Molecule dependent oxygen isotopic ratios in the coma of comet 67P/Churyumov-Gerasimenko
K. Altwegg, H. Balsiger, M. Combi, J. De Keyser, M. N. Drozdovskaya, S. A. Fuselier, T. I. Gombosi, N. Hänni, M. Rubin, M. Schuhmann, I. Schroeder, S. Wampfler
发表信息：
2020, Monthly Notices of the Royal Astronomical Society, 498(4), 5855-5862
The ratios of the three stable oxygen isotopes 16O, 17O and 18O on Earth and, as far as we know in the solar system, show variations on the order of a few percent at most, with a few outliers in meteorites. However, in the interstellar medium there are some highly fractionated oxygen isotopic ratios in some specific molecules. The goal of this work is to investigate the oxygen isotopic ratios in different volatile molecules found in the coma of comet 67P/Churyumov-Gerasimenko and compare them with findings from interstellar clouds in order to assess commonalities and differences. To accomplish this goal, we analyzed data from the ROSINA instrument on Rosetta during its mission around the comet. 16O/18O ratios could be determined for O2, methanol, formaldehyde, carbonyl sulfide and sulfur monoxide/dioxide. For O2 the 16O/17O ratio is also available. Some ratios are strongly enriched in the heavy isotopes, especially for sulfur bearing molecules and formaldehyde, whereas for methanol the ratios are compatible with the ones in the solar system. O2 falls in-between, but its oxygen isotopic ratios clearly differ from water, which likely rules out an origin of O2 from water, be it by radiolysis, dismutation during sublimation or the Eley-Rideal process from water ions hitting the nucleus as postulated in the literature.
We present a simple model for gas and dust flow from 67P/Churyumov-Gerasimenko that can be used to understand the grain impact observed by the DIM instrument on Philae (Krueger et al. 2015) We show how model results when applied to the GIADA measurements (Rotundi et al. 2015; Della Corte et al. 2015) can be used, in conjunction with the results found by the MIRO (Schloerb et al. 2015) and VIRTIS (De Sanctis et al. 2015) instruments to infer surface properties such as surface temperature and surface ice fraction.
One of the main aims of the ESA Rosetta mission is to study the origin of the solar system by exploring comet 67P/Churyumov-Gerasimenko at close range. In this paper we discuss the origin and evolution of comet 67P/Churyumov-Gerasimenko in relation to that of comets in general and in the framework of current solar system formation models. We use data from the OSIRIS scientific cameras as basic constraints. In particular, we discuss the overall bi-lobate shape and the presence of key geological features, such as layers and fractures. We also treat the problem of collisional evolution of comet n…
Grand Canonical Monte Carlo simulations are used to reproduce the N$_2$/CO ratio ranging between 1.7 $\times$ 10$^{-3}$ and 1.6 $\times$ 10$^{-2}$ observed {\it in situ} in the Jupiter family comet 67P/Churyumov-Gerasimenko by the ROSINA mass spectrometer aboard the Rosetta spacecraft, assuming that this body has been agglomerated from clathrates in the protosolar nebula. Simulations are done using an elaborated interatomic potentials for investigating the temperature dependence of the trapping within a multiple guest clathrate formed from a gas mixture of CO and N$_2$ in proportions correspon…
We show that the scattering phase functions of the coma and the nucleus of the comet 67P/Churyumov-Gerasimenko measured by the Rosetta/OSIRIS instrument can be reproduced by a particle model involving clustered densely packed submicrometer-sized grains composed of organic material and larger micrometer-sized silicate grains. The simulated and measured coma phase functions suggest that near the nucleus scattering is dominated by large particles, and the size distribution of dust particles varies with time and/or local coma environment. Further, we show that the measured nucleus phase function i…
Dust transport and deposition behind larger boulders on the comet 67P/Churyumov-Gerasimenko (67P/C-G) have been observed by the Rosetta mission. We present a mechanism for dust transport vectors based on a homogenous surface activity model incorporating in detail the topography of 67P/C-G. The combination of gravitation, gas drag, and Coriolis force leads to specific dust transfer pathways, which for higher dust velocities fuel the near nucleus coma. By distributing dust sources homogeneously across the whole cometary surface, we derive a global dust-transport map of 67P/C-G. The transport vec…
The OSIRIS/NAC camera onboard the Rosetta spacecraft acquired approximately 27000 images of comet 67PChuryumov-Gerasimenko at spatial scales down to a few centimeters. Numerous sequences of images separated by a few minutes suitable to stereo reconstruction allowed producing anaglyphs. They offer three-dimensional views complementary to other technics as a tool to understand the topography of the nucleus. Each one is documented by a set of 17 parameters. Over 1820 anaglyphs are available on a dedicated website at https://rosetta-3dcomet.cnes.fr
