Dust ejection from planetary bodies by temperature gradients: Laboratory experiments

Laboratory experiments show that dusty bodies in a gaseous environment eject dust particles if they are illuminated. We find that even more intense dust eruptions occur when the light source is turned off. We attribute this to a compression of gas by thermal creep in response to the changing temperature gradients in the top dust layers. The effect is studied at a light flux of 13 kW/m² and 1 mbar ambient pressure. The effect is applicable to protoplanetary disks and Mars. In the inner part of protoplanetary disks, planetesimals can be eroded especially at the terminator of a rotating body. This leads to the production of dust which can then be transported towards the disk edge or the outer disk regions. The generated dust might constitute a significant fraction of the warm dust observed in extrasolar protoplanetary disks. We estimate erosion rates of about 1 kg s^?1 for 100 m parent bodies. The dust might also contribute to subsequent planetary growth in different locations or on existing protoplanets which are large enough not to be susceptible to particle loss by light induced ejection. Due to the ejections, planetesimals and smaller bodies will be accelerated or decelerated and drift outward or inward, respectively. The effect might also explain the entrainment of dust in dust devils on Mars, especially at high altitudes where gas drag alone might not be sufficient.     

The gaseous Halo of the Virgo Cluster Galaxy 45

Observations of the Virgo Cluster galaxy NGC 4569 in soft X-rays and in Hα reveal both an asymmetrically distributed hot gaseous halo and a giant filament of diffuse emission, respectively, extending from the same side of the disk, the latter one to at least 8.8 kpc. A deep longslit spectrum along the filament shows velocities systematically different from the systemic velocity of NGC 4569. With the inclination of the disk one can determine the Hα spur as a giant outflow in NGC 4569. This revised version was published online in August 2006 with corrections to the Cover Date.     

Tracing the star stream through M31 using planetary nebula kinematics

We present a possible orbit for the Southern Stream of stars in M31, which connects it to the Northern Spur. Support for this model comes from the dynamics of planetary nebulae (PNe) in the disc of M31: analysis of a new sample of 2611 PNe obtained using the Planetary Nebula Spectrograph reveals ∼20 objects with kinematics inconsistent with the normal components of the galaxy, but which lie at the right positions and velocities to connect the two photometric features via this orbit. The satellite galaxy M32 is coincident with the stream both in position and velocity, adding weight to the hypothesis that the stream comprises its tidal debris.     

The Allende multicompound chondrule (ACC)—Chondrule formation in a local super‐dense region of the early solar system

In Allende, a very complex compound chondrule (Allende compound chondrule; ACC) was found consisting of at least 16 subchondrules (14 siblings and 2 independents). Its overall texture can roughly be described as a barred olivine object (BO). The BO texture is similar in all siblings, but does not exist in the two independents, which appear as relatively compact olivine‐rich units. Because of secondary alteration of pristine Allende components and the ACC in particular, only limited predictions can be made concerning the original compositions of the colliding melt droplets. Based on textural and mineralogical characteristics, the siblings must have been formed on a very short time scale in a dense, local environment. This is also supported by oxygen isotope systematics showing similar compositions for all 16 subchondrules. Furthermore, the ACC subchondrules are isotopically distinct from typical Allende chondrules, indicating formation in or reaction with a more ¹⁶O‐poor reservoir. We modeled constraints on the particle density required at the ACC formation location, using textural, mineral‐chemical, and isotopic observations on this multicompound chondrule to define melt droplet collision conditions. In this context, we discuss the possible relationship between the formation of complex chondrules and the formation of macrochondrules and cluster chondrites. While macrochondrules may have formed under similar or related conditions as complex chondrules, cluster chondrites certainly require different formation conditions. Cluster chondrites represent a mixture of viscously deformed, seemingly young chondrules of different chemical and textural types and a population of older chondrules. Concerning the formation of ACC calculations suggest the existence of very local, kilometer‐sized, and super‐dense chondrule‐forming regions with extremely high solid‐to‐gas mass ratios of 1000 or more.     

