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1.
After presenting a summary of what is presently known from cometary vibrational spectroscopy, we discuss briefly some possible results to be anticipated from future non-sample-retum cometary missions which, however, will leave a number of key questions unanswered. Major efforts have to be made in the laboratory to properly prepare the analysis of returned cometary samples. We report, in particular, on Raman spectroscopy of cometary analogs (frozen gases and irradiated organic materials) performed in our laboratory applying sufficiently low laser power so as not to significantly alter the sample. Also discussed are our attempts to use REELS (Reflection Electron Energy Loss Spectroscopy) which may yield information not only on the elemental composition of the sample but also on its optical constants, especially in the far UV region. 相似文献
2.
Analogies between interstellar and cometary matter can be found in their chemical compositions, both in the gaseous and solid phases, but also in the physical processes involved like evidence for ion-molecules reactions at low temperature and for ice irradiation processes. Such analogies can be observed from 3 types of measurements: interstellar spectra, cometary observations, and analyses of interplanetary dust particles, with the help of laboratory simulation experiments. Taking into account all the present available information, a compilation of the elemental abundances in interstellar matter and in comet Halley is derived, without any assumption about the dust to gas ratio. It is found that there is a significant apparent depletion of nitrogen, presently unexplained, in both interstellar and cometary materials. 相似文献
3.
W. Riedler K. Torkar H. Jeszenszky J. Romstedt H. St. C. Alleyne H. Arends W. Barth J. V. D. Biezen B. Butler P. Ehrenfreund M. Fehringer G. Fremuth J. Gavira O. Havnes E. K. Jessberger R. Kassing W. Klöck C. Koeberl A. C. Levasseur-Regourd M. Maurette F. Rüdenauer R. Schmidt G. Stangl M. Steller I. Weber 《Space Science Reviews》2007,128(1-4):869-904
The International Rosetta Mission is set for a rendezvous with Comet 67 P/Churyumov-Gerasimenko in 2014. On its 10 year journey
to the comet, the spacecraft will also perform a fly-by of the two asteroids Stein and Lutetia in 2008 and 2010, respectively.
The mission goal is to study the origin of comets, the relationship between cometary and interstellar material and its implications
with regard to the origin of the Solar System. Measurements will be performed that shed light into the development of cometary
activity and the processes in the surface layer of the nucleus and the inner coma.
The Micro-Imaging Dust Analysis System (MIDAS) instrument is an essential element of Rosetta’s scientific payload. It will
provide 3D images and statistical parameters of pristine cometary particles in the nm-μm range from Comet 67P/Churyumov-Gerasimenko.
According to cometary dust models and experience gained from the Giotto and Vega missions to 1P/Halley, there appears to be
an abundance of particles in this size range, which also covers the building blocks of pristine interplanetary dust particles.
The dust collector of MIDAS will point at the comet and collect particles drifting outwards from the nucleus surface. MIDAS
is based on an Atomic Force Microscope (AFM), a type of scanning microprobe able to image small structures in 3D. AFM images
provide morphological and statistical information on the dust population, including texture, shape, size and flux. Although
the AFM uses proven laboratory technology, MIDAS is its first such application in space. This paper describes the scientific
objectives and background, the technical implementation and the capabilities of MIDAS as they stand after the commissioning
of the flight instrument, and the implications for cometary measurements. 相似文献
4.
Fred Goesmann Helmut Rosenbauer Reinhard Roll Cyril Szopa Francois Raulin Robert Sternberg Guy Israel Uwe Meierhenrich Wolfram Thiemann Guillermo Munoz-Caro 《Space Science Reviews》2007,128(1-4):257-280
Comets are thought to preserve the most pristine material currently present in the solar system, as they are formed by agglomeration
of dust particles in the solar nebula, far from the Sun, and their interiors have remained cold. By approaching the Sun, volatile
components and dust particles are released forming the cometary coma. During the phase of Heavy Bombardment, 3.8--4 billion
years ago, cometary matter was delivered to the Early Earth. Precise knowledge on the physico-chemical composition of comets
is crucial to understand the formation of the Solar System, the evolution of Earth and particularly the starting conditions
for the origin of life on Earth. Here, we report on the COSAC instrument, part of the ESA cometary mission Rosetta, which
is designed to characterize, identify, and quantify volatile cometary compounds, including larger organic molecules, by in
situ measurements of surface and subsurface cometary samples. The technical concept of a multi-column enantio-selective gas
chromatograph (GC) coupled to a linear reflectron time-of-flight mass-spectrometer instrument is presented together with its
realisation under the scientific guidance of the Max-Planck-Institute for Solar System Research in Katlenburg-Lindau, Germany.
