| 1. |
- Hilchenbach, M., et al.
(författare)
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COMET 67P/CHURYUMOV-GERASIMENKO : CLOSE-UP on DUST PARTICLE FRAGMENTS
- 2016
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Ingår i: Astrophysical Journal Letters. - : Institute of Physics Publishing (IOPP). - 2041-8205 .- 2041-8213. ; 816:2
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Tidskriftsartikel (refereegranskat)abstract
- The COmetary Secondary Ion Mass Analyser instrument on board ESA's Rosetta mission has collected dust particles in the coma of comet 67P/Churyumov-Gerasimenko. During the early-orbit phase of the Rosetta mission, particles and particle agglomerates have been imaged and analyzed in the inner coma at distances between 100 km and 10 km off the cometary nucleus and at more than 3 AU from the Sun. We identified 585 particles of more than 14 μm in size. The particles are collected at low impact speeds and constitute a sample of the dust particles in the inner coma impacting and fragmenting on the targets. The sizes of the particles range from 14 μm up to sub-millimeter sizes and the differential dust flux size distribution is fitted with a power law exponent of -3.1. After impact, the larger particles tend to stick together, spread out or consist of single or a group of clumps, and the flocculent morphology of the fragmented particles is revealed. The elemental composition of the dust particles is heterogeneous and the particles could contain typical silicates like olivine and pyroxenes, as well as iron sulfides. The sodium to iron elemental ratio is enriched with regard to abundances in CI carbonaceous chondrites by a factor from ∼1.5 to ∼15. No clear evidence for organic matter has been identified. The composition and morphology of the collected dust particles appear to be similar to that of interplanetary dust particles.
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| 2. |
- Fuselier, S. A., et al.
(författare)
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Ion chemistry in the coma of comet 67P near perihelion
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 462, s. S67-S77
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Tidskriftsartikel (refereegranskat)abstract
- The coma and the comet-solar wind interaction of comet 67P/Churyumov-Gerasimenko changed dramatically from the initial Rosetta spacecraft encounter in 2014 August through perihelion in 2015 August. Just before equinox (at 1.6 au from the Sun), the solar wind signal disappeared and two regions of different cometary ion characteristics were observed. These 'outer' and 'inner' regions have cometary ion characteristics similar to outside and inside the ion pileup region observed during the Giotto approach to comet 1P/Halley. Rosetta/Double-Focusing Mass Spectrometer ion mass spectrometer observations are used here to investigate the H3O+/H2O+ ratio in the outer and inner regions at 67P/Churyumov-Gerasimenko. The H3O+/H2O+ ratio and the H3O+ signal are observed to increase in the transition from the outer to the inner region and the H3O+ signal appears to be weakly correlated with cometary ion energy. These ion composition changes are similar to the ones observed during the 1P/Halley flyby. Modelling is used to determine the importance of neutral composition and transport of neutrals and ions away from the nucleus. This modelling demonstrates that changes in the H3O+/H2O+ ratio appear to be driven largely by transport properties and only weakly by neutral composition in the coma.
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| 3. |
- Volwerk, M., et al.
(författare)
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Mass-loading, pile-up, and mirror-mode waves at comet 67P/Churyumov-Gerasimenko
- 2016
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 34:1, s. 1-15
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Tidskriftsartikel (refereegranskat)abstract
- The data from all Rosetta plasma consortium instruments and from the ROSINA COPS instrument are used to study the interaction of the solar wind with the outgassing cometary nucleus of 67P/Churyumov-Gerasimenko. During 6 and 7 June 2015, the interaction was first dominated by an increase in the solar wind dynamic pressure, caused by a higher solar wind ion density. This pressure compressed the draped magnetic field around the comet, and the increase in solar wind electrons enhanced the ionization of the outflow gas through collisional ionization. The new ions are picked up by the solar wind magnetic field, and create a ring/ring-beam distribution, which, in a high-beta plasma, is unstable for mirror mode wave generation. Two different kinds of mirror modes are observed: one of small size generated by locally ionized water and one of large size generated by ionization and pick-up farther away from the comet.
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| 4. |
- Beth, A., et al.
(författare)
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First in situ detection of the cometary ammonium ion NH4+ (protonated ammonia NH3) in the coma of 67P/C-G near perihelion
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966. ; 462, s. S562-S572
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we report the first in situ detection of the ammonium ion NH4+ at 67P/Churyumov-Gerasimenko (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 NH4+ from H2O+ 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 NH4+ is one of the most abundant ion species, as predicted, in the coma near perihelion.
