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1.
The thermo-mechanical properties of planetary surface and subsurface layers control to a high extent in which way a body interacts with its environment, in particular how it responds to solar irradiation and how it interacts with a potentially existing atmosphere. Furthermore, if the natural temperature profile over a certain depth can be measured in situ, this gives important information about the heat flux from the interior and thus about the thermal evolution of the body. Therefore, in most of the recent and planned planetary lander missions experiment packages for determining thermo-mechanical properties are part of the payload. Examples are the experiment MUPUS on Rosetta's comet lander Philae, the TECP instrument aboard NASA's Mars polar lander Phoenix, and the mole-type instrument HP3 currently developed for use on upcoming lunar and Mars missions. In this review we describe several methods applied for measuring thermal conductivity and heat flux and discuss the particular difficulties faced when these properties have to be measured in a low pressure and low temperature environment. We point out the abilities and disadvantages of the different instruments and outline the evaluation procedures necessary to extract reliable thermal conductivity and heat flux data from in situ measurements.  相似文献   

2.
The MErcury, Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission will send the first spacecraft to orbit the planet Mercury. A miniaturized set of seven instruments, along with the spacecraft telecommunications system, provide the means of achieving the scientific objectives that motivate the mission. The payload includes a combined wide- and narrow-angle imaging system; γ-ray, neutron, and X-ray spectrometers for remote geochemical sensing; a vector magnetometer; a laser altimeter; a combined ultraviolet-visible and visible-infrared spectrometer to detect atmospheric species and map mineralogical absorption features; and an energetic particle and plasma spectrometer to characterize ionized species in the magnetosphere.  相似文献   

3.
A basin with an interior about 1000 km across and an outer rim about 2000 km in diameter has been found on the side of Mercury that remained unknown after theMariner 10imaging in 1973–1975. In its size, which is as much as 1/2 of the Mercury's diameter, this formation is one of the largest basins on the terrestrial planets. The presence of other large features of global dimension on this side of the planet suggests their possible asymmetric allocation on Mercury, similar to that on the Moon. New methods of ground-based astronomical observations including data processing with a special software package have been used.  相似文献   

4.
Mercury holds answers to several critical questions regarding the formation and evolution of the terrestrial planets. These questions include the origin of Mercury's anomalously high ratio of metal to silicate and its implications for planetary accretion processes, the nature of Mercury's geological evolution and interior cooling history, the mechanism of global magnetic field generation, the state of Mercury's core, and the processes controlling volatile species in Mercury's polar deposits, exosphere, and magnetosphere. The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission has been designed to fly by and orbit Mercury to address all of these key questions. After launch by a Delta 2925H-9.5, two flybys of Venus, and two flybys of Mercury, orbit insertion is accomplished at the third Mercury encounter. The instrument payload includes a dual imaging system for wide and narrow fields-of-view, monochrome and color imaging, and stereo; X-ray and combined gamma-ray and neutron spectrometers for surface chemical mapping; a magnetometer; a laser altimeter; a combined ultraviolet–visible and visible-near-infrared spectrometer to survey both exospheric species and surface mineralogy; and an energetic particle and plasma spectrometer to sample charged species in the magnetosphere. During the flybys of Mercury, regions unexplored by Mariner 10 will be seen for the first time, and new data will be gathered on Mercury's exosphere, magnetosphere, and surface composition. During the orbital phase of the mission, one Earth year in duration, MESSENGER will complete global mapping and the detailed characterization of the exosphere, magnetosphere, surface, and interior.  相似文献   

5.
Model calculations show that the thermal history of a Moon which originated by fission from the proto-Earth is the same as that for the Moon as it is currently understood. In particular, a fissioned Moon currently has a small percent of partial melt or at least near solidus temperatures below depths of 800 km in accord with the seismic data which show that the deep interior of the Moon has a very lowQ. The models have moderate (20–50%) degrees of partial melting in the upper mantle (depths < 300 or 200 km) in the period between 3 to 4 × 109 years ago and, therefore, can account for the mare filling epoch. Finally the heat flow of the models is 18 ergs cm–2 s–1 which is close to the average of 19 ergs cm–2 s–1 derived from the Apollo heat flow experiments. These findings add further support for the fission origin of the Moon.  相似文献   

