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  • 1
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    The Spectrum of Titan near 3.4 Micron: Comparison of Spectral Features to Organic Molecules (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-08-15
    Description: In August 1993 we observed the spectrum of Titan from 2.9 to 4.1 micrometers at a resolving power of R=500-1000 (dw approx. 2-4 per cm). The spectrum shows, as expected, a strong absorption throughout this region from three strong bands Of CH4. However, comparison of the spectrum to simple radiative transfer models and to the spectrum of Jupiter reveal some interesting differences. A broad emission feature that we attribute to CH4 is centered at 3.3 micrometers. At 3.45 micrometers we see a distinct narrow absorption feature that is present in both the Jupiter and laboratory spectrum, but only when other features, absent in the Titan spectrum, are also present. In our attempt to understand the origin of this spectral feature we have compared the spectrum to CH4 and other organic molecules. Interesting similarities appear between the aliphatic hydrocarbons (CH2 and CH3 groups) seen in laboratory organics and the Titan spectrum, but only if we assume that the shorter wavelength feature (CH3) is masked by the broad CH4 emission. A second problem with the explanation is that like column abundance of organic haze (Toon et al. 1991) is insufficient to provide the required number of molecules to create a spectral feature with tau approx. 1. Laboratory organics produced through a variety of processes have been compared to the Titan spectrum and the results arc presented.
    Keywords: Space Sciences (General)
    Type: Division for Planetary Sciences Meeting; Oct 30, 1994 - Nov 04, 1994; Washington, DC; United States
    Format: text
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  • 2
    Electronic Resource
    Electronic Resource
    Planets The first movement (2007)
    [s.l.] : Nature Publishing Group
    Nature 448 (2007), S. 1003-1003 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Making planets is tricky, and probably takes several stages. First, tiny interstellar grains must accrete into mountain-sized objects massive enough to decouple from their cocoon of nebula gas. These objects probably then combine in collisions, growing ever larger, past asteroid-sized planetesimals ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/4481003a
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    Paper (German National Licenses)
    Fulltext
  • 3
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    The first movement (2007)
    Springer Nature
    Details
    Publication Date: 2007-08-01
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Springer Nature
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    PAPER CURRENT
  • 4
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    Gathering dust (2011)
    Springer Nature
    Details
    Publication Date: 2011-03-27
    Print ISSN: 1752-0894
    Electronic ISSN: 1752-0908
    Topics: Geosciences
    Published by Springer Nature
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  • 5
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    James B. Pollack (1938-1994) (1995)
    Elsevier
    Details
    Publication Date: 1995-02-01
    Print ISSN: 0019-1035
    Electronic ISSN: 1090-2643
    Topics: Physics
    Published by Elsevier
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  • 6
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    Chondrules of the Very First Generation in Bencubbin/CH-like Meteorites QUE94411 and Hammadah Al Hamra 237: Condensation Origin at High Ambient Nebular Temperatures (2000)
    In:  Other Sources
    Details
    Publication Date: 2017-10-02
    Description: Chondrules in QUE94411 and HH 237 formed at high ambient T prior to condensation of Fe,Ni-metal following a large scale thermal event that resulted in complete vaporization of a solar nebula region. These chondrules escaped subsequent remelting.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXI; LPI-Contrib-1000
    Format: text
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  • 7
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    HST-STIS Spectra of Saturn's Rings and Implications for Their Reddening Agent (2016)
    In:  CASI
    Details
    Publication Date: 2019-07-19
    Description: We obtained HST-STIS spectra of Saturn's main rings in May 2011, using the G230L (and G430L) gratings, with final averaged radial resolution of 160 (and 330) km/pixel. The dataset filled a previous 200-330nm "spectral gap" between Cassini and ground-based spectra. The data provide radial profiles as a function of wavelength, but our most basic product at this point is a set of very low-noise spectra, radially averaged over broad regions of the rings (A, B, C, and Cassini Division). The raw spectra required special processing to remove artifacts due to extended-source grating scatter. We have modeled the spectra using a new particle surface model, which corrects for on-surface shadowing due to the likely very rough ring particle surfaces, and avoids overestimation of intra-mixed "neutral absorber". We correct for non-classical layer effects and finite ring optical depth, and relate our observed reflectivities to the spherical albedos of individual smooth particles. We model these smooth particle albedos using standard Hapke theory for regolith grain mixtures that are either homogeneous and "intramixed" (nonicy absorbers dispersed in water ice regolith grains) or heterogeneous "intimate" mixtures. As candidates for the nonicy contaminants we have considered amorphous carbon, aromatic-rich and aliphatic-rich organic tholins, silicates, hematite and iron metal. For the A and B rings, we find that iron metal (including a new theoretical estimate of the refractive indices of nanometer-sized grains of iron) is not spectrally steep enough in the 200-300nm range, and that aliphatic-rich tholins are either too steep at short wavelengths or too flat at long wavelengths. However, less than 1% by mass of aromatic-rich tholins provides a very good fit across the entire spectral range with no gratuitous "neutral absorber" needed, and a minimum of additional free parameters. The best fits require forward-scattering regolith grains. For the C Ring and Cassini Division, additional absorbers are needed (updated results will be given).
