Comet Demo Comet Demo Supplies: Apron Zip Lock Bags Beakers Bowl; Large Gloves Safety Goggles Hammer Newspaper and/or Aluminum Foil Spoons Paper Towel (To Clean Up The Mess!) Plastic Table Cover Comet s Chemical Composition Ammonia (50mL) Water (150mL) Charcoal (1TBL) Syrup (1TBL) Soil (1TBL) Dry Ice (500mL) Sand; Organic (Dark) and Less-Organic (Light) (1 TBL) Caution: Dry ice can burn. Therefore, under no uncertain terms may you or any visitor touch, taste, or handle the dry ice without proper the gear. Any such misuse of materials will not be tolerated. Procedure: 1. Cover the table with the plastic table cover 2. Pour about 150 ml of water into a zip lock 3. Add a tablespoon of sand (can use 2 types of sand/soil) and a tablespoon of charcoal; mix thoroughly 4. Add the syrup (represents organic compounds ; mix thoroughly Comet Halley in the Milky Way 5. Add ammonia; about 50 ml; mix thoroughly 6. Add about 500 ml of crushed dry ice to simulate the formation of the nucleus over a period of time this should be added over a large bowl; the mixture has a tendency to overflow a lot! Chabot Space & Science Center Page 1of 6 5/13/2010
7. With gloves on, quickly begin forming a snowball from the outside of the bag. 8. After snowball nucleus has formed and water has frozen, take the nucleus out of the bag allow the nucleus sufficient time to freeze or the comet will break apart. 9. Snowball nucleus should be outgassing like the real thing! Capturing the Visitor: Try these for starters 1. Would you like to see me simulate a comet? 2. Hi, would you like to learn about comets? 3. Would you like to help me make a cosmic snowball? 4. Hello, would you like to see a demonstration about comets? 5. (create your own line here). Next start with a brief introduction to what comets are and the 3 main parts. Key Discussion Areas What is a comet? The name comet comes from the Latin word cometa which means "long-haired". The earliest known record of a comet sighting was made by an astrologer of the Chinese court in 1059 B.C. A ball of rock and ice, often referred to as a dirty snowball. Typically a few kilometers in diameter, comets orbit the Sun in paths that either allow them to pass by the Sun only once or that repeatedly bring them through the solar system (as in the 76-year orbit of Halley's Comet). A comet s signature long, glowing tail is formed when the Sun s heat warms the coma or nucleus, which releases vapors into space. Scientists believe that comets are the debris left from the solar nebula which condensed to form the Sun and planets in our solar system. Most comets are thought to originate in a huge cloud called the Oort Cloud. The Oort Cloud is believed to surround our solar system and reach over halfway to the nearest star, Alpha Centauri, which is 150,000 astronomical units away. Scientists think that about 100 million comets orbit the Sun. A comet has a distinct center called a Chabot Space & Science Center Page 2of 6 5/13/2010
nucleus. Most astronomers think the nucleus is made of frozen water and gases mixed with dust and rocky material. Comet nuclei are described as dirty snowballs. A hazy cloud called a coma surrounds the nucleus. The coma and the nucleus together form the comet's head. A comet typically has a head consisting of a solid nucleus surrounded by a nebulous coma up to 2.4 million kilometers (1.5 million miles) in diameter and an elongated curved vapor tail arising from the coma when sufficiently close to the sun. Comets are thought to consist chiefly of ammonia, methane, carbon dioxide, and water. What are the parts of a comet? Nucleus center of the comet typically only about 1 to 10 miles across. Also referred to as a giant dirty snowball because they contain a mixture of ices (the snowball component) and meteoritic material (the dirt ). The solid, centrally located part of the comet is known as the "nucleus". The nucleus is a repository of dust and frozen gases. When heated by the sun, the gases sublimate and produce an atmosphere surrounding the nucleus known as the coma, which is later, swept into the elongated tail. Coma - As the nucleus moves closer and closer to the Sun, it gets warmer and warmer, which causes its ices to evaporate. When the ices evaporate, they drag Dust particles (i.e., the meteoritic material) off of the surface of the nucleus. Sunlight reflecting off of these dust particles produces a coma, which is primarily what you see when you look at a comet. Tail - The dust particles leaving the nucleus are pushed by light from the Sun into a dust tail. The gas molecules (like water, carbon monoxide, and carbon dioxide) that evaporated from the ices are ionized by sunlight (the sunlight tears off one of their electrons) and are pushed by the solar wind into an ion tail. Where do comets come from? The comets that pass close to the Sun originally came from one of two places: either the Oort Cloud or the Kuiper Belt. You can think of the Oort Cloud as a giant spherical shell surrounding the solar system that's filled with about 1 million million comets (a 1 followed by 12 zeros). Its inner and outer boundaries are not very well defined, but the cloud's extent is roughly from about 900 thousand million miles (a 9 followed by 11 zeros) from the Sun to about 9 million million miles (a 9 followed by 12 zeros) from the Sun. Because they are so far from the Sun, the comets in the Oort Cloud take over 1 million years to make a single revolution around the Chabot Space & Science Center Page 3of 6 5/13/2010
