Spectral evidence for zeolite in the dust on Mars     

Steven W. Ruff 《Icarus》2004,168(1):131-143

Spectral features observed in Mars Global Surveyor Thermal Emission Spectrometer data (∼1670-220 cm⁻¹) of martian surface dust provide clues to its mineralogy. An emissivity peak at ∼1630 cm⁻¹ is consistent with the presence of an H₂O-bearing mineral. This spectral feature can be mapped globally and shows a distribution related to the classical bright regions on Mars that are known to be dust covered. An important spectral feature at ∼830 cm⁻¹ present in a newly derived average spectrum of surface dust likely is a transparency feature arising from the fine particulate nature of the dust. Its shape and location are consistent with plagioclase feldspars and also zeolites, which essentially are the hydrous form of feldspar. The generally favored visible/near-infrared spectral analog for martian dust, JSC Mars-1 altered tephra, does not display the ∼830 cm⁻¹ feature. Zeolites commonly form from the interaction of low temperature aqueous fluids and volcanic glass in a variety of geologic settings. The combination of spectral features that are consistent with zeolites and the likelihood that Mars has (or had) geologic conditions necessary to produce them makes a strong case for recognizing zeolite minerals as likely components of the martian regolith.  相似文献   

Neutron Capture Isotopes in the Martian Regolith and Implications for Martian Atmospheric Noble Gases   总被引：1，自引：0，他引：1  

M.N. RaoD.D. Bogard  L.E. NyquistD.S. McKay  J. Masarik 《Icarus》2002,156(2):352-372

Impact-produced glasses in some martian meteorites have trapped significant amounts of the recent martian atmosphere. From literature data, we estimate that ∼9% of the trapped ⁸⁰Kr in these meteorites was produced from neutron capture on ⁷⁹Br. Estimates of neutron fluences made from ⁸⁰Kr and ¹⁴⁹Sm for bulk samples of meteorite EET79001 indicate that ⁸⁰Kr excesses in the impact glass were not produced in situ. Theoretical calculations independently predict production of a large neutron-capture component of ⁸⁰Kr and ³⁶Ar in the martian regolith, and part of this component presumably escaped into the martian atmosphere. These calculations were made by using the Los Alamos High-Energy Transport Code to calculate the fluxes of galactic cosmic ray (GCR)-produced thermal neutrons as a function of depth in the uppermost 500 g cm⁻² of the martian surface, and by adopting average Cl, Br, and I concentrations of the upper martian surface of ∼0.3%, ∼20 ppm, and ∼0.5 ppm, respectively. Combining these data with the appropriate neutron-capture cross sections, we calculate Mars global production rates of ⁸⁰Kr_n=2.4×10¹⁶atoms sec⁻¹, ³⁶Ar_n=5.5×10¹⁸ atoms sec⁻¹, and ¹²⁸Xe_n=3×10¹³ atoms sec⁻¹. Calculated global production rates of spallogenic ⁸⁰Kr_sp, and ³⁶Ar_sp, are smaller by factors of ∼770 and ∼29, respectively. It would require ∼330 Myr to produce an amount of ⁸⁰Kr_n equivalent to the amount inferred to be present today in the martian atmosphere (∼2.5×10³² atoms). Production of these neutron-capture components probably has occurred over the past ∼4 Gyr, as only an atmospheric pressure substantially higher than today's would appreciably decrease the neutron flux in the regolith. Thus, most of the neutron-capture noble gases produced over time probably remain in the martian regolith and would make sensitive indicators of the time period a sample has resided near the martian surface. Assuming mixing of the martian surface to an average depth of 100 m, the predicted average regolith concentrations of ⁸⁰Kr_n, ³⁶Ar_n, and ¹²⁸Xe_n are ∼4×10⁻⁹ cm⁻³ g⁻¹, ∼1×10⁻⁶ cm³ g⁻¹, and ∼5×10⁻¹² cm³ g⁻¹, respectively. If similar fractions of these neutron-capture isotopes have escaped into the atmosphere, they would comprise ∼3% and ∼0.2% of the present atmospheric inventories of ³⁶Ar and ¹²⁸Xe, respectively. The fractional excess of ⁸⁰Kr_n in ancient martian meteorite ALH84001 appears similar to that in shock-glass phases of young shergottite meteorites. If ALH84001 acquired its atmospheric gases ∼4 Gyr ago, this implies that, prior to that time, halogens were greatly concentrated at the martian surface by crustal formational and weathering processes, impacts efficiently degassed the regolith, and Mars did not have a significant atmosphere to shield the surface.  相似文献   

