Boron isotopes as an artificial tracer     

Quast KW  Lansey K  Arnold R  Bassett RL  Rincon M 《Ground water》2006,44(3):453-466

A field study was conducted using a combination of intrinsic and artificial tracers to estimate travel times and dilution during transport of infiltrate from a reclaimed water infiltration basin to nearby monitoring wells. A major study objective was to validate boric acid enriched in (10)B as an artificial tracer. Basin 10E at the Rio Hondo Spreading Grounds in Whittier, California, was the site of the test. The basin normally receives a mixture of treated municipal waste water, purchased State Project water, and local runoff from the San Gabriel River. Approximately 3.5 kg of (10)B-enriched boric acid was dispersed among 2.05 x 10(5) m(3) of basin water to initiate the experiment. The resultant median delta(11)B in the infiltration basin was -71 per thousand. Prior to tracer addition, the basin water had an intrinsic delta(11)B of +2 per thousand. Local monitoring wells that were used to assess travel times had delta(11)B values of +5 per thousand and +8 per thousand at the time of tracer addition. Analytic results supported an assumption that boron is conserved during ground water transport and that boron enriched in (10)B is a useful artificial tracer. Several intrinsic tracers were used to reinforce the boric acid tracer findings. These included stable isotopes of oxygen (delta(18)O) and hydrogen (deltaD), sulfate concentration, and the boron to chloride ratio. Xenon isotopes, (136)Xe and (124)Xe, also supported boron isotope results. Xenon isotopes were added to the recharge basin as dissolved gases by investigators from the Lawrence Livermore National Laboratory.  相似文献   

Thermal convection in the porous methane-soaked regolith of Titan: Investigation of stability     

Leszek Czechowski  Konrad Kossacki 《Icarus》2009,202(2):599-606

Titan is the only body, other than the Earth where liquid is present on the surface. In the present work we consider behavior of methane in the pores of Titan's regolith. Using numerical model we investigate quantitative conditions necessary for the onset of convection. We have found that the methane convection in Titan's regolith is possible. It can be expected in regions where the regolith has sufficiently high porosity, independently of the geothermal heat flux.  相似文献   

GETEMME—a mission to explore the Martian satellites and the fundamentals of solar system physics     

Jürgen Oberst  Valéry Lainey  Christophe Le Poncin-Lafitte  Veronique Dehant  Pascal Rosenblatt  Stephan Ulamec  Jens Biele  J?rn Spurmann  Ralph Kahle  Volker Klein  Ulrich Schreiber  Anja Schlicht  Nicolas Rambaux  Philippe Laurent  Beno?t Noyelles  Bernard Foulon  Alexander Zakharov  Leonid Gurvits  Denis Uchaev  Scott Murchie  Cheryl Reed  Slava G. Turyshev  Jesus Gil  Mariella Graziano  Konrad Willner  Kai Wickhusen  Andreas Pasewaldt  Marita W?hlisch  Harald Hoffmann 《Experimental Astronomy》2012,34(2):243-271

GETEMME (Gravity, Einstein??s Theory, and Exploration of the Martian Moons?? Environment), a mission which is being proposed in ESA??s Cosmic Vision program, shall be launched for Mars on a Soyuz Fregat in 2020. The spacecraft will initially rendezvous with Phobos and Deimos in order to carry out a comprehensive mapping and characterization of the two satellites and to deploy passive Laser retro-reflectors on their surfaces. In the second stage of the mission, the spacecraft will be transferred into a lower 1500-km Mars orbit, to carry out routine Laser range measurements to the reflectors on Phobos and Deimos. Also, asynchronous two-way Laser ranging measurements between the spacecraft and stations of the ILRS (International Laser Ranging Service) on Earth are foreseen. An onboard accelerometer will ensure a high accuracy for the spacecraft orbit determination. The inversion of all range and accelerometer data will allow us to determine or improve dramatically on a host of dynamic parameters of the Martian satellite system. From the complex motion and rotation of Phobos and Deimos we will obtain clues on internal structures and the origins of the satellites. Also, crucial data on the time-varying gravity field of Mars related to climate variation and internal structure will be obtained. Ranging measurements will also be essential to improve on several parameters in fundamental physics, such as the Post-Newtonian parameter ?? as well as time-rate changes of the gravitational constant and the Lense-Thirring effect. Measurements by GETEMME will firmly embed Mars and its satellites into the Solar System reference frame.  相似文献   

