Lecture10 - Asteroid types • Asteroids shine by reflected...

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Unformatted text preview: Asteroid types • Asteroids shine by reflected sunlight ¾ Not all wavelengths are equally reflected. Reveals the presence of different materials ¾ Information in both the shape of the spectrum, and the presence of absorption features ¾ Identifies different classes of asteroids • Stony and metallic asteroids are found in the inner belt, while carbonaceous chondrites are more distant. Igneous rock is more commonly found in the inner belt ¾ This is likely imprinted at the time of formation ¾ Tells us something about the temperature structure of the solar nebula • Outermost moons of Jupiter, Saturn, Neptune and two moonlets of Mars: ¾ About half of these have retrograde orbits ¾ Low reflectivity, like the distant (>2.5 AU) asteroids ¾ Phoebe (retrograde moon of Saturn) clearly a C- type (carbonaceous chondrite) asteroid ¾ Others are controversial – in some ways resemble types of asteroids, but not others… could indicate that they are different from asteroids. Asteroids: Heating • Many asteroids are made up of igneous rock, showing that they were once heated. • The amount of energy required to raise the temperature by 1K is known as the specific heat capacity : u v m k c µ 3 ≈ (for solids) ¾ where k=1.38x10-23 J/K is the Boltzmann constant, and µ is the mean molecular mass. • The internal energy of a mass M is MT c kT m M NkT E v u = ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ = = µ 3 3 int int , where N is the total number of particles. • Solar : The energy absorbed from the Sun, by an object of radius R at a distance r , is ( ) ( ) 2 2 2 2 4 1 4 1 r R L A R r L A L Sun V Sun V − = × − = π π ¾ This keeps the surface heated to a temperature K AU r A A T IR V / 280 1 1 4 / 1 ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ − − ≈ • Gravity: The total amount of gravitational potential energy available is R GM E g 2 5 3 − = (for a uniform sphere....
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This note was uploaded on 04/15/2009 for the course PHYS 275 taught by Professor Harris during the Winter '09 term at Waterloo.

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Lecture10 - Asteroid types • Asteroids shine by reflected...

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