 % of the diameter.

The complex type impact craters have a single or multiple peaks in the middle of the crater. The complex craters have a diameter between 12 and 110 miles and the central uplift is about one or a few peaks. Craters with a diameter more then 110 miles can have ring shaped uplift within the crater.

Impact Basin is another type of an impact crater that has a rim diameter greater then 185 miles. These types of impacts produce faulting and other crust deformations.
Most craters on the Moon are circular and there are only few craters that are not circular. For instance the Messier and Messier A in the Mare Fecunditati are an enigma.
Even scientists donÕt know how these craters form.

- Most craters on the moon that have a simple bowl like form have about 15 kilometer in diameter.
- Craters that have a diameter over 15 km have more complex forms that have shallow, flat floors made of solidified lave, a d terraces on the inner-rim walls.
The craters on the near side of the moon differ from that of the far side of the moon. Even though we can never see the far side of the moon, but we can see and analyze the craters by relying on the pictures taken by satellites. From the studies and the research the scientist conclude that there are more craters on the far side of the moon. The reason that there are more craters on the far side then the near side is that the near side is protected by the earth.

Far Side of the Moon

Reference:
1)"Meteorite Crater." Encyclopedia Britannica. 2003. Encyclopedia Britannica Premium Service.
17 Sep, 2003 .

2)Cohen, B. A.,T. D. Swindle, D. A. Kring, 2000, Support for the Lunar Cataclysm Hypothesis from Lunar Meteorite Impact Melt Ages, Science, v. 290, no. 5497, p. 1754-1755.

3)Martel, Linda, "Damage by Impact." PSR Discoveries. Dec. 1997. .

4)"The Univerise in the Classroom." Astronomical Society of the Pacific. 1989.

5)"Moon," Microsoft¬ Encarta¬ Online Encyclopedia 2001
http://encarta.msn.com © 1997-2000 Microsoft Corporation.

6) BBC News. ÒAsteroid danger in 2004 downplayed.Ó 2 September, 2003. http://news.bbc.co.uk/2/hi/uk_news/3200019.stm

7) Cooley, Keith. ÒMoon Trivia.Ó September 2003. http://home.hiwaay.net/~krcool/Astro/moon/moonglossary/moontrivia.htm

(8) ÒCraters- The MoonÓ. Retrieved online: http://www.enchantedlearning.com/subjects/astronomy/moon/Craters.shtml

(9) ÒLunar Impact Crater Geology and StructureÓ. Retrieved online: http://www.lpi.usra.edu/expmoon/science/craterstructure.html

(10) Koeberl, Christian and Sharpton, Virgil L. ÒTerestrial Impact Craters Slide SetÓ. Lunar Planetary Institute. Retrieved online: http://www.lpi.usra.edu/publications/slidesets/craters/index.shtml

(11) ÒWequest: Impact CratersÓ. http://earthview.sdsu.edu/trees/impact.html

(12) ÒThe MoonÓ Retrieved online: http://www.thehubbletelescope.com/Moon.html

13) ÒImpact Craters on the Moon.Ó Enchanted Learning. 3 July 1999.
http://www.enchantedlearning.com/subjects/astronomy/moon/Craters.shtml

14) ÒSurface Properties of the Moon.Ó Astronomy 161. 4 September 2001.
http://csep10.phys.utk.edu/astr161/lect/moon/moon_surface.html

Materials and Methods:

Our experimental design involves: using the Miami University telescope to observe, photograph, and measure impact craters on the Moon, in depth research on past studies (relating to the far-side of the Moon), the use of a virtual Moon atlas, and a sample impact crater exercise.

Class Involvement
Next month, November, during a full moon we will hold a telescope viewing of the near-side of the Moon. We will divide the MoonÕs surface into quarters. We will split the class into four groups and have them count the craters in a predetermined quarter. We will have them count the number of craters three times to ensure accuracy.

We will also have the group take close up photographs of the MoonÕs surface.

Sample Impact Crater Exercise
The reason for a sample impact crater exercise is to demonstrate how the Earth protects the near-side of the Moon, not only from meteors in general, but also from head on collisions. The far-side of the Moon is susceptible to head on collisions, while any meteors heading toward the near-side of the Moon at a 90 degree angle will either burn up in the EarthÕs atmosphere, or collide with the Earth. Direct meteoric impacts on the MoonÕs surface can potentially cause a different type of surface depressions. This can provide insight as to why the near-side and the far-side have different surface features.

We will use a previously constructed demonstration to show the differences between the meteors that have head on collision with the moon, and meteors that hit at an angle . We will place a bed sheet on the concrete outside and spread a five centimeter layer of flour on top of it. The projectiles we will use are different sized rocks to represent different size meteors. The ratio we are planning on using is 1km: 1cm. We derived this ratio from the fact that a crater's diameter is about ten times that of the impact and its depth is 1/5 of the craters diameter. At first, we will drop the objects from a height of 30cm, 60cm, and 90cm directly perpendicular to the flour base. Then, we will throw the objects from an angle of 30 degrees and 60 degrees, to grasp the concept of meteors hitting the near side of the moon at an angle. We will not record the data because this demonstration is solely to grasp the visual concept of meteors hitting the MoonÕs surface at different angles.

Side of the Moon Hemisphere # of craters 2nd count 3rd count

near North East
near North West
near South East
near South West
near North East
near North West
near South East
near South West
near North East
near North West
near South East
near South West

far North East
far North West
far South East
far South West
far North East
far North West
far South East
far South West
far North East
far North West
far South East
far South West

Research Time Line
Our research project will progress as follows:
Week 1: Gather and analyze previously obtained data on the far-side of the MoonÉ
Saturday November 8th: Class telescope viewing of the Moon.
November 11th: Class receives photographs to count the number of craters.
Week 16th: Give in class demonstration. (Model Crater Project.)

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