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Blum, Jürgen, Dorothea Bischoff et Bastian Gundlach. « Formation of Comets ». Universe 8, no 7 (15 juillet 2022) : 381. http://dx.doi.org/10.3390/universe8070381.
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Questions regarding how primordial or pristine the comets of the solar system are have been an ongoing controversy. In this review, we describe comets’ physical evolution from dust and ice grains in the solar nebula to the contemporary small bodies in the outer solar system. This includes the phases of dust agglomeration, the formation of planetesimals, their thermal evolution and the outcomes of collisional processes. We use empirical evidence about comets, in particular from the Rosetta Mission to comet 67P/Churyumov–Gerasimenko, to draw conclusions about the possible thermal and collisional evolution of comets.
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Seiferlin, K., T. Spohn et J. Benkhoff. « Cometary ice texture and the thermal evolution of comets ». Advances in Space Research 15, no 10 (janvier 1995) : 35–38. http://dx.doi.org/10.1016/0273-1177(94)00148-t.
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Gkotsinas, Anastasios, Aurélie Guilbert-Lepoutre, Sean N. Raymond et David Nesvorny. « Thermal Processing of Jupiter-family Comets during Their Chaotic Orbital Evolution ». Astrophysical Journal 928, no 1 (1 mars 2022) : 43. http://dx.doi.org/10.3847/1538-4357/ac54ac.
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Abstract Evidence for cometary activity beyond Jupiter’s and Saturn’s orbits—such as that observed for Centaurs and long-period comets—suggests that the thermal processing of comet nuclei starts long before they enter the inner solar system, where they are typically observed and monitored. Such observations raise questions as to the depth of unprocessed material and whether the activity of Jupiter-family comets (JFCs) can be representative of any primitive material. Here we model the coupled thermal and dynamical evolution of JFCs, from the moment they leave their outer solar system reservoirs until their ejection into interstellar space. We apply a thermal evolution model to a sample of simulated JFCs obtained from dynamical simulations that successfully reproduce the orbital distribution of observed JFCs. We show that due to the stochastic nature of comet trajectories toward the inner solar system, all simulated JFCs undergo multiple heating episodes resulting in significant modifications of their initial volatile contents. A statistical analysis constrains the extent of such processing. We suggest that primordial condensed hypervolatile ices should be entirely lost from the layers that contribute to cometary activity observed today. Our results demonstrate that understanding the orbital (and thus, heating) history of JFCs is essential when putting observations in a broader context.
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Rigley, Jessica K., et Mark C. Wyatt. « Comet fragmentation as a source of the zodiacal cloud ». Monthly Notices of the Royal Astronomical Society 510, no 1 (1 décembre 2021) : 834–57. http://dx.doi.org/10.1093/mnras/stab3482.
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ABSTRACT Models of the zodiacal cloud’s thermal emission and sporadic meteoroids suggest Jupiter-family comets (JFCs) as the dominant source of interplanetary dust. However, comet sublimation is insufficient to sustain the quantity of dust presently in the inner Solar system, suggesting that spontaneous disruptions of JFCs may supply the zodiacal cloud. We present a model for the dust produced in comet fragmentations and its evolution. Using results from dynamical simulations, the model follows individual comets drawn from a size distribution as they evolve and undergo recurrent splitting events. The resulting dust is followed with a kinetic model which accounts for the effects of collisional evolution, Poynting–Robertson drag, and radiation pressure. This allows to model the evolution of both the size distribution and radial profile of dust, and we demonstrate the importance of including collisions (both as a source and sink of dust) in zodiacal cloud models. With physically motivated free parameters this model provides a good fit to zodiacal cloud observables, supporting comet fragmentation as the plausibly dominant dust source. The model implies that dust in the present zodiacal cloud likely originated primarily from disruptions of ∼50-km comets, since larger comets are ejected before losing all their mass. Thus much of the dust seen today was likely deposited as larger grains ∼0.1 Myr in the past. The model also finds the dust level to vary stochastically; e.g. every ∼50 Myr large (>100 km) comets with long dynamical lifetimes inside Jupiter cause dust spikes with order of magnitude increases in zodiacal light brightness lasting ∼1 Myr. If exozodiacal dust is cometary in origin, our model suggests it should be similarly variable.
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Mumma, Michael J. « Organics In Comets ». International Astronomical Union Colloquium 161 (janvier 1997) : 121–42. http://dx.doi.org/10.1017/s0252921100014640.
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AbstractThe birth-endowed organic fraction of the newly formed (hot) Earth was destroyed by thermal decomposition during the cooling epoch. After Earth cooled sufficiently, an early organic inventory was likely replenished by the impact of comets and asteroids — a process which continues even today. The present organic composition of comets and asteroids can provide information relevant to this secondary organic seeding of the planets, for comparison with scenarios leading to self-replicating organic entities. Although impacts no longer deliver organics in significant quantities, compared with the existing terrestrial inventory, small bodies can deliver their organics intact to Earth‘s surface while giant impacts may cause punctuated extinction of living species (and create opportunities for renewed speciation). Hence, the exogenous organic flux has great importance for life’s origins and terminations. Current knowledge of the organic composition of comets is reviewed, and recent progress in our understanding of the chemical evolution of organic material from its formation to its incorporation into comets and later into planets is outlined. The need for detailed quantitative chemical analysis of material obtained directly from the cometary nucleus is indicated.
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Gkotsinas, Anastasios, Aurélie Guilbert-Lepoutre et Sean N. Raymond. « On Averaging Eccentric Orbits : Implications for the Long-term Thermal Evolution of Comets ». Astronomical Journal 165, no 2 (24 janvier 2023) : 67. http://dx.doi.org/10.3847/1538-3881/acaafd.
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Abstract One of the common approximations in long-term evolution studies of small bodies is the use of circular orbits averaging the actual eccentric ones, facilitating the coupling of processes with very different timescales, such as the orbital changes and the thermal processing. Here we test a number of averaging schemes for elliptic orbits in the context of the long-term evolution of comets, aiming to identify the one that best reproduces the elliptic orbits’ heating patterns and the surface and subsurface temperature distributions. We use a simplified thermal evolution model applied on simulated comets both on elliptic and on their equivalent averaged circular orbits, in a range of orbital parameter space relevant to the inner solar system. We find that time-averaging schemes are more adequate than spatial-averaging ones. Circular orbits created by means of a time average of the equilibrium temperature approximate efficiently the subsurface temperature distributions of elliptic orbits in a large area of the orbital parameter space, rendering them a powerful tool for averaging elliptic orbits.
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Guilbert-Lepoutre, Aurélie, Anastasios Gkotsinas, Sean N. Raymond et David Nesvorny. « The Gateway from Centaurs to Jupiter-family Comets : Thermal and Dynamical Evolution ». Astrophysical Journal 942, no 2 (1 janvier 2023) : 92. http://dx.doi.org/10.3847/1538-4357/acaa3a.