The instrument's technical data are given; first measurements making use of standard samples are presented. The cometary science
community is looking forward to receive fascinating data from COSAC cometary in situ measurements in 2014. 相似文献
5.
Thomas Stephan 《Space Science Reviews》2008,138(1-4):247-258
One of the prime objectives in the analysis of cometary dust collected by the Stardust space mission is to determine the elemental composition of comet 81P/Wild 2. For this analysis, samples captured by two sampling media, silica aerogel and Al foil, were available. While aerogel was qualified to sample the dust almost intact, particles impinging on Al foils produced hypervelocity impact craters with residual cometary matter. Both sample types delivered valuable information on the cometary inventory, even though a slight loss of volatiles was observed for impact residues on Al foils. Altogether an elemental composition close to solar elemental abundances was observed, indicating that the early solar system was chemically rather homogeneous from the innermost regions close to the sun to the outer edge of the solar system, the presumed region of cometary origin. 相似文献
6.
Anny-Chantal Levasseur-Regourd Jessica Agarwal Hervé Cottin Cécile Engrand George Flynn Marco Fulle Tamas Gombosi Yves Langevin Jérémie Lasue Thurid Mannel Sihane Merouane Olivier Poch Nicolas Thomas Andrew Westphal 《Space Science Reviews》2018,214(3):64
This review presents our understanding of cometary dust at the end of 2017. For decades, insight about the dust ejected by nuclei of comets had stemmed from remote observations from Earth or Earth’s orbit, and from flybys, including the samples of dust returned to Earth for laboratory studies by the Stardust return capsule. The long-duration Rosetta mission has recently provided a huge and unique amount of data, obtained using numerous instruments, including innovative dust instruments, over a wide range of distances from the Sun and from the nucleus. The diverse approaches available to study dust in comets, together with the related theoretical and experimental studies, provide evidence of the composition and physical properties of dust particles, e.g., the presence of a large fraction of carbon in macromolecules, and of aggregates on a wide range of scales. The results have opened vivid discussions on the variety of dust-release processes and on the diversity of dust properties in comets, as well as on the formation of cometary dust, and on its presence in the near-Earth interplanetary medium. These discussions stress the significance of future explorations as a way to decipher the formation and evolution of our Solar System. 相似文献
7.
We review the evidence for the products of interstellar chemistry in volatile cometary matter. We compare the organic inventory of star-forming cores with that measured in various comets and point out the similarities and differences. The conditions necessary to fractionate interstellar molecules in the heavier isotopes of H, C, O and N are summarised and compared to the measured fractionation ratios in cometary ices. We give a list of future measurements that would shed further light on the putative connection between cometary and interstellar molecules. 相似文献
8.
The boundary conditions for a non-destructive sample acquisition system are outlined and the development of a new robotic sampling system suited for use on a cometary surface is briefly discussed. Additionally we present some new results on strength and deformation behaviour of synthetic cometary analogue material. 相似文献
9.
10.
Cometary nuclei consist of ices intermixed with dust grains and are thought to be the least modified solar system bodies remaining
from the time of planetary formation. Flyby missions to Comet P/Halley in 1986 showed that cometary dust is extremely rich
in organics (∼50% by mass). However, this proportion appears to be variable among different comets. In comparison with the
CI-chondritic abundances, the volatile elements H, C, and N are enriched in cometary dust indicating that cometary solid material
is more primitive than CI-chondrites. Relative to dust in dense molecular clouds, bulk cometary dust preserves the abundances
of C and N, but exhibits depletions in O and H. In most cases, the carbonaceous component of cometary particles can be characterized
as a multi-component mixture of carbon phases and organic compounds. Cluster analysis identified a few basic types of compounds,
such as elemental carbon, hydrocarbons, polymers of carbon suboxide and of cyanopolyynes. In smaller amounts, polymers of
formaldehyde, of hydrogen cyanide and various unsaturated nitriles also are present. These compositionally simple types, probably,
are essential "building blocks", which in various combinations give rise to the variety of involatile cometary organics.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
11.
