Interstellar water in meteorites?   总被引：1，自引：0，他引：1  

Deloule E  Robert F 《Geochimica et cosmochimica acta》1995,59(22):4695-4706

D/H ratios of two meteorites (Renazzo CR and Semarkona LL3), which are known to exhibit the largest departures from the terrestrial hydrogen isotopic ratios, have been determined with the CRPG Nancy ion microprobe. Correlations between the D/H ratios and the chemical compositions (H2O, K, Si, C/H) of plausible hydrogen carriers were observed. From these correlations, it is possible to show that, contrary to previous interpretations, phyllosilicates are the carriers of the deuterium-rich hydrogen in Semarkona and Renazzo: 870 x 10(-6) > or = D/H > or = 670 x 10(-6) (+4600 > or = deltaD > or = 3300%) and > or = 320 x 10(-6) (deltaD > or = 1050%), respectively. Hydrogen is also present in the chondrules of these two deuterium-rich meteorites. The large differences in D/H ratios between matrix (up to 700 x 10(-6), deltaD up to +3500%) and chondrules (from 120 x 10(-6) (deltaD = -230%) to 230 x 10(-6) (deltaD = +475%)) show that hydrogen in chondrules cannot originate from the matrix by simple contamination or diffusion processes. The high D/H ratios measured in water-bearing minerals could not have been produced thermally within a dense solar nebula. Chemical reactions (i.e., involving ions or radicals), taking place in interstellar space or in the outer regions of the nebula at 110-140K are presently the only conceivable mechanisms capable of yielding such isotopic enrichments. Water in these meteorites should no longer be considered as a simple product of nebular condensation under equilibrium thermodynamic conditions at T > or = 160K.  相似文献   

Rejuvenation of Lake Erie     

Robert A. Sweeney 《GeoJournal》1995,35(1):65-66

The positive ecological changes that have occurred in Lake Erie since the mid-1970, demonstrate that an extensively degraded aquatic ecosystem can be rejuventated. This rejuvenation should provide encouragement to other who are attempting to save such habitats as the Aral Sea. This paper summarizes the problems of Lake Erie, the meassures instituted to correct the problems and the result of remediation efforts.  相似文献   

On the use of ‘first spotless day’ as a predictor for sunspot minimum     

Robert M. Wilson 《Solar physics》1995,158(1):197-204

Defining the first spotless day of a sunspot cycle as the first day without spots relative to sunspot maximum during the decline of the solar cycle, one finds that the timing of that occurrence can be used as a predictor for the occurrence of solar minimum of the following cycle. For cycle 22, the first spotless day occurred in April 1994, based on the International sunspot number index, although other indices (Boulder and American) indicated the first spotless day to have occurred earlier (September 1993). For cycles 9–14, sunspot minimum followed the first spotless day by about 72 months, having a range of 62–82 months; for cycles 15–21, sunspot minimum followed the first spotless day by about 35 months, having a range of 27–40 months. Similarly, the timing of first spotless day relative to sunspot minimum and maximum for the same cycle reveals that it followed minimum (maximum) by about 69 (18) months during cycles 9–14 and by about 90 (44) months during cycles 15–21. Accepting April 1994 as the month of first spotless day occurrence for cycle 22, one finds that it occurred 91 months into the cycle and 57 months following sunspot maximum. Such values indicate that its behavior more closely matches that found for cycles 15–21 rather than for cycles 9–14. Therefore, one infers that sunspot minimum for cycle 23 will occur in about 2–3 years, or about April 1996 to April 1997. Accepting the earlier date of first spotless day occurrence indicates that sunspot minimum for cycle 23 could come several months earlier, perhaps late 1995.The U.S. Government right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledged.  相似文献   

The solar surface differential rotation from disk-integrated chromospheric fluxes     

