Drilling in ancient permafrost on Mars for evidence of a second genesis of life     

H.D. Smith  C.P. McKay 《Planetary and Space Science》2005,53(12):1302-1308

If life ever existed on Mars, a key question is the genetic relationship of that life to life on Earth. To determine if Martian life represents a separate, second genesis of life requires the analysis of organisms, not fossils. Ancient permafrost on Mars represents one potential source of intact, albeit probably dead by radiation, Martian organisms. Strong crustal magnetism in the ancient heavily cratered southern highlands between 60 and 80°S and at about 180°W indicates what may be the oldest, best preserved ice-rich permafrost on Mars. Drilling to depths of 1000 m would reach samples unaffected by possible warming due to cyclic changes in Mars’ obliquity. When drilling into the permafrost to retrieve ancient intact Martian organisms, it is necessary to take special precautions to avoid the possibility of contamination. Earth permafrost provides an analog for Martian permafrost and convenient sites for instrument development and field testing.  相似文献   

Long-term evolution of orbits about a precessing oblate planet: 3. A semianalytical and a purely numerical approach     

Pini Gurfil  Valéry Lainey  Michael Efroimsky 《Celestial Mechanics and Dynamical Astronomy》2007,99(4):261-292

Construction of an accurate theory of orbits about a precessing and nutating oblate planet, in terms of osculating elements defined in a frame associated with the equator of date, was started in Efroimsky and Goldreich (2004) and Efroimsky (2004, 2005, 2006a, b). Here we continue this line of research by combining that analytical machinery with numerical tools. Our model includes three factors: the J ₂ of the planet, its nonuniform equinoctial precession described by the Colombo formalism, and the gravitational pull of the Sun. This semianalytical and seminumerical theory, based on the Lagrange planetary equations for the Keplerian elements, is then applied to Deimos on very long time scales (up to 1 billion years). In parallel with the said semianalytical theory for the Keplerian elements defined in the co-precessing equatorial frame, we have also carried out a completely independent, purely numerical, integration in a quasi-inertial Cartesian frame. The results agree to within fractions of a percent, thus demonstrating the applicability of our semianalytical model over long timescales. Another goal of this work was to make an independent check of whether the equinoctial-precession variations predicted for a rigid Mars by the Colombo model could have been sufficient to repel its moons away from the equator. An answer to this question, in combination with our knowledge of the current position of Phobos and Deimos, will help us to understand whether the Martian obliquity could have undergone the large changes ensuing from the said model (Ward 1973; Touma and Wisdom 1993, 1994; Laskar and Robutel 1993), or whether the changes ought to have been less intensive (Bills 2006; Paige et al. 2007). It has turned out that, for low initial inclinations, the orbit inclination reckoned from the precessing equator of date is subject only to small variations. This is an extension, to non-uniform equinoctial precession given by the Colombo model, of an old result obtained by Goldreich (1965) for the case of uniform precession and a low initial inclination. However, near-polar initial inclinations may exhibit considerable variations for up to ±10 deg in magnitude. This result is accentuated when the obliquity is large. Nevertheless, the analysis confirms that an oblate planet can, indeed, afford large variations of the equinoctial precession over hundreds of millions of years, without repelling its near-equatorial satellites away from the equator of date: the satellite inclination oscillates but does not show a secular increase. Nor does it show secular decrease, a fact that is relevant to the discussion of the possibility of high-inclination capture of Phobos and Deimos. We use the term “precession” in its general meaning, which includes any change of the instantaneous spin axis. So generally defined precession embraces the entire spectrum of spin-axis variations—from the polar wander and nutations through the Chandler wobble through the equinoctial precession.  相似文献   

四元数火星快车立体测绘影像光束法平差   总被引：2，自引：0，他引：2  

耿迅  徐青  邢帅  蓝朝桢  侯一凡 《测绘科学》2016,41(1):23-27,38

针对火星表面缺乏控制点数据、影像匹配难度大,使用传统欧拉角解算时收敛性难以保证的问题,该文提出基于四元数以及定向片模型的HRSC线阵影像光束法平差方法:基于SIFT特征提取算子并结合影像金字塔分层匹配策略设计连接点自动生成算法,并对火星表面多个地形区域进行了试验,结果表明:设计的连接点自动生成算法高效、实用,利用该方法可显著提高欧洲火星快车HRSC线阵影像的定位精度。  相似文献   

Kaolinite deposition from moving suspensions: The roles of flocculation,salinity, suspended sediment concentration and flow velocity/bed shear     

