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1.
We report recent results in an investigation of source mechanisms for the origin of Na atoms in tenuous planetary atmospheres, focusing on non-thermal processes. Experiments include photon stimulated desorption (PSD), electron stimulated desorption (ESD), and ion sputtering of Na atoms from the surface of a lunar basalt sample. Bombardment of the sodium covered surface by 3 keV Ar+ ions removes Na from the surface by sputtering into vacuum and by implantation into the sample bulk. Bombardment of the Na covered surface by ultraviolet photons or by low energy electrons (E>3 to 4 eV) causes desorption of “hot” Na atoms. These results are consistent with our previous measurements of sodium and potassium desorption from a silica surface: electron- or photon-induced charge transfer from the substrate to the ionic adsorbate causes formation of a neutral alkali atom in a repulsive configuration, from which desorption occurs. There is a strong temperature-dependence of Na ESD and PSD signals, under conditions where the Na surface coverage is constant and thermal desorption is negligible. The yield of Na (atoms/photon) increases by 10× from 100 to 470 K; an activation energy of ∼20 meV is measured. This phenomenon may be attributed to thermally-induced changes in surface bonding sites, and will affect recent modeling of the sodium atmospheres of Mercury and the Moon.  相似文献   

2.
Abstract— A summary is given of our published observations showing a large (3 to 4) morning/afternoon ratio of the abundances of sodium and potassium. The proposed mechanism is deposition of ions and atoms on the cold night side, followed by their outward diffusion and evaporation as the Sun rises. Published criticisms of this mechanism are discussed and answered. The rate at which Na atoms can evaporate from the surfaces of the Moon and Mercury is uncertain, but, after a review of laboratory measurements, we propose that it is substantial at temperatures of 400 K and higher. Possible reasons are discussed why another group does not find the diurnal variation. There are differences in observing geometry, but the matter remains unclear.  相似文献   

3.
We now have four examples of planetary objects with detectable sodium (and potassium) in their atmospheres—Earth, Io, Mercury and the Moon. After a summary of the observational data, this survey discusses proposed sources and sinks. It appears that Io's surface material is rich in frozen SO2, but with around 1% of some sodium compound. The Io plasma torus contains ions of S, O and Na, also with at least one molecular ion containing Na. In turn, impact by these ions probably sustains the torus, as well as an extended neutral corona. A primary source for the Earth, Mercury and the Moon is meteoroidal bombardment; at Mercury and perhaps the Moon it may be supplemented by degassing of atoms from the regolith. Photoionization is important everywhere, although hot electrons are dominant at Io.  相似文献   

4.
Leif Holmlid 《Icarus》2006,180(2):555-564
The long-lived excited state of matter called Rydberg Matter (RM) may explain several spectroscopic features in space, like the diffuse interstellar bands (DIBs) and the unidentified infrared bands (UIR, UIB). RM is here used to interpret some previously unexplained or inconsistent features in comets: (1) line absorption in the emission from the nucleus, (2) IR band emission from the coma, (3) selective and variable molecular line emission from the coma, (4) extended sources of molecules in the coma, (5) degree of linear polarization of light scattered from the coma. (1) The unexplained IR absorptions observed in the flyby of the nucleus of the Comet Borrelly agree well with RM emission bands observed by stimulated emission in the laboratory. It is proposed that RM is the so-called ultrared matter or at least formed from it. (2) The IR bands previously attributed to silicate particles are shown to be better described by RM theory. Transitions in atoms in RM are shown to dominate. (3) The inverted RM medium will optically amplify light from molecular transitions in the comet comae, in agreement with observations that many of the molecular IR emission lines lie within the emission bands from RM, or much too close to Rydberg transitions to be accidental. (4) The unexplained extended sources observed, e.g., for CO are proposed to be due to release of molecules previously incorporated in the RM clusters at low temperature. Such clusters may be the very small particles observed by space probes. (5) Finally, the largely unexplained measurements of the degree of linear polarization of scattered sunlight from comets are explained as due to scattering by the planar RM clusters. Quantitative agreement is demonstrated.  相似文献   

