• Question: In outer space why do smaller comets and space rocks not break apart from lack of pressure: I know that no vacuum is perfect and there are always a few hydrogen atoms per cubic metre but, when the rocks are far from star or planet gravitational pull, why do the atoms not spread out and become space dust?

    Asked by kjackson113 to Alan on 12 Mar 2014.
    • Photo: Alan Fitzsimmons

      Alan Fitzsimmons answered on 12 Mar 2014:

      Most solid material isn’t held together by pressure. It’s held together by attractive forces between the atoms and molecules that make up an object.

      So comets and asteroids don’t fall apart for the same reason that walls, chairs or people don’t fall apart. The atoms stick to other atoms, and that’s what keeps them together.

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