Bulletin of the American Physical Society
21st Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 64, Number 8
Sunday–Friday, June 16–21, 2019; Portland, Oregon
Session S6: GPS: Planetary Impacts |
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Chair: Federica Coppari, Lawrence Livermore National Laboratory Room: Broadway III/IV |
Thursday, June 20, 2019 11:00AM - 11:30AM |
S6.00001: The delivery of water during impacts: The view from experiments Invited Speaker: R.Terik Daly The fate of water during impacts is of fundamental importance to planetary formation and evolution. However, the mechanisms that trap impactor-derived water remain poorly constrained. Isotopic evidence indicates that carbonaceous chondrite (CC)-like objects delivered water to the inner solar system. Recent hypervelocity impact experiments at the NASA Ames Vertical Gun Range address two fundamental questions. First, how much of the water carried by CC-like impactors can be trapped in impact products? Second, where does impactor-derived water reside? We focus on oblique impacts (30 and 45 degrees with respect to horizontal), scenarios that lead to a wide range of pressure and temperature conditions in the both the impactor and target. (45 degrees is also the most probable impact angle.) The experiments reveal that impact melts and breccias capture up to 30{\%} of the water carried by CC--like impactors under impact conditions typical of the main asteroid belt and the early phases of planet formation. This impactor-derived water resides in two distinct reservoirs: quenched impact melts and projectile survivors. Quenched impact melt hosts the bulk of the delivered water, and in these materials molecular water dominates over hydroxyl. Entrapment of water within impact glasses and melt-bearing breccias likely contributed to the early accretion of water during planet formation. Bodies too small to retain vaporized water could have nevertheless captured water in impact melt products. As such, water and other volatiles may have been sequestered within growing planets, with implications for geodynamics and planetary evolution. [Preview Abstract] |
Thursday, June 20, 2019 11:30AM - 11:45AM |
S6.00002: Multi-material hydrodynamics modeling of asteroid impacts at oblique shock interfaces Roseanne Cheng, Tariq Aslam We present a new Eulerian multi-material hydrodynamics code to simulate the mechanics of impact crater formation. It is based on the open source astrophysical radiation magnetohydrodynamics with adaptive mesh refinement code Athena++. The hydrodynamics method is a directionally unsplit, high-resolution shock capturing Godunov scheme. We have developed and implemented a new multi-material capability into Athena++, where the evolution of several materials (gas and/or solids) is modeled in a fluid approximation with a set of conservative equations coupled to the basic hydrodynamic equations. Each material is governed by a separate equation of state (EOS) where we assume pressure equilibrium closure for mixed cells. The current implementation includes analytic EOS, but an extension to tabular form is straightforward. In this talk, we describe the numerical method and apply it to early-time models of asteroid impacts into boundary layers of water and granite. Each layer is modeled using a Mie-Gr\"uneisen EOS based on experimental shock data. We focus the study on oblique shocks and compare simulation results with analytic solutions from shock polar analysis. We discuss the coupling to strength and fracture models with this code. [Preview Abstract] |
Thursday, June 20, 2019 11:45AM - 12:00PM |
S6.00003: Forsterite Shock-and-Release: Temperature and Density on the Liquid-Vapor Curve Erik Davies, Megan Duncan, Sarah Stewart, Dylan Spaulding, Seth Root, David Bliss, Richard Kraus, Stein Jacobsen We present experimental results on forsterite that probe the extreme conditions during melting and vaporization of rocky planets. Previous work probed the principal Hugoniot of forsterite. Here, we examine release to the liquid-vapor curve. Flyer plate impact experiments were performed on the Z-Machine at Sandia National Laboratories where planar, supported shock waves are generated in single crystal samples. Between the sample and window is a gap of known distance into which the sample expands upon shock breakout. Free expansion leads to a density plateau at the liquid-vapor phase boundary, generating a liquid wall that impacts a standard window. The density of the liquid flyer is derived from the measured liquid flyer velocity and shock velocity in the window. Temperature on the liquid-vapor phase boundary is measured by releasing the sample from the shocked state into vacuum and measuring the thermal emission spectrum of the liquid wall. These experiments directly access the liquid-vapor curve, allowing for more accurate predictions of melting and vaporization in planetary impact events. [Preview Abstract] |
Thursday, June 20, 2019 12:00PM - 12:15PM |
S6.00004: Shock physics of giant impacts: Transforming rocky planets into supercritical synestias Sarah Stewart, Erik Davies, Megan Duncan, Simon Lock, Seth Root, Joshua Townsend, Razvan Caracas, Richard Kraus, Stein Jacobsen Rocky planets form by a series of giant impacts with sufficient energy to vaporize the outer layers of the bodies. In many giant impacts, the colliding planets are transformed into a new type of astronomical object called a synestia, which is a body that exceeds the limit of a spheroidal shape. In most events that produce an Earth-mass body, the collision creates a supercritical synestia with an internal temperature-pressure profile that exceeds the critical point for silicates. Here, we present the results from numerical simulations of giant impacts using a forsterite equation of state for the silicate mantle. We compare our results to recently obtained critical points for silicates derived from experiments at the Sandia Z Machine and ab initial calculations. Transformation of planets into supercritical synestias affects the chemical and thermal evolution of the body. Cooling and differentiation of synestias follows a different thermodynamic path than previous models of magma oceans. We emphasize the critical need for studies of multicomponent chemical systems to understand the outcomes of giant impacts during planet formation. [Preview Abstract] |
Thursday, June 20, 2019 12:15PM - 12:30PM |
S6.00005: Planets and stars in the laboratory: the Z Fundamental Science Program Thomas R. Mattsson, Marcus D. Knudson Over the last few years, our ability to drive matter to unprecedented pressure / temperature states has produced significant new insights across many fields. Sandia’s Z facility has unique capabilities to deliver high-precision data at extreme conditions. In this talk, we will describe the evolution of the Z Fundamental Science Program, give examples of recent discoveries made the in the areas of planetary science and astrophysics, and finally describe the future of the program and the next call for proposals. This work is supported by the Z Fundamental Science Program at Sandia National Laboratories. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. [Preview Abstract] |
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