Research ArticlePLANETARY SCIENCE

The delivery of water by impacts from planetary accretion to present

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Science Advances  25 Apr 2018:
Vol. 4, no. 4, eaar2632
DOI: 10.1126/sciadv.aar2632
  • Fig. 1 Experimental setup.

    (A) A Mylar tray was filled with heat-treated powdered pumice. Thick plastic lines the impact chamber to facilitate sample recovery. (B) The tray was centered beneath the impact point, as shown in this pre-impact frame from a high-speed imaging sequence (130,000 frames/s, 3-μs exposure). (C) The same view as (B) but showing a frame 761.5 μs after impact. The Mylar has ruptured, directing most of the luminous melt downward into the well for recovery. White lines mark the extent of the glowing plume; the region outlined in gray contains abundant luminous melt.

  • Fig. 2 Impact products.

    The materials recovered from impact experiments fall into three categories: (A) impact glasses, (B) antigorite relics, and (C and D) breccia pieces. Both impact-generated glasses and melt-bearing breccia pieces contain quenched impact melts. However, the impact-generated glasses have no visible clastic material on their surfaces, whereas the melt-bearing breccias have unmelted, clastic material attached to quenched impact melt. The breccias contain impact-generated glasses, but they also contain comminuted, shock-lithified pumice.

  • Fig. 3 TG data.

    TG, DTG, and DSC profiles for impact glasses (A, C, and E) and melt-bearing breccias (B, D, and F). Each row corresponds to a single experiment. The y axis at left is for both TG and DSC profiles. DSC data have been divided by 7000 and offset by +0.97 to plot on the same axis as TG data. The y axis at right is for the DTG data. The gray rectangle marks the dehydroxylation interval for unshocked antigorite. The profiles reveal that impactor-derived water is stored in an amorphous, glassy component and in crystalline antigorite relics. The glassy reservoir dominates.

  • Fig. 4 Transmission spectra of impact glass from experiment 160715.

    (A) Optical micrograph of a doubly polished piece of impact glass. Colored squares show where spectra were collected. The colors of the squares correspond to the colors of spectra in (B) and (C). (B) Transmission spectra between 1000 and 4000 cm−1. Water-related peaks at both 3570 and 1630 cm−1 are present. Small absorbance peaks near ~2850 and 3000 cm−1 are attributed to C-H surface contamination. (C) Transmission spectra between 4000 and 6000 cm−1. The H2O feature near 5200 cm−1 is quite strong. The X-OH feature at 4500 cm−1 is small but discernible. Beer-Lambert calculations show that molecular water dominates over hydroxyl.

  • Table 1 Water delivery during hypervelocity impact experiments.
    Experiment numberAngle (°)Impact productAmount of
    water delivered
    % of water stored in
    crystalline antigorite relics
    % of water stored
    in amorphous component
    16071330Impact glasses3.3%8%92%
    Breccias13.2%21%79%
    Antigorite relics2.4%100%0%
    Total19%
    16071430Impact glasses3.1%23%77%
    Breccias16.2%11%89%
    Antigorite relics3.1%100%0%
    Total22%
    16071545Impact glasses2.5%29%71%
    Breccias19.5%30%70%
    Antigorite relics7.9%100%0%
    Total30%
  • Table 2 Analytical methods.
    TechniqueAbbreviationDescription of dataData constrain
    Inductively coupled plasma
    atomic emission spectroscopy
    ICP-AESElemental abundancesHow much of the nonvolatile components
    in the projectile are present in impact
    glasses and breccias
    X-ray diffractionXRDDiffraction pattern whose peaks correspond
    to minerals and amorphous material in
    impact glasses and breccias
    How much crystalline antigorite exists in
    impact glasses and breccias
    Thermogravimetry/derivative
    thermogravimetry/differential
    scanning calorimetry
    TG/DTG/DSCMass loss, rate of mass loss, and heat
    flow into samples during heating
    Bulk water content of impact glasses and
    breccias; distribution of water between
    impact glass and antigorite; water
    delivery efficiency
    Fourier transform infrared
    spectroscopy
    FTIRAbsorbance spectrumTotal and molecular water content in
    field of view; speciation of OH versus
    H2O in impact glasses
    Electron microprobeEMPIn situ compositions of antigorite relicsHydration state of antigorite clasts

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/4/eaar2632/DC1

    Supplementary Text

    fig. S1. TG data for the target and projectile.

    fig. S2. XRD data for the target and projectile.

    fig. S3. XRD patterns for impact glasses and breccias.

    fig. S4. Comparison between observed and modeled XRD patterns.

    table S1. Summary of experiments.

    table S2. Composition of antigorite relics measured by EMP (wt %).

    table S3. Results of TGA analyses.

    table S4. Results of FULLPAT modeling.

    table S5. Summary of Beer-Lambert results.

    table S6. Compositions of projectile, target, and impact products.

    table S7. Projectile retention efficiencies.

    Reference (48)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Text
    • fig. S1. TG data for the target and projectile.
    • fig. S2. XRD data for the target and projectile.
    • fig. S3. XRD patterns for impact glasses and breccias.
    • fig. S4. Comparison between observed and modeled XRD patterns.
    • table S1. Summary of experiments.
    • table S2. Composition of antigorite relics measured by EMP (wt %).
    • table S3. Results of TGA analyses.
    • table S4. Results of FULLPAT modeling.
    • table S5. Summary of Beer-Lambert results.
    • table S6. Compositions of projectile, target, and impact products.
    • table S7. Projectile retention efficiencies.
    • Reference (48)

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