6.
Several versions of a Mercury surface element, part of the ESA BepiColombo Mercury Cornerstone mission to be launched in 2009, have been studied. The major constraint on system design has been the need to maximise the useful system mass on the surface of Mercury. The absence of atmosphere on the planet forces the adoption of a purely propulsive descent and landing system. The need to maintain the shock level at landing below limits which are acceptable to the payload imposes the adoption of a precise guidance, navigation & control system, which allows a drastic reduction of the landing speed, and therefore the adoption of an airbag landing system. Surface mobility is an obvious requirement for the purpose of geochemical exploration, since selected rocks have a much higher scientific yield than the average regolith. Geophysical investigations require that thermal, accelerometric, and densitometric probes be brought in contact with subsurface regions, to a depth of several metres. Magnetometric measurements may need deployment of sensors to some distance from the bulk of the lander body. The thermal environment on the surface of Mercury is extreme, even in the polar regions that will be targeted by the BepiColombo lander, while the solar flux rises seasonally to 10 times the one experienced in Earth orbit. The need to provide a low-temperature heat sink to sensors is particularly critical, if these are installed on a small-size, small-mass mobile deployment device. A consequence of the landing in a polar region will be the extremely variable lighting conditions, with extended portions of the surface shrouded in darkness by any small surface obstacle. Limitations on communications between Earth and the deployed payload will be caused by the low available data rate and by visibility windows (contact may be restricted to as little as <10 min every 9.5 h). This will impose a high degree of autonomy to be built into the payload systems.  相似文献   

7.
An empirically derived lunar gravity field   总被引：1，自引：0，他引：1  
The heat-flow experiment is one of the Apollo Lunar Surface Experiment Package (ALSEP) instruments that was emplaced on the lunar surface on Apollo 15. This experiment is designed to make temperature and thermal property measurements in the lunar subsurface so as to determine the rate of heat loss from the lunar interior through the surface. About 45 days (1 1/2 lunations) of data has been analyzed in a preliminary way. This analysis indicates that the vertical heat flow through the regolith at one probe site is 3.3 × 10–6 W/cm2 (±15%). This value is approximately one-half the Earth's average heat flow. Further analysis of data over several lunations is required to demonstrate that this value is representative of the heat flow at the Hadley Rille site. The mean subsurface temperature at a depth of 1 m is approximately 252.4K at one probe site and 250.7K at the other. These temperatures are approximately 35K above the mean surface temperature and indicate that conductivity in the surficial layer of the Moon is highly temperature dependent. Between 1 and 1.5m, the rate of temperature increase as a function of depth is 1.75K/m (±2%) at the probe 1 site. In situ measurements indicate that the thermal conductivity of the regolith increases with depth. Thermal-conductivity values between 1.4 × 10–4 and 2.5 × 10–4 W/cm K were determined; these values are a factor of 7 to 10 greater than the values of the surface conductivity. If the observed heat flow at Hadley Base is representative of the moonwide rate of heat loss (an assumption which is not fully justified at this time), it would imply that overall radioactive heat production in the Moon is greater than in classes of meteorites that have formed the basis of Earth and Moon bulk composition models in the past.Lamont-Doherty Geological Observatory Contribution Number 1800.  相似文献   

8.
Measurements of the lateral distribution function (ldf) of Extensive Air Showers (EAS) as recorded by the array of water- erenkov detectors at Haverah Park are described, and accurate experimental parameterizations expressing the mean ldf for 2 × 1017 < E < 4 × 1018 eV, 50 < r < 700 m, and θ < 45° are given. An extrapolation of these relations to the regime E ≥ 1019 eV and r > 700 m is described: extrapolation in this energy domain appears valid, and an approximate correction term is given for the larger core distances. The results of recent Monte Carlo simulations of shower development and detector behavior are compared to the parameterized ldf. The agreement is good increasing confidence that these simulations may be trusted as design tools for the Auger project, a proposed ‘next generation’ detector system.  相似文献   

9.
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10.
The figure of Mercury is estimated in terms of an isostatic form of equilibrium which tends to be controlled by the situation near perihelion passage at the 32 resonance spin rate. The ratios of the principal moments of inertia for Mercury are: (1)(C–A)/C7×10–5; (2)(C–B)/C5×10–5 and (3)(B–A)/C2×10–5. The thermal effect on Mercury's figure during solidification forces Mercury's rotation to be trapped in the 32 resonance lock as its spin rate is being slowed by tidal effects. It is shown that the process of trapping of Mercury has been naturally affected by the instantaneous solidification of Mercury into a shape with two thermal bulges, and that the two permanent thermal bulges stabilize the planet's rotation.  相似文献   

