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Comets

Comet Hale-Bopp 1997 (Credit: NASA/JPL-Caltech)

Comets are small, fragile, irregularly shaped kilometre-sized bodies composed of a mixture of dust grains and frozen gases, such as water ice, methane, ammonia, carbon monoxide and carbon dioxide. Main cometary reservoirs are the Oort Cloud with a distance of 2000 to 100000 AU from the Sun and the Kuiper belt between 30 and 50 AU.

Comets are thought to be remnant material from the processes of formation and initial development of planets. Since comets formed in the outer parts of the solar nebula in a cold environment, they contain volatile material that has been only moderately altered. Comets have conserved information on the conditions in the early Solar System and are, therefore, of great interest scientifically.

As a result of gravitational disturbances comets can approach the Sun on highly elliptical orbits. Due to solar heating, the surface of the nucleus becomes active, volatiles evaporate, carrying small solid dust particles with them, which produce the comet's coma of gas and dust. The neutral gas species in the coma can be ionised by solar UV photons. The Sun's radiation pressure and solar wind accelerate dust grains and plasma, respectively, forming the dust and ion tails opposite the Sun. These large-scale structures (up to millions of kilometres) are the well-observed characteristic features of comets.

Work carried out by the Department addresses these questions and provides crucial information for the preparation and planning of space missions to comets. Activities of Department members include:

• Thermal modelling of cometary nuclei to simulate their activity
• Concept studies, design, hardware development, operation of space missions to comets and interpretation of the resulting data (e.g. ROSETTA, DS1).
• Simulations on the interaction of cometary plasma with the solar wind.
• Investigations of the role played by asteroids and comets in the development of planets and life on Earth.
• Hydrodynamic models to interpret the gas-dust interaction in the coma.
• Simulations of the impacts of asteroids and comets on planets and the development of strategies for risk mitigation.

For up-to-date details of the activities of Department personnel, see the latest report (click on the link in the right menu bar).