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1.
Carbon delivered to the Earth by interplanetary dust particles may have been an important source of pre-biotic organic matter (Anders, 1989). Interplanetary dust is shown to deliver an order-of-magnitude higher surface concentration of carbon onto Mars than onto Earth, suggesting interplanetary dust may be an important source of carbon on Mars as well.  相似文献   

2.
A review of non-local, deep transport mechanisms in the atmosphere of Earth provides a good foundation for examining whether similar mechanisms are operating in the atmospheres of Mars and Titan. On Earth, deep convective clouds in the tropics constitute the upward branch of the Hadley Cell and provide a conduit through which energy, moisture, momentum, aerosols, and chemical species are moved from the boundary layer to the upper troposphere and lower stratosphere. This transport produces mid-tropospheric minima in quantities such as water vapor and moist static energy and maxima where the clouds detrain. Analogs to this terrestrial transport are found in the strong and deep thermal circulations associated with topography on Mars and with Mars dust storms. Observations of elevated dust layers on Mars further support the notion that non-local deep transport is an important mechanism in the atmosphere of Mars. On Titan, the presence of deep convective clouds almost assures that non-local, deep transport is occurring and these clouds may play a role in global cycling of energy, momentum, and methane. Based on the potential importance of non-local deep transport in Earth's atmosphere and supported by evidence for such transport in the atmospheres of Mars and Titan, greater attention to this mechanism in extraterrestrial atmospheres is warranted.  相似文献   

3.
The suggestion that significant quantities of interplanetary dust are produced by both main-belt asteroids and comets is based on the Infrared Astronomical Satellite detection of dust trails or bands associated with these objects. Gravitational focusing strongly biases all near-Earth collections of interplanetary dust in favor of particles with the lowest geocentric velocities, that is the dust from main-belt asteroids spiraling into the Sun under the influence of Poynting-Robertson radiation drag.

The major dust bands in the main-belt appear to be associated with the catastrophic disruptions which produced the Eos, Themis and Koronis families of asteroids. If dust particles are produced in the catastrophic collision process, then Poynting-Robertson radiation drag is such an efficient transport mechanism from the main-belt to 1 AU that near-Earth collections of interplanetary dust should include, and perhaps be dominated by, this material. The physical, chemical and mineralogical properties of this asteroidal dust can provide constraints on the properties of the asteroidal parent bodies.

Interplanetary dust particles from 5 to 100 μm in diameter have been recovered from the stratosphere of the Earth by NASA sampling aircraft since the mid1970s. The densities of a large fraction of these interplanetary dust particles are significantly lower than the densities of their constituent silicate mineral phases, indicating significant porosities. Direct examination of ultra-microtome thin-sections of interplanetary dust particles also shows significant porosities. The majority of the particles are chemically and mineralogically similar to, but not identical to, the carbonaceous chondrite meteorites.

Most stony interplanetary dust particles have carbon contents exceeding those of Allende, a carbonaceous chondrite meteorite having a low albedo. The population of interplanetary dust does not appear to exhibit the full range of compositional diversity inferred from reflection spectroscopy of the main-belt asteroids. In particular, higher albedo particles corresponding to S-type asteroids are underrepresented or absent from the stratospheric collections, and primitive carbonaceous particles seem to be overrepresented in the stratospheric collections compared to the fraction of mainbelt asteroids classified as primitive. This suggests that much of the interplanetary dust may be generated by a stochastic process, probably preferentially sampling a few most recent collisional events.  相似文献   


4.
The scientific community has expressed strong interest to re-fly Stardust-like missions with improved instrumentation. We propose a new mission concept, SARIM, that collects interstellar and interplanetary dust particles and returns them to Earth. SARIM is optimised for the collection and discrimination of interstellar dust grains. Improved active dust collectors on-board allow us to perform in-situ determination of individual dust impacts and their impact location. This will provide important constraints for subsequent laboratory analysis. The SARIM spacecraft will be placed at the L2 libration point of the Sun–Earth system, outside the Earth’s debris belts and inside the solar-wind charging environment. SARIM is three-axes stabilised and collects interstellar grains between July and October when the relative encounter speeds with interstellar dust grains are lowest (4 to 20 km/s). During a 3-year dust collection period several hundred interstellar and several thousand interplanetary grains will be collected by a total sensitive area of 1 m2. At the end of the collection phase seven collector modules are stored and sealed in a MIRKA-type sample return capsule. SARIM will return the capsule containing the stardust to Earth to allow for an extraction and investigation of interstellar samples by latest laboratory technologies.  相似文献   