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Abstract It was recently proposed that there exists a “gateway” in the orbital parameter space through which Centaurs transition to Jupiter-family comets (JFCs). Further studies have implied that the majority of objects that eventually evolve into JFCs should leave the Centaur population through this gateway. This may be naively interpreted as gateway Centaurs being pristine progenitors of JFCs. This is the point we want to address in this work. We show that the opposite is true: gateway Centaurs are, on average, more thermally processed than the rest of the population of Centaurs crossing Jupiter’s orbit. Using a dynamically validated JFC population, we find that only ∼20% of Centaurs pass through the gateway prior to becoming JFCs, in accordance with previous studies. We show that more than half of JFC dynamical clones entering the gateway for the first time have already been JFCs—they simply avoided the gateway on their first pass into the inner solar system. By coupling a thermal evolution model to the orbital evolution of JFC dynamical clones, we find a higher than 50% chance that the layer currently contributing to the observed activity of gateway objects has been physically and chemically altered, due to previously sustained thermal processing. We further illustrate this effect by examining dynamical clones that match the present-day orbits of 29P/Schwassmann-Wachmann 1, P/2019 LD2 (ATLAS), and P/2008 CL94 (Lemmon).
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Kwon, Yuna G., Ludmilla Kolokolova, Jessica Agarwal et Johannes Markkanen. « An update of the correlation between polarimetric and thermal properties of cometary dust ». Astronomy & ; Astrophysics 650 (juin 2021) : L7. http://dx.doi.org/10.1051/0004-6361/202141199.
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Context. Comets are conglomerates of ice and dust particles, the latter of which encode information on changes in the radiative and thermal environments. Dust displays distinctive scattered and thermal radiation in the visible and mid-infrared (MIR) wavelengths, respectively, based on its inherent characteristics. Aims. We aim to identify a possible correlation between the properties of scattered and thermal radiation from dust and the principal dust characteristics responsible for this relationship, and therefrom gain insights into comet evolution. Methods. We use the NASA/PDS archival polarimetric data on cometary dust in the red (0.62−0.73 μm) and K (2.00−2.39 μm) domains to leverage the relative excess of the polarisation degree of a comet to the average trend at the given phase angle (Pexcess) as a metric of the dust’s scattered light characteristics. The flux excess of silicate emissions to the continuum around 10 μm (FSi/Fcont) is adopted from previous studies as a metric of the dust’s MIR feature. Results. The two observables – Pexcess and FSi/Fcont – show a positive correlation when Pexcess is measured in the K domain (Spearman’s rank correlation coefficient ρ = 0.71−0.19+0.10). No significant correlation was identified in the red domain (ρ = 0.13−0.15+0.16). The gas-rich comets have systematically weaker FSi/Fcont than the dust-rich ones, and yet both groups retain the same overall tendency with different slope values. Conclusions. The observed positive correlation between the two metrics indicates that composition is a peripheral factor in characterising the dust’s polarimetric and silicate emission properties. The systematic difference in FSi/Fcont for gas-rich versus dust-rich comets would instead correspond to the difference in their dust size distribution. Hence, our results suggest that the current MIR spectral models of cometary dust, which search for a minimum χ2 fit by considering various dust properties simultaneously, should prioritise the dust size and porosity over the composition. With light scattering being sensitive to different size scales in two wavebands, we expect the K-domain polarimetry to be sensitive to the properties of dust aggregates, such as size and porosity, which might have been influenced by evolutionary processes. On the other hand, the red-domain polarimetry reflects the characteristics of sub-micrometre constituents in the aggregate.
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Klinger, J. « Physical Properties of Frozen Volatiles–Their Relevance to the Study of Comet Nuclei ». International Astronomical Union Colloquium 116, no 1 (1989) : 227–41. http://dx.doi.org/10.1017/s0252921100109704.
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AbstractThe structural and thermodynamical properties of water ice and ice mixtures containing CO, CO2, CH4, and NH3 are thought to be important for the evolution of cometary nuclei. Based on recent laboratory studies performed by several groups, an overview is given of the properties of various ices condensed at low temperatures and of their evolution during heating up to a temperature of about 200 K, typical of the perihelion temperature of a comet such as P/Halley. It is shown that the porous surface of amorphous water ice plays an important role in the retention of other volatiles. The kinetics of formation and of decomposition of clathrate hydrates are discussed. The molecular hydrates formed by NH3 are briefly presented, and the possibility of their occurrence in comet nuclei is discussed. With special attention drawn to amorphous ices and clathrate hydrates, a qualitative discussion of the influence of the physical properties of various types of ices on the thermal behavior of comet nuclei and on gas production rates of comets is presented.
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Heggy, Essam, Elizabeth M. Palmer, Alain Hérique, Wlodek Kofman et M. Ramy El-Maarry. « Post-rendezvous radar properties of comet 67P/CG from the Rosetta Mission : understanding future Earth-based radar observations and the dynamical evolution of comets ». Monthly Notices of the Royal Astronomical Society 489, no 2 (12 août 2019) : 1667–83. http://dx.doi.org/10.1093/mnras/stz2174.
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ABSTRACT Radar observations provide crucial insights into the formation and dynamical evolution of comets. This ability is constrained by our knowledge of the dielectric and textural properties of these small-bodies. Using several observations by Rosetta as well as results from the Earth-based Arecibo radio telescope, we provide an updated and comprehensive dielectric and roughness description of Comet 67P/CG, which can provide new constraints on the radar properties of other nuclei. Furthermore, contrary to previous assumptions of cometary surfaces being dielectrically homogeneous and smooth, we find that cometary surfaces are dielectrically heterogeneous ( εr′≈1.6–3.2), and are rough at X- and S-band frequencies, which are widely used in characterization of small-bodies. We also investigate the lack of signal broadening in CONSERT observations through the comet head. Our results suggest that primordial building blocks in the subsurface are either absent, smaller than the radar wavelength, or have a weak dielectric contrast (Δ εr′). To constrain this ambiguity, we use optical albedo measurements by the OSIRIS camera of the freshly exposed subsurface after the Aswan cliff collapse. We find that the hypothetical subsurface blocks should have |Δ εr′|≳0.15, setting an upper limit of ∼ 1 m on the size of 67P/CG's primordial building blocks if they exist. Our analysis is consistent with a purely thermal origin for the ∼ 3 m surface bumps on pit walls and cliff-faces, hypothesized to be high-centred polygons formed from fracturing of the sintered shallow ice-bearing subsurface due to seasonal thermal expansion and contraction. Potential changes in 67P/CG's radar reflectivity at these at X- and S-bands can be associated with large-scale structural changes of the nucleus rather than small-scale textural ones. Monitoring changes in 67P/CG's radar properties during repeated close-approaches via Earth-based observations can constrain the dynamical evolution of its cometary nucleus.
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Guilbert-Lepoutre, Aurélie, Selma Benseguane, Laurine Martinien, Jérémie Lasue, Sébastien Besse, Björn Grieger et Arnaud Beth. « Pits on Jupiter-family Comets and the Age of Cometary Surfaces ». Planetary Science Journal 4, no 11 (1 novembre 2023) : 220. http://dx.doi.org/10.3847/psj/ad083a.
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Abstract Large and deep depressions, also known as pits, are observed at the surface of all Jupiter-family comets (JFCs) imaged by spacecraft missions. They offer the opportunity to glimpse the subsurface characteristics of comet nuclei and study the complex interplay between surface structures and cometary activity. This work investigates the evolution of pits at the surface of 81P/Wild 2, 9P/Tempel 1, and 103P/Hartley 2, in continuation of the work by Benseguane et al. on 67P/Churyumov–Gerasimenko. Pits are selected across the surface of each nucleus, and high-resolution shape models are used to compute the energy they receive. A thermal evolution model is applied to constrain how cometary activity sustained under current illumination conditions could modify them. Similar to what was found for 67P, we show that erosion resulting from water-driven activity is primarily controlled by seasonal patterns that are unique to each comet as a consequence of their shape and rotational properties. However, progressive erosion sustained after multiple perihelion passages is not able to carve any of the observed pits. Instead, cometary activity tends to erase sharp morphological features; they become wider and shallower over time. Our results reinforce the evolutionary sequence evidenced from independent measurables to transform “young” cometary surfaces, with sharp surface topography prone to outbursts, into “old” cometary surfaces. Finally, we suggest that the mechanism at the origin of the pits on JFCs should be able to carve these structures in a region of the solar system where water ice does not sublimate; the Centaur phase thus appears critical to understand JFC surface properties.