Robert A. Donahue  Steven L. Keil 《Solar physics》1995,159(1):53-62

Disk-integrated solar chromospheric Caii K-line (3933.68 ) fluxes have been measured almost daily at Sacramento Peak Observatory since 1977. Using observing windows selected to mimic seasonal windows for chromospheric measurements of lower Main-Sequence stars such as those observed by Mount Wilson Observatory's HK Project, we have measured the solar rotation from the modulation of the Caii K-line flux. We track the change of rotation period from the decline of cycle 21 through the maximum of cycle 22. This variation in rotation period is shown to behave as expected from the migration of active regions in latitude according to Maunder's butterfly diagram, including an abrupt change in rotation period at the transition from cycle 21 to cycle 22. These results indicate the successful detection of solar surface differential rotation from disk-integrated observations. We argue that the success of our study compared to previous investigations of the solar surface differential rotation from disk-integrated fluxes lies primarily with the choice of the length of the time-series window. Our selection of 200 days is shorter than in previous studies whose windows are typically on the order of one year. The 200-day window is long enough to permit an accurate determination of the rotation period, yet short enough to avoid complications arising from active region evolution. Thus, measurements of the variation of rotation period in lower Main-Sequence stars, especially those that appear to be correlated with long-term changes in chromospheric activity (i.e., cycles), are probably evidence for stellar surface differential rotation.  相似文献   

Evaluating the mobility of137Cs,239+240Pu and210Pb from their distributions in laminated lake sediments   总被引：1，自引：0，他引：1  

John Crusius  Robert F. Anderson 《Journal of Paleolimnology》1995,13(2):119-141

Post-depositional mobility of¹³⁷Cs,^239+240Pu and²¹⁰Pb was assessed in six small lake basins by comparing sedimentary nuclide profiles with their known fallout history. Laminae couplets, when present, were determined to be varves because the¹³⁷Cs and^239+240Pu 1963 fallout peaks are present in laminae couplets corresponding to years 1962–1964. There is no evidence of mobility of²¹⁰Pb, because 1) mass accumulation rates based on²¹⁰Pb agree with those based on¹³⁷Cs and^239+240Pu peak depths and with those based on varve counts, and 2)²¹⁰Pb ages agree with varve ages. Significant mobility of¹³⁷Cs is evident from the penetration of¹³⁷Cs to depths 15–20 cm deeper than^239+240Pu. Deep penetration of¹³⁷Cs in spite of a sharp gradient below the peak is interpreted by a numerical model to suggest that¹³⁷Cs is present in two distinct forms in these sediments, 67–82% as an immobile form and 18–33% reversibly adsorbed with a K _d of approximately 5000. The profiles can be interpreted equally well assuming a small portionof the total¹³⁷Cs was present as an extremely mobile phase (K _d 5000) in the months to years following peak fallout, slowly becoming more strongly adsorbed. High NH ₄ ⁺ concentrations in porewaters may enhance diffusion of the mobile form of¹³⁷Cs, but not of the immobile form of¹³⁷Cs that defines the sharp gradient. Mobility of¹³⁷Cs is likely also enhanced by the low clay content and the high porosity of these sediments. Thus the first detection of¹³⁷Cs in the sediments cannot automatically be assumed to correspond to a date of 1952 (initial testing of thermonuclear weapons), although the depth of the peak can be assumed to correspond to 1963 (the year of maximum fallout from testing of thermonuclear weapons).^239+240Pu is a more reliable sediment chronometer than¹³⁷Cs because it is significantly less mobile.This is the sixth of a series of papers to be published by this journal following the 20 ^th anniversary of the first application of²¹⁰Pb dating of lake sediments. Dr P.G. Appleby is guest editing this series.  相似文献   

Cosmic ray ionization of the Jovian atmosphere     

Louis A. Capone  John Dubach  Robert C. Whitten  Sheo S. Prasad 《Icarus》1979,39(3):433-449

An approximate form of the Boltzmann equation has been used to obtain local ionization rates due to the absorption of galactic cosmic rays in the Jovian atmosphere. It is shown that the muon flux component of the cosmic ray-induced cascade may be especially importannt in ionizing the atmosphere at levels where the total number density exceeds 10¹⁹ cm^?3 (well below the ionospheric layers produced by solar euv). A model containing both positive and negative ion reactions has been employed to compute equilibrium electron and ion number densities. Peak electron number densities on the order of 10³ cm^?3 may be expected even at relatively low magnetic latitudes. The dominant positive ions are NH₄⁺ and C_nH_m⁺ cluster ions, with n ? 2; it is suggested that the absorption of galactic cosmic ray energy at such relatively high pressures in the Jovian atmosphere $\text{(M ? 10}{}^{18}\text{to}\text{10}{}^{20}\text{cm}{}^{\mathrm{?3}}\text{)}$ and the subsequent chemical reactions may be instrumental in the local formation of complex hydrocarbons.  相似文献   

Spectral reflectance change and luminescence of selected salts during 2–10 KeV proton bombardment: Implications for Io     

