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1.
Jane L. Fox  Aleksander Ha? 《Icarus》2010,208(1):176-191
The production of energetic and escaping neutral O atoms at the current epoch in the martian thermosphere is thought to be dominated by the dissociative recombination process:
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2.
The non-thermal escape of neutral O atoms from Mars at the current epoch is largely due to dissociative recombination of :
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3.
Mars Global Surveyor (MGS) visible (solarband bolometer) and thermal infrared (IR) spectral limb observations from the Thermal Emission Spectrometer (TES) support quantitative profile retrievals for dust opacity and particle sizes during the 2001 global dust event on Mars. The current analysis considers the behavior of dust lifted to altitudes above 30 km during the course of this storm; in terms of dust vertical mixing, particle sizes, and global distribution. TES global maps of visible (solarband) limb brightness at 60 km altitude indicate a global-scale, seasonally evolving (over 190-240° solar longitudes, LS) longitudinal corridor of vertically extended dust loading (which may be associated with a retrograde propagating, wavenumber 1 Rossby wave). Spherical radiative transfer analysis of selected limb profiles for TES visible and thermal IR radiances provide quantitative vertical profiles of dust opacity, indicating regional conditions of altitude-increasing dust mixing ratios. Observed infrared spectral dependences and visible-to-infrared opacity ratios of dust scattering over 30-60 km altitudes indicate particle sizes characteristic of lower altitudes (cross-section weighted effective radius, ), during conditions of significant dust transport to these altitudes. Conditions of reduced dust loading at 30-60 km altitudes present smaller dust particle sizes . These observations suggest rapid meridional transport at 30-80 km altitudes, with substantial longitudinal variation, of dust lifted to these altitudes over southern hemisphere atmospheric regions characterized by extraordinary (m/s) vertical advection velocities. By LS=230° dust loading above 50 km altitudes decreased markedly at southern latitudes, with a high altitude (60-80 km) haze of fine (likely) water ice particles appearing over 10°S-40°N latitudes.  相似文献   

4.
With the collection of six years of MGS tracking data and three years of Mars Odyssey tracking data, there has been a continual improvement in the JPL Mars gravity field determination. This includes the measurement of the seasonal changes in the gravity coefficients (e.g., , , , , , ) caused by the mass exchange between the polar ice caps and atmosphere. This paper describes the latest gravity field MGS95J to degree and order 95. The improvement comes from additional tracking data and the adoption of a more complete Mars orientation model with nutation, instead of the IAU 2000 model. Free wobble of the Mars' spin axis, i.e. polar motion, has been constrained to be less than 10 mas by looking at the temporal history of and . A strong annual signature is observed in , and this is a mixture of polar motion and ice mass redistribution. The Love number solution with a subset of Odyssey tracking data is consistent with the previous liquid outer core determination from MGS tracking data [Yoder et al., 2003. Science 300, 299-303], giving a combined solution of k2=0.152±0.009 using MGS and Odyssey tracking data. The solutions for the masses of the Mars' moons show consistency between MGS, Odyssey, and Viking data sets; Phobos GM=(7.16±0.005)×10−4 km3/s2 and Deimos GM=(0.98±0.07)×10−4 km3/s2. Average MGS orbit errors, determined from differences in the overlaps of orbit solutions, have been reduced to 10-cm in the radial direction and 1.5 m along the spacecraft velocity and normal to the orbit plane. Hence, the ranging to the MGS and Odyssey spacecraft has resulted in position measurements of the Mars system center-of-mass relative to the Earth to an accuracy of one meter, greatly reducing the Mars ephemeris errors by several orders of magnitude, and providing mass estimates for Asteroids 1 Ceres, 2 Pallas, 3 Juno, 4 Vesta, and 324 Bamberga.  相似文献   

5.
The neutral particle detector (NPD) on board Mars Express has observed energetic neutral atoms (ENAs) from a broad region on the dayside of the martian upper atmosphere. We show one such example for which the observation was conducted at an altitude of 570 km, just above the induced magnetosphere boundary (IMB). The time of flight spectra of these ENAs show that they had energies of 0.2-2 keV/amu, with an average energy of ∼1.1 keV/amu. Both the spatial distribution and the energy of these ENAs are consistent with the backscattered ENAs, produced by an ENA albedo process. This is the first observation of backscattered ENAs from the martian upper atmosphere. The origin of these ENAs is considered to be the solar wind ENAs that are scattered back by collision processes in the martian upper atmosphere. The particle flux and energy flux of the backscattered ENAs are and , respectively.  相似文献   