Juergen Schieber  Zhiyang Li  Zalmai Yawar  Xiaomeng Cao  Thomas Ashley  Ryan Wilson 《Sedimentology》2023,70(1):121-144

Understanding how mud moves and deposits is essential for conceptualizing the dynamic nature of surface environments and their ancient counterparts. Experimental study has largely been pursued by civil engineers, using kaolinite as an active ingredient. Yet, applying their data to the physical comprehension of mudstone sedimentology is hampered by multiple flume configurations between labs, and data sets tailored to specific engineering needs. The need for a better grasp of underlying processes is acute, given recent flume studies that show that moving suspensions form large bedload floccules, migrating floccule ripples and bed accretion under currents capable of moving sand grains. To advance mudstone sedimentology, integrated study of suspended sediment concentration, salinity and bed shear stress on the deposition of floccules is crucial. Described here is a set of tightly controlled experiments that explored suspended sediment concentrations from 70 to 900 mg/l, freshwater, brackish and marine salinities, flow velocities in the 5 to 50 cm/s range (equivalent to 0.01 to 0.58 Pa bed shear), measured the size of in-flow and bedload floccules, and the critical velocity of sedimentation that marks the onset of sustained bedload accumulation. The critical velocity of sedimentation of kaolinite clays is in the 26 to 28 cm/s flow velocity range (0.22 to 0.25 Pa), appears insensitive to a wide range of suspended sediment concentrations and salinities, and coincides with the formation of sand-size bedload floccules. Further decrease of flow velocity/bed shear stress is accompanied by a steady increase in the size of bedload floccules. Large bedload floccules appear to form in the high-shear basal part of the flow, a phenomenon requiring further investigation. Better understanding of the mechanisms that facilitate mud deposition from moving suspensions is critical for more realistic assessments of the depositional conditions of mud and mudstones, as well as for refining predictive models for the flux of fine-grained sediments across the Earth's surface.  相似文献   

On Potential Spectroscopic Detection of Microfossils on Mars     

Giuseppe A. Marzo  Romolo Politi  Armando Blanco  Rosario Brunetto  Sergio Fonti  Vincenzo Orofino 《Earth, Moon, and Planets》2007,101(3-4):127-140

There is much evidence about the ancient presence of water on Mars and it is reasonable to suppose that simple forms of life may have developed during the geological evolution of the planet. In such a case traces of this extinct life could still be present on the planet in form of microfossils included into some geological layer. The rover payloads planned for the next decades will include spectrometers in order to accomplish various scientific tasks. In this respect, we have developed a quantitative model for microfossil inclusions into a crystalline matrix. Such a method foresees some visible effects on measurements obtained via spectroscopic techniques such as infrared reflectance and Raman spectroscopy. In this work we present the quantitative model of the fossilization process and the effects that the microfossil inclusions should have in the real spectra, evaluated by means of computer simulations. Preliminary measurements, in order to provide examples of future model testing, have been performed on samples of homogeneous composition, but with detectable microfossils content, collected at the K–T sequence placed near Gubbio (Italy). The preliminary results are presented and discussed in order to investigate the potential application of such spectroscopic techniques for the detection of extinct life.  相似文献   

High spectral resolution UV to near-IR observations of Mars using HST/STIS     

J.F. Bell III  T.M. Ansty 《Icarus》2007,191(2):581-602

We acquired high spectral and spatial resolution hyperspectral imaging spectrometer observations of Mars from near-UV to near-IR wavelengths (∼300 to 1020 nm) using the STIS instrument on the Hubble Space Telescope during the 1999, 2001, and 2003 oppositions. The data sets have been calibrated to radiance factor (I/F) and map-projected for comparison to each other and to other Mars remote sensing measurements. We searched for and (where detected) mapped a variety of iron-bearing mineral signatures within the data. The strong and smooth increase in I/F from the near-UV to the visible that gives Mars its distinctive reddish color indicates that poorly crystalline ferric oxides dominate the spectral properties of the high albedo regions (as well as many intermediate and low albedo regions), a result consistent with previous remote sensing studies of Mars at these wavelengths. In the near-IR, low albedo regions with a negative spectral slope and/or a distinctive ∼900 nm absorption feature are consistent with, but not unique indicators of, the presence of high-Ca pyroxene or possibly olivine. Mixed ferric-ferrous minerals could also be responsible for the ∼900 nm feature, especially in higher albedo regions with a stronger visible spectral slope. We searched for the presence of several known diagnostic absorption features from the hydrated ferric sulfate mineral jarosite, but did not find any unique evidence for its occurrence at the spatial scale of our observations. We identified a UV contrast reversal in some dark region spectra: at wavelengths shorter than about 340 nm these regions are actually brighter than classical bright regions. This contrast reversal may be indicative of extremely “clean” low albedo surfaces having very little ferric dust contamination. Ratios between the same regions observed during the planet-encircling dust storm of 2001 and during much clearer atmospheric conditions in 2003 provide a good direct estimate of the UV to visible spectral characteristics of airborne dust aerosols. These HST observations can help support the calibration of current and future Mars orbital UV to near-IR spectrometers, and they also provide a dramatic demonstration that even at the highest spatial resolution possible to achieve from the Earth, spectral variations on Mars at these wavelengths are subtle at best.  相似文献   

