D. S. Ebel

Lamont - Doherty Earth Observatory Columbia University, New York, New York, United States

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Publications (246)474.08 Total impact

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    ABSTRACT: Orbital measurements obtained by the MESSENGER Gamma-Ray Spectrometer have been analyzed to determine the surface abundance of chlorine in Mercury’s northern hemisphere. The derived Cl/Si mass ratio is 0.0057 ± 0.001, which for an assumed Si abundance of 24.6 wt% corresponds to 0.14 ± 0.03 wt% Cl. The abundance of Cl is a factor of 2.9 ± 1.3 higher in the north polar region (>80°N) than at latitudes 0−60°N, a latitudinal variation similar to that observed for Na. Our reported Cl abundances are consistent with measured bulk concentrations of neutron-absorbing elements on Mercury, particularly those observed at high northern latitudes. The Cl/K ratio on Mercury is chondritic, indicating a limited impact history akin to that of Mars, which accreted rapidly. Hypotheses for the origin of Mercury’s high metal-to-silicate ratio must be able to reproduce Mercury’s observed elemental abundances, including Cl. Chlorine is also an important magmatic volatile, and its elevated abundance in the northern polar region of Mercury indicates that it could have played a role in the production, ascent, and eruption of flood volcanic material in this region. We have identified several candidate primary mineralogical hosts for Cl on Mercury, including the halide minerals lawrencite (FeCl2), sylvite (KCl), and halite (NaCl), as well as Cl-bearing alkali sulfides. Amphiboles, micas, apatite, and aqueously deposited halides, in contrast, may be ruled out as mineralogical hosts of Cl on Mercury.
    Icarus 05/2015; 257. DOI:10.1016/j.icarus.2015.04.039 · 2.84 Impact Factor
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    ABSTRACT: We have mapped the major-element composition of Mercury's surface from orbital MESSENGER X-Ray Spectrometer measurements. These maps constitute the first global-scale survey of the surface composition of a Solar System body conducted with the technique of planetary X-ray fluorescence. Full maps of Mg and Al, together with partial maps of S, Ca, and Fe, each relative to Si, reveal highly variable compositions (e.g., Mg/Si and Al/Si range over 0.1–0.8 and 0.1–0.4, respectively). The geochemical variations that we observe are consistent with those inferred from other MESSENGER geochemical remote sensing datasets, but they do not correlate well with units mapped previously from spectral reflectance or morphology. Location-dependent, rather than temporally evolving, partial melt sources were likely the major influence on the compositions of the magmas that produced different geochemical terranes. A large ( ) region with the highest Mg/Si, Ca/Si, and S/Si ratios, as well as relatively thin crust, may be the site of an ancient and heavily degraded impact basin. The distinctive geochemical signature of this region could be the consequence of high-degree partial melting of a reservoir in a vertically heterogeneous mantle that was sampled primarily as a result of the impact event.
    Earth and Planetary Science Letters 04/2015; 416. DOI:10.1016/j.epsl.2015.01.023 · 4.72 Impact Factor
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    G Ustunisik · D S Ebel · D Walker
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    ABSTRACT: Introduction: Ca-, Al-rich inclusions (CAIs) in chondrite meteorites are the oldest crystalline solids in the solar system. Therefore, the variations of trace element concentrations within individual CAIs can provide crucial information into the nature of processes effective in the primitive solar nebula. Despite most CAIs having complex histories during and after their initial formation [1], high-temperature, Type B (igne-ous) CAIs [2, 3] offer a unique opportunity to understand the distribution of trace elements in a controlled magmatic system which underwent fractional crystalli-zation from a single starting liquid of a known bulk composition, crystallization sequence [4], and approximately known cooling rate [5, 6]. The mineralogy of Type B CAIs is dominated by refractory oxides and silicates such as spinel, melilite, Al-, Ti-bearing clinopyroxene, and grossite. These minerals are among the first solids predicted to condense from a hot cooling gas of solar composition [3,7] and therefore the trace element abundances and distribution among these minerals can reveal information about the processes of CAI formation including the role of volatilization, fractional condensation, and fractional crystallization. However, the accurate assessment of how Type B CAIs crystallized requires knowledge of the appropriate mineral–melt partition coefficients. While fairly extensive