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| 5. |
- Fuselier, S. A., et al.
(författare)
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ROSINA/DFMS and IES observations of 67P : Ion-neutral chemistry in the coma of a weakly outgassing comet
- 2015
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 583
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Tidskriftsartikel (refereegranskat)abstract
- Context. The Rosetta encounter with comet 67P/Churyumov-Gerasimenko provides a unique opportunity for an in situ, up-close investigation of ion-neutral chemistry in the coma of a weakly outgassing comet far from the Sun. Aims. Observations of primary and secondary ions and modeling are used to investigate the role of ion-neutral chemistry within the thin coma. Methods. Observations from late October through mid-December 2014 show the continuous presence of the solar wind 30 km from the comet nucleus. These and other observations indicate that there is no contact surface and the solar wind has direct access to the nucleus. On several occasions during this time period, the Rosetta/ROSINA/Double Focusing Mass Spectrometer measured the low-energy ion composition in the coma. Organic volatiles and water group ions and their breakup products (masses 14 through 19), COP, and CO, (masses 28 and 44) and other mass peaks (at masses 26, 27, and possibly 30) were observed. Secondary ions include H3O+ and HCO+ (masses 19 and 29). These secondary ions indicate ion-neutral chemistry in the thin coma of the comet. A relatively simple model is constructed to account for the low H3O /H2O+ and HCO /CO+ ratios observed in a water dominated coma. Results from this simple model are compared with results from models that include a more detailed chemical reaction network. Results. At low outgassing rates, predictions from the simple model agree with observations and with results from more complex models that include much more chemistry. At higher outgassing rates, the ion-neutral chemistry is still limited and high HCO /CO+ ratios are predicted and observed. However, at higher outgassing rates, the model predicts high H3O /H2O+ ratios and the observed ratios are often low. These low ratios may be the result of the highly heterogeneous nature of the coma, where CO and CO2 number densities can exceed that of water.
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| 6. |
- Galand, M., et al.
(författare)
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Ionospheric plasma of comet 67P probed by Rosetta at 3 au from the Sun
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 462, s. S331-S351
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Tidskriftsartikel (refereegranskat)abstract
- We propose to identify the main sources of ionization of the plasma in the coma of comet 67P/Churyumov-Gerasimenko at different locations in the coma and to quantify their relative importance, for the first time, for close cometocentric distances (< 20 km) and large heliocentric distances (> 3 au). The ionospheric model proposed is used as an organizing element of a multi-instrument data set from the Rosetta Plasma Consortium (RPC) plasma and particle sensors, from the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis and from the Microwave Instrument on the Rosetta Orbiter, all on board the ESA/Rosetta spacecraft. The calculated ionospheric density driven by Rosetta observations is compared to the RPC-Langmuir Probe and RPC-Mutual Impedance Probe electron density. The main cometary plasma sources identified are photoionization of solar extreme ultraviolet (EUV) radiation and energetic electron-impact ionization. Over the northern, summer hemisphere, the solar EUV radiation is found to drive the electron density - with occasional periods when energetic electrons are also significant. Over the southern, winter hemisphere, photoionization alone cannot explain the observed electron density, which reaches sometimes higher values than over the summer hemisphere; electron-impact ionization has to be taken into account. The bulk of the electron population is warm with temperature of the order of 7-10 eV. For increased neutral densities, we show evidence of partial energy degradation of the hot electron energy tail and cooling of the full electron population.
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| 7. |
- Hajra, R., et al.
(författare)
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Impact of a cometary outburst on its ionosphere Rosetta Plasma Consortium observations of the outburst exhibited by comet 67P/Churyumov-Gerasimenko on 19 February 2016
- 2017
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 607
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Tidskriftsartikel (refereegranskat)abstract
- We present a detailed study of the cometary ionospheric response to a cometary brightness outburst using in situ measurements for the first time. The comet 67P/Churyumov-Gerasimenko (67P) at a heliocentric distance of 2.4 AU from the Sun, exhibited an outburst at similar to 1000 UT on 19 February 2016, characterized by an increase in the coma surface brightness of two orders of magnitude. The Rosetta spacecraft monitored the plasma environment of 67P from a distance of 30 km, orbiting with a relative speed of similar to 0.2 m s(-1). The onset of the outburst was preceded by pre-outburst decreases in neutral gas density at Rosetta, in local plasma density, and in negative spacecraft potential at similar to 0950 UT. In response to the outburst, the neutral density increased by a factor of similar to 1.8 and the local plasma density increased by a factor of similar to 3, driving the spacecraft potential more negative. The energetic electrons (tens of eV) exhibited decreases in the flux of factors of similar to 2 to 9, depending on the energy of the electrons. The local magnetic field exhibited a slight increase in amplitude (similar to 5 nT) and an abrupt rotation (similar to 36.4 degrees) in response to the outburst. A weakening of 10-100 mHz magnetic field fluctuations was also noted during the outburst, suggesting alteration of the origin of the wave activity by the outburst. The plasma and magnetic field effects lasted for about 4 h, from similar to 1000 UT to 1400 UT. The plasma densities are compared with an ionospheric model. This shows that while photoionization is the main source of electrons, electron-impact ionization and a reduction in the ion outflow velocity need to be accounted for in order to explain the plasma density enhancement near the outburst peak.
