83 research outputs found
The Morphological, Elastic, and Electric Properties of Dust Aggregates in Comets: A Close Look at COSIMA/Rosetta's Data on Dust in Comet 67P/Churyumov-Gerasimenko
The Cometary Secondary Ion Mass Analyzer (COSIMA) onboard ESA's Rosetta
orbiter has revealed that dust particles in the coma of Comet
67P/Churyumov-Gerasimenko are aggregates of small grains. We study the
morphological, elastic, and electric properties of dust aggregates in the coma
of Comet 67P/Churyumov-Gerasimenko using optical microscopic images taken by
the COSIMA instrument. Dust aggregates in COSIMA images are well represented as
fractals in harmony with morphological data from MIDAS (Micro-Imaging Dust
Analysis System) and GIADA (Grain Impact Analyzer and Dust Accumulator) onboard
Rosetta. COSIMA's images, together with the data from the other Rosetta's
instruments such as MIDAS and GIADA do not contradict the so-called rainout
growth of -sized particles in the solar nebula. The elastic
and electric properties of dust aggregates measured by COSIMA suggest that the
surface chemistry of cometary dust is well represented as carbonaceous matter
rather than silicates or ices, consistent with the mass spectra, and that
organic matter is to some extent carbonized by solar radiation, as inferred
from optical and infrared observations of various comets. Electrostatic lofting
of cometary dust by intense electric fields at the terminator of its parent
comet is unlikely, unless the surface chemistry of the dust changes from a
dielectric to a conductor. Our findings are not in conflict with our current
understanding of comet formation and evolution, which begin with the
accumulation of condensates in the solar nebula and follow with the formation
of a dust mantle in the inner solar system.Comment: 17 pages, 12 figures, 1 tables, to appear in Planetary and Space
Scienc
COSIMA-Rosetta calibration for in-situ characterization of 67P/Churyumov-Gerasimenko cometary inorganic compounds
20 pages, 3 figures, 5 tablesInternational audienceCOSIMA (COmetary Secondary Ion Mass Analyser) is a time-of-flight secondary ion mass spectrometer (TOF-SIMS) on board the Rosetta space mission. COSIMA has been designed to measure the composition of cometary dust grains. It has a mass resolution m/{\Delta}m of 1400 at mass 100 u, thus enabling the discrimination of inorganic mass peaks from organic ones in the mass spectra. We have evaluated the identification capabilities of the reference model of COSIMA for inorganic compounds using a suite of terrestrial minerals that are relevant for cometary science. Ground calibration demonstrated that the performances of the flight model were similar to that of the reference model. The list of minerals used in this study was chosen based on the mineralogy of meteorites, interplanetary dust particles and Stardust samples. It contains anhydrous and hydrous ferromagnesian silicates, refractory silicates and oxides (present in meteoritic Ca-Al-rich inclusions), carbonates, and Fe-Ni sulfides. From the analyses of these minerals, we have calculated relative sensitivity factors for a suite of major and minor elements in order to provide a basis for element quantification for the possible identification of major mineral classes present in the cometary grains
The detection of solid phosphorus and fluorine in the dust from the coma of comet 67P/Churyumov-Gerasimenko
Here, we report the detection of phosphorus and fluorine in solid
particles collected from the inner coma of comet
67P/Churyumov-Gerasimenko measured with the COmetary Secondary Ion Mass
Analyser (COSIMA) instrument on-board the Rosetta spacecraft, only a few
kilometers away from the comet nucleus. We have detected
phosphorus-containing minerals from the presented COSIMA mass spectra,
and can rule out e.g. apatite minerals as the source of phosphorus. This
result completes the detection of life-necessary CHNOPS-elements in
solid cometary matter, indicating cometary delivery as a potential
source of these elements to the young Earth. Fluorine was also detected
with CF+ secondary ions originating from the cometary dust. </p
Similarities in element âcontent between comet 67P/ChuryumovâGerasimenko coma dust and selected meteorite samples
We have analysed the element composition and the context of particles
collected within the coma of 67P/ChuryumovâGerasimenko with Rosettaâs
COmetary Secondary Ion Mass Analyzer (COSIMA). A comparison has been
made between on board cometary samples and four meteorite samples
measured in the laboratory with the COSIMA reference model. Focusing on
the rock-forming elements, we have found similarities with chondrite
meteorites for some ion count ratios. The composition of
67P/ChuryumovâGerasimenko particles measured by COSIMA shows an
enrichment in volatile elements compared to that of the investigated
Renazzo (CR2) carbonaceous meteorite sample.</p
An Unexplained 10 Degree - 40 Degree Shift in the Location of Some Diverse Neutral Atom Data at 1 AU
Four different data sets pertaining to the neutral atom environment at 1 AU
are presented and discussed. These data sets include neutral solar wind and
interstellar neutral atom data from IMAGE/LENA, energetic hydrogen atom data
from SOHO/HSTOF and plasma wave data from the magnetometer on ISEE-3.
