50 research outputs found
First in-situ detection of the CN radical in comets and evidence for a distributed source
Although the debate regarding the origin of the cyano (CN) radical in comets
has been ongoing for many decades, it has yielded no definitive answer to date.
CN could previously only be studied remotely, strongly hampering efforts to
constrain its origin because of very limited spatial information. Thanks to the
European Space Agency's Rosetta spacecraft, which orbited comet
67P/Churyumov-Gerasimenko for two years, we can investigate, for the first
time, CN around a comet at high spatial and temporal resolution. On board
Rosetta's orbiter module, the high-resolution double-focusing mass spectrometer
DFMS, part of the ROSINA instrument suite, analyzed the neutral volatiles
(including HCN and the CN radical) in the inner coma of the comet throughout
that whole two-year phase and at variable cometocentric distances. From a
thorough analysis of the full-mission data, the abundance of CN radicals in the
cometary coma has been derived. Data from a close flyby event in February 2015
indicate a distributed origin for the CN radical in comet
67P/Churyumov-Gerasimenko.Comment: Accepted for publication in MNRA
Detection of volatiles undergoing sublimation from 67P/Churyumov-Gerasimenko coma particles using ROSINA/COPS. I. The ram gauge
The ESA Rosetta mission has allowed an extensive in-situ study of comet
67P/Churyumov-Gerasimenko. In measurements performed by the ram gauge of the
on-board COmet Pressure Sensor (COPS), features have been observed that deviate
from the nominal ram gauge signal. These are attributable to the sublimation of
the volatile fraction of cometary icy particles containing volatiles and
refractories.
The objective of this work is the investigation of the volatile content of
icy particles that entered the COPS ram gauge.
The ram gauge measurements are inspected for features that we associate to
the sublimation of the volatile component of cometary particles impacting the
instrument. All sublimation features with high enough signal to noise ratio are
modelled by fitting one or more exponential decay functions. The parameters of
these fits are used to categorise different compositions of the sublimating
component.
From features attributable to ice sublimation, we infer the detection of 73
icy particles containing volatiles. 25 detections have enough volatile content
for an in-depth study. From the values of the exponential decay constants, we
classified the 25 inferred icy particles into three types, interpreted as
different volatile compositions, possibly further complicated by different
morphologies. Available data do not give indication as to which molecules
compose the different types. Nevertheless, we can estimate the total volume of
volatiles, expressed as the diameter of an equivalent sphere of water (density
of 1 g cm). This was found to be on the order of hundreds of nanometres.Comment: 9 pages, 8 figures, 2 tables, published in A&A, figures with better
resolutio
Detection of volatiles undergoing sublimation from 67P/Churyumov-Gerasimenko coma particles using ROSINA/COPS. II. The nude gauge
In an earlier study, we reported that the ram gauge of the COmet Pressure
Sensor (COPS), one of the three instruments of the Rosetta Orbiter Spectrometer
for Ion and Neutral Analysis (ROSINA), could be used to obtain information
about the sublimating content of icy particles, made up of volatiles and
conceivably refractories coming from comet 67P/Churyumov-Gerasimenko.
In this work, we extend the investigation to the second COPS gauge, the nude
gauge. In particular, we analyse the volume of the volatile content of coma
particles, along with a search for possible dependencies between the nude gauge
detection rate (i.e. the rate at which icy particles are detected by the nude
gauge) and the position of the Rosetta spacecraft. We also investigate the
correlations of the nude gauge detection rate with the quantities associated
with cometary activity.
