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1.
We report observations of the radio disk temperatures of Mars and Jupiter made during October 1971, at a wavelength of 1.35 cm. The mean disk temperature of Jupiter is 136 ± 5°K, in good agreement with the value 139 ± 6°K obtained by Wrixon et al. (1971) with the same instrument three years earlier. The disk temperature of Mars is 181 ± 11°K, consistent with an essentially wavelength independent disk temperature for Mars at radio wavelengths. The ratio of the two disk temperatures, 1.33 ± .07, is largely free of the systematic uncertainties: antenna gain, pointing, and atmospheric extinction. 相似文献
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3.
Mars is the fourth planet out from the sun. It is a terrestrial planet with a density suggesting a composition roughly similar
to that of the Earth. Its orbital period is 687 days, its orbital eccentricity is 0.093 and its rotational period is about
24 hours. Mars has two small moons of asteroidal shapes and sizes (about 11 and 6 km mean radius), the bigger of which, Phobos,
orbits with decreasing semimajor orbit axis. The decrease of the orbit is caused by the dissipation of tidal energy in the
Martian mantle. The other satellite, Deimos, orbits close to the synchronous position where the rotation period of a planet
equals the orbital period of its satellite and has hardly evolved with time. Mars has a tenous atmosphere composed mostly
of CO with strong winds and with large scale aeolian transport of surface material during dust storms and in sublimation-condensation
cycles between the polar caps. The planet has a small magnetic field, probably not generated by dynamo action in the core
but possibly due to remnant magnetization of crustal rock acquired earlier from a stronger magnetic field generated by a now
dead core dynamo. A dynamo powered by thermal power alone would have ceased a few billions of years ago as the core cooled
to an extent that it became stably stratified. Mars' topography and its gravity field are dominated by the Tharsis bulge,
a huge dome of volcanic origin. Tharsis was the major center of volcanic activity, a second center is Elysium about 100° in
longitude away. The Tharsis bulge is a major contributor to the non-hydrostaticity of the planet's figure. The moment of inertia
factor together with the mass and the radius presently is the most useful constraint for geophysical models of the Martian
interior. It has recently been determined by Doppler range measurements to the Mars Pathfinder Lander to be (Folkner et al. 1997). In addition, models of the interior structure use the chemistry of the SNC meteorites which are widely
believed to have originated on Mars. According to the models, Mars is a differentiated planet with a 100 to 200 km thick basaltic
crust, a metallic core with a radius of approximately half the planetary radius, and a silicate mantle. Mantle dynamics is
essential in forming the elements of the surface tectonics. Models of mantle convection find that the pressure-induced phase
transformations of -olivine to -spinel, -spinel to -spinel, and -spinel to perovskite play major roles in the evolution of mantle flow fields and mantle temperature. It is not very likely
that the -spinel to perovskite transition is present in Mars today, but a few 100 km thick layer of perovskite may have been present
in the lower mantle immediately above the core-mantle boundary early in the Martian history when mantle temperatures were
hotter than today. The phase transitions act to reduce the number of upwellings to a few major plumes which is consistent
with the bipolar distribution of volcanic centers of Mars. The phase transitions also cause a partial layering of the lower
mantle which keeps the lower mantle and the core from extensive cooling over the past aeons. A relatively hot, fluid core
is the most widely accepted explanation for the present lack of a self-generated magnetic field. Growth of an inner core which
requires sub-liquidus temperatures in the core would have provided an efficient mechanism to power a dynamo up to the present
day.
Received 10 May 1997 相似文献
4.
