5 research outputs found
Sulphur-bearing species in the coma of comet 67P/ChuryumovâGerasimenko
Several sulphur-bearing species have already been observed in different families of comets. However, the knowledge on the minor sulphur species is still limited. The cometâs sulphur inventory is closely linked to the pre-solar cloud and holds important clues to the degree of reprocessing of the material in the solar nebula and during comet accretion. Sulphur in pre-solar clouds is highly depleted, which is quite puzzling as the S/O ratio in the diffuse interstellar medium is cosmic. This work focuses on the abundance of the previously known species H2S, OCS, SO, S2, SO2 and CS2 in the coma of comet 67P/ChuryumovâGerasimenko measured by Rosetta Orbiter Spectrometer for Ion and Neutral Analysis/Double Focusing Mass Spectrometer between equinox and perihelion 2015. Furthermore, we present the first detection of S3, S4, CH3SH and C2H6S in a comet, and we determine the elemental abundance of S/O in the bulk ice of (1.47 ± 0.05) Ă 10â2. We show that SO is present in the coma originating from the nucleus, but not CS in the case of 67P, and for the first time establish that S2 is present in a volatile and a refractory phase. The derived total elemental sulphur abundance of 67P is in agreement with solar photospheric elemental abundances and shows no sulphur depletion as reported for dense interstellar clouds. Also the presence of S2 at heliocentric distances larger than 3 au indicates that sulphur-bearing species have been processed by radiolysis in the
pre-solar cloud and that at least some of the ice from this cloud has survived in comets up the present
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
Sulfur Isotopic Ratios at 67P/Churyumov-Gerasimenko and Characterization of ROSINA-DFMS FM & FS
Comets are thought to be the most pristine bodies present in the Solar System. In
consequence of spending the majority of their existence beyond 30 AU, their composition
can give insights on the physical and chemical conditions during their formation. Since
August 2014 the European Space Agency spacecraft Rosetta accompanies the Jupiter
family comet 67P/Churyumov-Gerasimenko on its way to perihelion and beyond. In this
study the isotope fractionation of 34S are reported in H2S, OCS, SO2, S2, and CS2 at 67P.
In addition for the first time the isotope fractionation for 33S is presented for cometary
volatiles. The ratio 32S/33S is given for H2S, SO2 and a tentative value is given for CS2.
With a mean value of -50 ± 22Ⱐand -306 ± 31Ⱐfor Ύ34S and Ύ33S respectively, H2S
shows a significant depletion in both 34S and 33S. For SO2 the depletion is less distinct with
ÎŽ34S and ÎŽ33S being -67 ± 40â° and -130 ± 53â°, respectively. The strongest depletion is
present for CS2 with -114 ± 21â°and -276 ± 55â°, respectively. For OCS and S2 only ÎŽ34S
could be determined which is -252 ± 77â° and -357 ± 145â°, respectively. A comparison
with sulfur isotopic ratios measured in SiC grains revealed that both SiC grains and the
five volatile species have similar sulfur isotopic ratios. However, it is beyond the scope
of this work to investigate the possibility of a link between SiC grains and cometary ices.
Nevertheless, mass-dependent or mass-independent fractionation due to photo dissociation
can be ruled out as sole cause of the seen depletion of 33S and 34S. Furthermore, an upper
limit of (9.64 ± 0.19)·10.4 for D/H in HDS has been determined. This value is about a
factor two higher than D/H in H2O for the same comet reported by (Altwegg et al., 2015).
Besides the investigation concerning isotopic ratios of sulfur bearing species in this work
the calibration and characterization of ROSINA/DFMS has been continued. Here it is
reported about the deviation of the mass scale for MCP/LEDA low resolution spectra and
the calibration measurements performed in the laboratory. Furthermore the outcome of the
attempt to describe the sensitivity of DFMS with an empirical function will be discussed.
The last part of the characterization of DFMS is dedicated to determine the so-called
individual pixel gain for the laboratory and the flight model. Moreover, correlation between
the depletionâs manifestation of the MCP with respect to the applied voltages has been
investigated for both models. It has been found that further measurements are needed
to understand the manifestation of depletion at the laboratory model. For the model on
board of Rosetta it could be shown that most of the present feature are due to the usage
of the MCP and suggestions have been made in order to answer the remaining question
considering the depletion of the MCP
The ALMA-PILS survey: The sulphur connection between protostars and comets: IRASÂ 16293â2422Â B and 67P/ChuryumovâGerasimenko
The evolutionary past of our Solar System can be pieced together by comparing
analogous low-mass protostars with remnants of our Protosolar Nebula - comets.
Sulphur-bearing molecules may be unique tracers of the joint evolution of the
volatile and refractory components. ALMA Band 7 data from the large unbiased
Protostellar Interferometric Line Survey (PILS) are used to search for
S-bearing molecules in the outer disc-like structure, 60 au from IRAS
16293-2422 B, and are compared with data on 67P/C-G stemming from the ROSINA
instrument aboard Rosetta. Species such as SO, SO, OCS, CS, HCS,
HS and CHSH are detected via at least one of their isotopologues
towards IRAS 16293-2422 B. The search reveals a first-time detection of
OCS towards this source and a tentative first-time detection of
CS towards a low-mass protostar. The data show that IRAS 16293-2422 B
contains much more OCS than HS in comparison to 67P/C-G; meanwhile, the
SO/SO ratio is in close agreement between the two targets. IRAS
16293-2422 B has a CHSH/HCS ratio in range of that of our Solar
System (differences by a factor of 0.7-5.3). It is suggested that the levels of
UV radiation during the initial collapse of the systems may have varied and
have potentially been higher for IRAS 16293-2422 B due to its binary nature;
thereby, converting more HS into OCS. It remains to be conclusively
tested if this also promotes the formation of S-bearing complex organics.
Elevated UV levels of IRAS 16293-2422 B and a warmer birth cloud of our Solar
System may jointly explain the variations between the two low-mass systems.Comment: Accepted for publication in MNRAS; 47 pages, 43 figures, 6 table
First in-situ detection of the cometary ammonium ion NHâșâ (protonated ammonia NHâ) in the coma of 67P/C-G near perihelion
In this paper, we report the first in situ detection of the ammonium ion NHâșâ at 67P/ChuryumovâGerasimenko (67P/C-G) in a cometary coma, using the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA)/Double Focusing Mass Spectrometer (DFMS). Unlike neutral and ion spectrometers onboard previous cometary missions, the ROSINA/DFMS spectrometer, when operated in ion mode, offers the capability to distinguish NHâșâ from HâOâș in a cometary coma. We present here the ion data analysis of mass-to-charge ratios 18 and 19 at high spectral resolution and compare the results with an ionospheric model to put these results into context. The model confirms that the ammonium ion NHâșâ is one of the most abundant ion species, as predicted, in the coma near perihelion