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J. R. Green, L. S. Bruesch (Caltech/JPL)
Upcoming in situ and impact missions to cometary nuclei rely on realistic estimates of comet physical properties to aid in the design of spacecraft and mission operations. The unknowns of the in situ environment increase costs and risks to the missions. Laboratory investigations into the physical properties of simulated cometary nucleus materials provide insights, as well as bounding values for the expected in situ environment. We have performed comet simulation experiments for a wide range of comet compositions and evolution at JPL's Extraterrestrial Materials Simulation Laboratory. We create fine-grained cryogenic ice-dust mixtures, contain the materials in an instrumented canister in a cryogenic high vacuum chamber with a solar simulator, and study the effects of insolation and aging by measuring the changing physical properties of the cometary mixtures. In particular, we create suspensions of water and minerals with a composition similar to those expected of cometary nuclei, based on telescopic and spacecraft observations. A mechanical penetrator-scratcher is used to measure penetrability in situ and it disturbs the surface for assessment of surface changes. At the end of each experimental run, core samples are taken for tests of compression strength, surface shear strength, penetrability, porosity, and density. We will report on results for simulation experiments comparing the effects of composition, porosity, and insolation histories for simulated short period comets.
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