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Heavy rainfall during a thunderstorm

A test-tube model for rainfall

The understanding of rainfall is still far from complete. Michael Wilkinson has recently analysed a test-tube model for rainfall, in which partially miscible liquids show periodic cycles of precipitation. A theory based upon Ostwald ripening gives an excellent agreement with the experimental data.

An artist's impression of various types of planet formation

Planet formation and gravitational collapse

The standard model of planet formation builds planets from dust particles in a circumstellar accretion disc. Using estimates of relative velocities of particles in turbulent flows, Michael Wilkinson argued that the collisions are too energetic to allow dust grains to aggregate. An alternative hypothesis for planet formation, termed 'concurrent collapse', was proposed where planets form by gravitational collapse at the same time as their star.

This model explains way many extra-solar planets have highly eccentric orbits. It also stimulated a critical evaluation of existing models for gravitational collapse, resulting in a new model, termed the 'shock-fragmentation' model.

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