Main objective: Understanding comet activity

Tool: Extended comet simulation experiments accompanied by theoretical modeling

Top-level science objectives:

  1. Release of surface material:
  • a) How does the high dust-to-ice ratio affect the activity and evolution of surface properties?
  • b) How is a high dust-to-ice ratio capable of ejecting dust?
  • c) Can µm-sized dust particles (as found in the coma and tail) be separated by the outgassing processes despite their high (~kPa) tensile strengths?
  • d) What controls the size distribution of the ejected dust grains, or aggregates?
  • e) Is ejection of water-ice-containing aggregates possible by the outgassing of water ice, or is a super-volatile (CO2) necessary?
  1. Diffusion of volatiles:
    • a) Under which conditions can the transport of water molecules via sublimation and condensation inside the surface material lead to the formation of a solidified ice layer?
    • b) Is this layer capable of preventing sublimating gas molecules (originating from deeper layers) escaping to the exterior? Can this lead to a local pressure build-up beneath the ice crust, ultimately driving cometary outbursts?
    • c) Is the sublimation and re-condensation process capable of increasing the local thermal conductivity and the mechanical strength in a low-pressure environment?

3) Role of the organic material:

     a) How do organic materials affect the mechanical and thermophysical properties of the cometary surface?

     b) Is the evolution of the cometary thermal environment suitable to make organic components a major contributor to the subsurface texture with respect to pore space, mechanical strength, and thermal properties?

4) Surface texture:

     a) Are the observed surface textures original or a result of cometary activity? Can the observed surface textures and morphologies be used in combination with laboratory experiments to deduce details about the formation and evolution of comets?

     b) How do the chemical composition and the physical surface texture influence the spectro-photometric properties of the surface?

  1. Formation and evolution of comets:
    •      a)     Is it possible to understand how the icy and dusty components were mixed prior the formation of the comet nucleus?
    •      b)     How can the measured D/H ratio be used to gather information about the formation and evolution of cometary nuclei?