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Jindal, Abhinav S., Samuel P. D. Birch, Alexander G. Hayes, Orkan M. Umurhan, Raphael Marschall, Jason M. Soderblom, Jean-Baptiste Vincent et Dennis Bodewits. « Topographically Influenced Evolution of Large-scale Changes in Comet 67P/Churyumov–Gerasimenko's Imhotep Region ». Planetary Science Journal 3, no 8 (1 août 2022) : 193. http://dx.doi.org/10.3847/psj/ac7e48.
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Abstract Large portions of comet 67P/Churyumov–Gerasimenko’s northern hemisphere are blanketed by fallback material consisting of centimeter-sized particles termed the smooth terrains. Observations from the Rosetta mission show that the most drastic transient changes during 67P’s 2015 perihelion passage occurred within a subset of these deposits. However, we still do not understand the processes driving these changes, limiting our overall understanding of how comets evolve over both seasonal and multiorbit timescales. Herein we provide a complete documentation of scarp-driven activity on 67P’s largest smooth terrain deposit, a highly active portion of the Imhotep region that is the southernmost of all smooth terrain basins on 67P. We also present a thermal model that accurately predicts when and where scarps originate during the course of the observed activity. Assuming a uniform surface composition, our model shows that activity is heavily controlled by local topography rather than the presence of ice-enhanced hot spots on the surface. Scarps within the smooth terrain deposits in central Imhotep also exhibit a peculiar behavior, where three scarps originate from the same location but at different times and migrate in opposite directions. This behavior indicates that the landscape retains a memory of previous cycles of erosion and deposition, reflected by the depth of the volatile-rich layer. Future work will need to couple our thermal model with a landscape evolution model in order to explain the complete dynamic evolution of these terrains.
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Rezac, L., et Y. Zhao. « Accuracy of view factor calculations for digital terrain models of comets and asteroids ». Astronomy & ; Astrophysics 642 (octobre 2020) : A167. http://dx.doi.org/10.1051/0004-6361/202038462.
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Context. Detailed shape and topographic models coupled with sophisticated thermal physics are critical elements to proper characterization of surfaces of small bodies in our solar system. Calculations of self-heating effects are especially important in the context of thermal evolution of non-convex surfaces, including craters, cracks, or openings between “rocks”. Aims. Our aim is to provide quantitative comparisons of multiple numerical methods for computing view factors for concave geometries and provide a more rigorous criteria for the validity of their application. Methods. We contrasted five methods of estimating the view factors. First, we studied specific geometries, including shared-edge facets for a reduced two-facet problem. Then, we applied these methods to the shape model of 67P/Churyumov-Gerasimenko. Nevertheless, the presented results are general and could be extended to shape models of other bodies as well. Results. The close loop transformation of the double area integration method for evaluating view factors of nearby or shared-edge facets is the most accurate, although computationally expensive. Two methods of facet subdivision we evaluate in this work provide reasonably accurate results for modest facet subdivision numbers, however, may result in a degraded performance for specific facet geometries. Increasing the number of subdivisions improves their accuracy, but also increases their computational burden. In practical applications, a trade-off between accuracy and computational speed has to be found, therefore, we propose a combined method based on a simple metric that incorporates a conditional application of various methods and an adaptive number of subdivisions. In our study case of a pit on 67P/CG, this method can reach average accuracy of 2–3% while being about an order of magnitude faster than the (most accurate) line integral method.
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Marov, M. Ya, A. V. Rusol et V. A. Dorofeeva. « Numerical Simulation of the Long-Term Thermal Evolution of the Nuclei of Short-Period Comets Using the Nucleus of Comet 67P/Churyumov–Gerasimenko as an Example ». Doklady Physics 64, no 1 (janvier 2019) : 34–38. http://dx.doi.org/10.1134/s1028335819010063.
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Jones, A. P., et N. Ysard. « The essential elements of dust evolution ». Astronomy & ; Astrophysics 627 (27 juin 2019) : A38. http://dx.doi.org/10.1051/0004-6361/201935532.
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Context. There remain many open questions relating to the depletion of elements into dust, e.g., exactly how are C and O incorporated into dust in dense clouds and, in particular, what drives the disappearance of oxygen in the denser interstellar medium? Aims. This work is, in part, an attempt to explain the apparently anomalous incorporation of O atoms into dust in dense clouds. Methods. We re-visit the question of the depletion of the elements incorporated into the carbonaceous component of interstellar dust, i.e., C, H, O, N and S, in the light of recent analyses of the organics in comets, meteorites and interplanetary dust particles. Results. We find that oxygen could be combined with ≈10–20 % of the carbon in the dust in dense regions in the form of a difficult to observe, organic carbonate, (−O−O>C =O), which could explain the unaccounted for 170–255 ppm oxygen depletion. Conclusions. We conclude that, while C, O and N atoms are depleted into an amorphous a-C:H:O:N phase, we posit that a significant fraction of C and O atoms could be sequestered into an organic carbonate, which provides a viable solution to the oxygen depletion problem. Further, the thermal or photolytic decomposition of this carbonate may have a bearing on the formation of CO2 in the ISM.
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Courville, Samuel W., Julie C. Castillo-Rogez, Mohit Melwani Daswani, Elodie Gloesener, Mathieu Choukroun et Joseph G. O’Rourke. « Timing and Abundance of Clathrate Formation Control Ocean Evolution in Outer Solar System Bodies : Challenges of Maintaining a Thick Ocean within Pluto ». Planetary Science Journal 4, no 9 (1 septembre 2023) : 179. http://dx.doi.org/10.3847/psj/acf377.
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Abstract Clathrate hydrates may represent a sizable fraction of material within the icy shells of Kuiper Belt objects and icy moons. They influence the chemical and thermal evolution of subsurface oceans by locking volatiles into the ice shell and by providing more thermal insulation than pure water ice. We model the formation of these crystalline compounds in conditions relevant to outer solar system objects, using Pluto as an example. Although Pluto may have hosted a thick ocean in its early history, Pluto’s overall heat budget is probably insufficient to preserve liquid today if its outer shell is pure water ice. One previously proposed reconciliation is that Pluto’s ocean has a winter jacket: an insulating layer of methane clathrate hydrates. Unfortunately, assessments of the timing, quantity, and type of clathrate hydrates forming within planetary bodies are lacking. Our work quantifies the abundance of clathrate-forming gases present in Pluto’s ocean from accreted ices and volatiles released during thermal metamorphism throughout Pluto’s history. We find that if Pluto formed with the same relative abundances of ices found in comets, then a buoyant layer of mixed methane and carbon dioxide clathrate hydrates may form above Pluto’s ocean, though we find it insufficient to preserve a thick ocean today. In general, our study provides methodology for predicting clathrate formation in ocean worlds, which is necessary to predict the evolution of the ocean’s composition and whether a liquid layer remains at present.
