L9GH09Small_SS_Bodies_III_Asteroids

L9GH09Small_SS_Bodies_III_Asteroids - Small SS Bodies III:...

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February 3, 2009 asteroids Small SS Bodies III: Asteroids •Lecture topics: ¾ asteroids: shape, composition, heating •Text reading: Chapter 7
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February 3, 2009 asteroids Ida and Dactyl: binary system Orbital separation: 110 km • Size: 56x15 km • From (difficult) measurement of Dactyl’s orbit, mass is ~4.4x10 16 kg. • Density is therefore ~2700 kg/m 3 , about as expected for solid rock. • Similar density found for Eros (right), visited by the NEAR spacecraft
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February 3, 2009 asteroids Densities •Need to know mass, from orbiting spacecraft or small moons •E.g. Eugenia (below) ¾ Orbit of small moon can be measured. ¾ From this orbit we can get a pretty good mass estimate: 6x10 18 kg ¾ Inferring a size from its brightness, gives a density of only ~ 1200 kg/m 3 . ¾ Eugenia is probably a loosely bound rubble pile. V M = ρ
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February 3, 2009 asteroids Asteroid densities Low-density Mathilde: • huge crater = evidence of a large collision • impact probably broke up the asteroid, but it is still loosely held together Asteroid Density (kg/m 3 ) 1 Ceres 2050 2 Pallas 4200 4 Vesta 4300 16 Psyche 1800 20 Massalia 2700 45 Eugenia 1200 121 Herminoe 1800 243 Ida 2700 253 Mathilde 1300 433 Eros 2670 Why do we want to know asteroid densities?
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February 3, 2009 asteroids Asteroid shapes
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L9GH09Small_SS_Bodies_III_Asteroids - Small SS Bodies III:...

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