6.
We develop a parametric fit to the results of a detailed magnetohydrodynamic (MHD) study of the response of ion escape rates (O+, and ) to strongly varied solar forcing factors, as a way to efficiently extend the MHD results to different conditions. We then use this to develop a second, evolutionary model of solar forced ion escape. We treat the escape fluxes of ion species at Mars as proportional to the product of power laws of four factors - that of the EUV flux Reuv, the solar wind particle density Rρ, its velocity (squared) Rv2, and the interplanetary magnetic field pressure RB2, where forcing factors are expressed in units of the current epoch-averaged values. Our parametric model is: , where ?(i) is the escape flux of ion i. We base our study on the results of just six provided MHD model runs employing large forcing factor variations, and thus construct a successful, first-order parametric model of the MHD program. We perform a five-dimensional least squares fit of this power law model to the MHD results to derive the flux normalizations and the indices of the solar forcing factors. For O+, we obtain the values, 1.73 × 1024 s−1, 0.782, 0.251, 0.382, and 0.214, for ?0, α, β, γ, and δ, respectively. For , the corresponding values are 1.68 × 1024 s−1, −0.393, 0.798, 0.967, and 0.533. For , they are 8.66 × 1022 s−1, −0.427, 1.083, 1.214, and 0.690. The fit reproduces the MHD results to an average error of about 5%, suggesting that the power laws are broadly representative of the MHD model results. Our analysis of the MHD model shows that by itself an increase in REUV enhances O+ loss, but suppresses the escape of and , whereas increases in solar wind (i.e., in , and RB2, with Reuv constant) favors the escape of heavier ions more than light ions. The ratios of escaping ions detectable at Mars today can be predicted by this parametric fit as a function of the solar forcing factors. We also use the parametric model to compute escape rates over martian history. This second parametric model expresses ion escape functions of one variable (per ion), ?(i) = ?0(i)(t/t0)−ξ(i). The ξ(i) are linear combinations of the epoch-averaged ion escape sensitivities, which are seen to increase with ion mass. We integrate the and oxygen ion escape rates over time, and find that in the last 3.85 Gyr, Mars would have lost about mbars of , and of water (from O+ and ) from ion escape.  相似文献   

7.
With 2 years of tracking data collection from the MRO spacecraft, there is noticeable improvement in the high frequency portion of the spherical harmonic Mars gravity field. The new JPL Mars gravity fields, MRO110B and MRO110B2, show resolution near degree 90. Additional years of MGS and Mars Odyssey tracking data result in improvement for the seasonal gravity changes which compares well to global circulation models and Odyssey neutron data and Mars rotation and precession (). Once atmospheric dust is accounted for in the spacecraft solar pressure model, solutions for Mars solar tide are consistent between data sets and show slightly larger values (k2 = 0.164 ± 0.009, after correction for atmospheric tide) compared to previous results, further constraining core models. An additional 4 years of Mars range data improves the Mars ephemeris, determines 21 asteroid masses and bounds solar mass loss (dGMSun/dt < 1.6 × 10−13 GMSun year−1).  相似文献   

8.
Koji Matsuo 《Icarus》2009,202(1):90-578
The martian atmosphere seasonally exchanges CO2 with the surface by repeating condensation and sublimation, causing seasonal growth and decay of the polar CO2 snowcaps. These processes leave two kinds of geodetic signatures, i.e. seasonal changes of the martian gravity field and of surface elevation of the snow-covered regions. Here we study gradual increase of the volume density of the martian snow due to compaction, by combining these two data sets during 1999-2001 covering three martian winters. We found that light fresh snow of slowly becomes denser reaching or more immediately before it thaws. The maximum snow density varies slightly from year to year, and between hemispheres. In the second southern winter, the density became as high as . This might have been caused by a dust storm activity, e.g. increased mixing of silicate particles and/or enhancement of sintering.  相似文献   