There is increasing evidence that the nature of extended dark features on slopes of Martian craters and uplands is related to existing sources of liquid water located on these slopes and to confined water flows rather than to the movement of large masses of dry sand (dust) or rock falls. Images acquired by the Mars Global Surveyor Mars Orbiter Camera at spatial resolutions of a few meters per pixel make it possible to distinguish such objects. The availability of big reserves of ground ice on Mars and conditions for the local conversion of ice to the liquid phase is now universally accepted. Although the presence of liquid water on the Martian surface is usually thought to be impossible because of low pressures and low mean temperatures, there is a sufficient number of lowlands on Mars where pressure exceeds the critical value required for the existence of liquid water. The extended narrow gullies on slopes with tributaries were formed, as it is supposed, by water streams. The structure of gullies has an unusual appearance, reverse of that of mountain rivers on Earth: gullies are broad in the upper part of a slope, narrow downslope, end with a thin stream, and disappear at the valley or crater floor. Both tributaries and the major channel seem to be directed uphill. This paper provides a simple explanation of this apparent paradox. Under low-temperature conditions, the conversion of liquid water to the ice phase should be considered in dynamics: the water released by the source comes in contact with a cold ground, partly soaks in ground, and freezes, forming an ice bed along which the stream moves further and continues to interact with ground. The distance from the source at which water completely disappears depends on the initial temperature of the source, its abundance, and the ground temperature. The apparent paradox is explained by the interaction of a cooling stream with a very cold ground. As regards the side structures, they are not tributaries but branches, which rapidly freeze. This paper also shows that a high source debit and/or sufficiently high ambient temperature promote the formation on the valley floor of a small pond that accumulates water flows. The walls of this pond consist of frozen ground and ice. Objects that might be small water reservoirs are detected in some new images of Mars. High concentration of sources of groundwater in two equatorial regions of Mars may serve as a useful indication to the location of places promising for searching traces of life on this planet. 相似文献
5.
Knowledge of the interior structure of Mars is of fundamental importance to the understanding of its past and present state as well as its future evolution. The most prominent interior structure properties are the state of the core, solid or liquid, its radius, and its composition in terms of light elements, the thickness of the mantle, its composition, the presence of a lower mantle, and the density of the crust. In the absence of seismic sounding only geodesy data allow reliably constraining the deep interior of Mars. Those data are the mass, moment of inertia, and tides. They are related to Mars’ composition, to its internal mass distribution, and to its deformational response to principally the tidal forcing of the Sun. Here we use the most recent estimates of the moment of inertia and tidal Love number k2 in order to infer knowledge about the interior structure of the Mars.We have built precise models of the interior structure of Mars that are parameterized by the crust density and thickness, the volume fractions of upper mantle mineral phases, the bulk mantle iron concentration, and the size and the sulfur concentration of the core. From the bulk mantle iron concentration and from the volume fractions of the upper mantle mineral phases, the depth dependent mineralogy is deduced by using experimentally determined phase diagrams. The thermoelastic properties at each depth inside the mantle are calculated by using equations of state. Since it is difficult to determine the temperature inside the mantle of Mars we here use two end-member temperature profiles that have been deduced from studies dedicated to the thermal evolution of Mars. We calculate the pressure and temperature dependent thermoelastic properties of the core constituents by using equations state and recent data about reference thermoelastic properties of liquid iron, liquid iron-sulfur, and solid iron. To determine the size of a possible inner core we use recent data on the melting temperature of iron-sulfur.Within our model assumptions the geodesy data imply that Mars has no solid inner core and that the liquid core contains a large fraction of sulfur. The absence of a solid inner is in agreement with the absence of a global magnetic field. We estimate the radius of the core to be 1794 ± 65 km and its core sulfur concentration to be 16 ± 2 wt%. We also show that it is possible for Mars to have a thin layer of perovskite at the bottom of the mantle if it has a hot mantle temperature. Moreover a chondritic Fe/Si ratio is shown to be consistent with the geodesy data, although significantly different value are also possible. Our results demonstrate that geodesy data alone, even if a mantle temperature is assumed, can almost not constrain the mineralogy of the mantle and the crust. In order to obtain stronger constraints on the mantle mineralogy bulk properties, like a fixed Fe/Si ratio, have to be assumed. 相似文献
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C. Dickinson J.A. Whiteway M. Illnicki W. Junkermann J. Hacker 《Planetary and Space Science》2011,59(10):942-951
The LIDAR instrument operating from the surface of Mars on the Phoenix Mission measured vertical profiles of atmospheric dust and water ice clouds at temperatures around −65 °C. An equivalent lidar system was utilized for measurements in the atmosphere of Earth where dust and cloud conditions are similar to Mars. Coordinated aircraft in situ sampling provided a verification of lidar measurement and analysis methods and also insight for interpretation of lidar derived optical parameters in terms of the dust and cloud microphysical properties. It was found that the vertical distribution of airborne dust above the Australian desert is quite similar to what is observed in the planetary boundary layer above Mars. Comparison with the in situ sampling is used to demonstrate how the lidar derived optical extinction coefficient is related to the dust particle size distribution. The lidar measurement placed a constraint on the model size distribution that has been used for Mars. Airborne lidar measurements were also conducted to study cirrus clouds that form in the Earth’s atmosphere at a similar temperature and humidity as the clouds observed with the lidar on Mars. Comparison with the in situ sampling provides a method to derive the cloud ice water content (IWC) from the Mars lidar measurements. 相似文献
8.