5.
Astrophysical and cosmochemical data show that many kinds of hydrocarbons are widespread in space, including giant molecular clouds, diffuse interstellar medium, comets, interplanetary dust particles, and carbonaceous meteorites. Here an effort is made to show the close relation between high-molecular weight hydrocarbons observed in space and existing on Earth. Results of astrochemical modelling of dust grains in dense collapsing cores of giant molecular clouds are also presented. They show that about 10% of the total abundance of dust grains may be the result of aliphatic hydrocarbons. This dust serves as initial material for comets, formed in protosolar nebula. The problem of survival of cometary organics during impact onto the Earth is discussed, and it is shown that the so-called soft-landing comet hypothesis may explain the accumulation of complex hydrocarbons on the Earth's surface. We conclude that a significant fraction of terrestrial prebiotic petroleum was delivered by extraterrestrial matter.  相似文献   

6.
James B. Pollack 《Icarus》1979,37(3):479-553
In this paper, we review the observational data on climatic change for the terrestrial planets, discuss the basic factors that influence climate, and examine the manner in which these factors may have been responsible for some of the known changes. Emphasis is placed on trying to understand the similarities and differences in both the basic factors and their climatic impacts on Venus, the Earth, and Mars. Climatic changes have occurred on the Earth over a broad spectrum of time scales that range from the elevated temperatures of Pre-Cambrian times (～109 years ago), through the alternating glacial and interglacial epochs of the last few million years, to the small but significant decadal and centurial variations of the recent past. Evidence for climatic change on Mars is given by certain channel features, which suggest an early to intermediate aged epoch of warmer and wetter climate, and by layered polar deposits, which imply more recent periodic climate variations. No evidence for climatic change on Venus exists as yet, but comparison of its present climate state with that of outer terrestrial planets offers important clues on some of the mechanisms affecting climate. The important determinants of climate for a terrestrial planet include the Sun's output, astronomical perturbations of its orbital and axial characteristics, the gaseous and particulate content of its atmosphere, its land surface, volatile reservoirs, and its interior. All these factors appear to have played major roles in causing climatic changes on the terrestrial planets. Despite a lower solar luminosity in the past, the Earth and Mars have had warmer periods in their early history. In both cases, a more reducing atmosphere may have been the responsible agent through an enhanced greenhouse effect. In this paper, we present detailed calculations of the effect of atmospheric pressure and composition on the temperature state of Mars. We find that the higher temperature period is easier to explain with a reducing atmosphere than with the current fully oxidizing one. Both the very high surface temperature and massive atmosphere of Venus may be the result of the solar flux being a factor of two higher at its orbit than at the Earth's orbit. This difference may have led to a runaway greenhouse effect on Venus, i.e., the emplacement of volatiles entirely in the atmosphere rather than mostly in surface reservoirs. But if Venus formed with relatively little or no water, it may have always had an oxidizing atmosphere. In this case, a lower solar luminosity would have led to a moderate surface temperature in Venus' early history. Quasi-periodic variations in orbital eccentricity and axial obliquity may have contributed to the alternation between Pleistocene glacial and interglacial periods in the case of the Earth and to the formation of the layered polar deposits in the case of Mars. In this paper, we postulate that two mechanisms, acting jointly, account for the creation of the laminated terrain of Mars: dust particles serve as nucleation centers for the condensation of water vapor and carbon dioxide. The combined dust-H2O-CO2 particle is much larger and so has a much higher terminal velocity than either a dust-H2O or a plain dust particle. As a result, dust and water ice are preferentially deposited in the polar regions. In addition, we postulate that the obliquity variations are key drivers of the periodic layering because of their impact on both atmospheric pressure and polar surface temperature, which, in turn, influence the amounts of dust and water ice in the atmosphere. But eccentricity and precessional changes probably also play important roles in creating the polar layers. The drifting of continents on the Earth has caused substantial climatic changes on individual continents and may have helped to set the stage for the Pleistocene ice ages through a positioning of the continents near the poles. While continental drift apparently has not occurred on Mars, tectonic distortions of its lithosphere may, in some circumstances, cause an alteration in the mean value of that planet's obliquity, which would significantly impact its climate. Atmospheric aerosols can influemce climate through their radiative effects. In the case of the Earth, volcanic aerosols appear to have contributed to past climatic changes, while consideration needs to be given to the future impact of man-generated aerosols. In the case of Mars, the atmospheric temperature structure and thereby atmospheric dynamics are greatly altered by suspended dust particles. The sulfuric acid clouds of Venus play a major role in its heat balance. Cometary impacts may have added substantial quantities of water vapor and sulfur gases to Venus' atmosphere and thus have indirectly affected its cloud properties. Calculations presented in this paper indicate substantial changes in surface temperature accompany these compositional changes.  相似文献   

