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. ______

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