We investigate the thermal evolution of comet 67P/Churyumov-Gerasimenko's subsurface in the Seth_01 region, where active pits have been observed by the ESA/Rosetta mission. Our simulations show that clathrate destabilization and amorphous ice crystallization can occur at depths corresponding to those of the observed pits in a timescale shorter than 67P/Churyumov-Gerasimenko's lifetime in the comet's activity zone in the inner solar system. Sublimation of crystalline ice down to such depths is possible only in the absence of a dust mantle, which requires the presence of dust grains in the matri…
Starting from several monthly data sets of Rosetta's COmetary Pressure Sensor we reconstruct the gas density in the coma around comet 67P/Churyumov-Gerasimenko. The underlying inverse gas model is constructed by fitting ten thousands of measurements to thousands of potential gas sources distributed across the entire nucleus surface. The ensuing self-consistent solution for the entire coma density and surface activity reproduces the temporal and spatial variations seen in the data for monthly periods with Pearson correlation coefficients of 0.93 and higher. For different seasonal illumination c…
The Rosetta mission to comet 67P/Churyumov-Gerasimenko has provided new data to better understand what comets are made of. The weak tensile strength of the cometary surface materials suggests that the comet is a hierarchical dust aggregate formed through gravitational collapse of a bound clump of small dust aggregates so-called ``pebbles'' in the gaseous solar nebula. Since pebbles are the building blocks of comets, which are the survivors of planetesimals in the solar nebula, estimating the size of pebbles using a combination of thermal observations and numerical calculations is of great impo…
Comets are considered to be some of the most pristine and unprocessed solar system objects accessible to in-situ exploration. Investigating their molecular and elemental composition takes us on a journey back to the early period of our solar system and possibly even further. In this work, we deduce the bulk abundances of the major volatile species in comet 67P/Churyumov-Gerasimenko, the target of the European Space Agency's Rosetta mission. The basis are measurements obtained with the ROSINA instrument suite on board the Rosetta orbiter during a suitable period of high outgassing near periheli…
Aims. Polarimetric characteristics of comets at large heliocentric distances is a relatively unexplored area; we extend the idea by adding and analysing the data for three Jupiter family comets (JFCs). Methods. With the FORS2 instrument of the ESO VLT, we performed quasi-simultaneous photometry and polarimetry of three active JFCs 67P/Churyumov-Gerasimenko, 74P/Smirnova-Chernykh, and 152P/Helin-Lawrence. Results. We obtained in total 23 polarimetric measurements at different epochs, covering a phase-angle range ~1 -16 degrees and heliocentric distances from 3 to 4.6 au. From our observations w…
The ROSINA mass spectrometer DFMS on board ESA's Rosetta spacecraft detected the major isotopes of the noble gases argon, krypton, and xenon in the coma of comet 67P/Churyumov-Gerasimenko. Earlier, it has been shown that xenon exhibits an isotopic composition distinct from anywhere else in the solar system. However, argon isotopes, within error, were shown to be consistent with solar isotope abundances. This discrepancy suggested an additional exotic component of xenon in comet 67P/Churyumov-Gerasimenko. Here we show that also krypton exhibits an isotopic composition close to solar. Furthermor…
When interacting, the solar wind and the ionised atmosphere of a comet exchange energy and momentum. Our aim is to understand the influence of the average Parker spiral configuration of the solar wind magnetic field on this interaction. We compare the theoretical expectations of an analytical generalised gyromotion with Rosetta observations at comet 67P/Churyumov-Gerasimenko. A statistical approach allows one to overcome the lack of upstream solar wind measurement. We find that additionally to their acceleration along (for cometary pick-up ions) or against (for solar wind ions) the upstream el…
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 sour…
We reconstruct the temporal evolution of the source distribution for the four major gas species H2O, CO2, CO, and O2 on the surface of comet 67P/Churyumov-Gerasimenko during its 2015 apparition. The analysis applies an inverse coma model and fits to data between August 6th 2014 and September 5th 2016 measured with the Double Focusing Mass Spectrometer (DFMS) of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) and the COmet Pressure Sensor (COPS). The spatial distribution of gas sources with their temporal variation allows one to construct surface maps for gas emissions an…