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Golabek, Gregor J., et Martin Jutzi. « Modification of icy planetesimals by early thermal evolution and collisions : Constraints for formation time and initial size of comets and small KBOs ». Icarus 363 (juillet 2021) : 114437. http://dx.doi.org/10.1016/j.icarus.2021.114437.
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Hughes, A. Meredith, Gaspard Duchêne et Brenda C. Matthews. « Debris Disks : Structure, Composition, and Variability ». Annual Review of Astronomy and Astrophysics 56, no 1 (14 septembre 2018) : 541–91. http://dx.doi.org/10.1146/annurev-astro-081817-052035.
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Debris disks are tenuous, dust-dominated disks commonly observed around stars over a wide range of ages. Those around main sequence stars are analogous to the Solar System's Kuiper Belt and zodiacal light. The dust in debris disks is believed to be continuously regenerated, originating primarily with collisions of planetesimals. Observations of debris disks provide insight into the evolution of planetary systems; and the composition of dust, comets, and planetesimals outside the Solar System; as well as placing constraints on the orbital architecture and potentially the masses of exoplanets that are not otherwise detectable. This review highlights recent advances in multiwavelength, high-resolution scattered light and thermal imaging that have revealed a complex and intricate diversity of structures in debris disks and discusses how modeling methods are evolving with the breadth and depth of the available observations. Two rapidly advancing subfields highlighted in this review include observations of atomic and molecular gas around main sequence stars and variations in emission from debris disks on very short (days to years) timescales, providing evidence of non-steady-state collisional evolution particularly in young debris disks.
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Cordiner, Martin, Alexander Thelen, Thibault Cavalie, Richard Cosentino, Leigh N. Fletcher, Mark Gurwell, Katherine de Kleer et al. « Atacama Large Aperture Submillimeter Telescope (AtLAST) science : Planetary and cometary atmospheres ». Open Research Europe 4 (24 avril 2024) : 78. http://dx.doi.org/10.12688/openreseurope.17473.1.
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The study of planets and small bodies within our Solar System is fundamental for understanding the formation and evolution of the Earth and other planets. Compositional and meteorological studies of the giant planets provide a foundation for understanding the nature of the most commonly observed exoplanets, while spectroscopic observations of the atmospheres of terrestrial planets, moons, and comets provide insights into the past and present-day habitability of planetary environments, and the availability of the chemical ingredients for life. While prior and existing (sub)millimeter observations have led to major advances in these areas, progress is hindered by limitations in the dynamic range, spatial and temporal coverage, as well as sensitivity of existing telescopes and interferometers. Here, we summarize some of the key planetary science use cases that factor into the design of the Atacama Large Aperture Submillimeter Telescope (AtLAST), a proposed 50-m class single dish facility: (1) to more fully characterize planetary wind fields and atmospheric thermal structures, (2) to measure the compositions of icy moon atmospheres and plumes, (3) to obtain detections of new, astrobiologically relevant gases and perform isotopic surveys of comets, and (4) to perform synergistic, temporally-resolved measurements in support of dedicated interplanetary space missions. The improved spatial coverage (several arcminutes), resolution (~ 1.2′′ − 12′′), bandwidth (several tens of GHz), dynamic range (~ 105) and sensitivity (~ 1 mK km s−1) required by these science cases would enable new insights into the chemistry and physics of planetary environments, the origins of prebiotic molecules and the habitability of planetary systems in general.
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Biele, Jens, Jean-Baptiste Vincent et Jörg Knollenberg. « Mechanical Properties of Cometary Surfaces ». Universe 8, no 9 (15 septembre 2022) : 487. http://dx.doi.org/10.3390/universe8090487.
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Mechanical properties, in particular, strength (tensile, shear, compressive) and porosity, are important parameters for understanding the evolution and activity of comets. However, they are notoriously difficult to measure. Unfortunately, neither Deep Impact nor other comet observations prior to Rosetta provided firm data on the strength of cometary material. This changed with the Rosetta mission and its detailed close observation data and with the landing(s) of Philae in 2014. There are already many articles and reviews in the literature that derive or compile many different strength values from various Rosetta and Philae data. In this paper, we attempt to provide an overview of the available direct and indirect data; we focus on comet Churyumov–Gerasimenko/67P but include a discussion on the Deep Impact strength results. As a prerequisite, we start by giving precise definitions of ‘strength’, discuss soil mechanics based on the Mohr–Coulomb ‘law’ of micro-gravity, and discuss bulk density and porosity, sintering, and the physics of the strength of a cohesive granular medium. We proceed by discussing the scaling of strength with the size and strain rate, which is needed to understand the observational data. We show how measured elastic properties and thermal (conductivity) data can be correlated with strength. Finally, a singular very high strength value is reviewed as well as some particularly small-strength values inferred from the bouncing motion of Philae, data from its collisions with the surface of the comet, and scratch marks it left, allegedly, on the surface close to its final resting site. The synthesis is presented as an overview figure of the tensile and compressive strength of cometary matter as a function of the size scale; conclusions about the size dependence and apparent natural variability of strength are drawn.
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Ehrenfreund, P., et W. A. Schutte. « Infrared Observations of Interstellar Ices ». Symposium - International Astronomical Union 197 (2000) : 135–46. http://dx.doi.org/10.1017/s0074180900164745.
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In the recent years revolutionary results concerning the nature of icy dust particles have been obtained with the help of the Infrared Space Observatory (ISO) and ground based observations. To date interstellar ice features of H2O, CO, CO2, CH3OH, CH4, H2CO, OCS and HCOOH as well as other minor species are observed. Interstellar grains act as important catalysts in the interstellar medium. Processes such as UV irradiation, cosmic ray processing and temperature variations determine the grain mantle growth and chemical evolution. ISO has revealed that ice segregation is an important and ubiquitous process in the vicinity of massive protostars and reflects the extensive thermal processing of grains in such environments.In this paper a recent view on the inventory of interstellar ices is presented. Constraints on the reservoirs of oxygen in dense clouds are discussed, taking into account recent measurements of oxygen-bearing species. Large abundances of CO2 and CH3OH in dense molecular clouds provide challenging perspectives to investigate the differences of ice chemistry in the vicinity of high and low-mass protostars. Accurate abundances of ice species and knowledge on the ice distribution in the protostellar regions are an important tool to define the environmental conditions in molecular clouds. A global understanding of interstellar ice chemistry also allows monitoring the incorporation and evolution of volatiles in planetesimals and comets and to reveal processes predominant in the early Solar System.
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Hiraoka, K., T. Sato et T. Takayama. « Laboratory Simulation of Chemical Reactions in Interstellar Ices ». Symposium - International Astronomical Union 197 (2000) : 283–92. http://dx.doi.org/10.1017/s0074180900164873.