9.
The study of Mars linked to its climatic history, the presence of water and possible forms of life on the planet, are becoming more and more important in recent years. In this paper we present laboratory reflection measurements on olivine samples which are believed to be the product of alteration induced by their coexistence with water. The reflection spectra have been obtained in the wavelength range from 0.2 to and for different grain sizes; they exhibit, among various bands, some of which due to H2O and OH-, a characteristic absorption feature at about , whose emission wings at 0.56 and near have relative strengths which are size dependent and well correlated. The identification of such feature in the observed spectra of Mars would provide useful information about the grain size of the Martian regolith and, in association with other bands, also about the possible presence of olivine altered by water in the past.  相似文献   

10.
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11.
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12.
We have studied the escape and energization of several O+ populations and an population at Mars by using a hybrid model. The quasi-neutral hybrid model, HYB-Mars model, included five oxygen ion populations making it possible to distinguish photoions from oxygen ions originating from charge exchange processes and from the ionosphere.We have identified two high-energy ion components and one low-energy ion component of oxygen. They have different spatial and energy distributions near Mars. The two high-energy oxygen ion components, consisting of a high-energy “beam” and a high-energy “halo”, have different origins. (1) The high-energy (>∼100 eV) “beam” of O+ and ions are originating from the ionosphere. These ions form a highly asymmetric spatial distribution of escaping oxygen ions with respect to the direction of the convective electric field in the solar wind. (2) The high-energy (>∼100 eV) “halo” component contains O+ ions which are formed from the oxygen neutral exosphere by extreme ultraviolet radiation (EUV) and by charge exchange processes. These energetic halo ions can be found all around Mars. (3) The low energy O+ and ions (<∼100 eV) form a relatively symmetric spatial distribution around the Mars-Sun line. They originate from the ionosphere and from charge exchange processes between protons and exospheric oxygen atoms.The existence of the low- and the high-energy oxygen components is in agreement with recent in situ plasma measurements made by the ASPERA-3 instrument on the Mars Express mission. The analysis of the escaping oxygen ions suggests that the global energization of escaping planetary ions in the martian tail is controlled by the convective electric field.  相似文献   

13.
Measurements of energetic neutral atoms (ENA) generated in the magnetosheath at Mars are reported. These ENAs are the result of charge exchange collisions between solar wind protons and neutral oxygen and hydrogen in the exosphere of Mars. The peak of the observed ENA flux is . For the case studied here, i.e., the passage of Mars Express through the martian magnetosheath around 20:15 UT on 3 May 2004, the measurements agree with an analytical model of the ENA production at the planet. It is possible to find parameter values in the model such that the observed peak in the ENA count rate during the spacecraft passage through the magnetosheath is reproduced.  相似文献   

14.
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15.
Mars is continuously subjected to surface loading induced by seasonal mass changes in the atmosphere and ice caps due to the CO2 sublimation and condensation process. It results in surface deformations and in time variations of gravity. Large wavelength annual and semi-annual variations of gravity (particularly zonal coefficients ΔJn) have been determined using present day geodetic satellite measurements. However loading deformations have been poorly studied for a planet like Mars. In this paper, we compute these deformations and their effect on spacecraft orbiting around Mars. Loading deformations of terrestrial planet are typically investigated assuming a spherical planet, radially symmetric. The mean radial structure of Mars is not well known. In particular the radius of the liquid or solid core remains not precisely determined. One may then wonder what is the effect of these uncertainties on loading deformations. Moreover, Mars presents a strong topography and probably large lateral variations of crustal thickness (relative to the Earth). The paper answer the questions of what is the effect of such lateral heterogeneities on surface deformations, and is the classical way to calculate loading deformation well adapted for a planet like Mars. In order to answer these questions we have investigated theoretically loading deformations of Mars-like planets. We first investigated classical load Love numbers. We show that for degrees inferior to 10, the load Love numbers mainly depend on the radius of the core and on its state, and that for degree greater than 10, they depend on the mean radius of mantle-crust interface. Using a General Circulation Model (GCM) of atmosphere and ice caps dynamics we show that loading vertical displacements have a 4-5 cm magnitude and present a North-South pattern with periodic transitions. Finally we investigated the effect of lateral variations of the crustal thickness on these loading deformations. We show that thickness heterogeneities perturb the deformations and the time variation of gravity at about 0.5%. However this perturbation on ΔJn is only about 1‰ due to main direct attraction of surface fluid layers. We conclude that lateral variations of crustal thickness are today negligible. However, observation of load Love numbers would bring information on the radial internal structure of the planet, particularly on the core radius. ΔJn study would permit to infer the load Love number , particularly for degree 2 and 3, knowing surface fluid layer dynamics. However load Love numbers are quite small (about 0.05), and despite the present good agreement between GCM and ΔJn observations, will only be estimated in the near future when a slightly better precision in observation and modeling will make it possible to infer these numbers. The investigation of load Love number , which are larger than numbers, would be particularly interesting. It would permit to study degree 1 contribution of atmosphere and ice caps dynamics, which is the most important component of surface fluid dynamics on Mars. Surface displacement measurements would be necessary on a few places near the pole regions, which may be possible in the future, with a project involving precise positioning of a lander on the surface of Mars.  相似文献   

