CHAPTER 3: NEAR EARTH OBJECTS
SUMMARY
This chapter naturally interests students because it is a departure from standard topics taught in most introductory courses and you have probably seen movies related to this topic. The chapter begins with the Peekskill meteorite example. Near Earth Objects (NEO) are defined as asteroids originate in the asteroid belt between Mars and Jupiter and/or comets that come from the Kuiper Belt or Oort Cloud. The physical characteristics and orbits of these NEOs are discussed in some detail. Students are introduced to the impact features including simple and complex craters, smashed and melted rocks, and material ejected from the crater. The chapter continues with a discussion of NEO hazards. Data collection and analysis techniques such as computer-enhanced telescopes, satellites, and mathematical models are discussed. Students review what scientists are finding as they study the impact hazards associated with the encounter of a large NEO of more than 1 km in diameter with Earth. The chapter concludes by introducing the idea that the collision of an NEO with Earth is the only major natural hazard we may eventually have the potential to prevent.
Meteor Crater (above) is located in Arizona (within a days drive from Imperial Valley). How big was the meteorite that created this crater? Could another impact similar to this happen again?
Consider the known asteroids in the inner solar system (shown above); the ones in red are known to cross Earth's orbit.
3.2 Characteristics of Near-Earth Objects (page 55): near-Earth object (NEO) refers to any objects such as asteroids mor comets that approach Earth. Asteroids originate in the asteroid belt (as stated above), cosmic debris that lies in orbit between the planets Mars and Jupiter (between the inner and outer planets). When an asteroid comes toward Earth it can miss Earth completely, burn brightly in the sky (meteor), explode in the atmosphere (bolide) or strike Earth and become a meteorite. The composition of meteorites is the same as the composition of the terrestrial (inner) planets; what are the implications of this? (read on page 56).
Comets represent cosmic debris left over from the formation of our solar system. Much of a comet's mass is composed of ice, probably surrounding a rocky core. They can be thought of as icy dirtballs, or dirty iceballs. Some scientiste believe that because of the compositon of comets, they may have played a big role in supplying water for the Earth's oceans.
3.3 Impact Features (page 61): look at the photo of metor crater in Arizona (above) and also on page 61. It is a simple crater approximately 1,200 meters (1.2 km or less than one mile) across and is bowl-shaped with no central peaks or ring structures (associated with complex craters). This crater was created by a metorite that is hypothesized to have been approximately 165 feet in diameter (50 meters). This metorite is about the size of a:
Car
Two story house
15-floor office building
Mt. Everest
keep in mind while working on this question, each story of an office building or house is about 10 feet.
also, the book states on page 62 that as a rule of thumb, an NEO impact gouges out a crater about 10-20 times larger than the colliding asteroid or comet. Looking at the numbers for meteor crater discussed above,does this rule work for this impact site?
Section 3.4 is an interesting section on Impact Hazards and Section 3.5 covers interesting topics such as NEO detection. It is interesting to search NASA's website at the following address:
www.nasa.gov
there is much information on space exploration, discoveries and many other topics. Also, interesting observations can be found at NASA's NEO site where NEOs are detected and tracked. Click on the following link to view this website:
neo.jpl.nasa.gov/
LEARNING OBJECTIVES
1. Students will explain concepts related to near-Earth objects (NEOs).
2. Students will compare and contrast the characteristics of planets, asteroids, and comets.
3. Students will evaluate the potential consequences of a present-day impact event on Earth.
4. Students will explain how elements of the scientific method and products of technology are evident in the search for threatening NEOs.