5.
《Planetary and Space Science》2007,55(11):1494-1501
In this work, we calculate the neutral Na production rates on the Moon and Mercury, as due to the impacts of meteoroids having an impact probability on the surface that can influence the daily observations of the exosphere: the meteoroids radius range considered for the Moon and Mercury are 10−8–0.15 and 10−8–0.10 m, respectively. We also estimate the mass of meteoroids that has impacted the surfaces of the Moon and Mercury in the last 3.8 Gy (after the end of the Late Heavy Bombardment).The results of our model are that (i) the Na production rates are ∼(3–4.9)×104 and ∼(1.8–2.3)×106 atoms cm−2 s−1, for Moon and Mercury, respectively, and (ii) in the last 3.8 Gy, the mass of meteoroids that has impacted the whole surface of the Moon and Mercury has been 8.86×1018 and 2.66×1019 g, respectively.  相似文献   

6.
The supply rates of Na and K to the atmosphere of Mercury by processes acting on the extreme surface—thermal vaporization, photon-stimulated desorption (PSD), and ion-sputtering—are limited by the rates at which atoms can be supplied to the extreme surface by diffusion from inside the regolith grains. Supply rates to the atmosphere are further regulated by ion retention and by gardening rates that supply new grains to the surface. We consider the limits on supply of sodium and potassium atoms to the atmosphere, and rates of photoion recycling to the surface. Thermal vaporization rates are severely limited by the ability of atoms to diffuse to the surface of the grain. Therefore, the diffusion-limited thermal vaporization rates on Mercury's surface are comparable to or less than the PSD rates. Ion sputtering is primarily due to highly ionized heavy ions, even though they represent a small fraction of the solar wind. We have shown that up to 60% of the Na photoions are deposited on the surface of Mercury. Ion recycling to the surface can have a long-term effect on the regolith abundance if an average recycling pattern persists such that more ions return to a particular area than are launched there. It is unknown whether the formation of latitude bands of >100% ion retention persist on average despite a rapidly changing magnetosphere. The total exospheric column of sodium observed at Mercury between 1997 to 2003 varied by a factor of 2-3 from perihelion to aphelion.  相似文献   

7.
The detailed processes giving maser line radiation from various molecules in space are not well understood, as can be seen from many recent detailed studies of maser line emission with high spatial and velocity resolution, and with polarization measurements. We now propose an improved maser mechanism based on amplification of the original molecular line emission by stimulated emission in Rydberg Matter (RM) clouds in HII regions, containing clusters H N and (H2) N . This mechanism will amplify the molecular lines, depending on the position, velocity, cluster size and state of excitation of the clusters in the RM cloud. RM will only support certain frequencies, corresponding to rotational transitions of the clusters. The bond lengths in the RM clusters are known within 1% from radio frequency emission measurements in the laboratory, and it is now shown that all the commonly studied maser lines agree well with stimulated emission transitions in several types of RM clusters simultaneously. This may explain the strongly varying intensities of neighboring or related maser lines, an important effect that is not well understood previously. It is also pointed out that the magnetic field due to RM is of the same order of magnitude as observed from the Zeeman splitting in maser lines; thus, the molecules that are the original sources of the lines may be embedded in the RM clouds, for example in dense HII regions that are likely to be RM regions.  相似文献   

8.
Collisions of comets with planetary bodies are capable of impressing patterns of magnetization onto them that match those observed for the Moon and possibly for Mercury. The ambient solar wind magnetic field is briefly but strongly enhanced as the large partially ionized cometary atmosphere is compressed against the planetary surface. Just at the time of peak field enhancement, the solid part of the comet collides with the surface and the compressed fields are permanently imprinted by shock magnetization.  相似文献   

9.
In a scenario produced by the Capture Theory of planetary formation, a collision between erstwhile solar-system giant planets, of masses 798.75 and 598.37 M ⊕, is simulated using smoothed-particle hydrodynamics. Due to grain-surface chemistry that takes place in star-forming clouds, molecular species containing hydrogen, with a high D/H ratio taken as 0.01, form a layer around each planetary core. Temperatures generated by the collision initiate D–D reactions in these layers that, in their turn, trigger a reaction chain involving heavier elements. The nuclear explosion shatters and disperses both planets, leaving iron-plus-silicate stable residues identified as a proto-Venus and proto-Earth. A satellite of one of the colliding planets, captured or retained by the proto-Earth core, gave the Moon; two massive satellites released into heliocentric orbits became Mercury and Mars. For the Moon and Mars, abrasion of their surfaces exposed to collision debris results in hemispherical asymmetry. Mercury, having lost a large part of its mantle due to massive abrasion, reformed to give the present high-density body. Debris from the collision gave rise to asteroids and comets, much of the latter forming an inner reservoir stretching outwards from the inner Kuiper Belt that replenishes the Oort Cloud when it is depleted by a severe perturbation. Other features resulting from the outcome of the planetary collision are the relationship of Pluto and Triton to Neptune, the presence of dwarf planets and light-atom isotopic anomalies in meteorites.  相似文献   