A model of interaction of Phobos’ surface with the martian environment     

F. Cipriani  F. Leblanc  R.E. Johnson 《Icarus》2011,212(2):643-648

We simulate space weathering of Phobos’ surface due to both sputtering by solar wind ions (H⁺ and He²⁺) and planetary protons, and surface material vaporization by micrometeoroids impact. Assuming an Iron-rich composition of Phobos’ regolith, we find that densities of neutral species (Fe, O, Al, Ca, Mg, Na) in the martian environment are in the range (10⁻⁴-10⁻¹ cm⁻³), and observe an ejecta disk with a radius of 6 martian radii in the equatorial plane and a thickness of 3 martian radii in the perpendicular plane. In order to determine the observability of such species from space based instruments, we also estimate their solar scattering emission line intensities. We conclude that Magnesium would be the only potential candidate suitable for spectral detection.  相似文献   

The nature of coarse-grained crystalline hematite and its implications for the early environment of Mars     

David C Catling  Jeffrey M Moore 《Icarus》2003,165(2):277-300

The Thermal Emission Spectrometer (TES) on the Mars Global Surveyor spacecraft has detected deposits of coarse-grained, gray crystalline hematite in Sinus Meridiani, Aram Chaos, and Vallis Marineris. We argue that the key to the origin of gray hematite is that it requires crystallization at temperatures in excess of about 100 °C. We discuss thermal crystallization (1) as diagenesis at a depth of a few kilometers of sediments originally formed in low-temperature waters, or (2) as precipitation from hydrothermal solution. In Aram Chaos, a combination of TES data, Mars Orbiter Camera images, and Mars Orbiter Laser Altimeter (MOLA) topography suggests that high concentrations of hematite were formed in planar strata and have since been exposed by erosion of an overlying light-toned, caprock. Lesser concentrations of hematite are found adjacent to these strata at lower elevations, which we interpret as perhaps due to accumulation from physical weathering. The topography and the collapsed nature of the chaotic terrain favor a hydrothermally charged aquifer as the original setting where the hematite formed. Concentration of iron into such an ore-like body would be chemically favored by saline, Cl-rich hydrothermal fluids. An alternative sedimentary origin requires post-depositional burial to a depth of ∼3-5 km to induce thermally driven recrystallization of fine-grained iron oxides to coarse-grained hematite. This depth of burial and re-exposure is difficult to reconcile with commonly inferred martian geological processes. However, shallow burial accompanied by post-burial hydrothermal activity remains plausible. When the hematite regions originally formed, redox balance requires that much hydrogen must have been evolved to complement the extensive oxidation. Finally, we suggest that the coexistence of several factors required to form the gray hematite deposits would have produced a favorable environment for primitive life on early Mars, if it ever existed. These factors include liquid water, abundant electron donors in the form of H₂, and abundant electron acceptors in the form of Fe³⁺.  相似文献   

Methane evolution from UV-irradiated spacecraft materials under simulated martian conditions: Implications for the Mars Science Laboratory (MSL) mission     

