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Falling Particles

25 February 2017

At https://phys.org/print407145626.html … cosmic dust particles on  their entry into the atmosphere save themselves from disintegration by creating a bubble of protection. Cosmic dust originates in comets and asteroids, in the former debris trails left behind by the passage of comets for example. There is a lot of it out there as comets regularly break up as they round the sun and earth's orbit crosses such debris trails fairly commonly. Water rich minerals seem to survive at twice the number as water free dust particles, and the research was aimed at understanding why this is so. One reason may be that the former contains clays and muds which trap water. As the particle descends through the atmosphere the water boils and this creates a sort of bubble which expands and cools down the particle and slows the rate of descent. It subsequently descends more slowly as a parachute might do, which must be a major part of the survival as these particles hit the atmosphere at speeds of up 40,000 km an hour (or 11 km a second). They are intensely heated by colliding with molecules in the air and many of them are destroyed just by the heating alone. They evaporate into gases that are dissipated in the other atmospheric gases. The survivors, on the other hand, float down to the surface. Cosmic dust has been found on roof tops in urban locations and on the Antarctic ice sheet. It is just a matter of collecting the stuff and analysing it.

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