Because of the high fraction of refractory material present in comets, the heat produced by the radiogenic decay of elements such as aluminium and iron can be high enough to induce the loss of ultravolatile species such as nitrogen, argon or carbon monoxide during their accretion phase in the protosolar nebula. Here, we investigate how heat generated by the radioactive decay of 26Al and 60Fe influences the formation of comet 67P/Churyumov-Gerasimenko, as a function of its accretion time and size of parent body. We use an existing thermal evolution model that includes various phase transitions,…
The nature of the icy material accreted by comets during their formation in the outer regions of the protosolar nebula is a major open question in planetary science. Some scenarios of comet formation predict that these bodies agglomerated from crystalline ices condensed in the protosolar nebula. Concurrently, alternative scenarios suggest that comets accreted amorphous ice originating from the interstellar cloud or from the very distant regions of the protosolar nebula. On the basis of existing laboratory and modeling data, we find that the N$_2$/CO and Ar/CO ratios measured in the coma of the…
In 2004, the Rosetta spacecraft was sent to comet 67P/Churyumov-Gerasimenko for the first ever long-term investigation of a comet. After its arrival in 2014, the spacecraft spent more than two years in immediate proximity to the comet. During these two years, the ROSINA Double Focusing Mass Spectrometer (DFMS) onboard Rosetta discovered a coma with an unexpectedly complex chemical composition that included many oxygenated molecules. Determining the exact cometary composition is an essential first step to understanding of the organic rich chemistry in star forming regions and protoplanetary dis…
Molecular oxygen has been detected in the coma of comet 67P/Churyumov-Gerasimenko with abundances in the 1-10% range by the ROSINA-DFMS instrument on board the Rosetta spacecraft. Here we find that the radiolysis of icy grains in low-density environments such as the presolar cloud may induce the production of large amounts of molecular oxygen. We also show that molecular oxygen can be efficiently trapped in clathrates formed in the protosolar nebula, and that its incorporation as crystalline ice is highly implausible because this would imply much larger abundances of Ar and N2 than those obser…
The cometary materials are thought to be the reservoir of primitive materials in the Solar System. The recent detection of glycine and CH$_3$NH$_2$ by the ROSINA mass spectrometer in the coma of 67P/Churyumov-Gerasimenko suggests that amino acids and their precursors may have been formed in an early evolutionary phase of the Solar System. We investigate the evolution of cometary interior considering the evaporation process of water followed by the concentration of non-volatile species. We develop a Simplified Cometary Concentration Model (SCCM) to simulate the evaporation and concentration pro…
On November 12, 2014, the ESA/Rosetta descent module Philae landed on the Abydos site of comet 67P/Churyumov-Gerasimenko. Aboard this module, the Ptolemy mass spectrometer measured a CO/CO2 ratio of 0.07 +/- 0.04 which differs substantially from the value obtained in the coma by the Rosetta/ROSINA instrument, suggesting a heterogeneity in the comet nucleus. To understand this difference, we investigated the physico-chemical properties of the Abydos subsurface leading to CO/CO2 ratios close to that observed by Ptolemy at the surface of this region. We used a comet nucleus model that takes into …
The coma of comet 67P/Churyumov-Gerasimenko has been probed by the Rosetta spacecraft and shows a variety of different molecules. The ROSINA COmet Pressure Sensor and the Double Focusing Mass Spectrometer provide in-situ densities for many volatile compounds including the 14 gas species H2O, CO2, CO, H2S, O2, C2H6, CH3OH, H2CO, CH4, NH3, HCN, C2H5OH, OCS, and CS2. We fit the observed densities during the entire comet mission between August 2014 and September 2016 to an inverse coma model. We retrieve surface emissions on a cometary shape with 3996 triangular elements for 50 separated time inte…
Comets display with decreasing solar distance an increased emission of gas and dust particles, leading to the formation of the coma and tail. Spacecraft missions provide insight in the temporal and spatial variations of the dust and gas sources located on the cometary nucleus. For the case of comet 67P/Churyumov-Gerasimenko (67P/C-G), the long-term observations from the Rosetta mission point to a homogeneous dust emission across the entire illuminated surface. Despite the homogeneous initial distribution, a collimation in jet-like structures becomes visible. We propose that this observation is…