analytical data exists on trace element partitioning between certain phases (anorthite, clinopyroxene, hibonite, perovskite, and melilite) and CAI type melts, partition coefficients are very sparse for spinels-especially at various oxygen fugacities; and completely missing for rarer phases such as gros-site [8]. Furthermore, previous experimental partitioning data is only available for certain trace elements and is limited to phases such as melilite, perovskite, spinel, and diopside [9-12] and to a single bulk liquid composition. Here, we designed crystallization experiments using various bulk compositions from [13] to determine partitioning of trace and REEs in specific fields of condensation space (Fig. 1) between grossite, melilite and CAI-type liquids. These results will provide systematic constraints on compositional, temperature, and oxygen fugacity dependence of trace and REE partitioning between solids and CAI-type liquids. This abstract reports only on preliminary experiments on the partitioning of trace elements and REEs between grossite and CAI-type liquids.
    46th Lunar and Planetary Science Conference; 03/2015
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    ABSTRACT: Orientation and textural analysis of multiple, concentric metal layers in a layered chondrule from Acfer 139 yielding chondrule formation constraints.
  • G. Ustunisik · D. S. Ebel · D. Walker
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    ABSTRACT: Trace-element partitioning experiments between grossite and CAI-type melts reveal that REEs, HFSEs (Zr, Nb, Hf, Ta, Th), and LILE (B) are incompatible in grossite.
  • A. Hubbard · D. S. Ebel
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    ABSTRACT: We offer a model that explains Earth's volatile depletion pattern by baking dust and thermally altering its aerodynamics through accretion events such as FUors.
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    Herbert Palme · Dominik C. Hezel · Denton S. Ebel
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    ABSTRACT: One of the major unresolved problems in cosmochemistry is the origin of chondrules, once molten, spherical silicate droplets with diameters of 0.2 to 2 mm. Chondrules are an essential component of primitive meteorites and perhaps of all early solar system materials including the terrestrial planets. Numerous hypotheses have been proposed for their origin. Many carbonaceous chondrites are composed of about equal amounts of chondrules and fine-grained matrix. Recent data confirm that matrix in carbonaceous chondrites has high Si/Mg and Fe/Mg ratios when compared to bulk carbonaceous chondrites with solar abundance ratios. Chondrules have the opposite signature, low Si/Mg and Fe/Mg ratios. In some carbonaceous chondrites chondrules have low Al/Ti ratios, matrix has the opposite signature and the bulk is chondritic. It is shown in detail that these complementary relationships cannot have evolved on the parent asteroid(s) of carbonaceous chondrites. They reflect preaccretionary processes. Both chondrules and matrix must have formed from a single, solar-like reservoir. Consequences of complementarity for chondrule formation models are discussed. An independent origin and/or random mixing of chondrules and matrix can be excluded. Hence, complementarity is a strong constraint for all astrophysical–cosmochemical models of chondrule formation. Although chondrules and matrix formed from a single reservoir, the chondrule-matrix system was open to the addition of oxygen and other gaseous components.Keywordschondrulesmatrixcarbonaceous chondritescomplementarity chondrule matrixformation of chondrules
    Earth and Planetary Science Letters 02/2015; 411. DOI:10.1016/j.epsl.2014.11.033 · 4.72 Impact Factor
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    ABSTRACT: We examined the Al-Mg isotope systematics of plagioclase in a FeO-poor ferromagnesian Wild 2 particle (C2092,7,81,1,0; named Pyxie) using a ∼2 μm spot. Three analyses show average 27Al/24Mg ratio of ∼65 and excess δ26Mg⁎ value of + 0.1 ± 4.5 ‰ (2σ), indicating no resolvable 26Mg excess in the particle. The inferred initial (26Al/27Al)0 ratio of plagioclase in Pyxie is estimated as (- 0.6 ± 4.5) ×10-6 with an upper limit of 4 ×10-6. The result is very similar to that of the FeO-rich ferromagnesian particle “Iris” (Ogliore et al., 2012). Assuming homogeneous distribution of 26Al in the early solar system, Pyxie formed at least 2.6 Ma after the oldest Ca-Al-rich inclusions. This minimum formation age is marginally younger than formation ages of most chondrules in type ∼3.0 chondrites but comparable with those of Mg# < 98 chondrules in CR3 chondrites. Considered in conjunction with similar oxygen isotope ratios between Pyxie (and Iris) and Mg# < 98 chondrules in CR3 chondrites, it is inferred that the ferromagnesian Wild 2 particles and Mg# < 98 chondrules in CR3 chondrites formed late in local disk environments that had similar oxygen isotope ratios and redox states.