Andrew C. Schuerger  Christian Clausen 《Icarus》2011,213(1):393-403

Fifteen organic and three inorganic compounds were tested for methane (CH₄) evolution under simulated martian conditions of 6.9 mbar; UVC (200-280 nm) flux of 4 W m⁻²; 20 °C; simulated optical depth of 0.1; and a Mars gas composition of CO₂ (95.3%), N₂ (2.7%), Ar (1.7%), O₂ (0.13%), and water vapor (0.03%). All three inorganic compounds (i.e., NaCl, CaCO₃, graphite) failed to evolve methane at the minimum detection level 0.5 ppm, or above. In contrast, all organic compounds evolved methane when exposed to UV irradiation under simulated martian conditions. The polycyclic aromatic hydrocarbon, pyrene, released the most methane per unit of time at 0.175 nmol CH₄ g⁻¹ h⁻¹, and a spectral reflectance target material used for the MER rovers and Phoenix lander released the least methane at 0.00065 nmol CH₄ cm⁻² h⁻¹. Methane was also released from UV-killed bacterial endospores of Bacillus subtilis. Although all organic compounds evolved methane when irradiated with UV photons under martian conditions, the concentrations of residual organics, biogenic signature molecules, and dead microbial cells should be relatively low on the exterior surfaces of the MSL rover, and, thus, not significant sources of methane contamination. In contrast, kapton tape was found to evolve methane at the rate of 0.00165 nmol CH₄ cm⁻² h⁻¹ (16.5 nmol m⁻² h⁻¹) under the UV and martian conditions tested. Although the evolution of methane from kapton tape was found to decline over time, the large amount of kapton tape used on the MSL rover (lower bound estimated at 3 m²) is likely to create a significant source of terrestrial methane contamination during the early part of the mission.  相似文献   

The 390 cm feature of polycrystalline hematite—An optical crystallite size effect     

Thomas G. Mayerhöfer  Jürgen Popp 《Icarus》2009,203(1):303-384

The 390 cm⁻¹ spectral feature of polycrystalline hematite is shown to be caused by a crystallite size effect which is caused by the anisotropic nature of single crystalline hematite. This effect occurs if the probing light is able to resolve the heterogeneous nature of a polycrystalline material and if the corresponding single crystalline material is optically anisotropic. Therefore it does not depend on whether the material of interest is a powder or consolidated. As a consequence, the resulting macroscopic reflectance and transmittance of the polycrystalline material is an average of the microscopic reflectance and transmittance of the individual crystallites. Therefore, randomly oriented polycrystalline materials with large crystallites show characteristic changes in their spectral profile compared to the spectral profiles of polycrystalline materials consisting of crystallites that are small in comparison with the wavelength. The extent of the spectral changes depends on the degree of optical anisotropy of the corresponding single crystalline material. The spectral changes also comprise non-zero cross-polarization terms despite of random orientation. Therefore a characterization of a polycrystalline material with a scalar dielectric function is possible in general only if the material consists of randomly oriented crystallites small compared to the wavelength.  相似文献   

Minimum estimates of the amount and timing of gases released into the martian atmosphere from volcanic eruptions     

Robert A. Craddock  Ronald Greeley 《Icarus》2009,204(2):512-151

Volcanism has been a major process during most of the geologic history of Mars. Based on data collected from terrestrial basaltic eruptions, we assume that the volatile content of martian lavas was typically ∼0.5 wt.% water, ∼0.7 wt.% carbon dioxide, ∼0.14 wt.% sulfur dioxide, and contained several other important volatile constituents. From the geologic record of volcanism on Mars we find that during the late Noachian and through the Amazonian volcanic degassing contributed ∼0.8 bar to the martian atmosphere. Because most of the outgassing consisted of greenhouse gases (i.e., CO₂ and SO₂) warmer surface temperatures resulting from volcanic eruptions may have been possible. Our estimates suggest that ∼1.1 × 10²¹ g (∼8 ± 1 m m⁻²) of juvenile water were released by volcanism; slightly more than half the amount contained in the north polar cap and atmosphere. Estimates for released CO₂ (1.6 × 10²¹ g) suggests that a large reservoir of carbon dioxide is adsorbed in the martian regolith or alternatively ∼300 cm cm⁻² of carbonates may have formed, although these materials would not occur readily in the presence of excess SO₂. Up to ∼120 cm cm⁻² (2.2 × 10²⁰ g) of acid rain (H₂SO₄) may have precipitated onto the martian surface as the result of SO₂ degassing. The hydrogen flux resulting from volcanic outgassing may help explain the martian atmospheric D/H ratio. The amount of outgassed nitrogen (∼1.3 mbar) may also be capable of explaining the martian atmospheric ¹⁵N/¹⁴N ratio. Minor gas constituents (HF, HCl, and H₂S) could have formed hydroxyl salts on the surface resulting in the physical weathering of geologic materials. The amount of hydrogen fluoride emitted (1.82 × 10¹⁸ g) could be capable of dissolving a global layer of quartz sand ∼5 mm thick, possibly explaining why this mineral has not been positively identified in spectral observations. The estimates of volcanic outgassing presented here will be useful in understanding how the martian atmosphere evolved over time.  相似文献   