10.
Studying the origin and evolution of the Solar system is among the fundamental problems of modern natural science. This problem is interdisciplinary and requires the development of mathematical models for the physical structure and evolution of a gas–dust accretion disk from the initial stages of its formation to the formation of a planetary system. One of the key problems is the formation and growth of bodies in a protoplanetary disk, the basis for which is a study of the collisional processes of the solidbody component. We have performed a parametric analysis of the cluster–cluster collision processes occurring in a protoplanetary disk within the model of permeable particles being developed by us. The outcome of such collisions is shown to be affected significantly by the topological properties of colliding dust clusters with a fractal internal structure. The results of our parametric analysis show that for sufficiently “dense” fractal dust clusters, at low relative collision velocities, there exists a range in which the colliding clusters bounce. At the same time, for “porous” fractal clusters the bounce is impossible for any sets of collision parameters. As the relative collision velocities increase, the cluster coalescence processes begin to dominate due to a rearrangement of the fractal structure in the contact zone. However, as the kinetic energy of collisions increases further, a critical threshold is reached beyond which the collision energy exceeds the particle binding energy in clusters and the fractal dust cluster destruction processes are switched on during collisions. Thus, our parametric analysis imposes quite definite constraints on the dynamics and chronology of the evolution processes during the formation of primordial solid bodies and planetesimals. The proposed approach and the results obtained are fairly realistic and open prospects for more comprehensive model studies of the initial evolutionary phase of a protoplanetary disk.  相似文献   

11.
That the redshifts for galaxies in the local supercluster are quantizedwas recently confirmedby Guthrie and Napier(A&Amp;Amp;A310 (1996) 353). These redshifts are here proposed to be due to stimulatedStokes Raman processes in intergalactic matter in the form of Rydberg Matter (RM). Rydberg Matteris an electronically excited material, as demonstrated by its use as laser medium in a thermally excitedultra-broadband tunable IR laser (Chem. Phys. Lett. 376 (2003) 812). Its existence in interstellar andintergalactic space is demonstrated by several observational results, notably the unidentified IR bands,that agree well with the emission from Rydberg Matter. A stimulated Raman process will allow theH I 21 cm radiation to proceed without deflection, in agreement with observation. Such redshiftswill be additive during the passage through space. The process in Rydberg Matter here proposed togive rise to the Stokes Raman process is excitation of electronic translational modes in the planarclusters forming the matter. The specific cluster sizes found in laboratory experiments give rise toa few differently sized redshift quanta, which is in good agreement with the observed quanta. Anexcitation level (principal quantum number) of Rydberg Matter in intergalactic space between 175and 200 gives the correct size of the redshift quanta.  相似文献   

12.
A tenuous calcium atmosphere at Mercury, principally seen in the polar regions, was first observed in July, 1998, using the High Resolution Echelle Spectrograph (HIRES) at the W.M. Keck I telescope (Bida et al., Nature 404, 159, 2000). We report four years of observations of the calcium exosphere of Mercury, confirming the initial findings of a very tenuous atmosphere. These observations show a persistent but spatially variable blue shift, indicating an excess velocity toward the observer of up to 3 km s−1, with an average excess velocity of 2.2 km s−1 above the south pole. In addition, the line profiles reveal a hot corona at the equivalent of 12,000-20,000 K in a thermalized atmosphere, indicating a large range of motion with respect to the observer. The calcium is not confined to the polar-regions: rare and low Ca abundance is seen in the equatorial regions. Strong emission was seen anti-sunward on 3 May 2002. Apparent weak emission on the sunward hemisphere may be due to scattered light from the surface, or may indicate a high latitude source. We show that the likely source of the calcium is either impact vaporization in the form of CaO and clusters, which are subsequently photo-dissociated, or ion-sputtering of atoms, molecules and ions. The column abundance is somewhat, but not strongly, correlated with solar activity. We predict a very hot (probably escaping) oxygen component to the hermean exosphere.  相似文献   

