Name:_____________________________________ Date:_______________ Block: 1 2 3 4 Meteors, Asteroids, & Comets Notes Asteroids: Last remains of _____________________ that built the planets _____ billion years ago! Asteroids are ______________ and _______________ objects that orbit the Sun but are too small to be considered planets. They are known as minor planets. Asteroids range in size from Ceres, which has a diameter of about 1000 km, down to the size of _____________. Sixteen asteroids have a diameter of 240 km or greater. They have been found inside Earth's orbit to beyond Saturn's orbit. Most, however, are contained within a ____________ _____________ that exists between the orbits of Mars and Jupiter. Some have orbits that cross Earth's path and some have even hit the Earth in times past. Asteroid Classifications: Between __________ and ___________ , majority of known asteroids estimated to contain between _____ and _____ million asteroids larger than 1 kilometer (0.6 mile) in diameter, and millions of smaller ones. ______________________: __________ an _________ with a larger planet, but do not collide with it __________ trojans form the most significant population of Trojan asteroids There are Mars and Neptune Trojans, and NASA announced the discovery of an _________ trojan in 2011 _____________________ Asteroids: have orbits that pass ___________ by that of Earth As of June 19, 2013, ___________ near-Earth asteroids are known _____________ are classified as potentially hazardous asteroids - those that could pose a threat to Earth _______________________ Asteroids: Not all asteroids orbit within the asteroid belt. Asteroids with ________________ orbits, reaching into the inner solar system. Some potentially colliding with Mars or Earth. Trojans: Sharing stable orbits along the orbit of Jupiter, they are trapped in the Lagrangian points of Jupiter The Asteroid Belt: Small, irregular objects, mostly in the apparent __________ between the orbits of Mars and Jupiter. Thousands of asteroids with accurately determined _________ are known today. _______________________ Gaps: The asteroid orbits are _________________ evenly distributed throughout the asteroid belt between Mars and Jupiter. There are several gaps where __________________ are found: Near Earth Asteroids (NEA’s): NEA’s are grouped into three categories, named for famous members of each category: 1221 Amor, 1862 Apollo, and 2062 Aten. ______________: Asteroids which cross ___________ orbit but do not quite reach the orbit of Earth. Eros -- target of the NEAR mission -- is a typical Amor. ______________: Asteroids which cross _______________'s orbit with a period greater than 1 year. Geographos represents the Apollos. ______________: Asteroids which cross Earth's orbit with a period less than 1 year. Ra-Shalom is a typical Aten. Colors of Asteroids: M-type (________): ___________, less reddish asteroids, probably made out of ______________; probably iron cores of fragmented asteroids C-type (_______________): Most common; __________ asteroids, probably made out of ____________ materials (carbonaceous chondrites); common in the _____________ asteroid belt S-type (“_____________”): Brighter, redder asteroids, probably made out of _________ ___________ materials and _____________; very common in the ____________ asteroid belt “Colors” to be interpreted as albedo (________________) at different wavelengths. Asteroid Classification: Asteroids are classified into a number of types according to their spectra (and hence their chemical composition) and albedo: ______________ (and rarer B-, F-, & G-types) more than _______% of known asteroids, extremely dark (albedo 0.03) similar to carbonaceous chondrite meteorites? ______________ 15-20% of known asteroids, relatively ________ (albedo .10-.22), metallic nickel-iron mixed with iron- and magnesium-silicates similar to stony-iron meteorites and ordinary chondrites? _____________ most of the rest _______ (albedo .10-.18), nickel-iron similar to iron meteorites? _____ and _____type ______edge of main belt, Trojans, and Jupiter’s small moons. Very ______ Ultra-primitive organic compounds The Origin of Asteroids: Distribution: S-type asteroids in the _______ asteroid belt; C-type asteroids in ________ asteroid belt; they may reflect ______________ during the formation process. However, more complex features found: _____________ shows evidence for impact crater and lava flows. Heat for existence of lava flows probably from radioactive decay of 26Al. The first 10 ____________ profiled against the Earth's ____________. From left to right, 1 Ceres, 2 Pallas, 3 Juno, 4 Vesta, 5 Astraea, 6 Hebe, 7 Iris, 8 Flora, 9 Metis, and 10 Hygiea. Two types of Tails: ______________: Ionized gas pushed away from the comet by the ___________ ____________. Pointing straight away from the sun ______________: Dust set free from vaporizing ice in the comet; carried away from the comet by the sun’s radiation pressure. Lagging _______________ the comet along its trajectory Dust Jets from Comet Nuclei: Jets of dust are ejected _________________ from the nuclei of comets. Fragmentation and Geology of Comet Nuclei: (2 slides) Comet Linear apparently completely vaporized during its sun passage in 2000. Only small rocky ___________________ remained. Geology: Comet nuclei contain ______ of water, ______________, methane, ____________, etc.: Those compounds __________________ (transition from solid directly to gas phase) as comets approach the sun. Densities of comet nuclei: ~ 0.1 – 0.25 g/cm3. Not____________ice balls, but fluffy material with significant amounts of empty space. Fragmentation: Comet nuclei are very _________________ and are easily fragmented. Comet Shoemaker-Levy was disrupted by tidal forces of Jupiter The Origin of Comets: Comets are believed to originate in the ___________ cloud: _____________ influence of occasional passing stars may perturb some orbits and draw them ________________ the inner solar system. Interactions with planets may perturb orbits further, ________________ comets in short-period orbits. The ____________________________: Second ______________ of small, icy bodies in the outer solar system: __________ and __________ may be captured Kuiper belt objects. Meteorites: Distinguish between: _______________ = small body in space ______________ = meteoroid colliding with Earth and producing a visible light trace in the sky ______________ = meteor that survives the plunge through the atmosphere to strike the ground... Sizes range from microscopic dust to a few centimeters: _____________ = meteor that survives the plunge through the atmosphere to strike the ground. Statistically, one meteorite is expected to strike a building somewhere on Earth every _______ months. Typically impact onto the atmosphere with 10 – 30 km/s (≈ 30 times faster than a rifle bullet). Meteor Showers: Most meteors appear in ________________, peaking periodically at specific dates of the year. Radiants of Meteor Showers: Tracing the tracks of meteors in a shower _____________, they appear to come from a common origin, the ______________. Meteoroid Orbits: Meteoroids that contribute to a meteor shower are ____________ particles, orbiting in the path of a __________________. Spread out all along the orbit of the comet. Comet may still exist or have been ________________. Only a few sporadic meteors are not associated with comet orbits. Meteorite Impacts on Earth: Over ________ impact craters found on Earth. Famous example: _________ Crater near Flagstaff, AZ: Formed ~ ______________ years ago by a meteorite of ~ 80 – 100 m diameter. Impact Craters on Earth: Much larger impact features exist on Earth: Impact of a large body formed a crater ~ 180 – 300 km in diameter in the Yucatán peninsula, ~ 65 million years ago. It had a drastic influence on the climate of Earth; possibly responsible for _____________________ of dinosaurs. Finding Meteorites: Most meteorites are __________ and do not produce significant craters. A good place to find meteorites is ____________________! Distinguish between: _____________ = meteorites which have been observed to fall (fall time known). _____________ = meteorites with unknown fall time. Analysis of Meteorites: Meteorites are classified into 3 broad categories, 1. __________ 2. ___________ & 3.________________ What Does a “Meteorite” Look Like?: _________ meteorites are easy to recognize as meteorites (_______, _______ lumps of iron-nickel steel) ~ thus, they are more likely to be found and collected. The Allende Meteorite: Carbonaceous chondrite, fell in 1969 near Pueblito de Allende, Mexico. It showered an area about 50 km x 10 km with over _________ tons of fragments. Extremely temperature-_____________ materials. The Origins of Meteorites: Probably formed in the solar ________________, ~ 4.6 billion years ago. Almost certainly not from comets (in contrast to meteors in meteor showers!). Probably fragments of stony-iron ____________________ Some melted by heat produced by 26Al decay (half-life ~ 715,000 yr). 26Al possibly provided by a nearby ___________________, just a few 100,000 years before formation of the solar system (triggering formation of our sun?) Planetesimals ______________ and differentiate Collisions _____________ material from different depths with different compositions and temperatures. Meteorites cannot have been broken up from planetesimals very long ago, so remains of planetesimals should still exist. __________________ Complete & turn in the quiz questions on a separate sheet of paper WRITE THE QUESTION!! .