A New H2O Ice Hugoniot: Implications for Planetary Impact Events

Abstract

Abstract. Collisions on icy planetary bodies produce impact melt water, redistribute ground ice, and deposit thermal energy available for chemical reactions. The amount of melt generated from an impact is sensitive to the initial temperature, which ranges from the 273 K on Earth and Mars to 40 K on the surface of Pluto. Previous shock wave studies, centered at ~263 K for terrestrial applications, had difficulty defining the onset of phase transformations on the ice Hugoniot, and consequently, the criteria for shock melting was poorly constrained. Because ices on most planetary surfaces exist at ambient temperatures much below 263 K, we conducted a detailed study of the shock response of solid ice at 100 K and ~40 % porous ice at ~150 K to derive Hugoniots and critical pressures for shockinduced melting that are applicable to most of the solar system. New Hugoniots for solid and ~40 % porous ice are defined, and the critical pressures required to induce incipient melting and complete melting upon isentropic release from the shock state are revised using calculated shock temperatures and entropy. The critical pressures required for incipient melting of solid ice are only 0.6 and 4.5 GPa for 263 and 100 K respectively, and pressures between 0.1-0.5 GPa initiate melting of porous ice between 250 and 150 K. Therefore, hypervelocity impact cratering on planetary surfaces, with peak shock pressures >100 GPa, and mutual collisions between porous cometesimals in the outer solar system, with peak pressures of ~1 GPa, will generate prodigious amounts of shock-induced melt water.

Numerical modelling of ice: Mechanical behaviour of ice under high strain rates

“…According to the experimental work from Sterwart and Ahrens [29,30], s = 0.92, is used to calculate K 2 in the current work, whereas K 3 , was set as zero because the volume strain should be negligible for ice, as brittle materials always have low failure strength.…”

“…(11), (12) are: p * = p/p HEL and σ * t,m = σ * t,m /p HEL .Here, p HEL is the hydrostatic pressure of Hugoniot elastic strength, and it can be expressed by Hugoniot elastic strength. According to the planetary impact tests conducted by Sterwart and Ahrens [29,30],…”

“…While the ice projectile with high impact velocities can be accurately captured by the equation of state (EOS), material models including EOS also present good capabilities of ice impact simulation [26][27][28]. However, determining the parameters of EOS is difficult because planetary impact tests need to be performed, which require hyper impact velocity of ice projectiles and an extremely accurate monitoring system [29,30]. Besides, advanced numerical methodologies, such as the particle-subdomain method [31] and smoothed particle hydrodynamics [32], which always use rate-dependent material properties as input, are more appropriate for replicating the mechanical behaviour of ice impact, especially the failure process.…”

Cometary impact effects at the Moon: Implications for lunar swirl formation

“…Accounting for this porosity in comet impacts has important consequences for both the initial acoustic impedance matching conditions at the target and for the additional irreversible heating of the cometary ices from the PdV work done during the crushing out of pore space (Zel'dovich and Raizer, 1966). Hence, the molecular water ice EOS included a P-alpha model (Herrmann, 1969;Kerley, 1992) with a small crush strength of 0.1 GPa (Stewart and Ahrens, 2004) and an initial reference density of q $ 0:5 g=cm 3 .…”