Comets and Asteroids I. Comets A. What is a Comet?: It is a small body orbiting the Sun that develops a ______ (a fuzzy atmosphere) and/or a ____ as it approaches the Sun. Comet nuclei range from _____________ __________. B. Origin of Name: Latin “cometes” and Greek “komē” meaning “_______________". C. Composition: Comets are composed of _____, _____, ______ ___, and ____________ such as carbon monoxide, carbon dioxide, methane and ammonia. They are often popularly described as “_____________", though recent observations have revealed dry dusty or rocky surfaces, suggesting that the ices are hidden beneath a crust

D. Orbital Periods: Comets have orbital periods ranging from a _____ years to ____________________ of years. Some comets pass through the inner Solar System only once before being thrown out into interstellar space. 1. Short-period comets originate in the ___________, a disk of small rocky, icy bodies orbiting the Sun beyond the orbit of Neptune. 2. Long-period comets come from the ___________, a spherical collection of bodies outside of the Kuiper Belt that are left over from the formation of the Solar System. 3. The trip inward towards the Sun begins with gravitational interactions with the ____________ (in the case of Kuiper Belt objects) or nearby ______ (in the case of Oort Cloud objects) or can be a result of collisions between objects within these regions. 4. Comets do not orbit forever. Comets have been observed to regularly crash into ________. After many orbits, comets become _________ after they lose all of their volatile materials and become just orbiting hunks of rock.

E. Number of Known Comets: Currently ______ and increasing every year. F. Size of Coma and Tail: The coma may be larger than _______, and ion tails have been observed to extend ______ (150 million km) or more G. Shape of Nuclei: Because of their low mass, comet nuclei have _________ shapes. H. Tails: The streams of dust and gas each form their own distinct tail, pointing in slightly different directions. The tail of dust often forms a _______ tail. The gases form an ____ tail that always points _______________________.

I. Meteor Showers: In their orbits, comets leave a trail of ____ ______ behind them. It is this debris that results in a meteor shower when ______________________________. The Perseid meteor shower occurs every year between August 9 and August 13, when Earth passes through the orbit of the Swift– Tuttle comet. Halley's comet is the source of the Orionid shower in October. J. Rosetta: In ______, an ESA (_European Space Agency_) spacecraft will begin to ______ the comet 67P/Churyumov- Gerasimenko for a period of ________. It will also carry a lander to set down on its surface. II. Asteroids A. Also Known As: ____________ B. Characteristics: Made of _____________. No coma or tail. C. Size: Objects in the main asteroid belt vary greatly in size, from a diameter of ________ for the dwarf planet Ceres down to rocks just _____ of meters across. A few of the largest asteroids are roughly _________, but the vast majority are much smaller and ________.

D. Location: The vast majority are located in the ____________ between the orbits of _________________ in relatively circular orbits. The asteroid belt is estimated to contain between _____ ___ million asteroids larger than 1 km in diameter and millions of smaller ones. E. Mass: The mass of all the objects of the asteroid belt is estimated to be about ___ percent of the mass of the Moon. The dwarf planet, Ceres, alone makes up ____ percent of the total. Adding in the next three largest asteroids brings this figure up to 51%. F. Earth-Crossing Asteroids: There are _____________ ________, of asteroids that intersect the orbit of the Earth Apophis will approach the Earth so closely in ______ that it will pass under the orbit of Earth's geostationary satellites. The Earth will change the trajectory of Apophis and the result may be an even closer approach on April 13, 2036 (Friday the 13 th !!).