16.
Observations by the Mars Color Imager (MARCI) on board the Mars Reconnaissance Orbiter (MRO) in two ultraviolet (UV, Bands 6 and 7; 258 nm, and 320 nm, respectively) and one visible (Band 1, 436 nm) channels of the 2007 planet encircling dust storm are combined with those made by the two Mars Exploration Rovers (MERs) to better characterize the single scattering albedo (ω0) of martian dust aerosols. Exploiting the low contrast of the surface in the UV (and blue) as well as the reduced importance of surface reflectance under very dusty conditions, we utilize the sampling of photometric angles by the MARCI cross-track geometry to synthesize an analog of the classical Emergence Phase Function (EPF). This so-called “pseudo-EPF”, used in conjunction with the “ground-truth” measurements provided by the MERs, is able to effectively isolate the effects of the dust ω0. The motivation for this approach is the elimination of a significant portion of the type of uncertainty involved in many previous radiative transfer analyses. Furthermore, we produce a self-consistent set of complex refractive indices (m=n+ik) through our use of an explicit microphysical representation of the aerosol scattering properties. Because of uncertainty in the exact size of the dust particles during the epoch of the observations, we consider two effective particle radii (reff) to cover the range anticipated from the literature: 1.6 and 1.8 μm. The resulting set of model-data comparisons, ω0, and m are presented along with an assessment of potential sources of error and uncertainty. Analysis of the Band 1 results is limited to ω0 as a “proof-of-concept” for our approach through a comparison to contemporaneous CRISM EPF results at 440 nm. The derived ω0 are: assuming , and 0.765, for Bands 6, 7, and 1, respectively; for , for the same band order. For either reff case, the total estimated error is 0.022, 0.019, and 0.010, again for Bands 6, 7, and 1. We briefly discuss our retrievals, including the asymmetry parameter (g) associated with our model phase functions, within the context of previous efforts, with an emphasis on the improved precision of our results compared to those in the literature. We also suggest several applications of our results, including an extension of the dust climatological record using MARCI Band 7 pseudo-EPFs outside of 2007 global dust event. Initial work on this particular application using a sample of 135 pseudo-EPFs near the MERs suggests that optical depth retrievals with a precision in the range 0.2-0.4 may be possible under moderate loading conditions (i.e., τ < 1.5).  相似文献   

17.
A measurement of the martian planetary heat flow requires the determination of the subsurface temperature gradient, which is affected by surface insolation. I investigate the propagation of thermal disturbances caused by lander shadowing and derive measurement requirements for in situ heat flow experiments. I find that for short term measurements spanning 180 sol, a measurement depth of at least 2 m is needed to guarantee a stable thermal environment directly underneath the lander for Moon-like thermal conductivities of . For extremely large conductivities of , this depth needs to be increased to 4 m, but if the probe can be deployed outside the lander structure, the respective depths can be decreased by 1 m. For long term measurements spanning at least a full martian year heat flow perturbations are smaller than 5% below a depth of 3 m directly underneath the lander. Outside the lander structure, essentially unperturbed measurements may be conducted at depths of 0.5 and 1.5 m for thermal conductivities of 0.02 and , respectively.  相似文献   

