ESA’s Rosetta spacecraft has provided evidence for a daily water-ice cycle on and near the surface of comets.

ESA’s Rosetta spacecraft has provided evidence for a daily water-ice cycle on and near the surface of comets.

Comets are celestial bodies comprising a mixture of dust and ices, which they periodically shed as they swing towards their closest point to the Sun along their highly eccentric orbits.

As sunlight heats the frozen nucleus of a comet, the ice in it – mainly water but also other ‘volatiles’ such as carbon monoxide and carbon dioxide – turns directly into a gas.

This gas flows away from the comet, carrying dust particles along. Together, gas and dust build up the bright halo and tails that are characteristic of comets.

Source & further reading:
http://www.esa.int/Our_Activities/Space_Science/Rosetta/Rosetta_reveals_comet_s_water-ice_cycle

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