Robert M. Nelson  Douglas B. Nash 《Icarus》1979,39(2):277-285

Radiation damage and luminescence, caused by magnetospheric charged particles, have been suggested by several authors as mechanisms for explaining some of the peculiar spectral/albedo features of Io. We have pursued this possibility by measuring the uv-visual spectral reflectance and luminescent efficiency of several proposed Io surface constituents during 2 to 10-keV proton irradiation at room temperature and at low temperature (120 < T < 140°K). The spectral reflectance of NaCl and KCl during proton irradiation exhibits the well-known F-center absorption bands at 4580 and 5560 Å. Na₂SO₄ shows a generalized darkening which increases toward longer wavelengths. NaNO₃ shows a spectral reflectance change indicative of the partial alteration of NaNo₃ to NaNo₂. NaNO₂ shows no change. The luminescent efficiencies of NaCl and KCl are ～10^?4 at 300°K and increase by one-half order of magnitude at ～130°K. The efficiencies of K₂CO₃, Na₂CO₃, Na₂SO₄, and NaNO₃ are 10^?4, 10^?4, 10^?5 and 10^?6, respectively, at 300°K and they all decrease by one-half order of magnitude at ～130°K. These results indicate that magnetospheric proton irradiation of Io could cause spectral features in its observed ultraviolet and visible reflection spectrum if salts such as those studied here are present on its surface. However, because the magnitude of these spectral effects is dependent on competing factors such as surface temperature, incident particle energy flux, solar bleaching effects, and trace element abundance, we are unable at this time to make a quantitative estimate of the strength of these spectral effects on Io. The luminescent efficiencies of pure samples that we have studied in the laboratory suggest that charged-particle induced luminescence from Io's surface might be observable by a spacecraft such as Voyager when viewing Io's dark side.  相似文献   

Spectropolarimetry of the methane and ammonia bands of Jupiter between 6800 and 8200 Å     

Ramon D. Wolstencroft  Robert J. Smith 《Icarus》1979,38(2):155-165

Spectropolarimetry of Jupiter at resolutions between 22 and 35 Å reveals a strong increase of linear polarization in the 7250-$\text{A}\text{?}$ CH₄ band. This is very probably due to the decreasing contribution toward the band center of the higher orders of scattering, which have a smaller net polarization than the first few orders. The linear polarization is also enhanced in the band at 7900 $\text{A}\text{?}$ comprising the 7920-$\text{A}\text{?}$ NH₃ and 7600- to 8200-$\text{A}\text{?}$ CH₄ bands. The normalized circular polarization shows a feature at 7250 $\text{A}\text{?}$ with a dispersion shape. This is most probably produced in a double-scattering process involving either a solid or liquid aerosol with an absorption at 7250 $\text{A}\text{?}$. Methane aerosols, the obvious candidates from a spectroscopic point of view, are, however, forbidden if current estimates of the Jovian atmospheric temperature are correct.  相似文献   

An improved transformation-elimination technique for the solution of perturbed Hamiltonian systems     

Robert A. Howland Jr. 《Celestial Mechanics and Dynamical Astronomy》1979,19(1):95-110

A Lie transformation technique proposed by the author (1977) utilizing an approach due to Kolmogorov and Arnol'd is modified to eliminate the calculation of unproductive terms. Special features of the original method — the ability to eliminate simultaneously both short- and long-period terms, and [formal] quadratic convergence for non-degenerate system sand nearly quadratic convergence for degenerate systems—are retained in an even more efficient technique. Comparisons of the new method with other available Lie transform techniques is made.  相似文献   

A search for natural or artificial objects located at the Earth-Moon libration points     

Robert A. Freitas  Francisco Valdes 《Icarus》1980,42(3):442-447

Photographs in the vicinity of the Earth-Moon triangular libration points L4 and L5, and of the solar-synchronized positions in the associated halo orbits (A. A. Kamel, 1969, Ph.D. dissertation, Stanford University), were made during August–September 1979, using the 30-in Cassegrain telescope at Leuschner Observatory, Lafayette, California. An effective 2° square field was covered at each position. No discrete objects, either natural or artificial, were found. The detection limit was about 14th magnitude. The present work extends traditional SETI observations to include the search for interstellar probes (R. A. Freitas, Jr., 1980a, J. Brit. Interplanet. Soc.33, 95–100).  相似文献