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The reactions of H atoms with solid thin films at 10 K were studied by using thermal desorption mass spectrometry and FT-IR spectroscopy. The N, C, and O atoms trapped in solid matrices were converted efficiently to fully hydrogenated compounds. In the reaction of H atoms with a solid CO film, the formation of formaldehyde and methanol were confirmed. The relatively low yield of the reaction products suggests either the smaller rate constants of the H atom addition reactions to CO and/or the occurrence of the hydrogen abstraction reaction H + HCO → H2+ CO. The reactions of H atoms with thin films of acetone and 2-propanol were also studied. The major products from acetone were found to be methane and alcohols but 2-propanol was not detected as a reaction product. The reaction of H with 2-propanol led to the formation of methane, alcohols, and acetone as major products.In the reaction of H with C2H2, C2H6was found to be the major product but C2H4could not be detected. This is due to the fact that the first-step addition reaction H + C2H2→ C2H3is the rate-controlling process and the following reactions to form the final product C2H6proceed much faster than the initial one. This finding is in accord with the observation of comets Hyakutake and Hale-Bopp, i.e., C2H2and C2H6but not C2H4were detected in the coma of these comets. In the reactions of H with C2H2and C2H4, the C2H6product yields increased drastically with decrease of temperature from 50 to 10 K. This is most likely due to the increase of the sticking probability of H atoms on the solid films at lower temperature. These findings led us to conclude that the chemical evolution taking place on the dust grains via H-atom tunneling reactions becomes efficient only at cryogenic temperatures, i.e., ~ 10 K.
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Drouin, Brian J., Deacon J. Nemchick, Ananda Nole, Adrian Tang, Chung-Tse Michael Wu, Neda Khiabani, Maria Alonso et Mau-Chung Frank Chang. « Dual-band Fourier-transform Millimeter-wave Spectrometry for In Situ Gas Sensing ». Planetary Science Journal 4, no 6 (1 juin 2023) : 100. http://dx.doi.org/10.3847/psj/acd348.
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Abstract The exploration of icy body composition in the solar system has often involved spectroscopic measurements of volatiles detected with remote sensing, such measurements portray materials naturally expelled from the surface that enter the exosphere and potentially escape into space. Variations in the ratio of deuterium and hydrogen in these measurements have led to inconclusive hypotheses regarding potential cometary origins of Earth’s ocean water and/or organics. Observational biases regarding unknown previous processing of the observable ejected materials necessitates studies of more dormant, less-processed bodies. Landed missions on comets have brought focus onto the development of small, sensitive instrumentation capable of similar composition measurements of the nascent surface and near-surface materials. We present an evolution of our compact Fourier-transform millimeter-wave cavity spectrometer that is tuned for sensitivity at 80.6 and 183 GHz where HDO and H2O exhibit resonance features. We discuss both a low-SWaP (size–weight and power) architecture that uses custom microchip transceiver elements as well as a modular configuration using traditional GaAs-based millimeter-wave hardware. New design features for these systems including quartz-based coupling elements, system thermal management, and a separable clocking board are discussed in addition to sensitivity studies and applications in potential mission scenarios.
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Haack, David, Katharina Otto, Bastian Gundlach, Christopher Kreuzig, Dorothea Bischoff, Ekkehard Kührt et Jürgen Blum. « Tensile strength of dust-ice mixtures and their relevance as cometary analog material ». Astronomy & ; Astrophysics 642 (octobre 2020) : A218. http://dx.doi.org/10.1051/0004-6361/202037763.
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Aims. The tensile strength of granular matter is of great importance to our understanding of the evolution of comets and to our attempts to reproduce processes on cometary surfaces in laboratory experiments. In this work, we investigate the tensile strength of three different materials and their mixtures, which can be used as cometary analog materials in the laboratory. Methods. We used two types of siliceous dusts and granular water ice whose polydisperse particles were either angular or spherical. Our samples were cooled to below 150 K to better simulate the conditions of a cometary surface and to avoid thermal alteration of the material. We used the Brazilian disk test method to exert stress on the cooled samples and determine the tensile strength at the moment the samples broke. Results. We find that the tensile strength of two component mixtures is strongly dominated by the component with the higher tensile strength. The materials made of mostly angular dust particles have a lower filling fraction, but a higher tensile strength compared to materials made of spherical particles. Furthermore, the tensile strength of the cooled components is substantially lower than the tensile strength of the same components at room temperature. This implies that the surface energy of the investigated materials at low temperatures is significantly lower than previously assumed.
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Kruczkiewicz, F., J. Vitorino, E. Congiu, P. Theulé et F. Dulieu. « Ammonia snow lines and ammonium salts desorption ». Astronomy & ; Astrophysics 652 (août 2021) : A29. http://dx.doi.org/10.1051/0004-6361/202140579.
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Context. The nitrogen reservoir in planetary systems is a long-standing problem. Some of the N-bearing molecules are probably incorporated into the ice bulk during the cold phases of the stellar evolution, and may be gradually released into the gas phase when the ice is heated, for example in active comets. The chemical nature of the N-reservoir should greatly influence how, when, and in what form N returns to the gas phase, or is incorporated into the refractory material forming planetary bodies. Aims. We present the study of the thermal desorption of two ammonium salts, ammonium formate and ammonium acetate, from a gold surface and from a water ice substrate. Methods. Temperature-programmed desorption experiments and Fourier transform infrared reflection spectroscopy were conducted to investigate the desorption behavior of ammonium salts. Results. Ammonium salts are semi-volatile species releasing neutral species as major components upon desorption, namely ammonia and the corresponding organic acid (HCOOH and CH3COOH), at temperatures higher than the temperature of thermal desorption of water ice. Their desorption follows a first-order Wigner-Polanyi law. We find the first-order kinetic parameters A = 7.7 ± 0.6 × 1015 s−1 and Ebind = 68.9 ± 0.1 kJ mol−1 for ammonium formate and A = 3.0 ± 0.4 × 1020 s−1 and Ebind = 83.0 ± 0.2 kJ mol−1 for ammonium acetate. The presence of a water ice substrate does not influence the desorption kinetics. Ammonia molecules locked in salts desorb as neutral molecules at temperatures much higher than previously expected, and that are usually attributed to refractory materials. Conclusions. The ammonia snow line has a smaller radius than the water snow line. As a result, the NH3/H2O ratio content in Solar System bodies can be a hint to where they formed and subsequently migrated.
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Klinger, J. « Thermal evolution of comet nuclei ». Advances in Space Research 23, no 7 (janvier 1999) : 1309–18. http://dx.doi.org/10.1016/s0273-1177(99)00042-3.
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Coulson, S. G. « On the deceleration of cometary fragments in aerogel ». International Journal of Astrobiology 8, no 1 (22 décembre 2008) : 9–17. http://dx.doi.org/10.1017/s147355040800431x.
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AbstractDetermining the thermal history of the cometary grains captured by the Stardust mission presents a difficult problem. We consider two simplified models for the deceleration of hypervelocity particles captured in aerogel; both models assume a velocity squared drag force. The first model assumes that the mass of the particle remains constant during capture and the second that mass is lost due to ablation of the particle through interactions with the aerogel. It is found that the constant mass model adequately reproduces the track lengths, found from experiments by Hörz et al. in 2008, that impacted aluminium oxide spheres into aerogel at hypervelocities ~6 km s−1.Deceleration in aerogel heats volatile particles such as organic ices to high temperatures greater than 1,000 K, for durations of ~1 μs: more than sufficient to completely ablate the particle. Refractory particles also experience significant heating greater than 2500 K, greater than the particle's melting point, over similar timescales. This suggests that the fragments recovered to Earth by the Stardust mission were considerably altered by hypersonic capture by aerogel, and so limits the amount of information that can be obtained regarding the formation of mineral and organic particles within Kuiper Belt comets.
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Coletta, A., F. Fontani, V. M. Rivilla, C. Mininni, L. Colzi, Á. Sánchez-Monge et M. T. Beltrán. « Evolutionary study of complex organic molecules in high-mass star-forming regions ». Astronomy & ; Astrophysics 641 (septembre 2020) : A54. http://dx.doi.org/10.1051/0004-6361/202038212.