13.
The early phases of formation in the inner solar system were dominated by collisions and short-range dynamical interactions among planetesimals. But the later phases, which account for most of the differences among planets, are unsure because the dynamics are more subtle. Jupiter's influence became more important, leading to drastic clearing out of the asteroid belt and the stunting of Mars's growth. Further in, the effect of Jupiter-- both directly and indirectly, through ejection of mass in the outer solar system-- was probably to speed up the process without greatly affecting the outcome. The great variety in bulk properties of the terrestrial bodies indicate a terminal phase of great collisions, so that the outcome is the result of small-N statistics. Mercury, 65 percent iron, appears to be a residual core from a high-velocity collision. All planets appear to require a late phase of high energy impacts to erode their atmospheres: including the Earth, to remove CO2 so that its ocean could form by condensation of water.Consistent with this model is that the largest collision, about 0.2 Earth masses, was into the proto-Earth, although the only property that appears to require it is the great lack of iron in the Moon. The other large differences between the Earth and Venus, angular momentum (spin plus satellite) and inert gas abundances, must arise from origin circumstances, but neither require nor forbid the giant impact. Venus's higher ratio of light to heavy inert gases argues for it receiving a large icy impactor, about 10–6 Earth masses from far out, requiring some improbable dynamics to get a low enough approach velocity. Core formation in both planets probably started rather early during accretion.Some geochemical evidences argue for the Moon coming from the Earth's mantle, but are inconclusive. Large scale melting of the mantle by the giant impact would plausibly have led to stratification. But the "lock-up" at the end of turbulent mantle convection is a trade-off between rates: crystallization of constituents of small density difference versus overall freezing. Also, factors such as differences in melting temperatures and densities, melt compressibilities, and phase transitions may have had homogenizing effects in the subsequent mantle convection.  相似文献   

14.
We investigate the response of an atmosphere of argon to solar ultra-violet radiation. With the assumption that Mercury has an argon atmosphere that is optically thick to ionizing radiation the intensities of the ultra-violet dayglow lines resulting from photoelectron impact are calculated. For most of the model atmospheres, the predicted intensities are above the detection threshold of the 1973 Venus-Mercury ultra-violet spectrometer of Broadfoot, McElroy and Belton.  相似文献   

15.
Abstract— We propose that argon‐40 measured in the lunar atmosphere and that in Mercury's atmosphere is due to current diffusion into connected pore space within the crust. Higher temperatures at Mercury, along with more rapid loss from the atmosphere, will lead to a similar or smaller column abundance of argon at Mercury than at the Moon, given the same crustal abundance of potassium. Because the noble gas abundance in the mercurian atmosphere represents current effusion, it is a direct measure of the crustal potassium abundance. We assume a fractal distribution of distance to a connected pore space, with the shortest distance increasing with depth. Given this “rock size” distribution, we show that the diffusive flux is not a unique function of temperature. Even though the diffusion coefficient is an exponential function of temperature, the flux to the surface is fairly insensitive to the temperature.  相似文献   

16.
The basic geochemical model of the structure of the Moon proposed by Anderson, in which the Moon is formed by differentiation of the calcium, aluminium, titanium-rich inclusions in the Allende meteorite, is accepted, and the conditions for formation of this Moon within the solar nebula models of Cameron and Pine are discussed. The basic material condenses while iron remains in the gaseous phase, which places the formation of the Moon slightly inside the orbit of Mercury. Some condensed metallic iron is likely to enter the Moon in this position, and since the Moon is assembled at a very high temperature, it is likely to have been fully molten, so that the iron can remove the iridium from the silicate material and carry it down to form a small core. Interactions between the Moon and Mercury lead to the present rather eccentric Mercury orbit and to a much more eccentric orbit for the Moon, reaching past the orbit of the Earth, establishing conditions which are necessary for capture of the Moon by the Earth. In this orbit the Moon, no longer fully molten, will sweep up additional material containing iron oxide. This history accounts in principle for the two major ways in which the bulk composition of the Moon differs from that of the Allende inclusions.Paper dedicated to Professor Harold C. Urey on the occasion of his 80th birthday on 29 April 1973.  相似文献   

17.
Chemical processes associated with meteoroid bombardment of Mercury are considered. Meteoroid impacts lead to production of metal atoms as well as metal oxides and hydroxides in the planetary exosphere. By using quenching theory, the abundances of the main Na-, K-, Ca-, Fe-, Al-, Mg-, Si-, and Ti-containing species delivered to the exosphere during meteoroid impacts were estimated. Based on a correlation between the solar photo rates and the molecular constants of atmospheric diatomic molecules, photolysis lifetimes of metal oxides and SiO are estimated. Meteoroid impacts lead to the formation of hot metal atoms (0.2-0.4 eV) produced directly during impacts and of very hot metal atoms (1-2 eV) produced by the subsequent photolysis of oxides and hydroxides in the exosphere of Mercury. The concentrations of impact-produced atoms of the main elements in the exosphere are estimated relative to the observed concentrations of Ca, assumed to be produced mostly by ion sputtering. Condensation of dust grains can significantly reduce the concentrations of impact-produced atoms in the exosphere. Na, K, and Fe atoms are delivered to the exosphere directly by impacts while Ca, Al, Mg, Si, and Ti atoms are produced by the photolysis of their oxides and hydroxides. The chemistry of volatile elements such as H, S, C, and N during meteoroid bombardment is also considered. Our conclusions about the temperature and the concentrations of impact-produced atoms in the exosphere of Mercury may be checked by the Messenger spacecraft in the near future and by BepiColombo spacecraft some years later.  相似文献   

