Aerogel tracks made by impacts of glycine: Implications for formation of bulbous tracks in aerogel and the Stardust mission

Abstract

Abstract-Impacts of small particles of soda-lime glass and glycine onto low density aerogel are reported. The aerogel had a quality similar to the flight aerogels carried by the NASA Stardust mission that collected cometary dust during a flyby of comet 81P ⁄ Wild 2 in 2004. The types of track formed in the aerogel by the impacts of the soda-lime glass and glycine are shown to be different, both qualitatively and quantitatively. For example, the soda-lime glass tracks have a carrot-like appearance and are relatively long and slender (width to length ratio <0.11), whereas the glycine tracks consist of bulbous cavities (width to length ratio >0.26). In consequence, the glycine particles would be underestimated in diameter by a factor of 1.7-3.2, if the glycine tracks were analyzed using the soda-lime glass calibration and density. This implies that a single calibration for impacting particle size based on track properties, as previously used by Stardust to obtain cometary dust particle size, is inappropriate.

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

“…(2009b) showed that polystyrene beads leave well‐defined Type A tracks when impacted on low density aerogel at 1.2 km s −1 . However, subsequent reexamination of tracks from similar polystyrene beads impacted at approximately 6 km s −1 (Nixon et al. 2012) shows that these particles undergo substantial mass loss, and has revealed a rather different, much broader, track shape, like that which we have here designated as Type A*.…”

“…2011), although the depth of penetration may also partly depend upon the degree of ablation and abrasion suffered (for example, compare the alumina impacts of Hörz et al. [2009] with the glycine of Nixon et al. [2012]), and depth may therefore not be related to the particle density alone.…”

“…Glycine powder was purchased from Sigma Aldrich (catalogue number 410225), and used for both foil (Kearsley et al. 2010) and aerogel shots (see Nixon et al. 2012).…”

“…2011) have largely agreed with such models of simple Type A track formation. A curious type of short tapering tracks, similar in general outline to a squat Type A has now also been recognized (Nixon et al. 2012), being created by impact of the amino‐acid glycine.…”

Aerogel dust collection for in situ mass spectrometry analysis

“…However, it was difficult to clearly establish an extra-terrestrial origin for the glycine based on analysis of the aerogel alone -instead analysis of the surfaces of nearby aluminum foils was required (Elsila et al, 2009). Laboratory impact experiments firing glycine grains into aerogel (Nixon et al, 2012) showed that in impacts at 6 km s À1 the captured grains had lost the majority of their pre-impact mass in the capture process, but no tests were carried out on the aerogel to determine where the missing material had gone or how it may have been processed in the impact event. Similarly, impacts on aerogel by polystyrene microparticles show that 84% of the mass is lost during capture at speeds of 6 km s À1 (Burchell et al, 2009a).…”