18.
High-resolution spectra of Venus and Mars at the NO fundamental band at 5.3 μm with resolving power ν/δν=76,000 were acquired using the TEXES spectrograph at NASA IRTF on Mauna Kea, Hawaii. The observed spectrum of Venus covered three NO lines of the P-branch. One of the lines is strongly contaminated, and the other two lines reveal NO in the lower atmosphere at a detection level of 9 sigma. A simple photochemical model for NO and N at 50-112 km was coupled with a radiative transfer code to simulate the observed equivalent widths of the NO and some CO2 lines. The derived NO mixing ratio is 5.5±1.5 ppb below 60 km and its flux is . Predissociation of NO at the (0-0) 191 nm and (1-0) 183 nm bands of the δ-system and the reaction with N are the only important loss processes for NO in the lower atmosphere of Venus. The photochemical impact of the measured NO abundance is significant and should be taken into account in photochemical modeling of the Venus atmosphere. Lightning is the only known source of NO in the lower atmosphere of Venus, and the detection of NO is a convincing and independent proof of lightning on Venus. The required flux of NO is corrected for the production of NO and N by the cosmic ray ionization and corresponds to the lightning energy deposition of . For a flash energy on Venus similar to that on the Earth (∼109 J), the global flashing rate is ∼90 s−1 and ∼6 km−2 y−1 which is in reasonable agreement with the existing optical observations. The observed spectrum of Mars covered three NO lines of the R-branch. Two of these lines are contaminated by CO2 lines, and the line at 1900.076 cm−1 is clean and shows some excess over the continuum. Some photochemical reactions may result in a significant excitation of NO (v=1) in the lowest 20 km on Mars. However, quenching of NO (v=1) by CO2 is very effective below 40 km. Excitation of NO (v=1) in the collisions with atomic oxygen is weak because of the low temperature in the martian atmosphere, and we do not see any explanation of a possible emission of NO at 5.3 μm. Therefore the data are treated as the lack of absorption with a 2 sigma upper limit of 1.7 ppb to the NO abundance in the lower atmosphere of Mars. This limit is above the predictions of photochemical models by a factor of 3.  相似文献   

19.
We have used more than 4 years of Mars Express ion data to estimate the escape of heavy ions ( and ) from Mars. To take the limited field of view of the instrument into account, the data has been binned into spatial bins and angular bins to create average distribution functions for different positions in the near Mars space. The net escape flux for the studied low solar activity period, between May 2007 and May 2011, is 2.0 ± 0.2 × 1024 s−1. The escape has been calculated independently for four different quadrants in the YMSO − ZMSO plane, south, dusk, north and dawn. Escape is highest from the northern and dusk quadrants, 0.6 ± 0.1 × 1024 s−1, and smallest from the south and dawn quadrants, 0.4 ± 0.1 × 1024 s−1. The flux ratio of molecular ( and ) to O+ ions is 0.9 ± 0.1, averaged over all quadrants. The flux difference between the north and south quadrants is statistically significant, and is presumed to be due to the presence of significant crustal magnetic fields in the southern hemisphere, reducing the outflow. The difference between the dawn and dusk quadrants is likely due to the magnetic tension associated with the nominal Parker angle spiral, which should lead to higher average magnetic tension on the dusk side. The escape increases during periods of high solar wind flux and during times when co-rotating interaction regions (CIR) affect Mars. In the latter case the increase is a factor 2.4-2.9 as compared to average conditions.  相似文献   

20.
We present mid-infrared observations of the binary L5-Trojan system (617) Patroclus-Menoetius before, during, and after two shadowing events, using the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope. For the first time, we effectively observe changes in asteroid surface temperature in real time, allowing the thermal inertia to be determined very directly. A new detailed binary thermophysical model is presented which accounts for the system’s known mutual orbit, arbitrary component shapes, and thermal conduction in the presence of eclipses.We obtain two local thermal-inertia values, representative of the respective shadowed areas: and . The average thermal inertia is estimated to be , potentially with significant surface heterogeneity. This first thermal-inertia measurement for a Trojan asteroid indicates a surface covered in fine regolith. Independently, we establish the presence of fine-grained (<a few μm) silicates on the surface, based on emissivity features near 10 and similar to those previously found on other Trojans.We also report V-band observations and report a lightcurve with complete rotational coverage. The lightcurve has a low amplitude of peak-to-peak, implying a roughly spherical shape for both components, and is single-periodic with a period equal to the period of the mutual orbit, indicating that the system is fully synchronized.The diameters of Patroclus and Menoetius are 106±11 and , respectively, in agreement with previous findings. Taken together with the system’s known total mass, this implies a bulk mass density of , significantly below the mass density of L4-Trojan asteroid (624) Hektor and suggesting a bulk composition dominated by water ice.All known physical properties of Patroclus, arguably the best studied Trojan asteroid, are consistent with those expected in icy objects with devolatilized surface (extinct comets), consistent with what might be implied by recent dynamical modeling in the framework of the Nice Model.  相似文献   

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