Hydrogen peroxide on Mars: evidence for spatial and seasonal variations     

Th Encrenaz  B Bézard  M.J Richter  S.K Atreya  S Lebonnois  F Forget 《Icarus》2004,170(2):424-429

Hydrogen peroxide (H₂O₂) has been suggested as a possible oxidizer of the martian surface. Photochemical models predict a mean column density in the range of 10¹⁵-10¹⁶ cm⁻². However, a stringent upper limit of the H₂O₂ abundance on Mars (9×10¹⁴ cm⁻²) was derived in February 2001 from ground-based infrared spectroscopy, at a time corresponding to a maximum water vapor abundance in the northern summer (30 pr. μm, Ls=112°). Here we report the detection of H₂O₂ on Mars in June 2003, and its mapping over the martian disk using the same technique, during the southern spring (Ls=206°) when the global water vapor abundance was ∼10 pr. μm. The spatial distribution of H₂O₂ shows a maximum in the morning around the sub-solar latitude. The mean H₂O₂ column density (6×10¹⁵ cm⁻²) is significantly greater than our previous upper limit, pointing to seasonal variations. Our new result is globally consistent with the predictions of photochemical models, and also with submillimeter ground-based measurements obtained in September 2003 (Ls=254°), averaged over the martian disk (Clancy et al., 2004, Icarus 168, 116-121).  相似文献   

Cassini CIRS update on stratospheric ices at Titan's winter pole     

Robert E. Samuelson  Michael D. Smith  John C. Pearl 《Icarus》2007,189(1):63-71

A strong, broad spectral emission feature at 85° N latitude centered at 221 cm⁻¹ remains unidentified after candidate ices of H₂O and pure crystalline CH₃CH₂CN are unambiguously ruled out. A much shallower weak emission feature starts at 160 cm⁻¹ and blends into the strong feature at ∼190 cm⁻¹. This feature is consistent with one formed by an HCN ice cloud composed of ?5 μm radius particles that resides in the lower stratosphere somewhere below an altitude of 160 km. Titan's stratospheric aerosol appears to have a spectral emission feature at about 148 cm⁻¹. The aerosol abundance at 85° N is about a factor 2.2 greater than at 55° S.  相似文献   

A new hematite formation mechanism for Mars     

Michelle E. MINITTI  Melissa D. LANE  Janice L. BISHOP 《Meteoritics & planetary science》2005,40(1):55-69

Abstract— The origin of hematite detected in Martian surface materials is commonly attributed to weathering processes or aqueous precipitation. Here, we present a new hematite formation mechanism that requires neither water nor weathering. Glass‐rich basalts with Martian meteorite‐like chemistry (high FeO, low Al₂O₃) oxidized at high (700 and 900 °C) temperatures in air and CO₂, respectively, form thin (<1 μm) hematite coatings on their outermost surfaces. Hematite is manifested macroscopically by development of magnetism and a gray, metallic sheen on the glass surface and microscopically by Fe enrichment at the glass surface observed in element maps. Visible and near‐infrared, thermal infrared, and Raman spectroscopy confirm that the Fe enrichment at the oxidized glass surfaces corresponds to hematite mineralization. Hematite formation on basaltic glass is enabled by a mechanism that induces migration of Fe²⁺ to the surface of an oxidizing glass and subsequent oxidation to form hematite. A natural example of the hematite formation mechanism is provided by a Hawaiian basalt hosting a gray, metallic sheen that corresponds to a thin hematite coating. Hematite coating development on the Hawaiian basalt demonstrates that Martian meteorite‐like FeO contents are not required for hematite coating formation on basalt glass and that such coatings form during initial extrusion of the glassy basalt flows. If gray hematite originating as coatings on glassy basalt flows is an important source of Martian hematite, which is feasible given the predominance of igneous features on Mars, then the requirement of water as an agent of hematite formation is eliminated.  相似文献   