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| 8. |
- Heritier, K. L., et al.
(författare)
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Ion composition at comet 67P near perihelion : Rosetta observations and model-based interpretation
- 2017
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Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966. ; 469, s. S427-S442
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Tidskriftsartikel (refereegranskat)abstract
- We present the ion composition in the coma of comet 67P with newly detected ion species over the 28-37 u mass range, probed by Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA)/Double Focusing Mass Spectrometer (DFMS). In summer 2015, the nucleus reached its highest outgassing rate and ion-neutral reactions started to take place at low cometocentric distances. Minor neutrals can efficiently capture protons from the ion population, making the protonated version of these neutrals a major ion species. So far, only NH4+ has been reported at comet 67P. However, there are additional neutral species with proton affinities higher than that of water (besides NH3) that have been detected in the coma of comet 67P: CH3OH, HCN, H2CO and H2S. Their protonated versions have all been detected. Statistics showing the number of detections with respect to the number of scans are presented. The effect of the negative spacecraft potential probed by the Rosetta Plasma Consortium/LAngmuir Probe on ion detection is assessed. An ionospheric model has been developed to assess the different ion density profiles and compare them to the ROSINA/DFMS measurements. It is also used to interpret the ROSINA/DFMS observations when different ion species have similar masses, and their respective densities are not high enough to disentangle them using the ROSINA/DFMS high-resolution mode. The different ion species that have been reported in the coma of 67P are summarized and compared with the ions detected at comet 1P/Halley during the Giotto mission.
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| 9. |
- Richter, I., et al.
(författare)
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Observation of a new type of low-frequency waves at comet 67P/Churyumov-Gerasimenko
- 2015
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 33:8, s. 1031-1036
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Tidskriftsartikel (refereegranskat)abstract
- We report on magnetic field measurements made in the innermost coma of 67P/Churyumov-Gerasimenko in its low-activity state. Quasi-coherent, large-amplitude (delta B/B similar to 1), compressional magnetic field oscillations at similar to 40 mHz dominate the immediate plasma environment of the nucleus. This differs from previously studied cometary interaction regions where waves at the cometary ion gyro-frequencies are the main feature. Thus classical pickup-ion-driven instabilities are unable to explain the observations. We propose a cross-field current instability associated with newborn cometary ion currents as a possible source mechanism.
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| 10. |
- Fayolle, E. C., et al.
(författare)
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Protostellar and cometary detections of organohalogens
- 2017
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Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 1:10, s. 703-708
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Tidskriftsartikel (refereegranskat)abstract
- Organohalogens, a class of molecules that contain at least one halogen atom bonded to carbon, are abundant on the Earth where they are mainly produced through industrial and biological processes(1). Consequently, they have been proposed as biomarkers in the search for life on exoplanets(2). Simple halogen hydrides have been detected in interstellar sources and in comets, but the presence and possible incorporation of more complex halogen-containing molecules such as organohalogens into planet-forming regions is uncertain(3,4). Here we report the interstellar detection of two isotopologues of the organohalogen CH3Cl and put some constraints on CH3F in the gas surrounding the low-mass protostar IRAS 16293-2422, using the Atacama Large Millimeter/submillimeter Array (ALMA). We also find CH3Cl in the coma of comet 67P/Churyumov-Gerasimenko (67P/C-G) by using the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument. The detections reveal an efficient pre-planetary formation pathway of organohalogens. Cometary impacts may deliver these species to young planets and should thus be included as a potential abiotical production source when interpreting future organohalogen detections in atmospheres of rocky planets.