The processes that led to the formation of the planetary bodies in the Solar System are still not fully understood. Using the results obtained with the comprehensive suite of instruments on-board ESA's Rosetta mission, we present evidence that comet 67P/Churyumov-Gerasimenko likely formed through the gentle gravitational collapse of a bound clump of mm-sized dust aggregates ("pebbles"), intermixed with microscopic ice particles. This formation scenario leads to a cometary make-up that is simultaneously compatible with the global porosity, homogeneity, tensile strength, thermal inertia, vertica…
67P/Churyumov-Gerasimenko is a Jupiter-family comet that was the target of the Rosetta mission, the first mission to successfully orbit and land a probe on a comet. This mission was accompanied by a large ground-based observing campaign. We have developed a pipeline to calibrate and measure photometry of comet 67P during its 2016 perihelion passage, making use of all visible wavelength broadband imaging collected across a wide range of facilities. The pipeline calibrates the brightness of the comet to a common photometric system (Pan-STARRS 1) using background stars within the field allowing f…
The Rosetta probe around comet 67P/Churyumov-Gerasimenko (67P) reveals an anisotropic dust distribution of the inner coma with jet-like structures. The physical processes leading to jet formation are under debate, with most models for cometary activity focusing on localised emission sources, such as cliffs or terraced regions. Here we suggest, by correlating high-resolution simulations of the dust environment around 67P with observations, that the anisotropy and the background dust density of 67P originate from dust released across the entire sunlit surface of the nucleus rather than from few …
The first 1000 km of the ion tail of comet 67P/Churyumov-Gerasimenko were explored by the European Rosetta spacecraft, 2.7 au away from the Sun. We characterised the dynamics of both the solar wind and the cometary ions on the night-side of the comet's atmosphere. We analysed in situ ion and magnetic field measurements and compared the data to a semi-analytical model. The cometary ions are observed flowing close to radially away from the nucleus during the entire excursion. The solar wind is deflected by its interaction with the new-born cometary ions. Two concentric regions appear, an inner r…
We study the dynamics of the interaction between the solar wind ions and a partially ionized atmosphere around a comet, at a distance of 2.88 AU from the sun during a period of low nucleus activity. Comparing particle data and mag- netic field data for a case study, we highlight the prime role of the solar wind electric field in the cometary ion dynamics. Cometary ion and solar wind proton flow directions evolve in a correlated manner, as expected from the theory of mass loading. We find that the main component of the acceler- ated cometary ion flow direction is along the anti-sunward directio…
We have detected H$_2$O and O$_2$ absorption against the far-UV continuum of stars located on lines of sight near the nucleus of Comet 67P/Churyumov-Gerasimenko using the Alice imaging spectrograph on Rosetta. These stellar appulses occurred at impact parameters of $ρ=4$-20 km, and heliocentric distances ranging from $R_h=-1.8$ to 2.3 AU (negative values indicate pre-perihelion observations). The measured H$_2$O column densities agree well with nearly contemporaneous values measured by VIRTIS-H. The clear detection of O$_2$ independently confirms the initial detection by the ROSINA mass spectr…
Around the time of its perihelion passage the observability of 67P/Churyumov-Gerasimenko from Earth was limited to very short windows each morning from any given site, due to the low solar elongation of the comet. The peak in the comet's activity was therefore difficult to observe with conventionally scheduled telescopes, but was possible where service/queue scheduled mode was possible, and with robotic telescopes. We describe the robotic observations that allowed us to measure the total activity of the comet around perihelion, via photometry (dust) and spectroscopy (gas), and compare these re…
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 Rose…
In this work we aim to characterise the dust motion in the inner coma of comet 67P/Churyumov- Gerasimenko to provide constraints for theoretical 3D coma models. The OSIRIS camera onboard the Rosetta mission was able for the first time to acquire images of single dust particles from inside the cometary coma, very close to the nucleus. We analyse a large number of particles, performing a significant statistic of their behaviour during the post perihelion period, when the spacecraft covered distances from the nucleus ranging between 80 and 400 km. We describe the particle trajectories, investigat…