Laboratory simulations of Mars aqueous geochemistry     

Mark A Bullock  Jeffrey M Moore 《Icarus》2004,170(2):404-423

We report on laboratory experiments in which we allowed an SNC-derived mineral mix to react with pure water under a simulated Mars atmosphere for 7 months. These experiments were performed at one bar and at three different temperatures in order to simulate the subsurface conditions that most likely exist where liquid water and rock interact on Mars today. The dominant cations dissolved in the solutions we produced, which may be characterized as dilute brines, are Ca²⁺, Mg²⁺, Al³⁺, and Na⁺, while the major anions are dissolved C, F⁻, SO²⁻₄ and Cl⁻. Typical solution pH was in the range of 4.2-6.0. Abundance patterns of elements in our synthetic sulfate-chloride brines are distinctly unlike those of terrestrial ocean water or continental waters, however, they are quite similar to those measured in the martian fines at the Mars Pathfinder and Viking 1 and 2 Landing sites. This suggests that salts present in the martian regolith may have formed over time as a result of the interaction of surface or subsurface liquid water with basalts in the presence of a martian atmosphere similar in composition to that of today. If most of the mobile surface layer was formed during the Noachian when erosion rates were much higher than at present, and if this layer is homogeneous in salt composition, the total amount of salt in the martian fines is approximately the same as in the Earth's oceans. The minimum quantity of circulating water necessary to deposit this amount of salt is approximately equivalent to a global layer 625 m deep.  相似文献   

Under the shadow of the Magellanic Bridge: A measurement of the extragalactic background at ∼ 0.7 keV     

Q.Daniel Wang  Ye Taisheng 《New Astronomy》1996,1(3):245-253

We measured the extragalactic 0.7 keV X-ray background by observing the X-ray shadow of a neutral gas cloud in the Magellanic Bridge region. Two ROSAT PSPC observations of total 104 ks were complemented by a detailed H I mapping of the cloud with both the Parkes 64 m telescope and the Australia Telescope Compact Array. From the detected anti-correlation between the observed background intensity and the H I column density of the cloud, we derived the unabsorbed extragalactic background intensity as ∼ 28 keV s⁻¹ cm⁻² keV⁻¹ sr⁻¹ at ∼ 0.7 keV. The 95% confidence lower limit 18 keV s⁻¹ cm⁻² keV⁻¹ sr⁻¹ is greater than the expected point-like source contribution ? 14 keV s⁻¹ cm⁻² keV⁻¹ sr⁻¹, constrained by the mean source spectrum together with the total background intensity in the 1-2 keV band. A significant fraction of the 0.7 keV background likely arises in a diffuse hot intergalactic medium of a few million degrees, as has been predicted in hydrodynamic simulations of cosmological structure formation.Richard McCray  相似文献   

Midinfrared spectra and optical constants of bulk hematite: Comparison with particulate hematite spectra     

A.C. Marra  M.D. Lane  A. Blanco 《Icarus》2011,211(1):839-848

Hematite is an iron oxide that is very important for the study of climatic evolution of Mars. It can occur in three forms: nanophase (dark purple), fine-grained (red) and coarse-grained (gray).In a previous work, we studied the influence of particle size and shape on the infrared spectra (in the wavelength range 6.25-50 μm) of submicron red hematite particles and found that bulk optical constants did not fit the spectra of very fine particles with several classes of models.In the present paper, we derive bulk optical constants of a sample of the same parent material of hematite already used in a previous work in order to determine the particulate optical constants. As a first result we find that, also in this case, bulk and particulate optical constants are different from each other. Furthermore, we show that these bulk optical constants, although derived starting from the same parent material of hematite and used with a model adopting the laboratory measured grain size distribution of the sample, cannot be used to reproduce the spectra of submicron particles. Our results can help the scientific community to appropriately model the contribution of hematite submicron grains to the martian dust for a better understanding of the geologic evolution of the planet.  相似文献   