7.
Abstract— Using a nuclear microprobe, we measured the carbon and nitrogen concentrations and distributions in several interplanetary dust particles (IDPs) and Antarctic micrometeorites (MMs), and compared them to 2 carbonaceous chondrites: Tagish Lake and Murchison. We observed that IDPs are richest in both elements. All the MMs studied contain carbon, and all but the coarse‐grained and 1 melted MM contained nitrogen. We also observed a correlation in the distribution of carbon and nitrogen, suggesting that they may be held in an organic material. The implications for astrobiology of these results are discussed, as small extraterrestrial particles could have contributed to the origin of life on Earth by delivering important quantities of these 2 bio‐elements to the Earth's surface and their gas counterparts, CO2 and N2, to the early atmosphere.  相似文献   

8.
Temporal variations in the visible/near-infrared reflectance spectra of the radiometric calibration targets on the Mars Pathfinder (MPF) lander obtained by the Imager for Mars Pathfinder (IMP) camera reveal the effects of aeolian dust deposition at the MPF site throughout the mission. Sky brightness models in combination with two-layer radiative transfer models were used with these data to track changes in dust opacity on the radiometric calibration targets (RCTs) to constrain the dust deposition rate and the spectral properties of the deposited dust. Two-layer models were run assuming both linear and nonlinear dust accumulation rates, and suggest that RCT dust optical depth at the end of the 83-sol mission was 0.08 to 0.16, or on the order of 5- to 10-μm thickness for plausible values for dust porosity and grain size. These values correspond to dust fall rates of about 20-45 μm per Earth year, consistent with previous studies of dust deposition on Mars. The single scattering albedos of the dust derived from the models fall between those previously determined for atmospheric dust and bright soils. Comparisons of relative reflectance spectra calibrated using observed RCT radiances from late in the mission versus using radiances from modeled (dust-free) RCTs also reveal distinct spectral differences consistent with dust on the RCTs. Temporal variations in RCT dust opacity are not clearly linked to known passages of vortices at the MPF site, but overall suggest that deposition of dust onto the targets by local dust devils may be favored over erosion. Analyses of temporal changes in visible/near-infrared spectra will provide valuable information for future missions by constraining how dust deposition affects landed spacecraft operability (e.g., solar power availability), instrument calibration, and interpretations of surface mineralogy and composition.  相似文献   

9.
Abstract— The possibility of an abrupt origin of interplanetary dust as a result of a collision between asteroids or an extraordinary comet is considered. If all interplanetary dust were produced in one event within recorded history, it would have been visible from the Earth with the unaided eye. The rate, surface area, and brightness of asteroid collision remnants are derived. Ancient Chinese records are searched for extraordinary comets and bright pointlike objects with small angular motion and concentration to the ecliptic.  相似文献   

10.
Abstract– The successful return of the Stardust spacecraft provides a unique opportunity to investigate the nature and distribution of organic matter in cometary dust particles collected from comet 81P/Wild 2. Analysis of individual cometary impact tracks in silica aerogel using the technique of two‐step laser mass spectrometry demonstrates the presence of complex aromatic organic matter. While concerns remain as to the organic purity of the aerogel collection medium and the thermal effects associated with hypervelocity capture, the majority of the observed organic species appear indigenous to the impacting particles and are hence of cometary origin. While the aromatic fraction of the total organic matter present is believed to be small, it is notable in that it appears to be N rich. Spectral analysis in combination with instrumental detection sensitivies suggest that N is incorporated predominantly in the form of aromatic nitriles (R–C≡N). While organic species in the Stardust samples do share some similarities with those present in the matrices of carbonaceous chondrites, the closest match is found with stratospherically collected interplanetary dust particles. These findings are consistent with the notion that a fraction of interplanetary dust is of cometary origin. The presence of complex organic N containing species in comets has astrobiological implications as comets are likely to have contributed to the prebiotic chemical inventory of both the Earth and Mars.  相似文献   