On the polarization and anisotropy of solar X-radiation during flares

Starting from the idea that the electrons accelerated during a solar flare have originally a preferred direction, the angular distribution and the polarization of bremsstrahlung below 10 Å is calculated taking into account the influence of the magnetic field. The energy distribution of the nonthermal electrons is based on X-ray spectra measured by the Leicester group during flares in 1962 and 1967. In addition to the case of a fixed angle between the electron velocity and the magnetic field, an angular distribution of the form sin ⁿ is considered. The results may be used to test flare models. Recent measurements of the polarization of solar X-radiation yield the expected order of magnitude.Paper presented to the Int. Symp. on Solar-Terr. Phys., Leningrad, May 1970.     

Spectral and geological study of the sulfate-rich region of West Candor Chasma, Mars

Sulfates have been discovered by the OMEGA spectrometer in different locations of the planet Mars. They are strongly correlated to light toned layered deposits in the equatorial regions. West Candor Chasma is the canyon with the thickest stack of layers and one with the largest area covered by sulfates. A detailed study coupling mineralogy derived from OMEGA spectral data and geology derived from HRSC imager and other datasets leads to some straightforward issues. The monohydrated sulfate kieserite is found mainly over heavily eroded scarps of light toned material. It likely corresponds to a mineral present in the initial rock formed either during formation and diagenesis of sediments, or during hydrothermal alteration at depth, because it is typically found on outcrops that are eroded and steep. Polyhydrated sulfates, that match any Ca-, Na-, Fe-, or Mg-sulfates with more than one water molecule, are preferentially present on less eroded and darker outcrops than outcrops of kieserite. These variations can be the result of a diversity in the composition and/or of the rehydration of kieserite on surfaces with longer exposure. The latter possibility of rehydration in the current, or recent, atmosphere suggests the low surface temperatures preserve sulfates from desiccation, and, also can rehydrate part of them. Strong signatures of iron oxides are present on sulfate-rich scarps and at the base of layered deposits scarps. They are correlated with TES gray hematite signature and might correspond to iron oxides present in the rock as sand-size grains, or possibly larger concretions, that are eroded and transported down by gravity at the base of the scarp. Pyroxenes are present mainly on sand dunes in the low lying terrains. Pyroxene is strongly depleted or absent in the layered deposits. When mixed with kieserite, local observations favor a spatial mixing with dunes over layered deposits. Sulfates such as those detected in the studied area require the presence of liquid water to form by precipitation, either in an intermittent lacustrine environment or by hydrothermal fluid circulation. Both possibilities require the presence of sulfur-rich groundwater to explain fluid circulation. The elevation of the uppermost sulfate signatures suggests the presence of aquifers up to 2.5 km above datum, only 1 km below the plateau surface.     

Construction of three-phase data to model multiphase flow in porous media: Comparing an optimization approach to the finite element approach

Multiphase flow modelling is a major issue in the assessment of groundwater pollution. Three-phase flows are commonly governed by mathematical models that associate a pressure equation with two saturation equations. These equations involve a number of secondary variables that reflect the fluid behaviour in a porous medium. To improve the computational efficiency of multiphase flow simulators, several simplified reformulations of three-phase flow equations have been proposed. However, they require the construction of new secondary variables adapted to the reformulated flow equations. In this article, two different approaches are compared to quantify these variables. A numerical example is given for a typical fine sand.     

Die alpidischen Stockwerke der südlichen Ägäis

Zusammenfassung Im Bereich der südlichen Ägäis überlagern vier allochthone Stockwerke den autochthonen Plattenkalk (Perm-Oligozän). Die allochthonen Serien entstammen ursprünglich konzentrisch angeordneten mesozoisch-alttertiären Faziesräumen der zentralen Ägäis. Die tektonische Abfolge aus neritischen Karbonaten, pelagischen Karbonaten und einem vulkano-sedimentären Komplex, die durch inkompetente Zwischenmittel (Mélange) getrennt werden, besteht über den gesamten Bogen. Fazielle und stratigraphische Merkmale sowie die Art der Deformation ermöglichen die Korrelation der Teilprofile des südägäischen Deckenstapels und dessen Anknüpfung an die südwestliche Türkei. Die kinematische Analyse des Deckenbaus führt zu dem Bild eines sich ausbreitenden Mantel-Diapirs, an dessen geneigter Grenzfläche ein gravitativer Transport ausgelöst wurde.