11.
Using the data on sunspot groups compiled during 1879&amp;#x2013;1975, we determined variations in the differential rotation coefficientsA andB during the solar cycle. The variation in the equatorial rotation rateA is found to be significant only in the odd numbered cycles, with an amplitude &amp;#x223C; 0.01 &amp;#x03BC; rads-1. There exists a good anticorrelation between the variations of the differential rotation rateB derived from the odd and even numbered cycles, suggesting existence of a &amp;#x2018;22-year&amp;#x2019; periodicity inB. The amplitude of the variation ofB is &amp;#x223C; 0.05 &amp;#x03BC; rad s-1.  相似文献   

12.
Seismic data from the Apollo Passive Seismic Network stations are analyzed to determine the velocity structure and to infer the composition and physical properties of the lunar interior. Data from artificial impacts (S-IVB booster and LM ascent stage) cover a distance range of 70–1100 km. Travel times and amplitudes, as well as theoretical seismograms, are used to derive a velocity model for the outer 150 km of the Moon. TheP wave velocity model confirms our earlier report of a lunar crust in the eastern part of Oceanus Procellarum.The crust is about 60 km thick and may consist of two layers in the mare regions. Possible values for theP-wave velocity in the uppermost mantle are between 7.7 km s–1 and 9.0 km s–1. The 9 km s–1 velocity cannot extend below a depth of about 100 km and must decrease below this depth. The elastic properties of the deep interior as inferred from the seismograms of natural events (meteoroid impacts and moonquakes) occurring at great distance indicate that there is an increase in attenuation and a possible decrease of velocity at depths below about 1000 km. This verifies the high temperatures calculated for the deep lunar interior by thermal history models.Paper presented at the Lunar Science Institute Conference on Geophysical and Geochemical Exploration of the Moon and Planets, January 10–12, 1973.  相似文献   

13.
From the volume-limited Main galaxy sample of the Sloan Digital Sky Survey Data Release 6 (SDSS DR6), we construct three samples with g–r color bins , labeled S1–S3, to investigate how other properties of galaxies depend on environment at fixed color. For each sample, we measure the local three-dimensional galaxy density in a comoving sphere with radius equal to the distance to the 5th nearest galaxy for each galaxy, select about 5% galaxies and construct the two subsamples at both extremes of density. Our study suggests that the environmental dependence of luminosity is mainly due to the environmental dependence of galaxy color and the correlation between color and luminosity. In addition, we preferentially conclude that concentration index and morphologies are not strongly correlated with local density at fixed color, and that galaxy color is a galaxy property very predictive of the local environment. Because SDSS spectroscopy is incomplete for bright galaxies at very low redshifts, we also use a volume-limited Main galaxy sample with a lower redshift limit z = 0.05, which contains 94,954 galaxies at 0.05 < z < 0.089 with −22.40 < Mr < −20.16, and reach the same conclusions.Due to the bimodality of the u–r color distribution, we classify galaxies as ‘red’ and ‘blue’, respectively, and further subdivide the samples into star-forming galaxies and passive ones using Hα equivalent width, W0(Hα). Results show that color and star formation activity of galaxies are galaxy properties very predictive of the local environment.  相似文献   

14.
We use theoretical results derived in a previous paper (Lanzano, 1986) to numerically evaluate the temperature profile and radial deformation within a spherical, elastic Earth due to heat generated by the decay of radiogenic elements.We consider only the Uranium family and have assumed the diffusivity of the silicate mantle to be K = 8 × 10–3 cm2 s–1, the Poisson elastic ratio to be = 0.25 and the coefficient of thermal expansion to be = 2 × 10–5 (deg)–1. Our series solutions when applied to the interiors of the Moon, Mercury, and Mars yield results in agreement with Kopal's (1963) evaluations.  相似文献   

15.
For infinitesimal, homologous perturbations, stability analysis has found the solar radiative interior thermally stable. It is considered for the first time here whether stability is preserved when finite amplitude nonhomologous perturbations are present. We argue that local heated regions may develop in the solar core due to magnetic instabilities. Simple numerical estimations are derived for the timescales of the decay of these events and, when heated bubbles are generated that rise towards the surface, of their rising motion. These estimations suggest that the solar core is in a metastable state. For more detailed analysis, we developed a numerical code to solve the differential equation system. Our calculations determined the conditions of metastability and the evolution of timescales. We obtained two principal results. One of them shows that small amplitude heating events (with energy surplus Qo < 1026 ergs) contribute to subtle but long-lifetime heat waves and give the solar interior a persistently oscillating character. Interestingly, the slow decay of heat waves may make their accumulation possible and so their overlapping may contribute to the development of an intermittent, individual, local process of bubble generation, which may also be generated directly by stronger (Qo > 1026 ergs) heating events. Our second principal result is that for heated regions with ΔT/T ≥ 10−4 and radius 105–106cm, the generated bubbles may travel distances larger than their linear size. We point out to some possible observable consequences of the obtained results.  相似文献   