    Earth and Planetary Science Letters 12/2014; 410. DOI:10.1016/j.epsl.2014.11.020 · 4.72 Impact Factor
  • Amanda J White · Denton S Ebel
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    ABSTRACT: Light microscopy is a powerful tool that allows for many types of samples to be examined in a rapid, easy, and nondestructive manner. Subsequent image analysis, however, is compromised by distortion of signal by instrument optics. Deconvolution of images prior to analysis allows for the recovery of lost information by procedures that utilize either a theoretically or experimentally calculated point spread function (PSF). Using a laser scanning confocal microscope (LSCM), we have imaged whole impact tracks of comet particles captured in silica aerogel, a low density, porous SiO2 solid, by the NASA Stardust mission. In order to understand the dynamical interactions between the particles and the aerogel, precise grain location and track volume measurement are required. We report a method for measuring an experimental PSF suitable for three-dimensional deconvolution of imaged particles in aerogel. Using fluorescent beads manufactured into Stardust flight-grade aerogel, we have applied a deconvolution technique standard in the biological sciences to confocal images of whole Stardust tracks. The incorporation of an experimentally measured PSF allows for better quantitative measurements of the size and location of single grains in aerogel and more accurate measurements of track morphology.
    Microscopy and Microanalysis 12/2014; 21(01):1-7. DOI:10.1017/S1431927614013610 · 1.76 Impact Factor
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    ABSTRACT: Magnetic fields are proposed to have played a critical role in some of the most enigmatic processes of planetary formation by mediating the rapid accretion of disk material onto the central star and the formation of the first solids. However, there have been no experimental constraints on the intensity of these fields. Here we show that dusty olivine-bearing chondrules from the Semarkona meteorite were magnetized in a nebular field of 54 ± 21 microteslas. This intensity supports chondrule formation by nebular shocks or planetesimal collisions rather than by electric currents, the x-wind, or other mechanisms near the Sun. This implies that background magnetic fields in the terrestrial planet-forming region were likely 5 to 54 microteslas, which is sufficient to account for measured rates of mass and angular momentum transport in protoplanetary disks.
    Science 11/2014; 346(6213). DOI:10.1126/science.1258022 · 31.48 Impact Factor
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    Alexander Hubbard · Denton S. Ebel
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    ABSTRACT: We consider the evidence presented by the LL3.0 chondrite Semarkona, including its chondrule fraction, chondrule size distribution and matrix thermal history. We show that no more than a modest fraction of the ambient matrix material in the Solar Nebula could have been melted into chondrules; and that much of the unprocessed matrix material must have been filtered out at some stage of Semarkona's parent body formation process. We conclude that agglomerations of many chondrules must have formed in the Solar Nebula, which implies that chondrules and matrix grains had quite different collisional sticking parameters. Further, we note that the absence of large melted objects in Semarkona means that chondrules must have exited the melting zone rapidly, before the chondrule agglomerations could form. The simplest explanation for this rapid exit is that chondrule melting occurred in surface layers of the disk. The newly formed, compact, chondrules then settled out of those layers on short time scales.
    Icarus 09/2014; 245. DOI:10.1016/j.icarus.2014.09.025 · 2.84 Impact Factor
  • 77th Annual Meeting of the Meteoritical-Society; 09/2014
  • 77th Annual Meeting of the Meteoritical-Society; 09/2014
  • 77th Annual Meeting of the Meteoritical-Society; 09/2014
