On the sublimation of ice particles on the surface of Mars; with applications to the 2007/8 Phoenix Scout mission     

Peter A. Taylor  Konstantin Baibakov  Michael H. Hecht  P.-Y. Li  Luis Prieto 《Icarus》2006,181(2):375-387

Experimental studies related to the sublimation of ice, in bulk or as small particles, alone or mixed with dust similar to that expected on the surface of Mars, are reported. The experiments, a cloud physics particle sublimation model, and a convection model presented by Ingersoll, all indicate a strong dependence of sublimation rate on temperature, and this appears to be the dominant factor, assuming that the relative humidity of the air is fairly low. In addition the rate of loss of water vapour appears to depend primarily on exposed surface area and less on particle size and the total mass of the sample, or the mass of ice in the sample. The 2007/8 Phoenix Scout mission plans to obtain and analyse samples of sub-surface ice from about 70° N on Mars. A concern is that these samples, in the form of ice chips of size about 1 mm diameter, could be prone to sublimation when exposed for prolonged periods (many hours) to a relatively warm and dry atmosphere. Our laboratory simulations confirm that this could be a problem if particles are simply left lying on the surface, but also indicate that samples kept suitably cold and collected together in confined piles will survive long enough for the collection and delivery (to the analysis instruments) procedure to be completed.  相似文献   

空间数据计算模式分析与应用     

明冬萍  骆剑承  周成虎  沈占锋  李均力  盛昊 《地球信息科学学报》2006,8(2):84-90

随着传感器和其他数据采集技术的不断进步以及对地观测网络的建设和启动,空间数据的高性能处理和分析成为摆在地学工作者面前的瓶颈。本文以此为出发点,按照不同地学领域(陆地、大气、海洋)的空间数据载体的形态的不同,将空间数据划分为反映固态基质信息的陆地空间数据,反映液态基质信息的陆地水文空间数据,反映液态基质信息的海洋流体空间数据和反映气态基质信息的大气流体空间数据四类,并对每类数据的最小单元问题进行了初步的分析。本文详细阐述了地学空间计算的涵义,并根据计算行为模式及计算的侧重点的不同,将地学计算过程分为深度计算过程与主动计算过程(即“数据→特征→知识”的一般计算过程),并就此进行了阐释。以基于特征的遥感信息提取和目标识别工作为例,对上述理论进行了说明和验证。最后对空间数据计算模式相关问题进行了总结,并对以后的研究做了展望。  相似文献   

Atmospheric entry profiles from the Mars Exploration Rovers Spirit and Opportunity     

Paul Withers  Michael D. Smith 《Icarus》2006,185(1):133-142

Accelerometer measurements made by Spirit and Opportunity during their entries through the martian atmosphere are reported. Vertical profiles of atmospheric density, pressure, and temperature with sub-km vertical resolution were obtained using these data between 10 and 100 km. Spirit's temperature profile is ∼10 K warmer than Opportunity's between 20 and 80 km. Unlike all other martian entry profiles, Spirit's temperature profile does not contain any large amplitude, long wavelength oscillations and is nearly isothermal below 30 km. Opportunity's temperature profile contains a strong inversion between 8 and 12 km. A moderate dust storm, which occurred on Mars shortly before these two atmospheric entries, may account for some of the differences between the two profiles. The poorly known angle of attack and unknown wind velocity may cause the temperature profiles to contain errors of tens of Kelvin at 10 km, but these errors would be an order of magnitude smaller above 30 km. On broad scales, the two profiles are consistent with Mars Global Surveyor Thermal Emission Spectrometer (TES) pressure/temperature profiles. Differences exist on smaller scales, particularly associated with the near-isothermal portion of Spirit's profile and the temperature inversion in Opportunity's profile.  相似文献   

提高中性大气折射延迟改正精度的可能途径     

冒蔚  张捍卫  李彬华  杨磊  铁琼仙 《天文学报》2006,47(4):432-440

针对空间大地测量技术对中性大气折射延迟改正精度的要求,阐述了折射延迟改正值应随测站和随方位而异的必要性．指出,在尚不能直接测定天文大气折射值的情况下,现有的各种改正模型对大气分布模型的依赖性,不能达到预期的精度和降低观测的截止角．根据云南天文台低纬子午环的特殊结构,和测定大气折射的实践,提出了提高折射延迟改正精度的新方法,即：利用各观测站不同方位从天顶附近直到低地平高度角的天文大气折射实测数据,求解得到折射率差和映射函数的参数,从而建立随测站和随方位而异的大气折射延迟改正模型．这一新方法的实施,将能在不需采用大气分布模型的情况下,把天顶延迟的改正精度提高到1 mm以内,低地平高度角的折射延迟改正精度提高到厘米级,并且把截止高度角压缩到5°以内．  相似文献   