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| 11. |
- Galand, M., et al.
(författare)
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Far-ultraviolet aurora identified at comet 67P/Churyumov-Gerasimenko
- 2020
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Ingår i: Nature Astronomy. - : NATURE RESEARCH. - 2397-3366. ; 4:11, s. 1084-1091
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Tidskriftsartikel (refereegranskat)abstract
- In situ measurements from the Rosetta spacecraft reveal the presence of atomic emissions close to comet 67P's nucleus. Such emissions are due to dissociative excitation of molecules by the interaction with the solar wind, identifying them as a form of aurora. Having a nucleus darker than charcoal, comets are usually detected from Earth through the emissions from their coma. The coma is an envelope of gas that forms through the sublimation of ices from the nucleus as the comet gets closer to the Sun. In the far-ultraviolet portion of the spectrum, observations of comae have revealed the presence of atomic hydrogen and oxygen emissions. When observed over large spatial scales as seen from Earth, such emissions are dominated by resonance fluorescence pumped by solar radiation. Here, we analyse atomic emissions acquired close to the cometary nucleus by the Rosetta spacecraft and reveal their auroral nature. To identify their origin, we undertake a quantitative multi-instrument analysis of these emissions by combining coincident neutral gas, electron and far-ultraviolet observations. We establish that the atomic emissions detected from Rosetta around comet 67P/Churyumov-Gerasimenko at large heliocentric distances result from the dissociative excitation of cometary molecules by accelerated solar-wind electrons (and not by electrons produced from photo-ionization of cometary molecules). Like the discrete aurorae at Earth and Mars, this cometary aurora is driven by the interaction of the solar wind with the local environment. We also highlight how the oxygen line Oiat wavelength 1,356 A could be used as a tracer of solar-wind electron variability.
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| 12. |
- Goetz, C., et al.
(författare)
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First detection of a diamagnetic cavity at comet 67P/Churyumov-Gerasimenko
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 588
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Tidskriftsartikel (refereegranskat)abstract
- Context. The Rosetta magnetometer RPC-MAG has been exploring the plasma environment of comet 67P/Churyumov-Gerasimenko since August 2014. The first months were dominated by low-frequency waves which evolved into more complex features. However, at the end of July 2015, close to perihelion, the magnetometer detected a region that did not contain any magnetic field at all. Aims. These signatures match the appearance of a diamagnetic cavity as was observed at comet 1P/Halley in 1986. The cavity here is more extended than previously predicted by models and features unusual magnetic field configurations, which need to be explained. Methods. The onboard magnetometer data were analyzed in detail and used to estimate the outgassing rate. A minimum variance analysis was used to determine boundary normals. Results. Our analysis of the data acquired by the Rosetta Plasma Consortium instrumentation confirms the existence of a diamagnetic cavity. The size is larger than predicted by simulations, however. One possible explanation are instabilities that are propagating along the cavity boundary and possibly a low magnetic pressure in the solar wind. This conclusion is supported by a change in sign of the Sun-pointing component of the magnetic field. Evidence also indicates that the cavity boundary is moving with variable velocities ranging from 230 500m/s.
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| 13. |
- Goldstein, R., et al.
(författare)
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Observations of Modulation of Ion Flux in the Coma of Comet 67P/Churyumov-Gerasimenko
- 2022
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 49:11
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Tidskriftsartikel (refereegranskat)abstract
- On 6-8 June 2015, the Ion and Electron Sensor on board Rosetta observed keV-range water-group pickup ions arriving from the solar direction. Based on magnetic field intensification and variations, the appearance of the ions was likely to have been caused by a coronal mass ejection. During the 3-day period when Rosetta was 200 km from the comet, peak ion energy/charge (E/q) varied over a range from 50 eV to 1 keV in concert with neutral gas density variations caused by the rotation of the comet and its variable solar illumination. Thermal ion densities showed the same variations. The neutral density variations provided a unique opportunity to observe the repeated slowing of the solar wind by mass loading caused by charge exchange between energetic water-group ions and thermal water-group molecules. Such solar wind slowing was observed previously only by flyby missions that provided single events.
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| 14. |
- Gunell, H., et al.