11.
Experiments were conducted under atmospheric pressures appropriate for Earth and Mars to determine the efficiency of sand in saltation as a means for raising dust into the atmosphere under wind speeds which would otherwise be too low for dust entrainment. Experiments involving intimate mixtures of sand and dust (1:1 ratio by mass) showed that after an initial flurry of activity of a few seconds duration, the bed stabilized with little movement of either sand or dust. In contrast, sands set into saltation upwind from dust beds were efficient in injecting the dust into suspension, with low-pressure Martian conditions being some five times more efficient than terrestrial conditions. This result is attributed to the higher kinetic energies of the saltating grains on Mars, which is a consequence of the higher velocities of the grains. These results suggest that sands saltating across dust beds on Mars are an effective means for setting dust into suspension.  相似文献   

12.
Asteroidal dust particles resulting from family-forming events migrate from their source locations in the asteroid belt inwards towards the Sun under the effect of Poynting-Robertson (PR) drag. Understanding the distribution of these dust particle orbits in the inner solar system is of great importance to determining the asteroidal contribution to the zodiacal cloud, the accretion rate by the Earth, and the threat that these particles pose to spacecraft and satellites in near-Earth space. In order to correctly describe this distribution of orbits in the inner solar system, we must track the dynamical perturbations that the dust particle orbits experience as they migrate inwards. In a seminal paper Öpik (1951) determines that very few of the μm-cm sized dust particles suffer a collision with the planet face as they decay inwards past Mars. Here we re-analyze this problem, considering additionally the likelihood that the dust particle orbits pass through the Hill sphere of Mars (to various depths) and experience potentially significant perturbations to their orbits. We find that a considerable fraction of dust particle orbits will enter the Hill sphere of Mars. Furthermore, we find that there is a bias with inclination, particle size, and eccentricity of the particle orbits that enter the Martian Hill sphere. In particular the bias with inclination may create a bias towards higher-inclination sources in the proportions of asteroid family particles that reach near-Earth space.  相似文献   

13.
Laboratory simulations using the Arizona State University Vortex Generator (ASUVG) were run to simulate sediment flux in dust devils in terrestrial ambient and Mars-analog conditions. The objective of this study was to measure vortex sediment flux in the laboratory to yield estimations of natural dust devils on Earth and Mars, where all parameters may not be measured. These tests used particles ranging from 2 to 2000 μm in diameter and 1300 to 4800 kg m−3 in density, and the results were compared with data from natural dust devils on Earth and Mars. Typically, the cores of dust devils (regardless of planetary environment) have a pressure decrease of ∼0.1-1.5% of ambient atmospheric pressure, which enhances the lifting of particles from the surface. Core pressure decreases in our experiments ranged from ∼0.01% to 5.00% of ambient pressure (10 mbar Mars cases and 1000 mbar for Earth cases) corresponding to a few tenths of a millibar for Mars cases and a few millibars for Earth cases. Sediment flux experiments were run at vortex tangential wind velocities of 1-45 m s−1, which typically correspond to ∼30-70% above vortex threshold values for the test particle sizes and densities. Sediment flux was determined by time-averaged measurements of mass loss for a given vortex size. Sediment fluxes of ∼10−6-100 kg m−2 s−1 were obtained, similar to estimates and measurements for fluxes in dust devils on Earth and Mars. Sediment flux is closely related to the vortex intensity, which depends on the strength of the pressure decrease in the core (ΔP). This study found vortex size is less important for lifting materials because many different diameters can have the same ΔP. This finding is critical in scaling the laboratory results to natural dust devils that can be several orders of magnitude larger than the laboratory counterparts.  相似文献   