We make the following predictions: (1) Comet 67P/Churyumov-Gerasimenko. The Secular Light Curve (SLC) of this comet exhibits a photometric anomaly in magnitude that is present in 1982, 1996, 2002 and 2009. Thus it must be real. We interpret this anomaly as a topographic feature on the surface of the nucleus that may be a field of debris, a region made only of dust or an area of solid stones but in any case it is depleted in volatiles. We predict that images taken by spacecraft Rosseta will show a region morphologically different to the rest of the nucleus, at the pole pointing to the Sun near …
We here study the level of albedo variegation on the nucleus of Comet 67P/Churyumov-Gerasimenko. This is done by fitting the parameters of a standard photometric phase function model to disk-average radiance factor data in images acquired by the Rosetta/OSIRIS Narrow Angle Camera in the orange filter. Local discrepancies between the observed radiance factor and the disk-average solution are interpreted as a proxy W of the local single-scattering albedo. We find a wide range 0.02<W<0.09 around an average of W=0.055. The observed albedo variegation is strongly correlated with nucleus morphology …
This paper presents the past evolution of the orbital elements of comet 67P/Churyumov-Gerasimenko, target of the Rosetta spacecraft. The gravitational orbit of the comet is affected by the sublimation of ice from the nucleus that triggers non-gravitational forces. The comet also experienced several close encounters with Jupiter especially in 1959 and 1923 (less than 1 AU). These perturbations cause the chaoticity of the comet orbit at short time scale. The goal of this paper is to have a precise idea of the comet recent dynamical history. This is done in studying the mean trends of the comet o…
Comet 67P/Churyumov-Gerasimenko is the main target of ESA's Rosetta mission and will be encountered in May 2014. As the spacecraft shall be in orbit the comet nucleus before and after release of the lander {\it Philae}, it is necessary necessary to know the conditions in the coma. Study the dust environment, including the dust production rate and its variations along its preperihelion orbit. The comet was observed during its approach to the Sun on four epochs between early-June 2008 and mid-January 2009, over a large range of heliocentric distances that will be covered by the mission in 2014. …
(Context) The change of the rotation period and the orientation of the rotation axis of comet 67P/Churyumov-Gerasimenko (67P/C-G) is deducible from images taken by the scientific imaging instruments on-board the Rosetta mission with high precision. Non gravitational forces are a natural explanation for these data. (Aims) We describe observed changes for the orientation of the rotation axis and the rotation period of 67P/C-G. For these changes we give an explanation based on a sublimation model with a best-fit for the surface active fraction (model P). Torque effects of periodically changing ga…
Aims. The Alice far-ultraviolet spectrograph onboard Rosetta is designed to observe emissions from various atomic and molecular species from within the coma of comet 67P/ Churyumov-Gerasimenko and to determine their spatial distribution and evolution with time and heliocentric distance. Methods. Following orbit insertion in August 2014, Alice made observations of the inner coma above the limbs of the nucleus of the comet from cometocentric distances varying between 10 and 80 km. Depending on the position and orientation of the slit relative to the nucleus, emissions of atomic hydrogen and oxyg…
Following our previous detection of ubiquitous H2O and O2 absorption against the far-UV continuum of stars located near the nucleus of Comet 67P/Churyumov-Gerasimenko, we present a serendipitously observed stellar occultation that occurred on 2015 September 13, approximately one month after the comet's perihelion passage. The occultation appears in two consecutive 10-minute spectral images obtained by Alice, Rosetta's ultraviolet (700-2100 A) spectrograph, both of which show H2O absorption with column density $>10^{17.5} \mathrm{cm}^{-2}$ and significant O2 absorption ($\mathrm{O2/H2O} \approx…
Context. The first long-term in-situ observation of the plasma environment in the vicinity of a comet, as provided by the European Rosetta spacecraft. Aims. Here we offer characterisation of the solar wind flow near 67P/Churyumov-Gerasimenko (67P) and its long term evolution during low nucleus activity. We also aim to quantify and interpret the deflection and deceleration of the flow expected from ionization of neutral cometary particles within the undisturbed solar wind. Methods. We have analysed in situ ion and magnetic field data and combined this with hybrid modeling of the interaction bet…
