Experimental impact features in Stardust aerogel: How track morphology reflects particle structure, composition, and density

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.

Stardust Interstellar Preliminary Examination XI: Identification and elemental analysis of impact craters on Al foils from the Stardust Interstellar Dust Collector

“…Similarly, prior analog (Kearsley et al. ) and cometary crater studies (Leroux et al. , ; Stroud et al.…”

“…As demonstrated by studies of laboratory‐analog impact craters (Kearsley et al. ) and the Stardust cometary craters, asymmetric craters can result from either an oblique impact, or normal, or near‐normal, incidence impact of a particle with a highly nonspherical shape, e.g., a needle or whisker, or an aggregate grain. Similarly, prior analog (Kearsley et al.…”

Stardust Interstellar Preliminary Examination IX: High‐speed interstellar dust analog capture in Stardust flight‐spare aerogel

“…The differences were associated with the structure and composition of the impacting cometary dust particles (e.g., see Kearsley et al. , ).…”

Impact experiments of exotic dust grain capture by highly porous primitive bodies

“…4 shows the relationshi p between the MW/PD ratio and the initial dynamic pressure, normalized by the projectile's tensile strength. We also plotted the results of various projectile s into aerogel, as obtained in previous studies (Burchell et al, 2008;Hörz et al, 2009;Kearsley et al, 2012;Niimi et al, 2012), using the tensile strength of soda-lime glass, copper (60 MPa, 195 MPa, respectively;Kaye and Laby, 1986 ), alumina (258 MPa;Shackelford and Alexander , 2000 ), carbonaceous chondrite meteorit es (637, 614, 614 MPa for Allende, Murchison, Orgueil, respectively ; Tsuchiya ma et al, private communicati on, 2012), and graphite (10.9 MPa; Manhani et al, 2007 ). The MW/ PD ratio increases with increasing dynamic pressure.…”