Discovery of non‐random spatial distribution of impacts in the Stardust cometary collector

Abstract-The fluence of dust particles <10 lm in diameter was recorded by impacts on aluminum foil of the NASA Stardust spacecraft during a close flyby of comet 81P ⁄ Wild 2 in 2004. Initial interpretation of craters for impactor particle dimensions and mass was based upon laboratory experimental simulations using projectiles less than >10 lm in diameter and the resulting linear relationship of projectile to crater diameter was extrapolated to smaller sizes. We now describe a new experimental calibration program firing very small monodisperse silica projectiles (470 nm-10 lm) at approximately 6 km s )1. The results show an unexpected departure from linear relationship between 1 and 10 lm. We collated crater measurement data and, where applicable, impactor residue data for 596 craters gathered during the postmission preliminary examination phase. Using the new calibration, we recalculate the size of the particle responsible for each crater and hence reinterpret the cometary dust size distribution. We find a greater flux of small particles than previously reported. From crater morphology and residue composition of a subset of craters, the internal structure and dimensions of the fine dust particles are inferred and a ''maximumsize'' distribution for the subgrains composing aggregate particles is obtained. The size distribution of the small particles derived directly from the measured craters peaks at approximately 175 nm, but if this is corrected to allow for aggregate grains, the peak in subgrain sizes is at <100 nm.

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“…Supporting this is evidence of clustering in the impacts on the Stardust foils and aerogel (Burchell et al. 2008; Westphal et al. 2008).…”

Section: Wild 2 Dust Size: Impactor Composition Structure and Constmentioning

confidence: 86%

“…This is particularly likely if much of the released coarser dust was composed of weakly bound aggregates (as suggested by Kearsley et al. 2009) which may continue to disintegrate with time (Weissman and Lowry 2008; Westphal et al. 2008).…”

Section: Wild 2 Dust Size: Impactor Composition Structure and Constmentioning

confidence: 99%

Comet 81P/Wild 2: The size distribution of finer (sub‐10 μm) dust collected by the Stardust spacecraft

Price

Kearsley

Burchell

et al. 2010

Meteorit & Planetary Scien

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“…For particle sizes greater than 10 μm all the measurement methods used by Stardust produced similar results. However, at smaller sizes, measurement of the particle size (or mass) distribution by different methods produced significantly different results that are not readily explained at this time; they may relate to the differing detection thresholds of the diverse methods or to spatial and temporal heterogeneities of the coma dust at the scale of individual detector surfaces, e.g., stream effects in the coma and localized point sources (some of which may be close to the spacecraft, i.e., break-up of larger particles after emission from the comet nucleus, as discussed by Westphal et al 2008).…”

Section: Discussionmentioning

confidence: 99%

“…Given that this cluster is dominated by small particles, the cumulative size distribution is accordingly influenced at small sizes in the two analyses by the relative areas considered. As described in detail by Westphal et al (2008), this clustering is poorly understood at present. The results obtained during the post-flight analysis from the aerogel and foils can be compared to those obtained during the cometary encounter by the real-time DFMI .…”

Section: Cumulative Size Distribution and Fluxmentioning

confidence: 99%

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Characteristics of cometary dust tracks in Stardust aerogel and laboratory calibrations

Burchell

Fairey

Wozniakiewicz

et al. 2008

Meteorit & Planetary Scien

137

202

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Abstract-The cometary tray of the NASA Stardust spacecraft's aerogel collector was examined to study the dust captured during the 2004 flyby of comet 81P/Wild 2. An optical scan of the entire collector surface revealed 256 impact features in the aerogel (width >100 μm). Twenty aerogel blocks (out of a total of 132) were removed from the collector tray for a higher resolution optical scan and 186 tracks were observed (track length >50 μm and width >8 μm). The impact features were classified into three types based on their morphology. Laboratory calibrations were conducted that reproduced all three types. This work suggests that the cometary dust consisted of some cohesive, relatively strong particles as well as particles with a more friable or low cohesion matrix containing smaller strong grains. The calibrations also permitted a particle size distribution to be estimated for the cometary dust. We estimate that approximately 1200 particles bigger than 1 μm struck the aerogel. The cumulative size distribution of the captured particles was obtained and compared with observations made by active dust detectors during the encounter. At large sizes (>20 μm) all measures of the dust are compatible, but at micrometer scales and smaller discrepancies exist between the various measurement systems that may reflect structure in the dust flux (streams, clusters etc.) along with some possible instrument effects.

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Origin of the Saturn System

Johnson

Estrada

2009

Saturn From Cassini-Huygens

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Discovery of non‐random spatial distribution of impacts in the Stardust cometary collector

Cited by 17 publications

References 34 publications

Comet 81P/Wild 2: The size distribution of finer (sub‐10 μm) dust collected by the Stardust spacecraft

Comet 81P/Wild 2: The size distribution of finer (sub‐10 μm) dust collected by the Stardust spacecraft

Characteristics of cometary dust tracks in Stardust aerogel and laboratory calibrations

Origin of the Saturn System

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