Condensation in Titan's stratosphere during polar winter     

R. de Kok  P.G.J. Irwin  N.A. Teanby 《Icarus》2008,197(2):572-578

In Titan's north polar region stratospheric clouds are expected to form due to a combination of low temperatures and downward motion of volatile-enriched air. Here we investigate possible sources of stratospheric clouds at Titan's pole using data from the Cassini Composite Infrared Spectrometer and a simple condensation model. An upper limit for C₄N₂ gas was determined to be 9×¹⁰⁻⁹, which is less than required to make the C₄N₂ cloud at the Voyager epoch. Hence, the presence of this cloud after equinox remains a mystery. The largest cloud seen in far-infrared spectra has a feature around 220 cm⁻¹ and is located around an altitude of 140 km. The upper limit for propionitrile (C₂H₅CN) gas shows that the feature around 220 cm⁻¹ is probably not due to pure propionitrile ice. Instead, our model calculations show that HCN should cause by far the largest cloud around 140 km. We therefore propose that HCN ice plays an important role in the formation of the massive polar cloud, because of the unavailability of sufficient condensable gas other than HCN to produce a strong enough condensate feature. However, the signature at 220 cm⁻¹ is not consistent with that of pure HCN ice at 172 cm⁻¹ and mixing of HCN ice with other ices, or chemical alteration of HCN ice might mask the HCN ice signature.  相似文献   

Planetary Bioresources and Astroecology: 1. Planetary Microcosm Bioassays of Martian and Carbonaceous Chondrite Materials: Nutrients, Electrolyte Solutions, and Algal and Plant Responses     

Michael N. Mautner 《Icarus》2002,158(1):72-86

The biological fertilities of planetary materials can be assessed using microcosms based on meteorites. This study applies microcosm tests to martian meteorites and analogues and to carbonaceous chondrites. The biological fertilities of these materials are rated based on the soluble electrolyte nutrients, the growth of mesophile and cold-tolerant algae, and plant tissue cultures. The results show that the meteorites, in particular the Murchison CM2 carbonaceous chondrite and DaG 476 martian shergottite, contain high levels of water-extractable Ca, Mg, and SO₄-S. The martian meteorites DaG 476 and EETA 79001 also contain higher levels of extractable essential nutrients NO₃-N (0.013-0.017 g kg⁻¹) and PO₄-P (0.019-0.046 g kg⁻¹) than the terrestrial analogues. The yields of most of the water-extractable electrolytes vary only by factors of 2-3 under a wide range of planetary conditions. However, the long-term extractable phosphate increases significantly under a CO₂ atmosphere. The biological yields of algae and plant tissue cultures correlate with extractable NO₃-N and PO₄-P, identifying these as the limiting nutrients. Mesophilic algae and Asparagus officinalis cultures are identified as useful bioassay agents. A fertility rating system based on microcosm tests is proposed. The results rate the fertilities in the order martian basalts > terrestrial basalt, agricultural soil > carbonaceous chondrites, lava ash > cumulate igneous rock. The results demonstrate the application of planetary microcosms in experimental astroecology to rate planetary materials as targets for astrobiology exploration and as potential space bioresources. For example, the extractable materials in Murchison suggest that concentrated internal solutions in carbonaceous asteroids (3.8 mol L⁻¹ electrolytes and 10 g L⁻¹ organics) can support and disperse microorganisms introduced by natural or directed panspermia in early solar systems. The results also suggest that carbonaceous asteroids and martian basalts can serve as potential future resources for substantial biological populations in the Solar System.  相似文献   

Titan’s atmosphere from ISO mid-infrared spectroscopy     

Athena Coustenis  A Salama  S Ott  T.h Encrenaz  H Feuchtgruber 《Icarus》2003,161(2):383-403