X-rays from Venus observed with Chandra     

Konrad Dennerl 《Planetary and Space Science》2008,56(10):1414-1423

X-ray observations of Venus are so challenging that the first detection of Venusian X-rays succeeded only in January 2001, with the Chandra satellite. The X-rays from Venus were found to result from fluorescent scattering of solar X-rays in the Venusian thermosphere. An additional component, caused by charge exchange of highly charged heavy ions in the solar wind with atoms in the Venusian exosphere, was suspected, but could not be unambiguously detected. This was hampered by the fact that the observation occurred during solar maximum, when the solar X-ray flux is highest. In order to investigate the presence of an additional charge exchange component, Venus was observed again in March 2006 and October 2007 with Chandra, taking advantage of the fact that the solar X-ray flux had decreased considerably on its way to solar minimum. In fact, these subsequent observations were able to show that also the Venusian exosphere is emitting X-rays, due to its interaction with the solar wind. Here an overview of all the existing X-ray observations of Venus is presented, including first results from the most recent one, which took place after the arrival of Venus Express, providing the first ever opportunity to combine a remote X-ray observation of a planetary exosphere with simultaneous in situ measurements of the solar wind.  相似文献   

Microlensing by cosmic strings     

Konrad Kuijken  Xavier Siemens  Tanmay Vachaspati 《Monthly notices of the Royal Astronomical Society》2008,384(1):161-164

We consider the signature and detectability of gravitational microlensing of distant quasars by cosmic strings. Because of the simple image configuration such events will have a characteristic lightcurve, in which a source would appear to brighten by exactly a factor of 2, before reverting to its original apparent brightness. We calculate the optical depth and event rate, and conclude that current predictions and limits on the total length of strings on the sky imply optical depths of ≲ 10⁻⁸ and event rates of fewer than one event per 10⁹ sources per year. Disregarding those predictions but replacing them with limits on the density of cosmic strings from the cosmic microwave background fluctuation spectrum, leaves only a small region of parameter space (in which the sky contains about 3 × 10⁵ strings with deficit angle of the order of 0.3 milli-seconds) for which a microlensing survey of exposure 10⁷ source years, spanning a 20–40-year period, might reveal the presence of cosmic strings.  相似文献   

Comet 9P/Tempel 1: Sublimation beneath the dust cover     

Konrad J. Kossacki  Slawomira Szutowicz 《Icarus》2008,195(2):705-724

In the current work we analyze properties of the dust mantle, its thickness and thermal conductivity, necessary to reproduce observed rate of water production of Comet 9P/Tempel 1. For this purpose we considered simplified shape of the comet nucleus approximated by the symmetric prolate ellipsoid with smooth surface. We have performed simulations, using models with dust mantle of the thickness either constant, but nonuniform (Model A), or evolving (Model B). The simulated profiles of water production versus time were compared with observations. In addition, we compared the calculated surface temperature with the real temperatures derived from IR observations (the Deep Impact mission). This new double-stage verification procedure, shows that our model A is a good representation for the nucleus of Comet Tempel 1. This indicates, that the dust mantle thickness should be nonuniform, but does not change significantly with time. We show, that reproducing observed high temperatures of the nucleus requires dust mantle, that is almost everywhere thick and has extremely low thermal inertia. The latter should be close to zero as already predicted by others. The agreement between the simulated and measured water production can be obtained when the dust is regionally thin and has the thermal inertia higher than average, according to our simulations about 100 W s^1/2 K⁻¹ m⁻². Such regions should be located in the south hemisphere of the nucleus.  相似文献   

Long-term monitoring of wall paintings affected by soluble salts   总被引：1，自引：0，他引：1  

Konrad?ZehnderEmail author 《Environmental Geology》2007,52(2):353-367

Long-term monitoring of wall paintings in historical monuments aims at clarifying involved decay processes and at the same time controlling effects of interventions for conservation. Monitored decay processes relate to the crystallisation of various salts – particularly of nitronatrite and gypsum – from hygroscopic solutions accumulated in the zone of ground moisture. The salts crystallise in response to climatic variations and other environmental changes. Measures for conservation such as protection from water infiltration, reduction of heating temperature and reduction of surface salt accumulation cause a significant slow-down but not a stop of decay. The particular dynamics and causes of remaining slow decay processes are described on three sites in Switzerland: the convent church of Müstair, the crypt in the cathedral of Basel and the crypt in the Grossmünster church of Zürich.  相似文献   

The Deformational Response of a Viscoelastic Solid Earth Model Coupled to a Thermomechanical Ice Sheet Model     

Hannes Konrad  Malte Thoma  Ingo Sasgen  Volker Klemann  Klaus Grosfeld  Dirk Barbi  Zdeněk Martinec 《Surveys in Geophysics》2014,35(6):1441-1458