Brines, i.e. aqueous salty solutions, increasingly play a role in a better understanding of physics and chemistry (and eventually also putative biology) of the upper surface of Mars. Results of physico-chemical modeling and experimentally determined data to characterize properties of cryobrines of potential interest with respect to Mars are described. Eutectic diagrams, the related numerical eutectic values of composition and temperature, the water activity of Mars-relevant brines of sulfates, chlorides, perchlorides and carbonates, including related deliquescence relative humidity, are parameters and properties, which are described here in some detail. The results characterize conditions for liquid low-temperature brines (“cryobrines”) to evolve and to exist, at least temporarily, on present Mars. 相似文献
9.
In this paper we present the design and some results of an on-line chemical model of the atmosphere of Mars using a three-dimensional dynamical-chemical model. A chemistry module has been added to the 3D Mars Global Multiscale Model (GM3), a general circulation model based on the Canadian weather forecast model. As water is a major fuel for chemistry on Mars, we have taken care to simulate the atmospheric water vapor content, taking into account evaporation from and condensation to the polar caps and in the atmosphere we allow for freezing and formation of a bulk cloud and sedimentation. The chemical module includes the main neutral carbon-oxygen-hydrogen-nitrogen species and associated relevant reactions. The outputs of the model are analyzed in the light of our current understanding of the chemistry on Mars. The results are in general accordance with 1D models and with two other 3D models with more limited chemistry. The model does not require elevated diffusion coefficients to fit observational data in the thermosphere as was suggested in some 1D studies. The large scale transport and the downward thermospheric transport in the winter pole appear to have a significant role in the concentrations of some trace species. 相似文献
10.
The possibility of observing mirages on Mars from the Viking lander cameras is examined. A simple model for the production of both inferior and superior mirages is developed. Assuming the atmospheric index of refraction to be a linear function of density (i.e., temperature), ray curvatures are calculated through layers of large, expected thermal gradient.Assuming the Martian morning inversions of Gierasch and Goody (1968), calculations of ray curvature show the superior mirage to be an unlikely occurrence on Mars since the downward curvature of the ray through the inversion layer is less than the downward curvature of the planet. In order to examine the nature of inferior mirages we select a reasonable expression for temperature profile in the surface layer fitted to the midafternoon, midlatitude summer results of Gierasch and Goody. Integration of the expression for ray curvature yields a relation for the minimum distance between the lander cameras and an inferior mirage as a function of the surface superadiabatic lapse rate. Such calculations indicate that the Viking lander cameras will record inferior mirages at horizontal distances of a kilometer or so from the lander. Given the appearance of an inferior mirage at a measured minimum distance from the observer it should be a simple matter to calculate the corresponding mean temperature lapse rate at the surface. 相似文献
11.
Kent D. Trego 《Earth, Moon, and Planets》1991,53(3):237-238
The origins of outflow channels and sites of suspected karst terrain on Mars possibly indicate where aquifers once existed. Aquifers on Mars are potential hosts to ecosystem development because of the sustained presence of liquid water and subsurface warm temperature. 相似文献
12.