A top-down origin for martian mantle plumes     

P. van Thienen  A. Rivoldini 《Icarus》2006,185(1):197-210

The two main volcanic centers on Mars, Tharsis and Elysium, are often interpreted in terms of mantle plume hotspots, even though there are several problems with the plume hypothesis for Mars. We present results of 2D cylindrical shell numerical mantle convection experiments in which we try to ascertain whether flushing of the hot lower mantle could provide a mechanism for the generation of a small number of plume-like features, i.e., localized upwelling of hot material. In this scenario the formation of hot upwellings is driven from the top by cold downwellings rather than from a hot thermal boundary layer at the CMB. First we construct a range of Mars interior structure models consistent with observations in order to demonstrate that the presence of a thin lower mantle in the martian interior is a viable scenario. Then we use a series of numerical convection experiments to investigate the effects of solid-state phase transitions, different stratified and temperature-dependent viscosity models, and the presence of a thick southern hemisphere crust on the operation of such a mechanism. Our results show that it is possible to generate hot strong localized upwellings from top-down dynamics if the lithosphere is thin or actively involved in the convective pattern. The presence of a thick, immobile, insulating southern hemisphere crust reduces the number of upwellings, and the perovskite phase transition causes a focusing of the upwellings. Further experiments demonstrate that an initial 500 Myr phase of mobile lid is sufficient to start this process create an upwelling which is stable for billions of years.  相似文献   

Description of the University of Auckland global Mars mesoscale meteorological model     

David R. Wing  Geoff L. Austin 《Icarus》2006,185(2):370-382

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Natural superrotation of a rarefied planetary atmosphere     

P. A. Bespalov  O. N. Savina 《Astronomy Letters》2003,29(1):50-57

We consider the kinetics of a rarefied rotating planetary atmosphere. The spatial distributions of the atmospheric-gas density and mean angular velocity were determined by analyzing the exact solution of the two-dimensional kinetic equation. We show that the angular velocity of the gas at some distance from the planet could be higher than that in the initial layer starting from which the atmosphere is rarefied. Our model calculations elucidate the superrotation mechanism under consideration.  相似文献   

Photochemistry of the martian atmosphere: Seasonal, latitudinal, and diurnal variations     

Vladimir A. Krasnopolsky 《Icarus》2006,185(1):153-170

There is a significant progress in the observational data relevant to Mars photochemistry in the current decade. These data are not covered by and sometimes disagree with the published models. Therefore we consider three types of models for Mars photochemistry. A steady-state model for global-mean conditions is currently the only way to calculate the abundances of long living species (H₂, O₂, and CO). However, our model does not fit the observed CO abundance using gas-phase chemistry and reasonable values of heterogeneous loss of odd hydrogen on the water ice aerosol. The second type of the calculated models is steady-state models for local conditions. The MGS/TES data on temperature profiles, H₂O, and dust are input parameters for these models. The calculations have been made for nine seasonal points spread over the martian year and for twelve latitudes with a step of 10° for each season. The only adopted heterogeneous reaction is a weak loss of H₂O₂ on water ice with probability of 5×¹⁰⁻⁴. The results are in good agreement with the recent observations of the O₂ dayglow at 1.27 μm and the O₃ and H₂O₂ abundances. Global maps of the seasonal and latitudinal behavior of these species have been made. The third type of models is a time-dependent model for local conditions. These models show that odd hydrogen quickly converts to H₂O₂ at the nighttime and the chemistry is switched off while the association of O, the heterogeneous loss of H₂O₂, and eddy diffusion continue. This requires significant changes in the global-mean and local steady-state models discussed above, and these changes have been properly done. The calculated diurnal variations of Mars photochemistry are discussed. The martian photochemistry at low and middle latitudes is significantly different in the aphelion period at LS=10°-130° from that in the remaining part of the year.  相似文献