General Colloquium:
General Colloquium:November 8 - 4:00pm Phys 223
(Coffee at 3:30p.m. in room 242)
Vatican Observatory
Castelgandolfo (Italy) and Tucson, Arizona
The new data on the structure of asteroid Eros returned by the NEAR spacecraft shows that it has a density of 2.7 g/cm3, appears to be uniform throughout its interior, and its surface features strongly imply a relatively coherent structure. Yet its surface composition is comparable to meteorites that are 30% more dense than this asteroid. How is this possible? In fact, a number of asteroids now have reasonably reliable density measurements; comparing these data with the densities of meteorites, it appears that some asteroids have densities 50% or more lower than the meteorites thought to represent their composition. These bodies are clearly loose piles of rubble. Such a loosely-packed system will respond to geological processes in a very different manner than coherent rock does, absorbing impact energies that would completely shatter and disrupt a more coherent body. That changes the way we think about how planets were formed from the accretion of small bodies.