E. Kallio A. Fedorov T. Säles W. Schmidt P. Riihelä R. Lundin H. Gunell Y. Futaana M. Yamauchi J.-A. Sauvaud J.D. Winningham J.R. Sharber A.J. Coates D.O. Kataria J.G. Luhmann D. Williams C.C. Curtis B.R. Sandel M. Carter S. Orsini M. Maggi P. Bochsler J. Woch K. Asamura 《Icarus》2006,182(2):350-359
We have analysed ion escape at Mars by comparing ASPERA-3/Mars Express ion measurements and a 3-D quasi-neutral hybrid model. As Mars Express does not have a magnetometer onboard, the analysed IMA data are from an orbit when the IMF clock angle was possible to determine from the magnetic field measurements of Mars Global Surveyor. We found that fast escaping planetary ions were observed at the place which, according to the 3-D model, is anticipated to contain accelerated heavy ions originating from the martian ionosphere. The direction of the interplanetary magnetic field was found to affect noticeably which regions can be magnetically connected to Mars Express and to the overall 3-D Mars-solar wind interaction. 相似文献
13.
Michael C. Malin Bruce A. Cantor Robert M. Haberle Peter C. Thomas James F. Bell III 《Icarus》2008,194(2):501-512
The Mars Reconnaissance Orbiter observes Mars from a nearly circular, polar orbit. From this vantage point, the Mars Color Imager extends the ∼5 Mars years record of Mars Global Surveyor global, visible-wavelength multi-color observations of meteorological events and adds measurements at three additional visible and two ultraviolet wavelengths. Observations of the global distribution of ozone (which anti-correlates with water vapor) and water ice and dust clouds allow tracking of atmospheric circulation. Regional and local observations emphasize smaller scale atmospheric dynamics, especially those related to dust lifting and subsequent motion. Polar observations detail variations related to the polar heat budget, including changes in polar frosts and ices, and storms generated at high thermal contrast boundaries. 相似文献
14.
Mars is characterized by geological landforms familiar to terrestrial geologists. It has a tenuous atmosphere that evolved differently from that of Earth and Venus and a differentiated inner structure. Our knowledge of the structure and evolution of Mars has strongly improved thanks to a huge amount of data of various types (visible and infrared imagery, altimetry, radar, chemistry, etc) acquired by a dozen of missions over the last two decades. In situ data have provided ground truth for remote-sensing data and have opened a new era in the study of Mars geology. While large sections of Mars science have made progress and new topics have emerged, a major question in Mars exploration—the possibility of past or present life—is still unsolved. Without entering into the debate around the presence of life traces, our review develops various topics of Mars science to help the search of life on Mars, building on the most recent discoveries, going from the exosphere to the interior structure, from the magmatic evolution to the currently active processes, including the fate of volatiles and especially liquid water. 相似文献
15.
Many asteroids with a semimajor axis close to that of Mars have been discovered in the last several years. Potentially some of these could be in 1:1 resonance with Mars, much as are the classic Trojan asteroids with Jupiter, and its lesser-known horseshoe companions with Earth. In the 1990s, two Trojan companions of Mars, 5261 Eureka and 1998 VF31, were discovered, librating about the L5 Lagrange point, 60° behind Mars in its orbit. Although several other potential Mars Trojans have been identified, our orbital calculations show only one other known asteroid, 1999 UJ7, to be a Trojan, associated with the L4 Lagrange point, 60° ahead of Mars in its orbit. We further find that asteroid 36017 (1999 ND43) is a horseshoe librator, alternating with periods of Trojan motion. This asteroid makes repeated close approaches to Earth and has a chaotic orbit whose behavior can be confidently predicted for less than 3000 years. We identify two objects, 2001 HW15 and 2000 TG2, within the resonant region capable of undergoing what we designate “circulation transition”, in which objects can pass between circulation outside the orbit of Mars and circulation inside it, or vice versa. The eccentricity of the orbit of Mars appears to play an important role in circulation transition and in horseshoe motion. Based on the orbits and on spectroscopic data, the Trojan asteroids of Mars may be primordial bodies, while some co-orbital bodies may be in a temporary state of motion. 相似文献
16.