Surprisingly, these data sets are centered between 262 degrees and 292 degrees
ecliptic longitude, about 10 degrees - 40 degrees from the upstream
interstellar neutral flow direction at 254 degrees resulting from the motion of
the Sun relative to the local interstellar cloud. Some possible explanations
for this offset, none of which is completely satisfactory, are discussed.Comment: 6 pages, 6 figures, 2 color peer-reviewed paper, in press, COSPAR/WS
Halogens as tracers of protosolar nebula material in comet 67P/ChuryumovâGerasimenko
We report the first in situ detection of halogens in a cometary coma, that of 67P/ChuryumovGerasimenko. Neutral gas mass spectra collected by the European Space Agencyâs Rosetta spacecraft during four periods of interest from the first comet encounter up to perihelion indicate that the main halogen-bearing compounds are HF, HCl and HBr. The bulk elemental abundances relative to oxygen are ~8.9 Ă 10â»â” for F/O, ~1.2 Ă 10â»âŽ for Cl/O and ~2.5 Ă 10â»â¶ for Br/O, for the volatile fraction of the comet. The cometary isotopic ratios for Âłâ·Cl/Âłâ”Cl and âžÂčBr/â·âčBr match the Solar system values within the error margins. The observations point to an origin of the hydrogen halides in molecular cloud chemistry, with frozen hydrogen halides on dust grains, and a subsequent incorporation into comets as the cloud condensed and the Solar system formed
Carbon-rich dust in comet 67P/Churyumov-Gerasimenko measured by COSIMA/Rosetta
Cometary ices are rich in CO2, CO and organic volatile
compounds, but the carbon content of cometary dust was only measured for
the Oort Cloud comet 1P/Halley, during its flyby in 1986. The COmetary
Secondary Ion Mass Analyzer (COSIMA)/Rosetta mass spectrometer
analysed dust particles with sizes ranging from 50 to 1000Â ÎŒm, collected
over 2 yr, from 67P/Churyumov-Gerasimenko (67P), a Jupiter family
comet. Here, we report 67P dust composition focusing on the elements C
and O. It has a high carbon content (atomic | |â )
close to the solar value and comparable to the 1P/Halley data. From
COSIMA measurements, we conclude that 67P particles are made of nearly
50 per cent organic matter in mass, mixed with mineral phases that are
mostly anhydrous. The whole composition, rich in carbon and non-hydrated
minerals, points to a primitive matter that likely preserved its
initial characteristics since the comet accretion in the outer regions
of the protoplanetary disc.</p
Nitrogen-to-carbon atomic ratio measured by COSIMA in the particles of comet 67P/ChuryumovâGerasimenko
The COmetary Secondary Ion Mass Analyzer (COSIMA) on board the Rosetta mission has analysed numerous cometary dust particles collected at very low velocities (a few m sâ1)
in the environment of comet 67P/ChuryumovâGerasimenko (hereafter 67P).
In these particles, carbon and nitrogen are expected mainly to be part
of the organic matter. We have measured the nitrogen-to-carbon (N/C)
atomic ratio of 27 cometary particles. It ranges from 0.018 to 0.06 with
an averaged value of 0.035 ± 0.011. This is compatible with the
measurements of the particles of comet 1P/Halley and is in the lower
range of the values measured in comet 81P/Wild 2 particles brought back
to Earth by the Stardust mission. Moreover, the averaged value
found in 67P particles is also similar to the one found in the insoluble
organic matter extracted from CM, CI and CR carbonaceous chondrites and
to the bulk values measured in most interplanetary dust particles and
micrometeorites. The close agreement of the N/C atomic ratio in all
these objects indicates that their organic matters share some
similarities and could have a similar chemical origin. Furthermore,
compared to the abundances of all the detected elements in the particles
of 67P and to the elemental solar abundances, the nitrogen is depleted
in the particles and the nucleus of 67P as was previously inferred also
for comet 1P/Halley. This nitrogen depletion could constrain the
formation scenarios of cometary nuclei.</p
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