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    ABSTRACT: The examination of the physical properties of chondrules has generally received less emphasis than other properties of meteorites such as their mineralogy, petrology, and chemical and isotopic compositions. Among the various physical properties of chondrules, chondrule size is especially important for the classification of chondrites into chemical groups, since each chemical group possesses a distinct size-frequency distribution of chondrules. Knowledge of the physical properties of chondrules is also vital for the development of astrophysical models for chondrule formation, and for understanding how to utilize asteroidal resources in space exploration. To examine our current knowledge of chondrule sizes, we have compiled and provide commentary on available chondrule dimension literature data. We include all chondrite chemical groups as well as the acapulcoite primitive achondrites, some of which contain relict chondrules. We also compile and review current literature data for other astrophysically-relevant physical properties (chondrule mass and density). Finally, we briefly examine some additional physical aspects of chondrules such as the frequencies of compound and 'cratered' chondrules. A purpose of this compilation is to provide a useful resource for meteoriticists and astrophysicists alike.
    Chemie der Erde - Geochemistry 08/2014; DOI:10.1016/j.chemer.2014.08.003 · 1.40 Impact Factor
  • Amanda J. White · Denton S. Ebel
    Microscopy and Microanalysis 08/2014; 20(S3):1702-1703. DOI:10.1017/S1431927614010241 · 1.76 Impact Factor
  • Microscopy and Microanalysis 08/2014; 20(S3):752-753. DOI:10.1017/S1431927614005480 · 1.76 Impact Factor
  • Ellen J. Crapster-Pregont · Denton S. Ebel
    Microscopy and Microanalysis 08/2014; 20(S3):1688-1689. DOI:10.1017/S1431927614010174 · 1.76 Impact Factor
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    G Ustunisik · D S Ebel · And H Nekvasil
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    ABSTRACT: The variability of chondrule volatile element contents may provide information about the processes that shaped the early solar system and its compositional heterogeneity. An essential observation is that chondrule melts contain very low alkalies and other volatile elements (e.g., Cl). The reason for this depletion is the combined effects of cooling rates (10 to 1000K/h), the small size of chondrules, and their high melting temperatures (~1700 to 2100 K) resulting in extensive loss of volatiles at canonical pressures (e.g., 10-4 bar). However, we observe some chondrules with significant concentrations of volatiles (Na, Cl), that differ markedly from chondrules dominated by refractory elements. Could such heterogeneity arise from loss of alkalis and Cl to a gas phase that itself later condenses, thereby yielding variations in volatile enrichments in chondrules? Does Cl enhance volatility of the alkalis to varying extents? Experiments on Cl-bearing and Cl-free melts of equivalent composition for 10 min, 4 h, and 6 h reveal systematic effects of Cl on alkali volatility. Cl-bearing melts lose 48% of initial Na 2 O, 66% of K 2 O, 96% of Cl within the first 10 minutes of degassing. Then the amount of alkali loss decreases due to the absence of Cl. Cl-free melts loses only 15% of initial Na 2 O and 33% K 2 O. After 4 hours, melts lose 1/3 of initial Na 2 O and 1/2 of K 2 O. For both systems, Na 2 O is more compatible in the melt relative to K 2 O. Therefore, the vapor given off has a K/Na ratio higher than the melt through time in spite of the much higher initial Na abundance in the melt. Enhanced vaporization of alkalis from Cl-bearing melt suggests that Na and K evaporate more readily as volatile chlorides than as monatomic gases. Cl-free initial melts with normative plagioclase of An 50 Ab 44 Or 6 evolved into slightly normal zoned ones (An 49 Ab 50 Or 1) while Cl-bearing initial melts normative to albitic plagioclase (An 46 Ab 50 Or 4) evolved to reverse zoned ones (An 54 Ab 45 Or 1). The vapor phase over Cl-bearing chondrule melts may have a bimodal character over time. The heterogeneous volatile contents of chondrules may result from quenching melt droplets at different stages of repeated heating, chondrule fragment recycling, and recondensation of exsolved volatiles.
    Goldschmidt 2014; 06/2014

Publication Stats

2k Citations
474.08 Total Impact Points

Institutions

  • 2011–2015
    • Lamont - Doherty Earth Observatory Columbia University
      New York, New York, United States
  • 2004–2015
    • American Museum of Natural History
      • Division of Physical Sciences
      New York, New York, United States
  • 2012
    • Columbia University
      • Department of Earth and Environmental Sciences
      New York, New York, United States
  • 2010
    • Aix-Marseille Université
      Marsiglia, Provence-Alpes-Côte d'Azur, France
  • 2006
    • OFM Research
      Redmond, Washington, United States
  • 2005
    • New Mexico Museum of Natural History and Science
      Albuquerque, New Mexico, United States
    • Planetary Science Institute
      American Fork, Utah, United States
  • 2000–2002
    • University of Chicago
      • Department of Geophysical Sciences
      Chicago, Illinois, United States
  • 1989–1994
    • Purdue University
      • Department of Earth and Atmospheric Sciences
      ウェストラファイエット, Indiana, United States