We discuss the possibility that CI and CM carbonaceous chondrites are fragments of extinct cometary nuclei. Theoretical and
observational work suggests that comets evolve into asteroids, and several extinct cometary nuclei are now suspected to be
among the near Earth object population. This population is the most likely source of meteorites and consequently, we may expect
that some meteorites are from extinct comets in this population. The mineralogy and chemistry of CI and CM chondrites is consistent
with the view that they originate from asteroidal objects of carbonaceous spectral classes, and these objects in turn may
have a cometary origin. We do not suggest that CI or CM chondrites are directly delivered by active comets during perihelion
passage or that these chondrites come from cometary debris in meteor streams. Instead, we summarize arguments suggesting that
CI and CM chondrites represent fragments of cometary nuclei which evolved into near Earth asteroids after losing their volatiles.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
12.
K. J. Seidensticker D. Möhlmann I. Apathy W. Schmidt K. Thiel W. Arnold H.-H. Fischer M. Kretschmer D. Madlener A. Péter R. Trautner S. Schieke 《Space Science Reviews》2007,128(1-4):301-337
SESAME is an instrument complex built in international co-operation and carried by the Rosetta lander Philae intended to land
on comet 67P/Churyumov-Gerasimenko in 2014. The main goals of this instrument suite are to measure mechanical and electrical
properties of the cometary surface and the shallow subsurface as well as of the particles emitted from the cometary surface.
Most of the sensors are mounted within the six soles of the landing gear feet in order to provide good contact with or proximity
to the cometary surface. The measuring principles, instrument designs, technical layout, operational concepts and the results
from the first in-flight measurements are described. We conclude with comments on the consequences of the last minute change
of the target comet and how to improve and to preserve the knowledge during the long-duration Rosetta mission. 相似文献
13.
D. H. Wooden 《Space Science Reviews》2008,138(1-4):75-108
Comets are heterogeneous mixtures of interstellar and nebular materials. The degree of mixing of interstellar sources and nebular sources at different nuclear size scales holds the promise of revealing how cometary particles, cometesimals, and cometary nuclei accreted. We can ascribe cometary materials to interstellar and nebular sources and see how comets probe planet-forming process in our protoplanetary disk. Comets and cometary IDPs contain carbonaceous matter that appears to be either similar to poorly-graphitized (amorphous) carbon, a likely ISM source, or highly labile complex organics, with possible ISM or outer disk heritage. The oxygen fugacity of the solar nebula depends on the dynamical interplay between the inward migration of carbon-rich grains and of icy (water-rich) grains. Inside the water dissociation line, OH? reacts with carbon to form CO or CO2, consuming available oxygen and contributing to the canonical low oxygen fugacity. Alternatively, the influx of water vapor and/or oxygen rich dust grains from outer (cooler) disk regions can raise the oxygen fugacity. Low oxygen fugacity of the canonical solar nebula favors the condensation of Mg-rich crystalline silicates and Fe-metal, or the annealing of Fe-Mg amorphous silicates into Mg-rich crystals and Fe-metal via Fe-reduction. High oxygen fugacity nebular conditions favors the condensation of Fe-bearing to Fe-rich crystalline silicates. In the ISM, Fe-Mg amorphous silicates are prevalent, in stark contrast to Mg-rich crystalline silicates that are rare. Hence, cometary Mg-rich crystalline silicates formed in the hot, inner regions of the canonical solar nebula and they are the touchstone for models of the outward radial transport of nebular grains to the comet-forming zone. Stardust samples are dominated by Mg-rich crystalline silicates but also contain abundant Fe-bearing and Fe-rich crystalline silicates that are too large (?0.1 μm) to be annealed Fe-Mg amorphous silicates. By comparison with asteroids, the Stardust Fe-bearing and Fe-rich crystalline silicates suggests partial aqueous alteration in comet nuclei. However, aqueous alteration transforms Fe-rich olivine to phyllosilicates before Mg-rich olivine, and Stardust has Mg-rich and Fe-rich olivine and no phyllosilicates. Hence, we look to a nebular source for the moderately Fe-rich to nearly pure-Fe crystalline silicates. Primitive matrices have Mg-Fe silicates but no phyllosilicates, supporting the idea that Mg-Fe silicates but not phyllosilicates are products of water-rich shocks. Chondrule-formation is a late stage process in our protoplanetary disk. Stardust samples show comet 81P/Wild 2 formed at least as late to incorporate a few chondrules, requiring radial transport of chondrules out to perhaps >20 AU. By similar radial transport mechanisms, collisional fragments of aqueously altered asteroids, in particular achondrites that formed earlier than chondrules, might reach the comet-forming zones. However, Stardust samples do not have phyllosilicates and chondrules are rare. Hence, the nebular refractory grains in comet 81P/Wild 2, as well as other comets, appear to be pre-accretionary with respect to asteroid parent bodies. By discussing nebular pathways for the formation of Fe-rich crystalline silicates, and also phyllosilicates and carbonates, we put forth the view that comets contain both the interstellar ingredients for and the products of nebular transmutation. 相似文献
14.