(författare)
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Ion acoustic waves at comet 67P/Churyumov-Gerasimenko : Observations and computations
- 2017
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Ingår i: Astronomy and Astrophysics. - : EDP SCIENCES S A. - 0004-6361 .- 1432-0746. ; 600
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Tidskriftsartikel (refereegranskat)abstract
- Context. On 20 January 2015 the Rosetta spacecraft was at a heliocentric distance of 2.5 AU, accompanying comet 67P/Churyumov-Gerasimenko on its journey toward the Sun. The Ion Composition Analyser (RPC-ICA), other instruments of the Rosetta Plasma Consortium, and the ROSINA instrument made observations relevant to the generation of plasma waves in the cometary environment.Aims. Observations of plasma waves by the Rosetta Plasma Consortium Langmuir probe (RPC-LAP) can be explained by dispersion relations calculated based on measurements of ions by the Rosetta Plasma Consortium Ion Composition Analyser (RPC-ICA), and this gives insight into the relationship between plasma phenomena and the neutral coma, which is observed by the Comet Pressure Sensor of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis instrument (ROSINA-COPS).Methods. We use the simple pole expansion technique to compute dispersion relations for waves on ion timescales based on the observed ion distribution functions. These dispersion relations are then compared to the waves that are observed. Data from the instruments RPC-LAP, RPC-ICA and the mutual impedance probe (RPC-MIP) are compared to find the best estimate of the plasma density.Results. We find that ion acoustic waves are present in the plasma at comet 67P/Churyumov-Gerasimenko, where the major ion species is H2O+. The bulk of the ion distribution is cold, k(B)T(i) = 0.01 eV when the ion acoustic waves are observed. At times when the neutral density is high, ions are heated through acceleration by the solar wind electric field and scattered in collisions with the neutrals. This process heats the ions to about 1 eV, which leads to significant damping of the ion acoustic waves.Conclusions. In conclusion, we show that ion acoustic waves appear in the H2O+ plasmas at comet 67P/Churyumov-Gerasimenko and how the interaction between the neutral and ion populations affects the wave properties.
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| 15. |
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| 16. |
- Heritier, K. L., et al.
(författare)
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Plasma source and loss at comet 67P during the Rosetta mission
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP SCIENCES S A. - 0004-6361 .- 1432-0746. ; 618
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Tidskriftsartikel (refereegranskat)abstract
- Context. The Rosetta spacecraft provided us with a unique opportunity to study comet 67P/Churyumov-Gerasimenko (67P) from a close perspective and over a 2-yr time period. Comet 67P is a weakly active comet. It was therefore unexpected to find an active and dynamic ionosphere where the cometary ions were largely dominant over the solar wind ions, even at large heliocentric distances. Aims. Our goal is to understand the different drivers of the cometary ionosphere and assess their variability over time and over the different conditions encountered by the comet during the Rosetta mission. Methods. We used a multi-instrument data-based ionospheric model to compute the total ion number density at the position of Rosetta. In-situ measurements from the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) and the Rosetta Plasma Consortium (RPC)-Ion and Electron Sensor (IES), together with the RPC-LAngmuir Probe instrument (LAP) were used to compute the local ion total number density. The results are compared to the electron densities measured by RPC-Mutual Impedance Probe (MIP) and RPC-LAP. Results. We were able to disentangle the physical processes responsible for the formation of the cometary ions throughout the 2-yr escort phase and we evaluated their respective magnitudes. The main processes are photo-ionization and electron-impact ionization. The latter is a significant source of ionization at large heliocentric distance (>2 au) and was predominant during the last 4 months of the mission. The ionosphere was occasionally subject to singular solar events, temporarily increasing the ambient energetic electron population. Solar photons were the main ionizer near perihelion at 1.3 au from the Sun, during summer 2015.
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| 17. |
- Heritier, K. L., et al.
(författare)
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Vertical structure of the near-surface expanding ionosphere of comet 67P probed by Rosetta
- 2017
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 469, s. S118-S129
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Tidskriftsartikel (refereegranskat)abstract
- The plasma environment has been measured for the first time near the surface of a comet. This unique data set has been acquired at 67P/Churyumov-Gerasimenko during ESA/Rosetta spacecraft's final descent on 2016 September 30. The heliocentric distance was 3.8 au and the comet was weakly outgassing. Electron density was continuously measured with Rosetta Plasma Consortium (RPC)-Mutual Impedance Probe (MIP) and RPC-LAngmuir Probe (LAP) during the descent from a cometocentric distance of 20 km down to the surface. Data set from both instruments have been cross-calibrated for redundancy and accuracy. To analyse this data set, we have developed a model driven by Rosetta Orbiter Spectrometer for Ion and Neutral Analysis-COmetary Pressure Sensor total neutral density. The two ionization sources considered are solar extreme ultraviolet radiation and energetic electrons. The latter are estimated from the RPC-Ion and Electron Sensor (IES) and corrected for the spacecraft potential probed by RPC-LAP. We have compared the results of the model to the electron densities measured by RPC-MIP and RPC-LAP at the location of the spacecraft. We find good agreement between observed and modelled electron densities. The energetic electrons have access to the surface of the nucleus and contribute as the main ionization source. As predicted, the measurements exhibit a peak in the ionospheric density close to the surface. The location and magnitude of the peak are estimated analytically. The measured ionospheric densities cannot be explained with a constant outflow velocity model. The use of a neutral model with an expanding outflow is critical to explain the plasma observations.