Although it was not originally designed for such a purpose, the COPS nude
gauge has been able to detect 67000 features generated by the sublimation
of the volatile content of icy particles. The nude gauge detection rate follows
a trend that is inversely proportional to the heliocentric distance. This
result is interpreted as a confirmation of a possible relation between the nude
gauge detection rate and cometary activity. Thus, we compared the former with
parameters related to cometary activity and obtained significant correlations,
indicating that the frequency of icy particle detection is driven by cometary
activity. Furthermore, by representing the volatile part of the icy particles
as equivalent spheres with a density of 1 g cm, we obtained a range of
diameters between 60 and 793 nanometres, with the smaller ones
( in diameter) having a size distribution power index of
.Comment: 12 pages, 10 figures, accepted for publication in A&
Multi-instrument analysis of 67P/Churyumov-Gerasimenko coma particles: COPS-GIADA data fusion
The European Space Agency's Rosetta mission to comet
67P/Churyumov-Gerasimenko has offered scientists the opportunity to study a
comet in unprecedented detail. Four instruments of the Rosetta orbiter, namely,
the Micro-Imaging Dust Analysis System (MIDAS), the Grain Impact Analyzer and
Dust Accumulator (GIADA), the COmetary Secondary Ion Mass Analyser (COSIMA),
and the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) have
provided information on cometary dust particles. Cross-instrument comparisons
are crucial to characterize cometary dust particles beyond the capabilities of
individual sensors, as they are sensitive to different dust components. We
present the first comparison between detections of the ROSINA COmet Pressure
Sensor (COPS) and GIADA. These two instruments are complementary as the former
is sensitive solely to volatiles of icy particles, while the latter measured
the dust particle as a whole, including refractories and condensed
(semi)volatiles. Our goal is to correlate the particles detected by COPS and
GIADA and to assess whether they belong to a common group. We statistically
analyzed the in situ data of COPS and GIADA by calculating Pearson correlation
coefficients. Among the several types of particles detected by GIADA, we find
that COPS particles are significantly correlated solely with GIADA fluffy
agglomerates (Pearson correlation coefficient of 0.55 and p-value of ). This suggests that fluffy particles are composed of both
refractories and volatiles. COPS volatile volumes, which may be represented by
equivalent spheres with a diameter in the range between 0.06 m and 0.8
m, are similar to the sizes of the fractal particle's subunits identified
by MIDAS (i.e., 0.05-0.18 m).Comment: 6 pages, 3 figures, accepted for publication in A&
Complex organosulfur molecules on comet 67P: Evidence from the ROSINA measurements and insights from laboratory simulations.
The ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) instrument aboard the Rosetta mission revolutionized our understanding of cometary material composition. One of Rosetta's key findings is the complexity of the composition of comet 67P/Churyumov-Gerasimenko. Here, we used ROSINA data to analyze dust particles that were volatilized during a dust event in September 2016 and report the detection of large organosulfur species and an increase in the abundances of sulfurous species previously detected in the coma. Our data support the presence of complex sulfur-bearing organics on the surface of the comet. In addition, we conducted laboratory simulations that show that this material may have formed from chemical reactions that were initiated by the irradiation of mixed ices containing H2S. Our findings highlight the importance of sulfur chemistry in cometary and precometary materials and the possibility of characterizing organosulfur materials in other comets and small icy bodies using the James Webb Space Telescope
Chlorine-bearing species and the 37Cl/35Cl isotope ratio in the coma of comet 67P/Churyumov-Gerasimenko
A full-mission analysis of Cl-bearing species in the coma of comet 67P/Churyumov-Gerasimenko has been conducted using data from the Rosetta ROSINA/DFMS mass spectrometer. This contribution will focus on the challenges encountered to relate DFMS data on Cl-bearing species to the neutral abundances at the comet.DFMS was operated in neutral mode, in which electron impact ionizes a fraction of the incoming neutral gas in the ion source. Only ions in a narrow range around a certain commanded mass-over-charge ratio (m/z) pass through the mass analyser at a time and impact on a micro-channel plate (MCP), creating an electron avalanche that is recorded by a Linear Electron Detector Array chip with two rows of 512 pixels each (LEDA A and LEDA B). Data are obtained as Analog-to-Digital Converter (ADC) counts as a function of LEDA pixel number. The instrument scans over a sequence of m/z values.A well-defined approach exists to convert ADC counts as a function of pixel number to the number of ions that were detected on the MCP. However, to relate the number of ions detected this way to the abundance of neutrals in the coma gas, the sensitivity for each neutral needs to be known. The sensitivity for a certain neutral takes into account the total ionization cross section for the neutral and product ion fraction, instrument transmission and secondary electron yield for each product ion. Sensitivities can be determined experimentally by introducing the neutrals in the DFMS instrument copy in the laboratory, but such data are not available for Cl-bearing species and an alternative approach needs to be used. Fortunately, the use of ratios cancels out some of the factors that play a role in the sensitivity. As an example, for the 37Cl/35Cl ratio, total ionization cross sections and product ion fractions can be considered identical. In the case of 37Cl/35Cl, taking into account the sensitivity results in a correction of more than 15%, mainly due to the secondary electron yield.The 37Cl/35Cl ratio does not appear to change appreciably throughout the mission and is compared with known values from other solar system objects. The Cl/HCl ratio obtained with DFMS indicates that there must be at least one additional chlorine-bearing species on the comet next to HCl, CH3Cl and NH4Cl, the identity of which is unknown at this time
Volatiles in the HO and CO ices of comet 67P/Churyumov-Gerasimenko
ESA's Rosetta spacecraft at comet 67P/Churyumov-Gerasimenko (67P) was the
first mission that accompanied a comet over a substantial fraction of its
orbit. On board was the ROSINA mass spectrometer suite to measure the local
densities of the volatile species sublimating from the ices inside the comet's
nucleus. Understanding the nature of these ices was a key goal of Rosetta. We
analyzed the primary cometary molecules at 67P, namely HO and CO,
together with a suite of minor species for almost the entire mission. Our
investigation reveals that the local abundances of highly volatile species,
such as CH and CO, are reproduced by a linear combination of both HO
and CO densities. These findings bear similarities to laboratory-based
temperature programmed desorption experiments of amorphous ices and imply that
highly volatile species are trapped in HO and CO ices. Our results do
not show the presence of ices dominated by these highly volatile molecules.
