Comets contain the best-preserved material from the beginning of our planetary system. Their nuclei and comae composition reveal clues about physical and chemical conditions during the early solar ...system when comets formed. ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) onboard the Rosetta spacecraft has measured the coma composition of comet 67P/Churyumov-Gerasimenko with well-sampled time resolution per rotation. Measurements were made over many comet rotation periods and a wide range of latitudes. These measurements show large fluctuations in composition in a heterogeneous coma that has diurnal and possibly seasonal variations in the major outgassing species: water, carbon monoxide, and carbon dioxide. These results indicate a complex coma-nucleus relationship where seasonal variations may be driven by temperature differences just below the comet surface.
Molecular nitrogen (N2) is thought to have been the most abundant form of nitrogen in the protosolar nebula. It is the main N-bearing molecule in the atmospheres of Pluto and Triton and probably the ...main nitrogen reservoir from which the giant planets formed. Yet in comets, often considered the most primitive bodies in the solar system, N2 has not been detected. Here we report the direct in situ measurement of N2 in the Jupiter family comet 67P/Churyumov-Gerasimenko, made by the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis mass spectrometer aboard the Rosetta spacecraft. A N2/CO ratio of (5.70 ± 0.66) × 10–3 (2σ standard deviation of the sampled mean) corresponds to depletion by a factor of ∼25.4 ± 8.9 as compared to the protosolar value. This depletion suggests that cometary grains formed at low-temperature conditions below ∼30 kelvin.
The provenance of water and organic compounds on Earth and other terrestrial planets has been discussed for a long time without reaching a consensus. One of the best means to distinguish between ...different scenarios is by determining the deuterium-to-hydrogen (D/H) ratios in the reservoirs for comets and Earth’s oceans. Here, we report the direct in situ measurement of the D/H ratio in the Jupiter family comet 67P/Churyumov-Gerasimenko by the ROSINA mass spectrometer aboard the European Space Agency’s Rosetta spacecraft, which is found to be (5.3 ± 0.7) × 10
−4
—that is, approximately three times the terrestrial value. Previous cometary measurements and our new finding suggest a wide range of D/H ratios in the water within Jupiter family objects and preclude the idea that this reservoir is solely composed of Earth ocean–like water.
The origin of cometary matter and the potential contribution of comets to inner-planet atmospheres are long-standing problems. During a series of dedicated low-altitude orbits, the Rosetta Orbiter ...Spectrometer for Ion and Neutral Analysis (ROSINA) on the Rosetta spacecraft analyzed the isotopes of xenon in the coma of comet 67P/Churyumov-Gerasimenko. The xenon isotopic composition shows deficits in heavy xenon isotopes and matches that of a primordial atmospheric component. The present-day Earth atmosphere contains 22 ± 5% cometary xenon, in addition to chondritic (or solar) xenon.
The composition of the neutral gas comas of most comets is dominated by H2O, CO and CO2, typically comprising as much as 95 per cent of the total gas density. In addition, cometary comas have been ...found to contain a rich array of other molecules, including sulfuric compounds and complex hydrocarbons. Molecular oxygen (O2), however, despite its detection on other icy bodies such as the moons of Jupiter and Saturn, has remained undetected in cometary comas. Here we report in situ measurement of O2 in the coma of comet 67P/Churyumov-Gerasimenko, with local abundances ranging from one per cent to ten per cent relative to H2O and with a mean value of 3.80 ± 0.85 per cent. Our observations indicate that the O2/H2O ratio is isotropic in the coma and does not change systematically with heliocentric distance. This suggests that primordial O2 was incorporated into the nucleus during the comet's formation, which is unexpected given the low upper limits from remote sensing observations. Current Solar System formation models do not predict conditions that would allow this to occur.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK
•This is one of three companion papers entitled “One Moon, Many Measurements”.•Paper describes the features of the each instrument data aboard two lunar orbiters.•Paper describes the data-processing ...conversion to reflectance of each instrument.•Demonstrates what we can achieve by combining data obtained by different instruments.
Remote-sensing datasets obtained by each instrument aboard Selenological and Engineering Explorer (SELENE) and Chandrayaan-1 have not been compared directly, and the characteristics of each instrument’s data, which may reflect the observation conditions of each instrument and/or residual error in instrument calibration, are unknown. This paper describes the basic characteristics of the data derived by each instrument, briefly describes the data-processing conversion from radiance to reflectance, and demonstrates what we can achieve by combining data obtained by different instruments on different missions (five remote-sensing instruments and an Earth-based telescope). The results clearly demonstrate that the spectral shapes of the instruments are comparable and thus enable us to estimate the composition of each geologic unit, although absolute reflectances differ slightly in some cases.