We have analyzed Titan observations performed by the Infrared Space Observatory (ISO) in the range 7-30 μm. The spectra obtained by three of the instruments on board the mission (the short wavelength spectrometer, the photometer, and the camera) were combined to provide new and more precise thermal and compositional knowledge of Titan’s stratosphere. With the high spectral resolution achieved by the SWS (much higher than that of the Voyager 1 IRIS spectrometer), we were able to detect and separate the contributions of most of the atmospheric gases present on Titan and to determine disk-averaged mole fractions. We have also tested existing vertical distributions for C₂H₂, HCN, C₂H₆, and CO₂ and inferred some information on the abundance of the first species as a function of altitude. From the CH₃D band at 1161 cm⁻¹ and for a CH₄ mole fraction assumed to be 1.9% in Titan’s stratosphere, we have obtained the monodeuterated methane-averaged abundance and retrieved a D/H isotopic ratio of 8.7−1.9+3.2 × 10⁻⁵. We discuss the implications of this value with respect to current evolutionary scenarios for Titan. The ν₅ band of HC₃N at 663 cm⁻¹ was observed for the first time in a disk-averaged spectrum. We have also obtained a first tentative detection of benzene at 674 cm⁻¹, where the fit of the ISO/SWS spectrum at R = 1980 is significantly improved when a constant mean mole fraction of 4 × 10⁻¹⁰ of C₆H₆ is incorporated into the atmospheric model. This corresponds to a column density of ∼ 2 × 10¹⁵ molecules cm⁻² above the 30-mbar level. We have also tested available vertical profiles for HC₃N and C₆H₆ and adjusted them to fit the data. Finally, we have inferred upper limits of a few 10⁻¹⁰ for a number of molecules proposed as likely candidates on Titan (such as allene, acetonitrile, propionitrile, and other more complex gases).  相似文献   

The Unusual Absorption Line Spectrum of Quasar SDSS J2220+0109     

Ji Tuo  Zhou Hong-yan  Wang Ting-gui  Wang Hui-yuan 《Chinese Astronomy and Astrophysics》2013

We report the Balmer broad absorption lines (BALs) in the quasar SDSS J2220 + 0109 discovered from the SDSS data, and present a detailed analysis of the peculiar absorption line spectrum, including the He I* multiplet at λλ3189, 3889 arising from the metastable 2³s-state helium and the Balmer Hα and Hβ lines from the excited hydrogen H I of n = 2 level, which are rarely seen in quasar spectra, as well as many absorption lines arising from the excited Fe II* of the levels 7 955 cm⁻¹, 13 474 cm⁻¹ and 13 673 cm⁻¹ in the wavelength range 3100∼3300 Å. Ca II H, K absorption line doublets also clearly appear in the SDSS spectrum. All absorption lines show a similar blueshifted velocity structure of Δv ≈ − 1500 ∼ 0 km·s⁻¹ relative to the quasar's systematic redshift determined from the emission lines. Detailed analysis suggests that the Balmer absorption lines should arise from the partially ionized region with a column density of N_HI ≈ 10²¹ cm⁻² for an electron density of ne ∼ 10⁶ cm⁻³; and that the hydrogen n = 2 level may be populated via collisional excitation with Lyα pumping.  相似文献   

Low energy atmospheric gamma rays near geomagnetic equator     

K. KasturiranganU.R. Rao  P.D. Bhavsar 《Planetary and Space Science》1972

Based on the results from three balloon flights, made at Hyderabad(7.6°N geomagnetic latitude) using omnidirectional gamma ray spectrometers, the different aspects of the low energy atmospheric gamma rays at equatorial latitudes in the energy interval 100 keV to 1 MeV are investigated and detailed discussion is presented. The energy loss spectrum in this energy range is found to consist of a continuum superimposed on which is a photopeak due to 0.51 MeV line arising from electron positron annihilation. The continuous background spectrum is similar to that observed at mid and high latitudes. The intensity of 0.51 MeV line is estimated to be 0.079 ± 0.01 photons cm⁻² sec⁻¹ at 6 g cm⁻² over Hyderabad and the altitude dependence of its intensity is established for this low latitude station. The latitude effect of the intensity of this line at 6 g cm⁻² is derived for the first time by comparing the results of the present measurements with those available for mid and high latitudes. The contribution of the cosmic gamma rays to the observed count rates at 6 g cm⁻² is shown to be negligible in the case of the omnidirectional spectrometers of the type used in the present observations even for low latitude stations.  相似文献   

