Experimental impact features in Stardust aerogel: How track morphology reflects particle structure,composition, and density |
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| Authors: | Anton T KEARSLEY Mark J BURCHELL Mark C PRICE Michael J COLE Penelope J WOZNIAKIEWICZ Hope A ISHII John P BRADLEY Marc FRIES Nicholas J FOSTER |
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| Institution: | 1. Impacts and Astromaterials Research Centre, Department of Mineralogy, The Natural History Museum, London SW7 5BD, UK;2. School of Physical Science, University of Kent, Canterbury CT2 7NH, UK;3. Institute of Geophysics and Planetary Physics, Lawrence Livermore National Laboratory, Livermore, California 94550, USA;4. Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, Arizona 85719, USA;5. SENCR‐MIC, Fayetteville State University, Fayetteville, North Carolina 28301, USA |
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| Abstract: | Abstract– The Stardust collector shows diverse aerogel track shapes created by impacts of cometary dust. Tracks have been classified into three broad types (A, B, and C), based on relative dimensions of the elongate “stylus” (in Type A “carrots”) and broad “bulb” regions (Types B and C), with occurrence of smaller “styli” in Type B. From our experiments, using a diverse suite of projectile particles shot under Stardust cometary encounter conditions onto similar aerogel targets, we describe differences in impactor behavior and aerogel response resulting in the observed range of Stardust track shapes. We compare tracks made by mineral grains, natural and artificial aggregates of differing subgrain sizes, and diverse organic materials. Impacts of glasses and robust mineral grains generate elongate, narrow Type A tracks (as expected), but with differing levels of abrasion and lateral branch creation. Aggregate particles, both natural and artificial, of a wide range of compositions and volatile contents produce diverse Type B or C shapes. Creation of bulbous tracks is dependent upon impactor internal structure, grain size distribution, and strength, rather than overall grain density or content of volatile components. Nevertheless, pure organic particles do create Type C, or squat Type A* tracks, with length to width ratios dependent upon both specific organic composition and impactor grain size. From comparison with the published shape data for Stardust aerogel tracks, we conclude that the abundant larger Type B tracks on the Stardust collector represent impacts by particles similar to our carbonaceous chondrite meteorite powders. |
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