The role of shape-dependent flight stability in the origin of oriented meteorites

Abstract

The atmospheric ablation of meteoroids is a striking example of the reshaping of a solid object due to its motion through a fluid. Motivated by meteorite samples collected on Earth that suggest fixed orientation during flight—most notably the conical shape of so-called oriented meteorites—we hypothesize that such forms result from an aerodynamic stabilization of posture that may be achieved only by specific shapes. Here, we investigate this issue of flight stability in the parallel context of fluid mechanical erosion of clay bodies in flowing water, which yields shapes resembling oriented meteorites. We conduct laboratory experiments on conical objects freely moving through water and fixed within imposed flows to determine the dependence of orientational stability on shape. During free motion, slender cones undergo postural instabilities, such as inversion and tumbling, and broad or dull forms exhibit oscillatory modes, such as rocking and fluttering. Only intermediate shapes, including the stereotypical form carved by erosion, achieve stable orientation and straight flight with apex leading. We corroborate these findings with systematic measurements of torque and stability potentials across cones of varying apex angle, which furnish a complete map of equilibrium postures and their stability. By showing that the particular conical form carved in unidirectional flows is also posturally stable as a free body in flight, these results suggest a self-consistent picture for the origin of oriented meteorites.

Ultra-sharp pinnacles sculpted by natural convective dissolution

“…Viewed mathematically and physically, the action of erosion, dissolution, or melting on stone, soil, sand, ice, and other natural materials can be categorized as free-or moving-boundary problems (12,13). This perspective is especially useful for understanding fundamental shape-changing mechanisms and for disentangling the interdependent solid and fluid dynamics that arise when boundaries are carved by flowing air or water (14)(15)(16). The study of shape-flow interactions also benefits from laboratory experiments, which complement geomorphological field studies by permitting observation and measurement on tractable length and time scales and under controlled and reproducible conditions (17).…”

Swimming and Sinking Behavior of Warm Water Pelagic Snails

“…These different orientations will differentially affect the coefficient of drag. The species C. atlantica is larger than the other elongated species and thus may energetically benefit from a larger coefficient of drag resulting from its more horizontal sinking position, which slows its sinking (Field et al, 1997;Amin et al, 2019). For those elongated species that tend to rotate to a horizontal position while sinking, we suspect that their center of mass is located close to or above their geometric center.…”

Viscous transport in eroding porous media

“…This coupling between geometry and flow occurs, for example, in applications involving melting (Beckermann & Viskanta 1988;Rycroft & Bazant 2016;Jambon-Puillet, Shahidzadeh & Bonn 2018;Favier, Purseed & Duchemin 2019;Morrow et al 2019), dissolution (Kang et al 2002;Huang, Moore & Ristroph 2015;Moore 2017;Wykes, Huang & Ristroph 2018), deposition (Johnson & Elimelech 1995;Hewett & Sellier 2018), biofilm growth (Tang, Valocchi & Werth 2015) and crack formation (Cho et al 2019). We focus on erosion, a fluid-mechanical process that is prevalent in many geophysical, hydrological and industrial applications (Berhanu et al 2012;Ristroph et al 2012;Hewett & Sellier 2017;Lachaussée et al 2018;López, Stickland & Dempster 2018;Allen 2019;Amin et al 2019).…”