Comets are small (km-sized) icy bodies that consist of a large proportion of H2O ice accounting for between 10 and 50 % of their mass. They contain organic matter, ice, and silicates/metal in comparable proportions (Greenberg, 1998). Comets have elliptic trajectories that crosscut the midplane of planetary orbits, which mean they can impact planets. In 1994, comet Shoemaker-Levy 9 crashed into Jupiter at a velocity of 60 km/s after orbiting the planet for ~30 years. This event, which left visible scars on Jupiter’s surface, illustrates well the comet delivery of volatile elements to a planet. The...

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