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| 18. |
- Kueppers, Michael, et al.
(författare)
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Triple F-a comet nucleus sample return mission
- 2009
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Ingår i: Experimental astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 23:3, s. 809-847
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Tidskriftsartikel (refereegranskat)abstract
- The Triple F (Fresh From the Fridge) mission, a Comet Nucleus Sample Return, has been proposed to ESA's Cosmic Vision program. A sample return from a comet enables us to reach the ultimate goal of cometary research. Since comets are the least processed bodies in the solar system, the proposal goes far beyond cometary science topics (like the explanation of cometary activity) and delivers invaluable information about the formation of the solar system and the interstellar molecular cloud from which it formed. The proposed mission would extract three sample cores of the upper 50 cm from three locations on a cometary nucleus and return them cooled to Earth for analysis in the laboratory. The simple mission concept with a touch-and-go sampling by a single spacecraft was proposed as an M-class mission in collaboration with the Russian space agency ROSCOSMOS.
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| 19. |
- Mousis, O., et al.
(författare)
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Scientific rationale for Saturn's in situ exploration
- 2014
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Ingår i: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 104, s. 29-47
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Tidskriftsartikel (refereegranskat)abstract
- Remote sensing observations meet some limitations when used to study the bulk atmospheric composition of the giant planets of our solar system. A remarkable example of the superiority of in situ probe measurements is illustrated by the exploration of Jupiter, where key measurements such as the determination of the noble gases' abundances and the precise measurement of the helium mixing ratio have only been made available through in situ measurements by the Galileo probe. This paper describes the main scientific goals to be addressed by the future in situ exploration of Saturn placing the Galileo probe exploration of Jupiter in a broader context and before the future probe exploration of the more remote ice giants. In situ exploration of Saturn's atmosphere addresses two broad themes that are discussed throughout this paper: first, the formation history of our solar system and second, the processes at play in planetary atmospheres. In this context, we detail the reasons why measurements of Saturn's bulk elemental and isotopic composition would place important constraints on the volatile reservoirs in the protosolar nebula. We also show that the in situ measurement of CO (or any other disequilibrium species that is depleted by reaction with water) in Saturn's upper troposphere may help constraining its bulk O/H ratio. We compare predictions of Jupiter and Saturn's bulk compositions from different formation scenarios, and highlight the key measurements required to distinguish competing theories to shed light on giant planet formation as a common process in planetary systems with potential applications to most extrasolar systems. In situ measurements of Saturn's stratospheric and tropospheric dynamics, chemistry and cloud-forming processes will provide access to phenomena unreachable to remote sensing studies. Different mission architectures are envisaged, which would benefit from strong international collaborations, all based on an entry probe that would descend through Saturn's stratosphere and troposphere under parachute down to a minimum of 10 bar of atmospheric pressure. We finally discuss the science payload required on a Saturn probe to match the measurement requirements.
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| 20. |
- Snodgrass, C., et al.
(författare)
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Asteroids, Comets and the Water on Earth - A European Mission to the Main Belt Comets
- 2012
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Ingår i: European Planetary Science Congress 2012, held 23-28 September, 2012 in Madrid, Spain. http://meetings.copernicus.org/epsc2012, id. EPSC2012-206.
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Konferensbidrag (refereegranskat)abstract
- Main Belt Comets (MBCs) are a newly found population in the main asteroid belt. A spacecraft mission to MBCs can provide key insights into the formation and evolution of the planetary system and the early evolution of Earth. The scientific key questions of the mission, its instrumentation and mission profile is studied with the goal to prepare for future mission calls of international space agencies.
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| 21. |
- Beth, Arnaud, et al.