Abstract
Pinnacles are local topographic promontories of different shapes considered to be formed due to uneven surface erosion. In the case of comets, areal changes in the degree of erosion could be ...related to inhomogeneities of the nucleus. However, the amount of solar radiation and the thermal gradient is different across the orbit for geomorphological regions, which can result in different erosion and shape for a similar composition among two differently illuminated areas. Therefore, a study of the areal distribution of pinnacles on the nucleus surface and their morphology may help to understand the structure and properties of the nucleus material. We mapped 166 pinnacles on the comet nucleus surface of 67P/Churyumov-Gerasimenko. About a third of them have planimetrically rounded shape (rounded pinnacles) and the rest are planimetrically elongated (local ridges). In the southern hemisphere, number of both round pinnacles and local ridges is larger than in the northern hemisphere. This difference possibly indicates the higher effectiveness of the pinnacles’ formation in the southern hemisphere. At the same time the mean values of the measured parameters, including the height, show no statistically reliable difference between the north and south. We found that the maximum height of the pinnacles is about a hundred meters. Suggesting that they have been formed by sublimational erosion, this value allows estimating the minimum thickness of the eroded material and thus the degree of the evolutionary changes of the nucleus. In our future study, we will model pinnacles formation based on the here presented analysis of observations.
Context. The ESA Rosetta mission investigated the environment of comet 67P/Churyumov-Gerasimenko (hereafter 67P) from August 2014 to September 2016. One of the experiments on board the spacecraft, ...the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) included a COmet Pressure Sensor (COPS) and two mass spectrometers to analyze the composition of neutrals and ions, the Reflectron-type Time-Of-Flight mass spectrometer (RTOF), and the Double Focusing Mass Spectrometer (DFMS). Aims. RTOF species detections cover the whole mission. This allows us to study the seasonal evolution of the main volatiles (H2O, CO2, and CO) and their spatial distributions. Methods. We studied the RTOF dataset during the two-year long comet escort phase focusing on the study of H2O, CO2, and CO. We also present the detection by RTOF of O2, the fourth main volatile recorded in the coma of 67P. This work includes the calibration of spectra and the analysis of the signature of the four volatiles. We present the analysis of the dynamics of the main volatiles and visualize the distribution by projecting our results onto the surface of the nucleus. The temporal and spatial heterogeneities of H2O, CO2, and CO are studied over the two years of mission, but the O2 is only studied over a two-month period. Results. The global outgassing evolution follows the expected asymmetry with respect to perihelion. The CO/CO2 ratio is not constant through the mission, even though both species appear to originate from the same regions of the nucleus. The outgassing of CO2 and CO was more pronounced in the southern than in the northern hemisphere, except for the time from August to October 2014. We provide a new and independent estimate of the relative abundance of O2. Conclusions. We show evidence of a change in molecular ratios throughout the mission. We observe a clear north-south dichotomy in the coma composition, suggesting a composition dichotomy between the outgassing layers of the two hemispheres. Our work indicates that CO2 and CO are located on the surface of the southern hemisphere as a result of the strong erosion during the previous perihelion. We also report a cyclic occurrence of CO and CO2 detections in the northern hemisphere. We discuss two scenarios: devolatilization of transported wet dust grains from south to north, and different stratigraphy for the upper layers of the cometary nucleus between the two hemispheres.
Context.
Following a multi-year minimum of solar activity, a solar energetic particle event on 2020 Nov. 29 was observed by multiple spacecraft covering a wide range of solar longitudes including ...ACE, the Solar Terrestrial Relations Observatory-A, and the recently launched Parker Solar Probe and Solar Orbiter.
Aims.
Multi-point observations of a solar particle event, combined with remote-sensing imaging of flaring, shocks, and coronal mass ejections allows for a global picture of the event to be synthesized, and made available to the modeling community to test, constrain, and refine models of particle acceleration and transport according to such parameters as shock geometries and particle mass-to-charge ratios.
Methods.
Detailed measurements of heavy ion intensities, time dependence, fluences, and spectral slopes provided the required test data for this study.
Results.
The heavy ion abundances, timing, and spectral forms for this event fall well within the range found in prior surveys at 1 au. The spectra were well fitted by broken power law shapes; the Fe/O ratio was somewhat lower than the average of other events. In addition,
3
He/
4
He was very low, with only the upper limits established here.
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), CO2+ (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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