Christensen [2003. Nature 422, 45-48] suggested that runoff from melting snowpacks on martian slopes might be responsible for carving gullies. He also suggested that snowpacks currently exist on Mars, for example on the walls of Dao Valles (approximately 33° S). Such snowpacks were presumably formed during the last obliquity cycle, which occurred about 70,000 years ago. In this paper we investigate a specific scenario under conditions we believe are favorable for snowpack melting. We model the rate at which a snowpack located at 33° S on a poleward-facing slope sublimates and melts on Mars, as well as the temperature profile within the snowpack. Our model includes the energy and mass balance of a snowpack experiencing diurnal variations in insolation. Our results indicate that a dirty snowpack would quickly sublimate and melt under current martian climate conditions. For example a 1 m thick dusty snowpack of moderate density (550 kg/m3) and albedo (0.39) would sublimate in less than two seasons, producing a small amount of meltwater runoff. Similarly, a cleaner snowpack (albedo 0.53) would disappear in less than 9 seasons. These results suggest that the putative snowpack almost certainly could not have survived for 70,000 years. For most of the parameter settings snowpack interior temperatures at this latitude and slope do reach the melting point. Under most conditions melting occurs when the snowpack is less than 10 cm thick. The modeled snowpack will not melt if it is covered by a 1 cm dust lag. In general, these findings raise interesting possibilities regarding gully formation, but perhaps mostly during a past climate regime when snowfall was expected to have occurred. If there currently are exposed snowpacks on martian mid-latitude slopes, then these ice sheets cannot last long. Hence they might be time variable features on Mars and should be searched for. 相似文献
17.
I. A. FRANCHI I. P. WRIGHT A. S. SEXTON C. T. PILLINGER 《Meteoritics & planetary science》1999,34(4):657-661
Abstract— The small difference between the O-isotopic mass fractionation lines of the Earth and Mars has been measured precisely using a laser fluorination system. The precision achieved from the two sample sets is better than ±0.014‰, with the offset (Δ17O) between Mars and Earth measured as +0.321‰. This result shows that all the Shergotty—Nakhla—Chassigny (SNC) meteorites define a high level of isotopic homogeneity, comparable to that of crustal material on the Earth, indicating that these meteorites originate, unequivocally, from a single, common parent body (Mars). Allan Hills 84001, with its ancient age (4.56 Ga), shows that any initial heterogeneity imparted into Mars from the nebula was homogenised very early in the formation history of the planet. 相似文献
18.
Salt compounds are apparently an important component of the finite-grained regolith on Mars. Salt enrichment may be explained either as a secondary concentration of chemical weathering products or as direct incorporation of planetary released volatiles. Geochemical measurements and chemical relationships constrain the salt species and resultant physicochemical consequences. A likely assemblage is dominated by (Mg,Na)SO4, NaCl, and (Mg,Ca)CO3. Formation of brine in equilibrium with such a salt mixture is unlikely under the temperature and water-vapor restrictions prevalent over most, if not all, of the Martian surface. Acidic conditions, accompanying salt formation, favor the preferential destruction of susceptible igneous minerals. 相似文献
19.
We have identified and characterized a basaltic Mars simulant that is available as whole rocks, sand and dust. The source rock for the simulant is a basalt mined from the Tertiary Tropico Group in the western Mojave Desert. The Mojave Mars Simulant (MMS) was chosen for its inert hygroscopic characteristics, its availability in a variety of forms, and its physical and chemical characteristics. The MMS dust and MMS sand are produced by mechanically crushing basaltic boulders. This is a process that more closely resembles the weathering/comminution processes on Mars where impact events and aerodynamic interactions provide comminution in the (relative) absence of water and organics. MMS is among the suite of test rocks and soils that was used in the development of the 2007/8 Phoenix Scout and is being used in the 2009 Mars Science Laboratory (MSL) missions. The MMS development team is using the simulant for research that centers on sampling tool interactions in icy soils. Herein we describe the physical properties and chemical composition of this new Mars simulant. 相似文献
20.
We have used Mars Reconnaissance Orbiter data from 2007 and 2009 to compare summer behaviors of the seasonal and residual south polar caps of Mars in those two years. We find that the planet-encircling dust storm that occurred in the first of the two Mars years enhanced the loss of seasonal CO2 deposits relative to the second year but did not have a large effect on the continuing erosion of the pits and mesas within the residual cap materials. This suggests that the increase of bright frost in some regions of the residual cap observed between Mariner 9 and Viking can be accommodated within observed martian weather variability and does not require unknown processes or climate change. 相似文献