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We have studied four complex organic molecules (COMs), the oxygen-bearing methyl formate (CH3OCHO) and dimethyl ether (CH3OCH3) as well as the nitrogen-bearing formamide (NH2CHO) and ethyl cyanide (C2H5CN), towards a large sample of 39 high-mass star-forming regions representing different evolutionary stages, from early to evolved phases. We aim to identify potential correlations and chemical links between the molecules and to trace their evolutionary sequence through the star formation process. We analysed spectra obtained at 3, 2, and 0.9 mm with the IRAM-30m telescope. We derived the main physical parameters for each species by fitting the molecular lines. We compared them and evaluated their evolution while also taking several other interstellar environments into account. We report detections in 20 sources, revealing a clear dust absorption effect on column densities. Derived abundances range between ~ 10−10−10−7 for CH3OCHO and CH3OCH3, ~ 10−12−10−10 for NH2CHO, and ~ 10−11−10−9 for C2H5CN. The abundances of CH3OCHO, CH3OCH3, and C2H5CN are very strongly correlated (r ≥ 0.92) across ~ 4 orders of magnitude. We note that CH3OCHO and CH3OCH3 show the strongest correlations in most parameters, and a nearly constant ratio (~ 1) over a remarkable ~ 9 orders of magnitude in luminosity for the following wide variety of sources: pre-stellar to evolved cores, low- to high-mass objects, shocks, Galactic clouds, and comets. This indicates that COMs chemistry is likely early developed and then preserved through evolved phases. Moreover, the molecular abundances clearly increase with evolution, covering ~ 6 orders of magnitude in the luminosity/mass ratio. We consider CH3OCHO and CH3OCH3 to be most likely chemically linked. They could, for example, share a common precursor, or be formed one from the other. Based on correlations, ratios, and the evolutionary trend, we propose a general scenario for all COMs, involving a formation in the cold, earliest phases of star formation and a following increasing desorption with the progressive thermal and shock-induced heating of the evolving core.
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Yang Yunkai, 杨云开, 成家霖 Cheng Jialin, 文宇杰 Wen Yujie, 申恒 Shen Heng, 闫智辉 Yan Zhihui et 贾晓军 Jia Xiaojun. « 氮化硅微腔中光频梳的演化及热自稳定性分析 ». Laser & ; Optoelectronics Progress 60, no 11 (2023) : 1106029. http://dx.doi.org/10.3788/lop230441.
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Cecchi-Pestellini, Cesare, Flavio Scappini, Rosalba Saija, Maria Antonia Iatì, Arianna Giusto, Santi Aiello, Ferdinando Borghese et Paolo Denti. « On the formation and survival of complex prebiotic molecules in interstellar grain aggregates ». International Journal of Astrobiology 3, no 4 (octobre 2004) : 287–93. http://dx.doi.org/10.1017/s1473550404001971.
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The aggregation of interstellar grains as a result of ballistic collisions produces loosely packed structures with much of their internal volume composed by vacuum (cavities). The molecular material present on the surfaces of the cavities gives rise to a series of reactions induced by cosmic rays, UV radiation, thermal shocks, etc., in high reducing conditions. Thus, a terrestrial type chemistry is given the possibility to evolve inside these cavities. The resulting products are different and of a wider range than those from gas-phase or surface chemistry in molecular clouds. Under conditions similar to those in the aggregate cavities, laboratory experiments have produced amino acids, sugars and other organic compounds from simple precursors. In dense star-forming regions, the molecular species inside aggregates are efficiently shielded against the local UV field. The same molecules were incorporated in the material which formed the Earth, as well as other planets, during the process of its formation and afterwards fell on the surface via comets, meteorites, interstellar dust, etc. This was the source material that can produce, under favorable circumstances, the biopolymers needed for life. The astronomical observations of organic molecules in star-forming regions and the results of analyses of meteorites and cometary dust seem to support the present hypothesis that complex prebiotic molecules form inside dust aggregates and therein survive the journey to planetary systems. The Miller experiment is revisited through innumerable repetitions inside dust grain aggregates.
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Ioppolo, S., Z. Kaňuchová, R. L. James, A. Dawes, N. C. Jones, S. V. Hoffmann, N. J. Mason et G. Strazzulla. « Vacuum ultraviolet photoabsorption spectroscopy of space-related ices : 1 keV electron irradiation of nitrogen- and oxygen-rich ices ». Astronomy & ; Astrophysics 641 (septembre 2020) : A154. http://dx.doi.org/10.1051/0004-6361/201935477.
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Context. Molecular oxygen, nitrogen, and ozone have been detected on some satellites of Saturn and Jupiter, as well as on comets. They are also expected to be present in ice-grain mantles within star-forming regions. The continuous energetic processing of icy objects in the Solar System induces physical and chemical changes within the ice. Laboratory experiments that simulate energetic processing (ions, photons, and electrons) of ices are therefore essential for interpreting and directing future astronomical observations. Aims. We provide vacuum ultraviolet (VUV) photoabsorption spectroscopic data of energetically processed nitrogen- and oxygen-rich ices that will help to identify absorption bands and/or spectral slopes observed on icy objects in the Solar System and on ice-grain mantles of the interstellar medium. Methods. We present VUV photoabsorption spectra of frozen O2 and N2, a 1:1 mixture of both, and a new systematic set of pure and mixed nitrogen oxide ices. Spectra were obtained at 22 K before and after 1 keV electron bombardment of the ice sample. Ices were then annealed to higher temperatures to study their thermal evolution. In addition, Fourier-transform infrared spectroscopy was used as a secondary probe of molecular synthesis to better identify the physical and chemical processes at play. Results. Our VUV data show that ozone and the azide radical (N3) are observed in our experiments after electron irradiation of pure O2 and N2 ices, respectively. Energetic processing of an O2:N2 = 1:1 ice mixture leads to the formation of ozone along with a series of nitrogen oxides. The electron irradiation of solid nitrogen oxides, pure and in mixtures, induces the formation of new species such as O2, N2, and other nitrogen oxides not present in the initial ice. Results are discussed here in light of their relevance to various astrophysical environments. Finally, we show that VUV spectra of solid NO2 and water can reproduce the observational VUV profile of the cold surface of Enceladus, Dione, and Rhea, strongly suggesting the presence of nitrogen oxides on the surface of the icy Saturn moons.
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Espinasse, S., A. Coradini, M. T. Capria, F. Capaccioni, R. Orosei, M. Salomone et C. Federico. « Thermal evolution and differentiation of a short-period comet ». Planetary and Space Science 41, no 6 (juin 1993) : 409–27. http://dx.doi.org/10.1016/0032-0633(93)90001-i.
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Kouchi, A., J. M. Greenberg, T. Yamamoto et T. Mukai. « Extremely low thermal conductivity of amorphous ice - Relevance to comet evolution ». Astrophysical Journal 388 (avril 1992) : L73. http://dx.doi.org/10.1086/186333.
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Prialnik, Dina, Gal Sarid, Eric D. Rosenberg et Rainer Merk. « Thermal and Chemical Evolution of Comet Nuclei and Kuiper Belt Objects ». Space Science Reviews 138, no 1-4 (12 janvier 2008) : 147–64. http://dx.doi.org/10.1007/s11214-007-9301-4.
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Rusol, Andrey V., et Vera A. Dorofeeva. « Thermal Evolution of the Nucleus of the Comet 67P for 120 Years : Numerical Simulations ». Open Astronomy 27, no 1 (1 septembre 2018) : 175–82. http://dx.doi.org/10.1515/astro-2018-0030.