18.
To ascertain the importance of sputtering by solar wind ions on the formation of a sodium exosphere around Mercury and the Moon, we have irradiated with 4 keV He ions, the Na bearing tectosilicates: albite, labradorite, and anorthoclase, as well as adsorbed Na layers deposited on albite and on olivine (a neosilicate that does not contain Na). Sodium at the surface and near surface (<40 Å) was quantified with X-ray photoelectron spectroscopy before and after each irradiation to determine the depletion cross section. We measured a cross section for sputtering of Na adsorbed on mineral surfaces, σs ≈ 1 × 10?15 cm2 atom?1. In addition, mass spectrometric analyses of the sputtered flux show that a large fraction of the Na is sputtered as ions rather than as neutral atoms. These results have strong implications for modeling the sodium population within the mercurian and the lunar exospheres.  相似文献   

19.
The descent imager/spectral radiometer (DISR) onboard the Huygens probe investigated the radiation balance inside Titan's atmosphere and took hundreds of images and spectra of the ground during the descent. The scattering of the aerosols in the atmosphere and the absorption by methane strongly influence the irradiation reaching the surface and the signals received by the various instruments. The physical properties of the surface can only be assessed after the influence of the atmosphere has been taken into account and properly removed. In the broadband visible images (660 to 1000 nm) the contrast of surface features is strongly reduced by the aerosol scattering. Calculations show that for an image taken from an altitude of 14.5 km, the corrected contrast is about three times higher than in the raw image.Spectral information of the surface by the imaging spectrometers in the visible and near infrared range can only be retrieved in the methane absorption windows. Intensity ratios from the methane windows can be used to make false color maps. The elevated bright ‘land’ terrain is redder than the flat dark ‘lake bed’ terrain.The reflectance spectra of the land and lake bed area in the IR are derived, as well as the reflectance phase function in the limited range from 20° to 50° phase angle. An absorption feature at 1.55 μm which may be attributed tentatively to water ice is found in the lake bed, but not in the land area. Otherwise the surface exhibits a featureless blue slope in the near-IR region (0.9-). Brightness profiles perpendicular to the coast line show that the bottoms of the channels of the large scale flow pattern become darker the further they are away from the land area. This could be interpreted as sedimentation of the bright land material transported by the rivers into the lake bed area. The river beds in the deeply incised valleys need not to be covered by dark material. Their roughly 10% brightness decrease could be caused by the illumination as illustrated by a model calculation. The size distribution of cobbles seen in the images after landing is in agreement with a single major flooding of the area with a flow speed of about .  相似文献   

20.
New crater size-shape data were compiled for 221 fresh lunar craters and 152 youthful mercurian craters. Terraces and central peaks develop initially in fresh craters on the Moon in the 0–10 km diameter interval. Above a diameter of 65 km all craters are terraced and have central peaks. Swirl floor texture is most common in craters in the size range 20–30 km, but it occurs less frequently as terraces become a dominant feature of crater interiors. For the Moon there is a correlation between crater shape and geomorphic terrain type. For example, craters on the maria are more complex in terms of central peak and terrace detail at any given crater diameter than are craters in the highlands. These crater data suggest that there are significant differences in substrate and/or target properties between maria and highlands. Size-shape profiles for Mercury show that central peak and terrace onset is in the 10–20 km diameter interval; all craters are terraced at 65 km, and all have central peaks at 45 km. The crater data for Mercury show no clear cut terrain correlation. Comparison of lunar and mercurian data indicates that both central peaks and terraces are more abundant in craters in the diameter range 5–75 km on Mercury. Differences in crater shape between Mercury and the Moon may be due to differences in planetary gravitational acceleration (gMercury=2.3gMoon). Also differences between Mercury and the Moon in target and substrate and in modal impact velocity may contribute to affect crater shape.  相似文献   

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