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Loose Ends

Loose Ends. Finishing our tour of the Solar System. Loose Ends…. Overview: In this unit we will finish our tour of the Solar System with a look at asteroids and comets. We will also examine the possibility of life off the Earth. Objectives:

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Loose Ends

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  1. Loose Ends Finishing our tour of the Solar System

  2. Loose Ends…. • Overview: In this unit we will finish our tour of the Solar System with a look at asteroids and comets. We will also examine the possibility of life off the Earth. • Objectives: • 1. To recognize the properties of asteroids and comets. • 2. Differentiate between Trojan and Apollo asteroids. • 3. Recognize the abundance and positions of asteroids. • 4. Recognize the parts of comets. • 5. Understand what the Oort cloud is. • 6. Differentiate between meteoroids , meteors and meteorites. • 7. Examine cratering. • 8. Examine the possibilities of life with the factors in the Drake equation. • 9. Examine the methods for the search for life.

  3. I. Asteroids • A. What are they? • 1. Asteroids are relatively small rocky objects that orbit the sun. • a. They are sometimes referred to as "minor planets" or "planetoids". • b. We know of ~4000 asteroids although the total number is probably closer to 100,000. http://dsc.discovery.com/video-topics/other/asteroid-belt.htm

  4. 2. Asteroids vary is size from the largest ,Ceres at 940 km across, to ~1/10 of kilometer. The average is probably closer to 300 m in diameter. • 3. Some of the larger asteroids are spherical, but most are highly irregular is their shape. • 4. Composition • a. They seem to vary a lot from each other and knowledge is limited due to their size and distance. • b. Iron and silicates dominate some while others show large amounts of carbon based compounds.

  5. B. Orbits • 1. In general the asteroids have very elliptical orbits compared to the planets. • 2. The vast majority of these orbits lie in a region about halfway between the orbits of Mars and Jupiter called the asteroid belt.

  6. a. The concentration of asteroids within this region suggests that either they are fragments of a broken planet or they are fragments that failed to form a planet in the first place. • b. The small mass, variable composition and gravitational forces from Jupiter all favor the pre-planet explanation for asteroid origin.

  7. 3. Many of the asteroids have orbits that tilt as much as 30 degrees from the plane with the rest of the solar system. • 4. Most orbit in the counter clockwise direction with the rest of the solar system.

  8. C. Trojan Asteroids • 1. There are positions between major gravitational sources where the attraction for object cancels each other out. These points are called LaGrange points. • 2. Two of Jupiter's five LaGrange points lie 60 degrees before and behind Jupiter's position along its orbit. • 3. These positions contain ~50 asteroids called the Trojan asteroids.

  9. D. Apollo Asteroids • 1. The Apollo asteroids are those with such an elliptical orbit that they actually cross Earth's orbit. • 2. We know of a couple a dozen Apollo asteroids ranging from 1 to 10 km in diameter

  10. 3. Calculations of the orbits imply that most Apollo asteroids will eventually hit the Earth. • a. A 1 km sized asteroid would release energy equivalent to a million 1 megaton nuclear weapons when it impacted the planet. • b. Crater numbers suggest that we are hit by an Apollo asteroid every 300,000 years on average.

  11. II. Comets - Dirty Snowballs • A. What are Comets? • 1. Comets are minor icy bodies that orbit the sun in extremely elliptical orbits. • 2. Their name comes from the Greek word Kome meaning "hair", which probably refers to their fuzzy appearance. http://science.discovery.com/video-topics/space-videos/comets.htm

  12. B. Orbits • 1. Comets have highly elliptical orbits that carry them from 50,000 astronomical units to as close as a few hundred thousand kilometers from the Sun. • 2. Their orbits can be in any orientation and direction so they are uniformly distributed around the Sun.

  13. 3. Oort Cloud • a. Most comets are believed to orbit the Sun in a vast region of space called the Oort cloud. • b. The comets that come close to the sun are believed to have been dislodged from longer orbits in the Oort cloud by the gravitational affects of passing stars.

  14. C. Composition and Structure • 1. The nucleus is the main solid body of the comet. • a. The nucleus is small. It is only a few kilometers in diameter. • b. The nucleus is made up of dust particles mixed in a frozen soup of methane, ammonia and water. • 2. As the nucleus nears the Sun the heat produces the coma. • a. The coma is a diffuse halo of dust and ionized gases. • b. The coma can be as big as Jupiter at its maximum size of 100,000 km.

  15. 3. Tale of Two Tails • a. As the comet gets closer to the Sun, the tail, the most prominent feature of comets gets larger. • b. The tail can be as long as an astronomical unit. • c. Tails of either type are created by the solar wind and always point away from the general direction of the Sun. • d. Type I comets have tails that are straight and made of ionized gases such as carbon monoxide, nitrogen and water. • e. Type II comets have broad diffuse tails made of dust. • f. A comet can lose as much as 10 tons of material every second at the height of tail formation.

  16. III. Meteoroids - Might need to sweat the small stuff. • A. Meteoroids - are the small chunks of debris found in space. • 1. Meteoroids and asteroids are both interplanetary fragments. • 2. The difference depends on the size of the fragments. Meteoroids are smaller than 100 meters in diameter. • 3. The sources for these fragments include material left by comets and pieces from asteroid collisions.

  17. B. Meteors - are objects that enter the Earth's atmosphere. • 1. Meteors create bright streaks of light in the sky called "shooting stars" . • 2. These bright lights are caused by great amounts of heat from friction ionizing the air as the meteor accelerates toward the Earth. • 3. Meteors range in speed from 20-75 kilometers per second

  18. 4. Meteor shower • a. As comets orbit the sun they leave micrometeors ranging in size from dust sized particles to pebbles in their wake. • b. Meteor showers occur when the Earth passes through these comet orbital paths. • c. These showers usually have 50-100 meteors per hour but the Leonids have peaked with as many as 100,000 meteors per hour.

  19. C. Meteorite - is a meteor that survives long enough to actually hit the Earth • 1. Craters - The Earth has ~100 craters greater than 0.1 kilometers in diameter. • 2. The diameter of the eventual crater is typically 10 times the diameter of the incoming meteorite.

  20. IV. Life - What are the chances? • A. Nobody really knows. • B. The Green Bank or Drake equation is a formula that attempts to estimate the number of technologically intelligent civilizations in our galaxy. • C. The Drake equation is N = Rstar x fp x ne x fl x fi x ft x L

  21. N = Rstar x fp x ne x fl x fi x ft x L • 1. Rstar - Rate of Star Formation . • 2. fp - Fraction with Planetary Systems. • 3. ne - Number of Habitable Planets. • 4. fl - Fraction of Habitable Planets Where Life Actually Arises. • 5. fi - Fraction of Planets with Life where Intelligence Occurs. • 6. ft - Fraction of Intelligent species that Develop Technology. • 7. L - Average Life Time of a Technological Civilization.

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