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Abstract The purpose of this paper is to estimate to what temperatures and to what depth the outer layers of the cometary nuclei are heated for several dozen revolutions around the Sun, and what changes in the composition of the volatiles occur in this case. This is important because it is not clear how much the experimentally obtained results on the composition of cometary comes depend on how long the comet is in the current orbit. Our approach to this problem is based on using 3D model of the geometry and dynamics of a cometary nucleus that takes into account the diurnal rotation and orientation of the rotation axis relative to the Sun to simulate the irradiance to take value of temperature the surface of the nucleus and 1D thermal model of the porous ice-rock body. The results of the numerical simulation of heat propagation in the subsurface layers of some points the MA’AT region of the 67P core, obtained for the 20 orbital cycles (close to 130 years), are presented in this paper.
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Orosei, R., A. Coradini, M. C. De Sanctis et C. Federico. « Collision-induced thermal evolution of a comet nucleus in the Edgeworth-Kuiper Belt ». Advances in Space Research 28, no 10 (janvier 2001) : 1563–69. http://dx.doi.org/10.1016/s0273-1177(01)00362-3.
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Alan Stern, S., James C. Green, Webster Cash et Timothy A. Cook. « Helium and argon abundance constraints and the thermal evolution of Comet Austin (1989c1) ». Icarus 95, no 1 (janvier 1992) : 157–61. http://dx.doi.org/10.1016/0019-1035(92)90198-g.
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Boehnhardt, Hermann, Jean-Pierre Bibring, Istvan Apathy, Hans Ulrich Auster, Amalia Ercoli Finzi, Fred Goesmann, Göstar Klingelhöfer et al. « The Philae lander mission and science overview ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 375, no 2097 (29 mai 2017) : 20160248. http://dx.doi.org/10.1098/rsta.2016.0248.
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The Philae lander accomplished the first soft landing and the first scientific experiments of a human-made spacecraft on the surface of a comet. Planned, expected and unexpected activities and events happened during the descent, the touch-downs, the hopping across and the stay and operations on the surface. The key results were obtained during 12–14 November 2014, at 3 AU from the Sun, during the 63 h long period of the descent and of the first science sequence on the surface. Thereafter, Philae went into hibernation, waking up again in late April 2015 with subsequent communication periods with Earth (via the orbiter), too short to enable new scientific activities. The science return of the mission comes from eight of the 10 instruments on-board and focuses on morphological, thermal, mechanical and electrical properties of the surface as well as on the surface composition. It allows a first characterization of the local environment of the touch-down and landing sites. Unique conclusions on the organics in the cometary material, the nucleus interior, the comet formation and evolution became available through measurements of the Philae lander in the context of the Rosetta mission. This article is part of the themed issue ‘Cometary science after Rosetta’.
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Sarid, Gal, Dina Prialnik, Karen J. Meech, Jana Pittichová et Tony L. Farnham. « Thermal Evolution and Activity of Comet 9P/Tempel 1 and Simulation of a Deep Impact ». Publications of the Astronomical Society of the Pacific 117, no 834 (août 2005) : 796–809. http://dx.doi.org/10.1086/431657.
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Jia, Pan, Bruno Andreotti et Philippe Claudin. « Giant ripples on comet 67P/Churyumov–Gerasimenko sculpted by sunset thermal wind ». Proceedings of the National Academy of Sciences 114, no 10 (21 février 2017) : 2509–14. http://dx.doi.org/10.1073/pnas.1612176114.
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Explaining the unexpected presence of dune-like patterns at the surface of the comet 67P/Churyumov–Gerasimenko requires conceptual and quantitative advances in the understanding of surface and outgassing processes. We show here that vapor flow emitted by the comet around its perihelion spreads laterally in a surface layer, due to the strong pressure difference between zones illuminated by sunlight and those in shadow. For such thermal winds to be dense enough to transport grains—10 times greater than previous estimates—outgassing must take place through a surface porous granular layer, and that layer must be composed of grains whose roughness lowers cohesion consistently with contact mechanics. The linear stability analysis of the problem, entirely tested against laboratory experiments, quantitatively predicts the emergence of bedforms in the observed wavelength range and their propagation at the scale of a comet revolution. Although generated by a rarefied atmosphere, they are paradoxically analogous to ripples emerging on granular beds submitted to viscous shear flows. This quantitative agreement shows that our understanding of the coupling between hydrodynamics and sediment transport is able to account for bedform emergence in extreme conditions and provides a reliable tool to predict the erosion and accretion processes controlling the evolution of small solar system bodies.
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Rickman, Hans. « The Thermal History and Structure of Cometary Nuclei ». International Astronomical Union Colloquium 116, no 2 (1991) : 733–60. http://dx.doi.org/10.1017/s0252921100012707.
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Abstract.Cometary nuclei are often considered to be the most primitive bodies of the solar system. Thus it is particularly important to find out what structural changes may have been brought about as a result of their thermal evolution. Is there reason to believe that the bulk composition of the nucleus of a present-day short-period comet may differ from that of the original planetesimal in the solar nebula? Apart from the development of a non-volatile surface layer (‘dust mantle’), what further depth-dependent differentiation can we expect in such a nucleus? These are the ultimate questions addressed in this paper, and attention is focused on the two most active stages of thermal evolution: the early planetesimal stage with internal heating basically due to radioactive decay, and the recent or present cometary phase with strong external heating due to insolation of the surface.
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Ibadinov, Kh I. « Covering of cometary nucleus by refractory crust and its evolution into asteroid-like body ». International Astronomical Union Colloquium 173 (1999) : 365–70. http://dx.doi.org/10.1017/s0252921100031675.
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AbstractFrom the established dependence of the brightness decrease of a short-period comet dependence on the perihelion distance of its orbit it follows that part of the surface of these cometary nuclei gradually covers by a refractory crust. The results of cometary nucleus simulation show that at constant insolation energy the crust thickness is proportional to the square root of the insolation time and the ice sublimation rate is inversely proportional to the crust thickness. From laboratory experiments resulted the thermal regime, the gas productivity of the nucleus, covering of the nucleus by the crust, and the tempo of evolution of a short-period comet into the asteroid-like body studied.
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De Sanctis, M. Cristina, M. Teresa Capria, Angioletta Coradini et Eleonora Ammannito. « Thermal Evolution Models of the 9P/Tempel 1 Comet Nucleus for Interpreting the Deep Impact Results ». Astronomical Journal 133, no 4 (15 mars 2007) : 1836–46. http://dx.doi.org/10.1086/512053.
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Rivero, Juan Manuel, et Miguel Hermanns. « Modeling the time evolution of geothermal boreholes during peak heating and cooling demands ». Journal of Physics : Conference Series 2116, no 1 (1 novembre 2021) : 012101. http://dx.doi.org/10.1088/1742-6596/2116/1/012101.
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Abstract A geothermal heat exchanger requires special care in its design when it comes to peak heating and cooling demands of the building as the installation may incur in material damages due to the extreme temperatures reached by the heat carrying liquid. The peak demands tend to last a few days at most and the theoretical model used to predict the thermal response of the geothermal heat exchanger has, therefore, to consider the thermal inertia of the heat carrying liquid, the grout, and the ground close to the boreholes. With this in mind, the present work discusses a theoretical model that provides, among other things, the heat injection rates per unit pipe length of the different pipes in the borehole in terms of the bulk temperatures of the heat carrying liquid during those peak heating and cooling demands.