We present a method to analyze images of the coma of 67P/Churyumov-Gerasimenko obtained using OSIRIS, the main imaging system onboard \textit{Rosetta}, where dust aggregates can be seen as bright tracks because of their relative velocity with respect to the spacecraft. We applied this method to 105 images taken in 2015 July, 2015 December and 2016 January, identifying more than 20000 individual objects. We performed a photometric analysis of them, finding their phase function. This phase function follows the same trend as the one found for the nucleus, consistent with the detected particles ha…
The Alice far-ultraviolet imaging spectrograph onboard Rosetta observed emissions from atomic and molecular species from within the coma of comet 67P/Churyumov-Gerasimenko during the entire escort phase of the mission from 2014 August to 2016 September. The initial observations showed that emissions of atomic hydrogen and oxygen close to the surface were produced by energetic electron impact dissociation of H2O. Following delivery of the lander, Philae, on 2014 November 12, the trajectory of Rosetta shifted to near-terminator orbits that allowed for these emissions to be observed against the s…
We analyze the physical properties and dynamical origin of a curved jet of comet 67P/Churyumov-Gerasimenko that was observed repeatedly in several nucleus rotations starting on May 30 and persisting until early August, 2015. We simulated the motion of dust grains ejected from the nucleus surface under the influence of the gravity and viscous drag effect of the expanding gas flow from the rotating nucleus. The formation of the curved jet is a combination of the size of the dust particles (~0.1-1 mm) and the location of the source region near the nucleus equator. This enhances the spiral feature…
Remote observation of spectroscopic emissions is a potential tool for the identification and quantification of various species in comets. CO Cameron band (to trace \cod) and atomic oxygen emissions (to trace H$_2$O and/or CO$_2$, CO) have been used to probe neutral composition in the cometary coma. Using a coupled-chemistry emission model, various excitation processes controlling CO Cameron band and different atomic oxygen and atomic carbon have been modelled in comet 67P-Churyumov-Gerasimenko at 1.29~AU (perihelion) and at 3~AU heliocentric distances, which is being explored by ESA's Rosetta …
On January 18-19 and June 28-29 of 2010, the Wide-field Infrared Survey Explorer (WISE) spacecraft imaged the Rosetta mission target, comet 67P/Churyumov-Gerasimenko. We present a preliminary analysis of the images, which provide a characterization of the dust environment at heliocentric distances similar to those planned for the initial spacecraft encounter, but on the outbound leg of its orbit rather than the inbound. Broad-band photometry yields low levels of CO2 production at a comet heliocentric distance of 3.32 AU and no detectable production at 4.18 AU. We find that at these heliocentri…
We use the gravitational instability formation scenario of cometesimals to derive the aggregate size that can be released by the gas pressure from the nucleus of comet 67P/Churyumov-Gerasimenko for different heliocentric distances and different volatile ices. To derive the ejected aggregate sizes, we developed a model based on the assumption that the entire heat absorbed by the surface is consumed by the sublimation process of one volatile species. The calculations were performed for the three most prominent volatile materials in comets, namely, H_20 ice, CO_2 ice, and CO ice. We find that the…
Alice ultraviolet spectrometer onboard Rosetta space mission observed several spectroscopic emissions emanated from volatile species of comet 67P/Churyumov-Gerasimenko (hear after 67P/C-G) during its entire escorting phase. We have developed a photochemical model for comet 67P/C-G to study the atomic hydrogen (HI 1216, 1025, & 973 Ang), oxygen (OI 1152, 1304, & 1356 Ang), and carbon (CI 1561 & 1657 Ang) line emissions by accounting for major production pathways. The developed model has been used to calculate the emission intensities of these lines as a function of nucleocentric projected dista…
We report Spitzer Space Telescope observations of comet 67P/Churyumov-Gerasimenko at 5.5 and 4.3 AU from the Sun, post-aphelion. Comet 67P is the primary target of the European Space Agency's Rosetta mission. The Rosetta spacecraft will rendezvous with the nucleus at heliocentric distances similar to our observations. Rotationally resolved observations at 8 and 24 microns (at a heliocentric distance, rh, of 4.8 AU) that sample the size and color-temperature of the nucleus are combined with aphelion R-band light curves observed at the Very Large Telescope (VLT) and yield a mean effective radius…
