Icy ocean worlds, plumes, and tasting the water

Abstract

This paper considers how space missions that fly through the plumes known, or suspected, to erupt naturally from some icy ocean worlds (IOW), such as Enceladus, or that aim to intercept icy ejecta from impact cratering processes on such bodies can sample the water and ice within the plumes. The mechanics of how grains (either in the plumes or the ejecta) would interact with a passing spacecraft (i.e., impact speeds, shock pressures, etc.) are introduced. The impact speeds are estimated and vary with both the mass of the IOW and the orbital parameters of a space mission. This can lead to large differences in impact speeds (and hence collection methods) at bodies such as Enceladus and Europa. The implications of these different impact speeds (a few hundred m s−1 to several km s−1, and even greater than 10 km s−1) for the collection of organic materials from the plumes are shown to be significant.

Synthesis of Phenanthrene/Pyrene Hybrid Microparticles: Useful Synthetic Mimics for Polycyclic Aromatic Hydrocarbon-Based Cosmic Dust

“…For example, sampling dust particles within the icy plumes emanating from Enceladus could in principle involve either orbiting this moon at just a few hundred m s –1 or by undertaking a fly-by at an encounter velocity of 3–5 km s –1 . 21 The present study suggests that the successful collection of intact PAH-based dust particles is only likely to be achieved in the first scenario. It is also envisaged that further light gas gun experiments performed at higher hypervelocities (e.g., up to 7 km s –1 ) should enable identification of the maximum encounter velocity at which the most thermally stable PAH molecules can be captured intact.…”

“…Knowledge of such a remarkable selection bias for simple PAHs is essential for any space mission that attempts to capture PAH-based grains intact within aerogel targets. For example, sampling dust particles within the icy plumes emanating from Enceladus could in principle involve either orbiting this moon at just a few hundred m s –1 or by undertaking a fly-by at an encounter velocity of 3–5 km s –1 . The present study suggests that the successful collection of intact PAH-based dust particles is only likely to be achieved in the first scenario.…”

“…Projectile impacts on aluminum foils are believed to involvewith increasing impact velocitythe following sequence of events: rebound, rebound and fracture, sticking, sticking with fracture, cratering with projectile fragmentation, and cratering with melted residue. ,, Depending on the projectile composition, this sequence spans a velocity regime of 0.2–3.0 km s –1 (which corresponds to a peak pressure of typically 0.1–10 GPa) . The boundaries between this series of regimes depend not only on the impact velocity but also on projectile/target properties such as tensile strength, melting point, etc.…”

“… 21 , 41 , 42 Depending on the projectile composition, this sequence spans a velocity regime of 0.2–3.0 km s –1 (which corresponds to a peak pressure of typically 0.1–10 GPa). 21 The boundaries between this series of regimes depend not only on the impact velocity but also on projectile/target properties such as tensile strength, melting point, etc. For example, it has been reported that 4–10 μm diameter poly(methyl methacrylate) microparticles either adhere intact (stick) or rebound from aluminum foil when fired at 0.8–1.0 km s –1 but form craters with molten residues at 2 km s –1 .…”

“…In such cases, no conductive coating is required and the microparticles are fired as a “buckshot”, with many near-simultaneous impact events per experiment. Such studies have been conducted for a wide range of micrometer-sized organic projectiles, which has provided valuable information with regard to impact cratering and capture processes under conditions that are comparable to those envisaged for cosmic dust collection in future space missions. − Alternatively, icy grains of up to 50 μm have been doped with organic molecules of interest (e.g., fluorescent dyes) and fired at up to 3 km s –1 using a light gas gun . Similarly, 800 nm icy grains loaded with amino acids have been generated via electrospray techniques and accelerated electrostatically up to 4 km s –1 …”