16.
In this paper, series of a rigid model of Mercury nutations are computed. The method used is based on the calculation of the forces produced by the Sun on Mercury as considered as a rigid body. In order to take into account the indirect effects coming from the orbit perturbations of Mercury, we used the ephemerides VSOP87 (Bretagnon and Francou, 1988). Due to non-negligible difference between the principal moment of inertia A and B in the case of Mercury, we compute also terms due to the triaxiality in addition to the general terms coming from J 2. With a truncation level of 10 –3 mas (milliarcsecond), related to the present-day precision of the Mercury precession constant, 173 terms in longitude ( sin ) and 166 terms in obliquity () are computed. The value of the dynamical flattening used is H D = (C – A)/C = 2.3 × 10–4 (Anderson, 1987).  相似文献   

17.
The temperature profile of the KTB pilot drillhole, T(z)KTB-PH,is distinctly nonlinear: a temperature deficit ΔT (relative to a linear temperature-depth profile) is especially pronounced in the depth range 500–3500 m. The depth dependence of the deficit, Δ(z) is compared to be anticipated effect of surface paleoclimatic variations, ΔTpc(z), at the drillsite on the temperature profile. The latter can be calculated from available paleo-climatic models. If ΔTpc(z) is added to T(z)KTB-PH, a nearly linear temperature-depth curve results with an average geothermal gradient of 27.9°C/km. This, together with an average vertical thermal conductivity of 3.0 W/mK, estimated from KTB drillcore data, implies a heat flow density at the KTB site of 84 mW/m2. This modelled value is in good agreement with heat flow determinations in the adjacent Eger graben structure (Western Bohemian massif).  相似文献   

18.
We present a Monte Carlo model of the distribution of neutral sodium in Mercury’s exosphere and tail using data from the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft during the first two flybys of the planet in January and September 2008. We show that the dominant source mechanism for ejecting sodium from the surface is photon-stimulated desorption (PSD) and that the desorption rate is limited by the diffusion rate of sodium from the interior of grains in the regolith to the topmost few monolayers where PSD is effective. In the absence of ion precipitation, we find that the sodium source rate is limited to ∼106-107 cm−2 s−1, depending on the sticking efficiency of exospheric sodium that returns to the surface. The diffusion rate must be at least a factor of 5 higher in regions of ion precipitation to explain the MASCS observations during the second MESSENGER flyby. We estimate that impact vaporization of micrometeoroids may provide up to 15% of the total sodium source rate in the regions observed. Although sputtering by precipitating ions was found not to be a significant source of sodium during the MESSENGER flybys, ion precipitation is responsible for increasing the source rate at high latitudes through ion-enhanced diffusion.  相似文献   

19.
Polar brightness temperatures on Io are higher than expected for any passive surface heated by absorbed sunlight. This discrepancy implies large scale volcanic activity from which we derive a new component of Io's heat flow. We present a ‘Three Component’ thermal background, infrared emission model for Io that includes active polar regions. The widespread polar activity contributes an additional ∼0.6 W m−2 to Io's heat flow budget above the ∼2.5 W m−2 from thermal anomalies. Our estimate for Io's global average heat flow increases to ∼3±1 W m−2 and ∼1.3±0.4×1014 watts total.  相似文献   

20.
The Bare Essentials of Surface Transfer (BEST) land surface scheme is briefly described and the key physical parameterisations discussed. Results are then presented to illustrate how the model performs, with forcing data for HAPEX-MOBILHY, compared to a series of other schemes in the simulation of evaporation and sensible heat. The implications of the models performance, and some indications of the future development of the scheme are provided. The basic version of BEST was found to overestimate evaporation for the HAPEX-MOBILHY data, simulating 816 mm yr−1 compared to a range of 550 to 816 mm yr−1 for all models. A modification to the β parameterisation reduced the evaporation to 759 mm yr−1 which, although an improvement, is still probably too high.  相似文献   

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