14.
Abstract— We have identified four comets which have produced low‐velocity Earth‐crossing dust streams within the past century: 7P/Pons‐Winnecke, 26P/Grigg‐Skjellerup, 73P/Schwassmann‐Wachmann 3, and 103P/Hartley 2. These comets have had the rare characteristics of low eccentricity, low inclination orbits with nodes very close to 1 AU. Dust from these comets is directly injected into Earth‐crossing orbits by radiation pressure, unlike the great majority of interplanetary dust particles collected in the stratosphere which spend millennia in space prior to Earth‐encounter. Complete dust streams from these comets form within a few decades, and appreciable amounts of dust are accreted by the Earth each year regardless of the positions of the parent comets. Dust from these comets could be collected in the stratosphere and identified by its short space exposure age, as indicated by low abundances of implanted solar‐wind noble gases and/or lack of solar flare tracks. Dust from Grigg‐Skjellerup probably has the highest concentration at Earth orbit. We estimate that the proportion of dust from this comet will reach at least several percent of the background interplanetary dust flux in the >40 μm size range during April 23–24 of 2003.  相似文献   

15.
Dust is a major environmental factor on the surface and in the atmosphere of Mars. Knowing the electrical charge state of this dust would be of both scientific interest and important for the safety of instruments on the Martian surface. In this study the first measurements have been performed of dust electrification using suspended Mars analogue material. This has been achieved by attracting suspended dust onto electrodes placed inside a Mars simulation wind tunnel. The Mars analogue used was from Salten Skov in Denmark, this contained a high concentration of ferric oxide precipitate. Once suspended, this dust was found to consist of almost equal quantities of negatively (46±6%) and positively (44±15%) charged grains.These grains were estimated to typically carry a net charge of around 105e, this is sufficient to dominate the processes of adhesion and cohesion of this suspended dust. Evidence is presented for electrostatic aggregation of the dust while in suspension. Development of a simple instrument for measuring electrical charging of the suspended dust on Mars will be discussed.  相似文献   

16.
The timing and extent to which the initial interstellar material was thermally processed provide fundamental constraints for models of the formation and early evolution of the solar protoplanetary disk. We argue that the nonsolar (solar Δ17O ≈ ?29‰) and near‐terrestrial (Δ17O ≈ 0‰) O‐isotopic compositions of the Earth and most extraterrestrial materials (Moon, Mars, asteroids, and comet dust) were established very early by heating of regions of the disk that were modestly enriched (dust/gas ≥ 5–10 times solar) in primordial silicates (Δ17O ≈ ?29‰) and water‐dominated ice (Δ17O ≈ 24‰) relative to the gas. Such modest enrichments could be achieved by grain growth and settling of dust to the midplane in regions where the levels of turbulence were modest. The episodic heating of the disk associated with FU Orionis outbursts were the likely causes of this early thermal processing of dust. We also estimate that at the time of accretion the CI chondrite and interplanetary dust particle parent bodies were composed of ~5–10% of pristine interstellar material. The matrices of all chondrites included roughly similar interstellar fractions. Whether this interstellar material avoided the thermal processing experienced by most dust during FU Orionis outbursts or was accreted by the disk after the outbursts ceased to be important remains to be established.  相似文献   

17.
The following problems related to the origin of methane on Mars have been considered. (1) Laboratory simulations of the impact phenomena confirm effective heterogeneous chemistry between the products of the fireball. This chemistry lowers the fireball freezing temperature from 2000 to 750 K for methane and to 1100 K for CO/CO2. Production of methane on Mars by cometary impacts is 0.8% of the total production. A probability that the observed methane on Mars came from impact of a single comet is 0.0011. (2) The PFS observations of variations of methane on Mars require a very effective heterogeneous loss of methane. Heterogeneous effect of dust is half that of the surface rocks. Thermochemical equilibrium requires production, not loss, of methane. Existing kinetic data show a very low efficiency of heterogeneous reactions of methane. Highly reactive superoxide ions generated by the solar UV photons on the martian rocks cannot remove methane. The required efficiency of heterogeneous loss of methane on Mars is higher than that on Earth by a factor of ?1000, although the expected efficiency on Earth is stronger than that on Mars because of the liquid ocean and the abundant oxygen. All these inconsistencies may be removed if variations of the rock reflectivity contribute to the PFS observations of methane on Mars. The PFS data on H2CO, HCl, HF, and HBr also raise doubts. (3) Although geologic sources of methane are possible, the lack of current volcanism, hydrothermal activity, hot spots, and very low seepage of gases from the interior are not favorable for geologic methane. Any proposed geological source of methane on Mars should address these problems. Some weak points in the suggested geologic sources are discussed. (4) Measurements of 13C/12C and D/H in methane would be difficult because of the low methane abundance. These ratios are mostly sensitive to a temperature of methane formation and cannot distinguish between biogenic and low-temperature geologic sources. Their analysis requires the carbon isotope ratio in CO2 on Mars, which is known with the insufficient accuracy, and D/H in water, which is different in the atmosphere, polar caps, regolith and interior. Therefore, the stable isotope ratios may not give a unique answer on the origin of methane. (5) Ethane and propane react with OH much faster than methane. If their production relative to methane is similar to that on Earth, then their expected abundances on Mars are of a few parts per trillion. (6) Loss of SO2 in the reaction with peroxide on ice is smaller than its gas-phase loss by an order of magnitude. The overall results strengthen the biogenic origin of martian methane and its low variability.  相似文献   