(författare)
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ROSINA ion zoo at Comet 67P
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 642
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Tidskriftsartikel (refereegranskat)abstract
- Context: The Rosetta spacecraft escorted Comet 67P/Churyumov-Gerasimenko for 2 yr along its journey through the Solar System between 3.8 and 1.24 au. Thanks to the high resolution mass spectrometer on board Rosetta, the detailed ion composition within a coma has been accurately assessed in situ for the very first time.Aims: Previous cometary missions, such as Giotto, did not have the instrumental capabilities to identify the exact nature of the plasma in a coma because the mass resolution of the spectrometers onboard was too low to separate ion species with similar masses. In contrast, the Double Focusing Mass Spectrometer (DFMS), part of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis on board Rosetta (ROSINA), with its high mass resolution mode, outperformed all of them, revealing the diversity of cometary ions.Methods: We calibrated and analysed the set of spectra acquired by DFMS in ion mode from October 2014 to April 2016. In particular, we focused on the range from 13–39 u q−1. The high mass resolution of DFMS allows for accurate identifications of ions with quasi-similar masses, separating 13C+ from CH+, for instance.Results: We confirm the presence in situ of predicted cations at comets, such as CHm+ (m = 1−4), HnO+ (n = 1−3), O+, Na+, and several ionised and protonated molecules. Prior to Rosetta, only a fraction of them had been confirmed from Earth-based observations. In addition, we report for the first time the unambiguous presence of a molecular dication in the gas envelope of a Solar System body, namely CO2++.
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| 22. |
- Drozdovskaya, M. N., et al.
(författare)
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The ALMA-PILS survey: The sulphur connection between protostars and comets: IRAS 16293-2422 B and 67P/Churyumov-Gerasimenko
- 2018
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 476:4, s. 4949-4964
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Tidskriftsartikel (refereegranskat)abstract
- The evolutionary past of our Solar system can be pieced together by comparing analogous lowmass 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 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/Churyumov-Gerasimenko (67P/C-G) stemming from the ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) instrument aboard Rosetta. Species such as SO 2 , SO, OCS, CS, H 2 CS, H 2 S, and CH 3 SH are detected via at least one of their isotopologues towards IRAS 16293-2422 B. The search reveals a first-time detection of OC 33 S towards this source and a tentative first-time detection of C 36 S towards a low-mass protostar. The data show that IRAS 16293-2422 B contains much more OCS than H 2 S in comparison to 67P/C-G; meanwhile, the SO/SO 2 ratio is in close agreement between the two targets. IRAS 16293-2422 B has a CH 3 SH/H 2 CS 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 H 2 S 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.
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| 23. |
- Fray, Nicolas, et al.
(författare)
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High-molecular-weight organic matter in the particles of comet 67P/Churyumov–Gerasimenko
- 2016
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Ingår i: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 538:7623, s. 72-74
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Tidskriftsartikel (refereegranskat)abstract
- The presence of solid carbonaceous matter in cometary dust was established by the detection of elements such as carbon, hydrogen, oxygen and nitrogen in particles from comet 1P/Halley1, 2. Such matter is generally thought to have originated in the interstellar medium3, but it might have formed in the solar nebula—the cloud of gas and dust that was left over after the Sun formed4. This solid carbonaceous material cannot be observed from Earth, so it has eluded unambiguous characterization5. Many gaseous organic molecules, however, have been observed6, 7, 8, 9; they come mostly from the sublimation of ices at the surface or in the subsurface of cometary nuclei8. These ices could have been formed from material inherited from the interstellar medium that suffered little processing in the solar nebula10. Here we report the in situ detection of solid organic matter in the dust particles emitted by comet 67P/Churyumov–Gerasimenko; the carbon in this organic material is bound in very large macromolecular compounds, analogous to the insoluble organic matter found in the carbonaceous chondrite meteorites11, 12. The organic matter in meteorites might have formed in the interstellar medium and/or the solar nebula, but was almost certainly modified in the meteorites’ parent bodies11. We conclude that the observed cometary carbonaceous solid matter could have the same origin as the meteoritic insoluble organic matter, but suffered less modification before and/or after being incorporated into the comet.
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| 24. |
- Grun, E., et al.