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In the realm of the Southern Aegean Arc four allochthonous units are piled up above the autochthonous Cherty Limestone (Permian-Oligocene). The allochthonous units are derived from different Mesozoic to Paleogene facies zones which originally were arranged in concentric belts in the Central Aegean Sea. The nappe pile consists — from bottom to top — of neritic carbonates, pelagic carbonates and a volcano-sedimentary complex along the entire arc. These competent units are separated by incompetent members of mainly flyschoid sediments, acting as lubricants. The intercalated sediments were deformed to mélanges due to tectonic transport. Facies analysis, stratigraphy and the style of deformation lead to a correlation of type sections of the southern Aegean nappe pile and its relation to the southwestern part of Turkey. The nappe transport is caused by diapiric uplift and lateral shifting of a thermal dome. A radial gravity transport occurred on its inclined boundary plane.

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Résumé Dans la région de l'Egée méridionale le Calcaire en plaquettes, en position autochthone (Permian-Oligocène) repose sous quatre unités allochthones. Les séries allochthones proviennent de différentes zones de faciès mésozoique-paléogène qui à l'origine étaient disposées concentriquement dans l'Égée centrale. Les nappes sont constituées tout le long de l'arc entier pour des carbonates néritiques, des carbonates pélagiques et un complexe volcano-sédimentaire. Ces unités compétentes sont séparées par des formations incompétentes, notamment des sédiments flyschoides qui ont servi de lubrificant. Ces sédiments intercalés ont été déformés en mélanges par le transport tectonique. Des caractéristiques de faciès et d'ordre stratigraphique, et le style de la déformation rendent possible la corrélation entre les fractions des nappes sud-égéennes et leur rattachement au sud-ouest de la Turquie. Le transport des nappes est lié au déploiement latéral de l'enveloppe d'un dôme diapirique, qui a déclanché un transport radial, par gravité, le long de sa base inclinée.

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Diese Untersuchungen wurden im Rahmen des Schwerpunktprogrammes Geodynamik des mediterranen Raumes der Deutschen Forschungsgemeinschaft durchgeführt und gefördert. Ausgehend von einer Geländetätigkeit auf Kreta in den Jahren 1973–1975 erfolgten im Herbst 1975 Vergleichsbegehungen auf dem Peloponnes, auf Rhodos und den Kykladen. Von den Mitarbeitern des Institutes für Geologie und Paläontologie der TU Braunschweig übernahmen dankenswerterweise FrauBeddies und FrauBusch die Niederschrift des Manuskriptes sowie Übersetzungsarbeiten. HerrStosnach führte freundlicherweise die Reinzeichnung der Abbildungen und Fotoarbeiten aus.     

Modelling of the vertical fluxes of nitric acid,ammonia, and ammonium nitrate

Results from numerical investigations regarding the exchange of HNO₃, NH₃, and NH₄NO₃ between the atmosphere and the biosphere are presented. The investigations were performed with a modified inferential method which is based on the generally accepted micrometeorological ideas of the transfer of momentum, sensible heat and matter near the Earth's surface and the chemical reactions among these nitrogen compounds. This modified inferential method calculates the micrometeorological quantities (such as the friction velocity and the fluxes of sensible and latent heat), the height-invariant fluxes of the composed chemically conservative trace species with group concentrationsc ₁=[HNO₃]+[NH₄NO₃] (total nitrate),c ₂=[NH₃]+[NH₄NO₃] (total ammonia), andc ₃=[HNO₃]-[NH₃] as well as the fluxes of the individual nitrogen compounds. The parameterization of the fluxes is based on the flux-gradient relationships in the turbulent region of the atmospheric surface layer. The modified inferential method requires only the data of wind velocity, temperature, humidity and concentrations (HNO₃, NH₃, and NH₄NO₃) measured at a reference height by stations of a monitoring network.