The present understanding of cometary ionospheres and plasma tails is critically evaluated. Following a brief introduction of the significance of the study of cometary ionospheres and tails (Section 1), the observational statistics and spectroscopic observations are summarized in Sections 2 and 3.The complicated and time varying morphology of the plasma tail and the ionosphere as revealed both by photographs as well as visual drawings is discussed in Section 4.The evidence for a strong comet-solar wind interaction, the possible nature of this interaction and also the use of comets as probes of the solar wind are considered in the next 3 sections (5, 6, 7). This is followed by a discussion of the various processes so far proposed for the ionization of cometary gases and their limitations (Section 8).Hydrodynamic models of the solar wind-comet interaction, which refers essentially to the region outside the tangential discontinuity, are presented and evaluated in Section 9. A discussion of the ion chemistry and structure of the region inside the tangential discontinuity (which is here referred to as the cometary ionosphere) follows in Section 10.The largely indirect evidence for the existence of substantial magnetic fields in cometary ionospheres and type 1 tails is evaluated and their likely origin is considered in Section 11. The associated electric currents; their size and closure as well as their importance as sources of ionization in the inner coma are also discussed.Finally in Section 12, some of the directions in which future research should progress, in order to provide a more complete and secure knowledge of cometary ionospheres and plasma tails, are stressed. 相似文献
15.
The determination of the chemical composition of solid cometary dust particles was one of the prime objectives of the three
missions to Comet Halley in 1986. The dust analysis was performed by time-of-flight mass-spectrometry. Within the experimental
uncertainty the mean abundances of the rock-forming elements in cometary dust particles are comparable to their abundances
in CI-chondrites and in the solar photosphere, i.e. they are cosmic. H, C, and N, on the other hand, in cometary dust are
significantly more abundant than in CI-chondrites, approach solar abundances, are to some extent related to O, and reside
in an omnipresent refractory organic component dubbed CHON. Element variations between individual dust grains are characterized
by correlations of Mg, Si, and O, and to a lesser extent of Fe and S. From particle-to-particle variations of the rock forming
elements information on the mineralogy of cometary dust can be obtained. Cluster analysis revealed certain groups that partly
match the classifications of stratospheric interplanetary dust particles. About half of Halley's analyzed particles are characterized
by anhydrous Fe-poor Mg-silicates, Fe-sulfides, and rarely Fe metal. The Fe-poor Mg-silicates link Halley's dust to that of
Hale-Bopp as shown by recent IR observations. No significant deviation from normal of the isotopic composition of the elements is unequivocally present with the notable exception carbon: 12C-rich grains with 12C/13C-ratios up to ≈ 5,000 link cometary dust to presolar circumstellar grains identified in certain chondrites.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
16.