(författare)
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The 2016 Feb 19 outburst of comet 67P/CG : an ESA Rosetta multi-instrument study
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 462, s. S220-S234
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Tidskriftsartikel (refereegranskat)abstract
- On 2016 Feb 19, nine Rosetta instruments serendipitously observed an outburst of gas and dust from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras and spectrometers ranging from UV over visible to microwave wavelengths, in situ gas, dust and plasma instruments, and one dust collector. At 09: 40 a dust cloud developed at the edge of an image in the shadowed region of the nucleus. Over the next two hours the instruments recorded a signature of the outburst that significantly exceeded the background. The enhancement ranged from 50 per cent of the neutral gas density at Rosetta to factors > 100 of the brightness of the coma near the nucleus. Dust related phenomena (dust counts or brightness due to illuminated dust) showed the strongest enhancements (factors > 10). However, even the electron density at Rosetta increased by a factor 3 and consequently the spacecraft potential changed from similar to-16 V to -20 V during the outburst. A clear sequence of events was observed at the distance of Rosetta ( 34 km from the nucleus): within 15 min the Star Tracker camera detected fast particles (similar to 25 m s(-1)) while 100 mu m radius particles were detected by the GIADA dust instrument similar to 1 h later at a speed of 6 m s(-1). The slowest were individual mm to cm sized grains observed by the OSIRIS cameras. Although the outburst originated just outside the FOV of the instruments, the source region and the magnitude of the outburst could be determined.
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| 25. |
- Taquet, V., et al.
(författare)
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Linking interstellar and cometary O2: A deep search for 16O18O in the solar-Type protostar IRAS 16293b-2422
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 618
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Tidskriftsartikel (refereegranskat)abstract
- Recent measurements carried out at comet 67P/Churyumov-Gerasimenko (67P) with the Rosetta probe revealed that molecular oxygen, O2, is the fourth most abundant molecule in comets. Models show that O2 is likely of primordial nature, coming from the interstellar cloud from which our solar system was formed. However, gaseous O2 is an elusive molecule in the interstellar medium with only one detection towards quiescent molecular clouds, in the ρ Oph A core. We perform a deep search for molecular oxygen, through the 21-01 rotational transition at 234 GHz of its 16O18O isotopologue, towards the warm compact gas surrounding the nearby Class 0 protostar IRAS 16293-2422 B with the ALMA interferometer. We also look for the chemical daughters of O2, HO2, and H2O2. Unfortunately, the H2O2 rotational transition is dominated by ethylene oxide c-C2H4O while HO2 is not detected. The targeted 16O18O transition is surrounded by two brighter transitions at ± 1 km s-1 relative to the expected 16O18O transition frequency. After subtraction of these two transitions, residual emission at a 3σ level remains, but with a velocity offset of 0.3-0.5 km s-1 relative to the source velocity, rendering the detection "tentative". We derive the O2 column density for two excitation temperatures Tex of 125 and 300 K, as indicated by other molecules, in order to compare the O2 abundance between IRAS 16293 and comet 67P. Assuming that 16O18O is not detected and using methanol CH3OH as a reference species, we obtain a [O2]/[CH3OH] abundance ratio lower than 2-5, depending on the assumed Tex, a three to four times lower abundance than the [O2]/[CH3OH] ratio of 5-15 found in comet 67P. Such a low O2 abundance could be explained by the lower temperature of the dense cloud precursor of IRAS 16293 with respect to the one at the origin of our solar system that prevented efficient formation of O2 in interstellar ices.
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| 26. |
- Vigren, Erik, et al.
(författare)
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Model-Observation Comparisons Of Electron Number Densities In The Coma Of 67P/Churyumov-Gerasimenko During 2015 January
- 2016
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Ingår i: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 152:3
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Tidskriftsartikel (refereegranskat)abstract
- During 2015 January 9-11, at a heliocentric distance of similar to 2.58-2.57 au, the ESA Rosetta spacecraft resided at a cometocentric distance of similar to 28 km from the nucleus of comet 67P/Churyumov-Gerasimenko, sweeping the terminator at northern latitudes of 43 degrees N-58 degrees N. Measurements by the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis/Comet Pressure Sensor (ROSINA/COPS) provided neutral number densities. We have computed modeled electron number densities using the neutral number densities as input into a Field Free Chemistry Free model, assuming H2O dominance and ion-electron pair formation by photoionization only. A good agreement (typically within 25%) is found between the modeled electron number densities and those observed from measurements by the Mutual Impedance Probe (RPC/MIP) and the Langmuir Probe (RPC/LAP), both being subsystems of the Rosetta Plasma Consortium. This indicates that ions along the nucleus-spacecraft line were strongly coupled to the neutrals, moving radially outward with about the same speed. Such a statement, we propose, can be further tested by observations of H3O+/H2O+ number density ratios and associated comparisons with model results.
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