GIADA investigates comet’s “fluffy” dust grains

In a recent paper published in the Astrophysical Journal Letters, the GIADA team present their findings on the properties of dust particles from Comet 67P/Churyumov-Gerasimenko. This blog post has been prepared with inputs from lead author Marco Fulle, and GIADA principal investigator Alessandra Rotundi. GIADA, the Grain Impact Analyser and Dust Accumulator, is designed to capture dust particles in the coma of Comet 67P/Churyumov–Gerasimenko as Rosetta flies around it. The characteristic properties of the dust grains can be used to infer the history of the material being ejected from comet. The latest study focuses on the dust particles collected between 1 August 2014 and 14 January 2015. The GIADA team find that the dust particles impacting on their detectors can be separated into two families: ‘compact’ particles with sizes in the range 0.03–1 mm, and somewhat larger ‘fluffy aggregates’ with sizes between 0.2 and 2.5 mm. The individual compact particles have a bulk density of 800–3000 kg/m3, consistent with a variety of minerals or mixtures of minerals. On the other hand, the larger aggregates are made up of many sub-micron sized grains with void spaces in between, resulting in fluffy, highly porous structures that are mostly empty space. These aggregates are associated with the fluffy particles seen by Rosetta’s COSIMA instrument. Indeed, the fluffy particles have effective densities of less than 1 kg/m3, literally lighter than air (at sea-level), and which Marco likens to the equivalent density of a dandelion seed head in a vacuum. During the study period, a total of 193 compact particles were detected, impacting the GIADA detectors at an average speed of 3 m/s. A total of 853 detections of fluffy particles were made, the great majority associated with 45 dust ‘showers’. Roughly 2–3 of these showers were seen by GIADA each week, lasting anywhere between […]



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