    Keywords: Astronomy
    Type: ARC-E-DAA-TN35711 , Division of Planetary Science Meeting (DPS); Oct 16, 2016 - Oct 21, 2016; Pasadena, CA; United States
    Format: application/pdf
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  • 8
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    Limits on Deceleration and Asymmetry of Solar Wind Speed (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: It has been suggested by Richardson et al. [1995] that the solar wind shows signs of deceleration due to mass-loading by interstellar pickup ions. They based their conclusion on observations from the Voyager 2 and IMP 8 spacecraft. Observations from the Pioneer Venus Orbiter (PVO), Voyager 2, and Pioneer 10 spacecraft are compared to look for this deceleration. While these comparisons suggests the possibility of deceleration at Voyager 2, the magnitude of this deceleration appears to be significantly less than the deceleration reported by Richardson et al. [1995]. Some of this difference could be explained by a north-south asymmetry in solar wind speed. The implications of these results are discussed, along with possibilities for further investigations.
    Keywords: Solar Physics
    Format: text
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  • 9
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    The Response of Disks to Oscillatory Modes in Galaxies (1996)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: Recent studies suggest that galaxies can oscillate in normal modes with essentially no damping over a Hubble time. These modes may play an important role in the structure and evolution of disk/halo systems. Motivated by the possibility that normal mode oscillations exist in real galaxies, we are investigating the response of galactic disks to halo oscillations. The goal of these investigations is to ascertain whether or not observational signatures exist for such oscillations. Our approach is to perform numerical experiments on the response of a self-gravitating disk to a time-varying halo potential. We assume that a significant fraction of the mass in a galaxy is in a dark halo. The halo oscillates and the luminous disk material responds to these oscillations. Preliminary results are reported for disks embedded in a radially oscillating gravitational potential. The equilibrium initial disk is represented by an exponential density profile. Considerable care was taken to build an initial disk model that was "stable" over long time scales. A control experiment was run with the disk in a static halo potential. The disk responds to the time-varying potential by developing a ring structure, which forms and disappears during each halo oscillation cycle. The density of stars becomes depressed in an annular region at the radius where the disk epicycle frequency is equal to the halo oscillation period. This pattern of response persists over time periods approaching a Hubble time. In the oscillating potential, a bar develops in the inner disk. This bar is absent when the halo remains static. Specific targets of this study include the implications for large-scale disk structure, the gas dynamical response of the interstellar medium in such systems, and the inflow of material into the central regions of the galaxy.
    Keywords: Astrophysics
    Type: Dynamical Astronomy Meeting; Apr 15, 1996 - Apr 17, 1996; Washington, DC; United States
    Format: text
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  • 10
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    Long-term Enhancements in Solar Wind Speed (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: Long-term enhancements in solar wind speed over timescales on the order of a year appear to be a common feature throughout the heliosphere over heliocentric distances that range from less than 0.72 AU to greater than 60. The origin of these events remains to be determined, but they are almost certainly associated with long-term variations at the solar wind source, in contrast with smaller-scale structures such as CIRs, MIRs, and GMIRs which are dynamical in origin. We present a survey of the long-term speed enhancements observed at the Pioneer Venus Orbiter (PVO), IMP 8, Voyager 2, and Pioneer 10 between 1974 and 1994 and compare this with published reports of smaller-scale events such as MIRs. We examine several of these long-term speed enhancements in detail to identify and characterize aspects of their structure, then describe how that structure evolves with heliocentric distance. Finally we discuss some of the implications of these events.
    Keywords: Solar Physics
    Format: text
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