Most likely, they were lost due to thermal processing of 67P's interior prior
to its deflection to the inner solar system. Deviations in the proportions
co-released with HO and CO can only be observed before the inbound
equinox, when the comet was still far from the sun and the abundance of highly
volatile molecules associated with CO outgassing were lower. The
corresponding CO is likely seasonal frost, which sublimated and lost its
trapped highly volatile species before re-freezing during the previous
apparition. CO, on the other hand, was elevated during the same time and
requires further investigation.Comment: This is a pre-copyedited, author-produced PDF of an article accepted
for publication in Monthly Notices of the Royal Astronomical Society
following peer review. The version of record is available online at:
https://doi.org/10.1093/mnras/stad300
Volatiles in the H2O and CO2 ices of comet 67P/Churyumov–Gerasimenko
European Space Agency’s Rosetta spacecraft at comet 67P/Churyumov–Gerasimenko (67P) was the first mission that accompanied a comet over a substantial fraction of its orbit. On board was the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis mass spectrometer suite to measure the local densities of the volatile species sublimating from the ices inside the comet’s nucleus. Understanding the nature of these ices was a key goal of Rosetta. We analysed the primary cometary molecules at 67P, namely H2O and CO2, together with a suite of minor species for almost the entire mission. Our investigation reveals that the local abundances of highly volatile species, such as CH4 and CO, are reproduced by a linear combination of both H2O and CO2 densities. These findings bear similarities to laboratory-based temperature-programmed desorption experiments of amorphous ices and imply that highly volatile species are trapped in H2O and CO2 ices. Our results do not show the presence of ices dominated by these highly volatile molecules. Most likely, they were lost due to thermal processing of 67P’s interior prior to its deflection to the inner solar system. Deviations in the proportions co-released with H2O and CO2 can only be observed before the inbound equinox, when the comet was still far from the sun and the abundance of highly volatile molecules associated with CO2 outgassing were lower. The corresponding CO2 is likely seasonal frost, which sublimated and lost its trapped highly volatile species before re-freezing during the previous apparition. CO, on the other hand, was elevated during the same time and requires further investigation
On the origin and evolution of the material in 67P/Churyumov-Gerasimenko
International audiencePrimitive objects like comets hold important information on the material that formed our solar system. Several comets have been visited by spacecraft and many more have been observed through Earth- and space-based telescopes. Still our understanding remains limited. Molecular abundances in comets have been shown to be similar to interstellar ices and thus indicate that common processes and conditions were involved in their formation. The samples returned by the Stardust mission to comet Wild 2 showed that the bulk refractory material was processed by high temperatures in the vicinity of the early sun. The recent Rosetta mission acquired a wealth of new data on the composition of comet 67P/Churyumov-Gerasimenko (hereafter 67P/C-G) and complemented earlier observations of other comets. The isotopic, elemental, and molecular abundances of the volatile, semi-volatile, and refractory phases brought many new insights into the origin and processing of the incorporated material. The emerging picture after Rosetta is that at least part of the volatile material was formed before the solar system and that cometary nuclei agglomerated over a wide range of heliocentric distances, different from where they are found today. Deviations from bulk solar system abundances indicate that the material was not fully homogenized at the location of comet formation, despite the radial mixing implied by the Stardust results. Post-formation evolution of the material might play an important role, which further complicates the picture. This paper discusses these major findings of the Rosetta mission with respect to the origin of the material and puts them in the context of what we know from other comets and solar system objects