18.
S. Vennerstrom 《Icarus》2011,215(1):234-241
Based on data from the Mars Global Surveyor magnetometer we examine periods of significantly enhanced magnetic disturbances in the martian space environment. Using almost seven years of observations during the maximum and early declining phase of the previous solar cycle the occurrence pattern and typical time profile of such periods is investigated and compared to solar wind measurements at Earth. Typical durations of the events are 20-40 h, and there is a tendency for large events to last longer, but a large spread in duration and intensity are found. The large and medium intensity events at Mars are found to occur predominantly in association with interplanetary sector boundaries, with solar wind dynamic pressure enhancements being the most likely interplanetary driver. In addition it is found that, on time scales of months to several years, the dominant cause of global variability of the magnetic field disturbance at Mars is solar wind dynamic pressure variations associated with the eccentricity of the martian orbit around the Sun.  相似文献   

19.
Using the Fourier Transform Spectrometer at the Canada-France-Hawaii Telescope, we observed a spectrum of Mars at the P-branch of the strongest CH4 band at 3.3 μm with resolving power of 180,000 for the apodized spectrum. Summing up the spectral intervals at the expected positions of the 15 strongest Doppler-shifted martian lines, we detected the absorption by martian methane at a 3.7 sigma level which is exactly centered in the summed spectrum. The observed CH4 mixing ratio is 10±3 ppb. Total photochemical loss of CH4 in the martian atmosphere is equal to , the CH4 lifetime is 340 years and methane should be uniformly mixed in the atmosphere. Heterogeneous loss of atmospheric methane is probably negligible, while the sink of CH4 during its diffusion through the regolith may be significant. There are no processes of CH4 formation in the atmosphere, so the photochemical loss must therefore be balanced by abiogenic and biogenic sources. Outgassing from Mars is weak, the latest volcanism is at least 10 million years old, and thermal emission imaging from the Mars Odyssey orbiter does not reveal any hot spots on Mars. Hydrothermal systems can hardly be warmer than the room temperature at which production of methane is very low in terrestrial waters. Therefore a significant production of hydrothermal and magmatic methane is not very likely on Mars. The calculated average production of CH4 by cometary impacts is 2% of the methane loss. Production of methane by meteorites and interplanetary dust does not exceed 4% of the methane loss. Methane cannot originate from an extinct biosphere, as in the case of “natural gas” on Earth, given the exceedingly low limits on organic matter set by the Viking landers and the dry recent history which has been extremely hostile to the macroscopic life needed to generate the gas. Therefore, methanogenesis by living subterranean organisms is a plausible explanation for this discovery. Our estimates of the biomass and its production using the measured CH4 abundance show that the martian biota may be extremely scarce and Mars may be generally sterile except for some oases.  相似文献   

20.
A.V. Pathare  M.R. Balme  M.C. Towner 《Icarus》2010,209(2):851-853
Competing hypotheses for the diameter dependence of terrestrial and martian dust devil frequency are assessed using new field observations from two sites in the southwestern United States. We show that at diameters less than 12 m, our observed dust devil size-frequency distributions are better fit by an exponential function than by a power law formulation, and discuss the implications for larger dust devils on Earth and Mars.  相似文献   

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