We analysed layering-related linear features on the surface of comet 67P/Churyumov-Gerasimenko (67P) to determine the internal configuration of the layerings within the nucleus. We used high-resolution images from the OSIRIS Narrow Angle Camera onboard the Rosetta spacecraft, projected onto the SHAP7 shape model of the nucleus, to map 171 layering-related linear features which we believe to represent terrace margins and strata heads. From these curved lineaments, extending laterally to up to 1925 m, we extrapolated the subsurface layering planes and their normals. We furthermore fitted the lin…
The so-called "early activity" of comet 67P/Churyumov-Gerasimenko has been observed to originate mostly in parts of the concave region or "neck" between its two lobes. Since activity is driven by the sublimation of volatiles, this is a puzzling result because this area is less exposed to the Sun and is therefore expected to be cooler on average (Sierks et al. 2015). We used a thermophysical model that takes into account thermal inertia, global self-heating, and shadowing, to compute surface temperatures of the comet. We found that, for every rotation in the August--December 2014 period, some p…
The Alice far-UV imaging spectrograph (700-2050 A) acquired over 70,000 spectral images during Rosetta's 2-year escort mission, including over 20,000 in the months surrounding perihelion when the comet activity level was highest. We have developed automated software to fit and remove ubiquitous H, O, C, S, and CO emissions from Alice spectra, along with reflected solar continuum and absorption from gaseous H2O in the comet's coma, which we apply to a "grand sum" of integrations taken near perihelion. We present upper limits on the presence of one ion and 17 neutral atomic species for this time…
Context. Comets are primitive objects, remnants of the volatile-rich planetesimals from which the solar system condensed. Knowing their structure and composition is thus crucial for the understanding of our origins. After the successful landing of Philae on the nucleus of 67P/Churyumov-Gerasimenko in November 2014, for the first time, the Rosetta mission provided the opportunity to measure the low frequency electrical properties of a cometary mantle with the permittivity probe SESAME-PP (Surface Electric Sounding and Acoustic Monitoring Experiment - Permittivity Probe). Aims. In this paper, we…
Results. We found that gas-phase silicon was present throughout the Rosetta mission. Furthermore, the presence of sodium and iron atoms near the comet's perihelion confirms that sputtering cannot be the sole release process for refractory elements into the gas phase. Nickel was found to be below the detection limit. The search for parent species of any of the identified gas phase refractories has not been successful. Upper limits for a suite of possible fragment species (SiH, SiC, NaH, etc.) of larger parent and daughter species have been obtained. Furthermore, Si did not exhibit the same drop…
Cometary outbursts offer a valuable window into the composition of comet nuclei with their forceful ejection of dust and volatiles in explosive events, revealing the interior components of the comet. Understanding how different types of outbursts influence the dust properties and volatile abundances to better interpret what signatures can be attributed to primordial composition and what features are the result of processing is an important task best undertaken with a multi-instrument approach. The European Space Agency \textit{Rosetta} mission to 67P/Churyumov-Gerasimenko carried a suite of in…
Observations of comet 67P/Churyumov-Gerasimenko were performed with MUSE at large heliocentric distances post-perihelion, between March 3 and 7, 2016. Those observations were part of a simultaneous ground-based campaign aimed at providing large-scale information about comet 67P that complement the ESA/Rosetta mission. We obtained a total of 38 datacubes over 5 nights. We take advantage of the integral field unit (IFU) nature of the instrument to study simultaneously the spectrum of 67P's dust and its spatial distribution in the coma. We also look for evidence of gas emission in the coma. We pr…
We present Rosetta RPC case study from four events at various radial distance, phase angle and local time from autumn 2015, just after perihelion of comet 67P/Churyumov-Gerasimenko. Pulse like (high amplitude, up to minutes in time) signatures are seen with several RPC instruments in the plasma density (LAP, MIP), ion energy and flux (ICA) as well as magnetic field intensity (MAG). Furthermore the cometocentric distance relative to the electron exobase is seen to be a good organizing parameter for the measured plasma variations. The closer Rosetta is to this boundary, the more pulses are measu…