Sun. Occasionally one of these comets feels a tug by another star in our galaxy and gets pushed closer to the Sun. Since such comets are probably making their first such trip near the Sun, they are called "new" comets. Approximately a dozen "new" comets are discovered every year. Around a dozen "new" comets are discovered each year. Short-period comets are more predictable because they take less than 200 years to orbit the Sun. Most come from a region of icy bodies beyond the orbit of Neptune. These icy bodies are variously called Kuiper Belt Objects, Edgeworth-Kuiper Belt Objects, or trans- Neptunian objects. Less predictable are long-period comets, many of which arrive from a distant region called the Oort cloud about 100,000 astronomical units (that is, 100,000 times the mean distance between Earth and the Sun) from the Sun. These comets can take as long as 30 million years to complete one trip around the Sun. (It takes Earth only 1 year to orbit the Sun.) As many as a trillion comets may reside in the Oort cloud, orbiting the Sun near the edge of the Sun's gravitational influence. What types of comets exist? Long-Period Comet A comet having an orbital period greater than 200 years and usually moving in a highly elliptical, eccentric orbit. Comets have orbits that take them great distances from the Sun. Most long-period comets pass through the inner solar system only once. Hale-Bopp is an example of a long-period comet. Periodic Comet A comet in a closed, elliptical orbit within our solar system. These comets typically have orbital periods of less than 200 years. Many comets have orbits that keep them in the inner solar system and allow their trajectories to be calculated with great accuracy and precision. Perhaps the best-known periodic comet is Halley s comet, whose orbital period is 76 years. Short-Period Comet Comets that orbit mainly in the inner solar system. Usually these objects orbit the Sun in less than 200 years. Halley s comet is an example of a short-period comet. Do comets ever crash? Comet Shoemaker-Levy 9 (SL-9), A comet that became gravitationally bound to Jupiter, colliding with the planet in July 1994. Prior to entering the planet s Chabot Space & Science Center Page 4of 6 5/13/2010
atmosphere, the comet broke into several distinct pieces, each with a separate coma and tail. What is dry ice? Dry Ice is frozen carbon dioxide (C02), the gas we exhale as we breathe. It is much denser and colder than traditional ice. Dry Ice is -109.3 F (-79.5 C). Traditional ice is 32 F (0 degrees C). Does dry ice melt? In addition, Dry Ice doesn't melt - it sublimates. Sublimation is the process of going directly from a solid to a gas. Dry Ice by-passes the liquid form, giving it its name "Dry" Ice. Where can you buy dry ice? Some Abertsons & A few AM/PM Mini Markets If You Went to a Comet If you stood on a comet as it approached the Sun, it might vanish beneath your feet! Comets are giant snowballs, but as they approach the Sun, some of their ices vaporize. The gas is expelled from the comet in high-speed jets that also carry tiny bits of rock. Bits of rock from Halley crippled the Giotto spacecraft when it flew through the comet's tail in 1986. What are some of the famous comets? Why study comets? Since comets have spent most of their existence in the outer regions of the solar system, they are essentially ``cosmic refrigerators.'' They are so cold that they have been able to preserve a record of the physical and chemical conditions of the solar system as it existed 4.6 billion years ago, during the time when the planets and Sun were formed. When we observe comets today, in a very real sense we are looking back into the past and learning about the origin of the solar system. Although there are still many things about comets that we do not understand, scientific investigations over the past couple of decades have enabled us to identify at least some of the ices that are contained in comets. For example, we know that plain old water ice is the most abundant constituent of a comet. Since comets frequently collided with the Earth in the first billion years after the solar system was Chabot Space & Science Center Page 5of 6 5/13/2010
formed, it's quite possible that comets provided most of the water on our planet. Life as we know it requires abundant water in order to be viable, so cometary bombardments may have been key to the development of life on the Earth. A large comet or asteroid impacted the Earth just off the Yucatan peninsula in Mexico approximately 65 million years which almost certainly caused global-wide catastrophes, which probably contributed to the extinction of the dinosaurs. While such collisions are few and far between, efforts are being made to map all of the comets and asteroids that pass close to the Earth's orbit so that we can produce a reliable quantitative assessment of the impact hazard. Additional Background Kuiper Belt This region begins beyond Neptune s orbit and encompasses an estimated distance of between 30 and 100 astronomical units. There may be as many as 100 million Kuiper belt comets. Kuiper Belt It is widely believed that the Kuiper Belt is the source of the short-period comets. It acts as a reservoir for these bodies in the same way that the Oort Cloud acts as a reservoir for the long-period comets. Oort Cloud A vast spherical region in the outer reaches of our solar system where a trillion long-period comets (those with orbital periods greater than 200 years) reside. Comets from the Oort Cloud come from all directions, often from as far away as 50,000 astronomical units. As a comet nears the Sun, its surface warms up. Ice vaporizes from its surface and forms a tenuous atmosphere, called a coma, which can span hundreds of thousands of miles. Solar radiation and a steady flow of charged particles called the solar wind push material from the coma away from the Sun, forming a long, glowing tail. English astronomer Edmund Halley was the first person to suggest that comets are members of our solar system. Halley thought that several of the bright comets recorded long before he was born might really be a single comet approaching the Sun once every 76 years or so. The comet was recorded in 1531, 1607, and 1682. Halley predicted the comet would appear again in 1758. When it did, Halley's theory was proved correct. Comet Halley was named in his honor. It last approached the Sun in 1986, and will return again in 2061. The polar caps of Mars have a fair amount of frozen carbon dioxide. Chabot Space & Science Center Page 6of 6 5/13/2010