2 research outputs found
Cometary dust collected by MIDAS on board Rosetta II. Particle shape descriptors and pristineness evaluation
The MIDAS (Micro-Imaging Dust Analysis System) atomic force microscope on
board the Rosetta comet orbiter investigated and measured the 3D topography of
a few hundred nm to tens of m sized dust particles of
67P/Churyumov-Gerasimenko with resolutions down to a few nanometers, giving
insights into the physical processes of our early Solar System. We analyze the
shapes of the cometary dust particles collected by MIDAS on the basis of a
recently updated particle catalog with the aim to determine which structural
properties remained pristine. We develop a set of shape descriptors and metrics
such as aspect ratio, elongation, circularity, convexity, and particle
surface/volume distribution, which can be used to describe the distribution of
particle shapes. Furthermore, we compare the structure of the MIDAS dust
particles and the clusters in which the particles were deposited to those found
in previous laboratory experiments and by Rosetta/COSIMA. Finally, we combine
our findings to calculate a pristineness score for MIDAS particles and
determine the most pristine particles and their properties. We find that the
morphological properties of all cometary dust particles at the micrometer scale
are surprisingly homogeneous despite originating from diverse cometary
environments (e.g., different collection targets that are associated with
cometary activities/source regions and collection velocities/periods). We next
find that the types of clusters found by MIDAS show good agreement with those
defined by previous laboratory experiments, however, there are some differences
to those found by Rosetta/COSIMA. Based on our result, we rate 19 out of 1082
MIDAS particles at least moderately pristine, i.e., they are not substantially
flattened by impact, not fragmented, and/or not part of a fragmentation
cluster.Comment: 40 pages, 31 figures, 1 online tabl
Cometary dust collected by MIDAS on board Rosetta. I. Dust particle catalog and statistics
We aim to catalog all dust particles collected and analyzed by MIDAS,
together with their main statistical properties such as size, height, basic
shape descriptors, and collection time. Furthermore, we aim to present the
scientific results that can be extracted from the catalog (e.g., the size
distribution and statistical characteristics of cometary dust particles). The
existing MIDAS particle catalog has been greatly improved by a careful
re-analysis of the AFM images, leading to the addition of more dust particles
and a detailed description of the particle properties. The catalog documents
all images of identified dust particles and includes a variety of derived
information tabulated one record per particle. Furthermore, the best image of
each particle was chosen for subsequent studies. Finally, we created dust
coverage maps and clustering maps of the MIDAS collection targets and traced
any possible fragmentation of collected particles with a detailed algorithm.
The revised MIDAS catalog includes 3523 MIDAS particles in total, where 1857
particles are expected to be usable for further analysis (418 scans of
particles before perihelion + 1439 scans of particles after perihelion, both
after the removal of duplicates), ranging from about 40 nm to about 8 m
in size. The mean value of the equivalent radius derived from the 2D projection
of the particles is 0.91 0.79 m. A slightly improved equivalent
radius based on the particle's volume coincides in the range of uncertainties
with a value of 0.56 0.45 m. We note that those sizes and all
following MIDAS particle size distributions are expected to be influenced by
the fragmentation of MIDAS particles upon impact on the collection targets.
Furthermore, fitting the slope of the MIDAS particle size distribution with a
power law of a r yields an index b of -1.67 to -1.88.Comment: 28 pages, 5 figure, 2 online table