We apply a coupled thermomechanical ice sheet—self-gravitating viscoelastic solid Earth model (SGVEM), allowing for the dynamic exchange of ice thickness and bedrock deformation, in order to investigate the effect of viscoelastic deformation on ice dynamics and vice versa. In a synthetic glaciation scenario, we investigate the interaction between the ice sheet and the solid Earth deformation, the glacial-isostatic adjustment (GIA), accounting for an atmospheric forcing depending on the ice sheet surface altitude. We compare the results from the coupled model to runs with the common elastic lithosphere/relaxing asthenosphere (ELRA) model, where the lithosphere is represented by a thin plate and the mantle relaxes with one characteristic relaxation time, as well as to a rigid Earth without any deformation. We find that the deformational behaviour of the SGVEM on ice dynamics (i.e. stored ice volume, ice thickness and velocity field) is comparable to the ELRA for an optimal choice of the parameters in steady state, but exhibits differences in the transient behaviour. Beyond the ice sheet, in the region of peripheral forebulge, the differences in the transient surface deformation between ELRA and SGVEM are substantial, demonstrating the inadequacy of the ELRA model for interpreting constraints on GIA in the periphery of the ice sheet, such as sea-level indicators and GPS uplift rates.  相似文献   

Comet 17P/Holmes: Possibility of a CO driven explosion     

Konrad J. Kossacki  Slawomira Szutowicz 《Icarus》2011,212(2):847-857

This work is a continuation of our previous paper about brightening of Comet 17P/Holmes (Kossacki, K.J., Szutowicz, S. [2010]. Icarus 207, 320–340). In that paper we presented results of simulations indicating that the nonuniform crystallization of amorphous water ice itself is probably not sufficient for an explosion. In the present work we investigate the possibility that the explosion is caused by a rapid sublimation of the CO ice leading to the rise of gas pressure above the tensile strength of the nucleus. We simulated evolution of a model nucleus in the orbit of Comet 17P/Holmes. The nucleus is composed of water ice, carbon monoxide ice and dust and has the shape of an elongated ellipsoid. The simulations include crystallization of amorphous ice in the nucleus, changes of the dust mantle thickness, and sublimation of the CO ice. In our model CO is mantling grains composed of dust and amorphous water ice. Orientation of the nuclear spin axis in space is the same as derived in Moreno et al. (Moreno, F., Ortiz, J.L., Santos-Sanz, P., Morales, N., Vidal-Nunez, M.J., Lara, L.M., Gutierrez, P.J. [2008]. Astrophys. J. 677, L63–L66) for Comet Holmes during recent brightening event. Hence, the angle between the orbital and the equatorial planes of the comet is I = 95°, and the cometocentric solar longitude at perihelion is Φ = 210°. The calculations are performed for the south pole being the sub-solar point close to time of the outburst. Our computations indicate, that the CO pressure within the comet nucleus can rise to high values. When the layer between the dust mantle and the crystallization front of the amorphous water ice is very fine grained, few microns in radius, the CO pressure within the nucleus can exceed 10 kPa. This value is the lowest estimate for the tensile strength of the nucleus of Comet Holmes (Reach, W.T., Vaubaillon, J., Lisse, C.M., Holloway, M., Rho, J. [2010]. Icarus 208, 276–292). Hence, when the gas pressure reaches this value the nucleus may explode.  相似文献   

The evolution of exposed ice in a fresh mid-latitude crater on Mars     

Konrad J. Kossacki  Ganna Portyankina 《Icarus》2011,211(1):195-206

Recent observations of the surface of Mars have shown several fresh mid-latitude craters. Some of these craters show exposed ice (Byrne, S. et al. [2009]. Science 325, 1674-1676.). In some craters, albedo of ice slowly decreases, while in others, it remains nearly constant. We attempt to determine influence of the regolith structure on the rate of sublimation of ice. For this purpose we performed numerical simulations describing evolution of the exposed ice in model craters located at middle latitudes.We consider a new model for the structure and evolution of the material at- and beneath the crater floors. In contrast to the previous study by Dundas and Byrne (Dundas, C.M., Byrne, S. [2010]. Icarus 206, 716-728.) we do not investigate sublimation of dirty ice, and the related formation of a sublimation lag. Instead, we consider sublimation of a pure ice layer on top of layered regolith. In our model the observed reflectivity decreases due to the sublimation-driven changes of the optical properties of thinning clean ice. This offers an alternative to the deposition of the dust embedded in ice (sublimation lag).We have shown that in our model among many parameters affecting ice sublimation rate, volumetric fraction of water ice in the subsurface beneath the crater has the strongest influence. Hence observed darkening of the ice patch on the crater floor might be sufficient to determine the content of water ice in the subsurface. Our calculations show that an albedo decrease of fresh ice patches in mid-latitude craters can be explained by either strong dust sedimentation or, if this is excluded, by sublimation of a thin layer of water ice from the regolith with large thermal inertia. This is consistent with a large volumetric fraction of water ice beneath the crater floor and contributes to evidence for an extended subsurface water reservoir on Mars.The overall conclusion of our work is that a thin post-impact surface ice coating over ice-rich ground beneath the crater floors is consistent with the observations.  相似文献