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The hydroxil radical is a highly reactive type of water molecule that is "nature's cleaner", combining with many polutants in the atmosphere, but levels are dropping, possibly due to increased aerosol use. Cosmic ripples in space are sounds from the early universe. NASA has regained contact with the space probe Pioneer 10, launched in 1972 and now 11.5 billion kilometres from Earth. A conference about sex determination and the evolution of the human male's Y chromosome.