Ion winds in Saturn's southern auroral/polar region     

Tom S Stallard  Steve Miller  Laurence M Trafton  Robert D Joseph 《Icarus》2004,167(1):204-211

We present profiles of the line-of-sight (l.o.s.) ionospheric wind velocities in the southern auroral/polar region of Saturn. Our velocities are derived from the measurement of Doppler shifting of the H₃⁺ν₂Q(1,0⁻) line at 3.953 microns. The data for this study were obtained using the facility high-resolution spectrometer CSHELL on the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii, during the night of February 6, 2003 (UT). The l.o.s. velocity profiles finally derived are consistent with an extended region of the upper atmosphere sub-corotating with the planet: the ion velocities in the inertial reference are only 1/3 of those expected for full planetary corotation. We discuss the results in the light of recent proposals for the kronian magnetosphere, and suggest that, in this region, Saturn's ion winds may be under solar wind control.  相似文献   

Optimal orbits for Mars atmosphere remote sensing   总被引：1，自引：0，他引：1  

Michel Capderou  François Forget 《Planetary and Space Science》2004,52(9):789-798

Most of the spacecrafts currently around Mars (or planned to reach Mars in the near future) use Sun-synchronous or near-polar orbits. Such orbits offer a very poor sampling of the diurnal cycle. Yet, sampling the diurnal cycle is of key importance to study Mars meteorology and climate. A comprehensive remote sensing data set should have been obtained by the end of the MRO mission, launched in 2005. For later windows, time-varying phenomena should be given the highest priority for remote sensing investigations. We present possible orbits for such missions which provide a rich spatial and temporal sampling with a relatively short repeat cycle (50 sols). After computation and determination of these orbits, said “optimal orbits”, we illustrate our results by tables of sampling and comparison with other orbits.  相似文献   

Spectro-imaging observations of Jupiter's 2-μm auroral emission. I. H₃ distribution and temperature     

E. Raynaud  J.-P. Maillard  J.H. Waite Jr.  P. Drossart 《Icarus》2004,171(1):133-152

We report on spectro-imaging infrared observations of Jupiter's auroral zones, acquired in October 1999 and October 2000 with the FTS/BEAR instrument at the Canada-France-Hawaii Telescope. The use of narrow-band filters at 2.09 and 2.12 μm, combined with high spectral resolution (0.2 cm⁻¹), allowed us to map emission from the H₂S₁(1) quadrupole line and from several H₃⁺ lines. The H₂ and H₃⁺ emission appears to be morphologically different, especially in the north, where the latter notably exhibits a “hot spot” near 150°-170° System III longitude. This hot spot coincides in position with the region of increased and variable hydrocarbon, FUV and X-ray emission, but is not seen in the more uniform H₂S₁(1) emission. We also present the first images of the H₂ emission in the southern polar region. The spectra include a total of 14 H₃⁺ lines, including two hot lines from the 3ν₂-ν₂ band, detected on Jupiter for the first time. They can be used to determine H₃⁺ column densities, rotational (T_rot) and vibrational (T_vib) temperatures. We find the mean T_vib of the v₂=3 state to be lower (960±50 K) than the mean T_rot in v₂=2 (1170±75 K), indicating an underpopulation of the v₂=3 level with respect to local thermodynamical equilibrium. Rotational temperatures and associated column densities are generally higher and lower, respectively, than inferred previously from ν₂ observations. This is a likely consequence of a large positive temperature gradient in the sub-microbar auroral atmosphere. While the signal-to-noise is not sufficient to take full advantage of the 2-D capabilities of the observations, the search for correlations between line intensities, T_vib and column densities, indicates that variations in line intensities are mostly due to correlated variations in the H₃⁺ column densities. The thermostatic role played by H₃⁺ at ionospheric levels may provide an explanation. The exception is the northern “hot spot,” which exhibits a T_vib about 250 K higher than other regions. A partial explanation might invoke a homopause elevation in this region, but a fully consistent scenario is not yet available. The different distributions of the H₂ and H₃⁺ emission are equally difficult to explain.  相似文献   

Saturn's cloud structure and temporal evolution from ten years of Hubble Space Telescope images (1994-2003)     

