HR: 1330h
AN: P52A-0473    [PDF]
TI: Accretion of Cometary Material as a Function of Impact Angle
AU: * Karlow, B A
EM: karlow1@llnl.gov
AF: Chemistry \& Materials Science Directorate, Lawrence Livermore National Laboratory, Livermore, CA 94550 United States
AU: Lomov, I
EM: lomov1@llnl.gov
AF: Energy \& Environment Directorate, Lawrence Livermore National Laboratory, Livermore, CA 94550 United States
AU: Antoun, T
EM: antoun1@llnl.gov
AF: Energy \& Environment Directorate, Lawrence Livermore National Laboratory, Livermore, CA 94550 United States
AU: Blank, J G
EM: blank4@llnl.gov
AF: Chemistry \& Materials Science Directorate, Lawrence Livermore National Laboratory, Livermore, CA 94550 United States
AB: It has been proposed that comets provided the raw ingredients for life during the first billion years of our planet's history. To investigate this possibility, we simulated comet-Earth impacts at a variety of impact angles. Our goal was to determine the mass fraction of material that would be likely to survive a terrestrial impact and come to rest as an isolated pond of water. We employed the Eulerian adaptive mesh refinement (AMR) code, GEODYN, in a 2-D, Cartesian (plane-strain) system. In the calculations, the impactors were modeled as solid-ice comets 1 km in diameter impacting into granite at escape velocity (11.2 km/s). The simulations were computed to a time of 2 seconds, long enough for multiple reverberations of the compression and rarefaction waves to propagate through the comet. Thermomechanical variables relevant to assessing comet conditions during the impact event were monitored at 1000 evenly distributed locations throughout the comet. At each location, the magnitude and orientation of the particle velocity vector were used to determine the fraction of comet mass that escapes Earth's gravity during the impact event. Pressure, density and temperature were also monitored to assess the survivability of organic matter distributed thoughout the comet. We determined that the fraction of comet mass that escapes Earth's gravity is not a simple monotonic function of impact angle. For example, the 15$\deg$ impact showed the least accretion (61%) and the 90$\deg$ impact had total accretion, but the 10$\deg$ impact retained significantly more mass (at 71%) than the 15$\deg$ impact. We also found that a significant amount of the comet experiences low peak temperatures; this was somewhat surprising given that the Earth target was a granitic hard rock. Approximately 80% (or 3x108kg) of the 10$\deg$ impactor experienced temperatures between 250-350$\deg$C and corresponding pressures of 4.5-8.2 GPa. If the organic matter present in comets experienced similar conditions, we would expect it to survive with little deleterious alteration. We will consider the dispersion and final aerial distribution of our comet impactors. We will present our results using the phase diagram for H$_{2}$O and experimental data from hypervelocity impact experiments. This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.
DE: 5420 Impact phenomena (includes cratering)
DE: 6022 Impact phenomena
SC: Planetary Sciences [P]
MN: 2003 Fall Meeting