Geological features indicative of processes related to the hematite formation in Meridiani Planum and Aram Chaos, Mars: a comparison with diagenetic hematite deposits in southern Utah, USA     

Jens Ormö  Goro Komatsu  Brenda Beitler 《Icarus》2004,171(2):295-316

In order to understand the formation of the few but large, hematite deposits on Mars, comparisons are often made with terrestrial hematite occurrences. In southern Utah, hematite concretions have formed within continental sandstones and are exposed as extensive weathered-out beds. The hematite deposits are linked to geological and geomorphological features such as knobs, buttes, bleached beds, fractures and rings. These terrestrial features are visible in aerial and satellite images, which enables a comparison with similar features occurring extensively in the martian hematite-rich areas. The combination of processes involved in the movement and precipitation of iron in southern Utah can provide new insights in the context of the hematite formation on Mars. Here we present a mapping of the analogue geological and geomorphological features in parts of Meridiani Planum and Aram Chaos. Based on mapping comparisons with the Utah occurrences, we present models for the formation of the martian analogues, as well as a model for iron transport and precipitation on Mars. Following the Utah model, high albedo layers and rings in the mapped area on Mars are due to removal or lack of iron, and precipitation of secondary diagenetic minerals as fluids moved up along fractures and permeable materials. Hematite was precipitated intraformationally where the fluid transporting the reduced iron met oxidizing conditions. Our study shows that certain geological/geomorphological features can be linked to the hematite formation on Mars and that pH differences could suffice for the transport of the iron from an orthopyroxene volcanoclastic source rock. The presence of organic compounds can enhance the iron mobilization and precipitation processes. Continued studies will focus on possible influence of biological activity and/or methane in the formation of the hematite concretions in Utah and on Mars.  相似文献   

A potentially new type of nonchondritic interplanetary dust particle with hematite,organic carbon,amorphous Na,Ca‐aluminosilicate,and FeO‐spheres     

Guillermo M. MUÑOZ CARO  Frans J. M. RIETMEIJER  Virginia SOUZA‐EGIPSY  Maria Pilar VALLES‐GONZÁLEZ 《Meteoritics & planetary science》2012,47(2):248-261

Abstract– We used a combination of different analytical techniques to study particle W7190‐D12 using microinfrared spectroscopy, micro‐Raman spectroscopy, and field emission scanning electron microscopy (FESEM) energy dispersive X‐ray spectroscopy (EDS). The particle consists mainly of hematite (α‐Fe₂O₃) with considerable variations in structural disorder. It further contains amorphous (Na,K)‐bearing Ca,Al‐silicate and organic carbon. Iron‐bearing spherules (<150 nm in diameter) cover the surface of this particle. At local sites of structural disorder at the hematite surface, the hematite spheres were reduced to FeO in the presence of organic carbons forming FeO‐spheres. However, metallic Fe spheres cannot be excluded based on the available data. To the best of our knowledge, this particle is the first detection of such spherules at the surface of a stratospheric dust particle. Although there is no definitive evidence for an extraterrestrial origin of particle W7190‐D12, we suggest that it could be an IDP that had moved away from the asteroid‐forming region of the early solar system into the outer solar system of the accreting Kuiper Belt objects. After it was released from a Jupiter family comet, this particle became part of the zodiacal cloud. Atmospheric entry flash‐heating caused (1) the formation of microenvironments of reduced iron oxide when indigenous carbon materials reacted with hematite covering its surface resulting in the formation of FeO‐spheres and (2) Na‐loss from Na,Al‐plagioclase. The particle of this study, and other similar particles on this collector, may represent a potentially new type of nonchondritic IDPs associated with Jupiter family comets, although an origin in the asteroid belt cannot be ignored.  相似文献