S. Pérez-Hoyos  A. Sánchez-Lavega  J.F. Rojas 《Icarus》2005,176(1):155-174

We present a study of the vertical structure of clouds and hazes in the upper atmosphere of Saturn's Southern Hemisphere during 1994-2003, about one third of a Saturn year, based on Hubble Space Telescope images. The photometrically calibrated WFPC2 images cover the spectral region between the near-UV (218-255 nm) and the near-IR (953-1042 nm), including the 890 nm methane band. Using a radiative transfer code, we have reproduced the observed center-to-limb variations in absolute reflectivity at selected latitudes which allowed us to characterize the vertical structure of the entire hemisphere during this period. A model atmosphere with two haze layers has been used to study the variation of hazes with latitude and to characterize their temporal changes. Both hazes are located above a thick cloud, putatively composed of ammonia ice. An upper thin haze in the stratosphere (between 1 and 10 mbar) is found to be persistent and formed by small particles (radii ∼0.2 μm). The lower thicker haze close to the tropopause level shows a strong latitudinal dependence in its optical thickness (typically τ∼20-40 at the equator but τ∼5 at the pole, at 814 nm). This tropospheric haze is blue-absorbent and extends from 50 to 100 mbar to about ∼400 mbar. Both hazes show temporal variability, but at different time-scales. First, there is a tendency for the optical thickness of the stratospheric haze to increase at all latitudes as insolation increases. Second, the tropospheric haze shows mid-term changes (over time scales from months to 1-2 years) in its optical thickness (typically by a factor of 2). Such changes always occur within a rather narrow latitude band (width ∼5-10°), affecting almost all latitudes but at different times. Third, we detected a long-term (∼10 year) decrease in the blue single-scattering albedo of the tropospheric haze particles, most intense in the equatorial and polar areas. Long-term changes follow seasonal insolation variations smoothly without any apparent delay, suggesting photochemical processes that affect the particles optical properties as well as their size. In contrast, mid-term changes are sudden and show various time-scales, pointing to a dynamical origin.  相似文献   

Connecting atmospheric science and atmospheric models for aerocapture at Titan and the outer planets     

C.G. Justus  Vernon W. Keller  Mary Kae Lockwood 《Planetary and Space Science》2005,53(5):601-605

Many atmospheric measurement systems, such as the sounding instruments on Voyager, gather atmospheric information in the form of temperature versus pressure level. In these terms, there is considerable consistency among the mean atmospheric profiles of the outer planets Jupiter through Neptune, including Titan. On a given planet or on Titan, the range of variability of temperature versus pressure level due to seasonal, latitudinal, and diurnal variations is also not large. However, many engineering needs for atmospheric models relate not to temperature versus pressure level but atmospheric density versus geometric altitude. This need is especially true for design and analysis of aerocapture systems. Drag force available for aerocapture is directly proportional to atmospheric density. Available aerocapture “corridor width” (allowable range of atmospheric entry angle) also depends on height rate of change of atmospheric density, as characterized by density scale height. Characteristics of hydrostatics and the gas law equation mean that relatively small systematic differences in temperature versus pressure profiles can integrate at high altitudes to very large differences in density versus altitude profiles. Thus, a given periapsis density required to accomplish successful aerocapture can occur at substantially different altitudes (∼150-300 km) on the various outer planets, and significantly different density scale heights (∼20-50 km) can occur at these periapsis altitudes. This paper will illustrate these effects and discuss implications for improvements in atmospheric measurements to yield significant impact on design of aerocapture systems for future missions to Titan and the outer planets. Relatively small-scale atmospheric perturbations, such as gravity waves, tides, and other atmospheric variations can also have significant effect on design details for aerocapture guidance and control systems. This paper will discuss benefits that would result from improved understanding of Titan and outer planetary atmospheric perturbation characteristics. Details of recent engineering-level atmospheric models for Titan and Neptune will be presented, and effects of present and future levels of atmospheric uncertainty and variability characteristics will be examined.  相似文献   

Interannual variability of water ice clouds over major martian volcanoes observed by MOC     

Jennifer L. Benson  Philip B. James  Ryan Remigio 《Icarus》2006,184(2):365-371

Using Mars Global Surveyor Mars Orbiter Camera daily global maps, cloud areas have been measured daily for water ice clouds associated with the topography of the major volcanoes Olympus Mons, Ascraeus Mons, Pavonis Mons, Arsia Mons, Elysium Mons, and Alba Patera. This study expands on that of Benson et al. [Benson, J.L., Bonev, B.P., James, P.B., Shan, K.J., Cantor, B.A., Caplinger, M.A., 2003. Icarus 165, 34-52] by continuing their cloud area measurements of the Tharsis volcanoes, Olympus Mons and Alba Patera for an additional martian year (August 2001-May 2003) and by also including Elysium Mons measurements from March 1999 through May 2003. The seasonal trends in cloud activity established by Benson et al. [Benson, J.L., Bonev, B.P., James, P.B., Shan, K.J., Cantor, B.A., Caplinger, M.A., 2003. Icarus 165, 34-52] for the five volcanoes studied earlier are corroborated here with an additional year of coverage. For volcanoes other than Arsia Mons, interannual variations that could be associated with the large 2001 planet encircling dust storm are minimal. At Arsia Mons, where cloud activity was continuous in the first two years, clouds disappeared totally for ∼85° of LS (LS=188°-275°) due to the dust storm. Elysium Mons cloud activity is similar to that of Olympus Mons, however the peak in cloud area is near LS=130° rather than near LS=100°.  相似文献