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Bar-Nun, Akiva, Eyal Heifetz et Dina Prialnik. « Thermal evolution of Comet P/Tempel 1—Representing the group of targets for the CRAF and CNSR missions ». Icarus 79, no 1 (mai 1989) : 116–24. http://dx.doi.org/10.1016/0019-1035(89)90111-5.
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Myllys, M., P. Henri, M. Galand, K. L. Heritier, N. Gilet, R. Goldstein, A. I. Eriksson, F. Johansson et J. Deca. « Plasma properties of suprathermal electrons near comet 67P/Churyumov-Gerasimenko with Rosetta ». Astronomy & ; Astrophysics 630 (20 septembre 2019) : A42. http://dx.doi.org/10.1051/0004-6361/201834964.
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Context. The Rosetta spacecraft escorted comet 67P/Churyumov-Gerasimenko from 2014 to September 2016. The mission provided in situ observations of the cometary plasma during different phases of the cometary activity, which enabled us to better understand its evolution as a function of heliocentric distance. Aims. In this study, different electron populations, called warm and hot, observed by the Ion and Electron Sensor (IES) of the Rosetta Plasma Consortium (RPC) are investigated near the comet during the escorting phase of the Rosetta mission. Methods. The estimates for the suprathermal electron densities and temperatures were extracted using IES electron data by fitting a double-kappa function to the measured velocity distributions. The fitting results were validated using observations from other RPC instruments. We give upgraded estimates for the warm and hot population densities compared to values previously shown in literature. Results. The fitted density and temperature estimates for both electron populations seen by IES are expressed as a function of heliocentric distance to study their evolution with the cometary activity. In addition, we studied the dependence between the electron properties and cometocentric distance. Conclusions. We observed that when the neutral outgassing rate of the nucleus is high (i.e., near perihelion) the suprathermal electrons are well characterized by a double-kappa distribution. In addition, warm and hot populations show a significant dependence with the heliocentric distance. The populations become clearly denser near perihelion while their temperatures are observed to remain almost constant. Moreover, the warm electron population density is shown to be strongly dependent on the radial distance from the comet. Finally, based on our results we reject the hypothesis that hot electron population seen by IES consists of solely suprathermal (halo) solar wind electrons, while we suggest that the hot electron population mainly consists of solar wind thermal electrons that have undergone acceleration near the comet.
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Marov, M. Ya, A. V. Rusol et V. A. Dorofeeva. « Numerical simulation of the long-term thermal evolution of the nuclei of short-period comets:using the nucleus of comet 67p/Churyumov–Gerasimenko as an example ». Доклады Академии наук 484, no 2 (13 avril 2019) : 150–55. http://dx.doi.org/10.31857/s0869-56524842150-155.
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Using numerical models, we have studied what depth of the outer layer the comet nuclei are degassed to when they are in orbits whose perihelion is close to the Sun for tens of years. The problem is topical, because it helps to understand how much the experimentally obtained results on the composition of comet comas depend on how long the comet is in its present-day orbit and how adequately the data obtained reflect the composition of comet nuclei as a whole. The proposed approach, which is demonstrated using comet 67P/Churyumov–Gerasimenko as an example, is based on a 3D comet nucleus surface relief model and takes into account not only its orbital motion, but also its diurnal rotation. The propagation of heat in the nucleus subsurface layers is described by a 1D heat conduction equation for a porous rock-ice composition of matter. Based on this approach, we have derived the temperature distributions in the subsurface layers for several surface patches located in the Ma’at region in 20 revolutions around the Sun, ~130 years.
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Markkanen, Johannes, et Jessica Agarwal. « Scattering, absorption, and thermal emission by large cometary dust particles : Synoptic numerical solution ». Astronomy & ; Astrophysics 631 (novembre 2019) : A164. http://dx.doi.org/10.1051/0004-6361/201936235.
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Context. Remote light scattering and thermal infrared observations provide clues about the physical properties of cometary and interplanetary dust particles. Identifying these properties will lead to a better understanding of the formation and evolution of the Solar System. Aims. We present a numerical solution for the radiative and conductive heat transport in a random particulate medium enclosed by an arbitrarily shaped surface. The method will be applied to study thermal properties of cometary dust particles. Methods. The recently introduced incoherent Monte Carlo radiative transfer method developed for scattering, absorption, and propagation of electromagnetic waves in dense discrete random media is extended for radiative heat transfer and thermal emission. The solution is coupled with the conductive Fourier transport equation that is solved with the finite-element method. Results. The proposed method allows the synoptic analysis of light scattering and thermal emission by large cometary dust particles consisting of submicrometer-sized grains. In particular, we show that these particles can sustain significant temperature gradients resulting in the superheating factor phase function observed for the coma of comet 67P/Churyumov–Gerasimenko.
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Kuppam, Poshan Kumar Reddy, K. M. M. D. K. Kimbulapitiya, Srikanth Vuppala, Kuangye Wang, G. Phaneendra Reddy, Krishna P. Pande, Po-Tsung Lee et Yun-Lun Chueh. « A Nickel Coated Copper Substrate as a Hydrogen Evolution Catalyst ». Catalysts 12, no 1 (5 janvier 2022) : 58. http://dx.doi.org/10.3390/catal12010058.
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Replacing precious metals with low-cost metals is the best solution for large scale production. Copper is known for its excellent conductivity and thermal management applications. When it comes to hydrogen evolution reaction, it is highly unstable, especially in KOH solution. In this paper, we approached a simple method to reduce corrosion and improve the performance by depositing nickel-molybdenum oxide and nickel on copper substrates and the achieved tafel slopes of 115 mV/dec and 117 mV/dec at 10 mA/cm2. While at first, molybdenum oxide coated samples showed better performance after 100 cycles of stability tests, the onset potential rapidly changed. Cu-Ni, which was deposited using the electron gun evaporation (e-gun), has shown better performance with 0.28 V at 10 mA/cm2 and led to stability after 100 cycles. Our results show that when copper is alloyed with nickel, it acts as a promising hydrogen evolution reaction (HER) catalyst.
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Sherje, Dr Nitin. « Thermal Property Investigation in Nanolubricants via Nano- Scaled Particle Addition ». International Journal of New Practices in Management and Engineering 10, no 01 (31 mars 2021) : 12–15. http://dx.doi.org/10.17762/ijnpme.v10i01.96.
Texte intégralRésumé :
In nanolubricants, the increase in scholarly attention has been attributed to the affirmation that they exhibit enhanced thermo-physical features and that they can also be used in various thermal applications. Some of these applications where they could be incorporated include solar energy harvesting, industrial applications, and heat exchanger effectiveness enhancement. Recently, various approaches have been employed to enhance the coefficient of heat transfer, especially between the fluid contact surfaces and the working fluids. When it comes to conventional fluids of heat transfer, examples being ethylene glycol/water, thermal oils, and water, some studies document that they exhibit limitations. For instance, these fluids exhibit low thermal properties when compared to the solids with which they interact. To respond to this dilemma, there have been efforts in this study to have the fluids’ thermal properties improved via nano-scaled particle addition, causing marked evolutions in the evaluations of the behavior of fluids of heat transfer. Indeed, findings suggest that in base fluids, when the solid particles are suspended, there tends to be an enhancement in the fluid’s energy transmission; hence, notable improvements in material thermal conductivity properties, besides the betterment of material heat transfer characteristics.