Deuterium fractionations in cometary ices provide important clues to the origin and evolution of comets. Mass spectrometers
aboard spaceprobe Giotto revealed the first accurate D/H ratios in the water of Comet 1P/Halley. Ground-based observations
of HDO in Comets C/1996 B2 (Hyakutake) and C/1995 O1 (Hale-Bopp), the detection of DCN in Comet Hale-Bopp, and upper limits
for several other D-bearing molecules complement our limited sample of D/H measurements. On the basis of this data set all
Oort cloud comets seem to exhibit a similar
ratio in H2O, enriched by about a factor of two relative to terrestrial water and approximately one order of magnitude relative to the
protosolar value. Oort cloud comets, and by inference also classical short-period comets derived from the Kuiper Belt cannot
be the only source for the Earth's oceans. The cometary O/C ratio and dynamical reasons make it difficult to defend an early
influx of icy planetesimals from the Jupiter zone to the early Earth. D/H measurements of OH groups in phyllosilicate rich
meteorites suggest a mixture of cometary water and water adsorbed from the nebula by the rocky grains that formed the bulk
of the Earth may be responsible for the terrestrial D/H. The D/H ratio in cometary HCN is 7 times higher than the value in
cometary H2O. Species-dependent D-fractionations occur at low temperatures and low gas densities via ion-molecule or grain-surface reactions and cannot be explained by a pure solar nebula chemistry. It is plausible that cometary
volatiles preserved the interstellar D fractionation. The observed D abundances set a lower limit to the formation temperature
of (30 ± 10) K. Similar numbers can be derived from the ortho-to-para ratio in cometary water, from the absence of neon in
cometary ices and the presence of S2. Noble gases on Earth and Mars, and the relative abundance of cometary hydrocarbons place the comet formation temperature
near 50 K. So far all cometary D/H measurements refer to bulk compositions, and it is conceivable that significant departures
from the mean value could occur at the grain-size level. Strong isotope effects as a result of coma chemistry can be excluded
for molecules H2O and HCN. A comparison of the cometary
ratio with values found in the atmospheres of the outer planets is consistent with the long-held idea that the gas planets
formed around icy cores with a high cometary D/H ratio and subsequently accumulated significant amounts of H2 from the solar nebula with a low protosolar D/H.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
17.
Peter C. Thomas Joseph Veverka Michael F. A’Hearn Lucy Mcfadden Michael J. S. Belton Jessica M. Sunshine 《Space Science Reviews》2005,117(1-2):193-205
The Deep Impact mission will provide the highest resolution images yet of a comet nucleus. Our knowledge of the makeup and
structure of cometary nuclei, and the processes shaping their surfaces, is extremely limited, thus use of the Deep Impact
data to show the geological context of the cratering experiment is crucial. This article briefly discusses some of the geological
issues of cometary nuclei. 相似文献
18.
Peter Hoppe 《Space Science Reviews》2008,138(1-4):43-57
Primitive meteorites and interplanetary dust particles contain small quantities of dust grains with highly anomalous isotopic compositions. These grains formed in the winds of evolved stars and in the ejecta of stellar explosions, i.e., they represent a sample of circumstellar grains that can be analyzed with high precision in the laboratory. Such studies have provided a wealth of information on stellar evolution and nucleosynthesis, Galactic chemical evolution, grain growth in stellar environments, interstellar chemistry, and the inventory of stars that contributed dust to the Solar System. Among the identified circumstellar grains in primitive solar system matter are diamond, graphite, silicon carbide, silicon nitride, oxides, and silicates. Circumstellar grains have also been found in cometary matter. To date the available information on circumstellar grains in comets is limited, but extended studies of matter returned by the Stardust mission may help to overcome the existing gaps. 相似文献
19.
John F. Kerridge 《Space Science Reviews》1991,56(1-2):177-184
Carbon isotope ratios have been measured for CN in the coma of comet Halley and for several CHON particles emitted by Halley. Of these, only the CHON-particle data may be reasonably related to organic matter in the cometary nucleus, but the true range of 13C/12C values in those particles is quite uncertain. The D/H ratio in H2O in the Halley coma resembles that in Titan/Uranus. The next decade should substantially improve our understanding of the distribution of C, H, N, and O isotopes in cometary organics. The isotopic composition of meteoritic organic matter is better understood and can serve as a useful analog for the cometary case. 相似文献
20.
The investigation of the volatile material in the coma of comets is a key to understanding the origin of cometary material,
the physical and chemical conditions in the early solar system, the process of comet formation, and the changes that comets
have undergone during the last 4.6 billion years. So far, in situ investigations of the volatile constituents have been confined
to a single comet, namely P/Halley in 1986. Although, the Giotto mission gave only a few hours of data from the coma, it has
yielded a surprising amount of new data and has advanced cometary science by a large step. In the present article the most
important results of the measurements of the volatile material of Halley's comet are summarized and an overview of the identified
molecules is given. Furthermore, a list of identified radicals and unstable molecules is presented for the first time. At
least one of the radicals, namely CH2, seems to be present as such in the cometary ice.
As an outlook to the future we present a list of open questions concerning cometary volatiles and a short preview on the next
generation of mass spectrometers that are being built for the International Rosetta Mission to explore the coma of Comet Wirtanen.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献