During atmospheric deceleration, micrometeoroids are subjected to strong gravitational forces. Additionally, many particles have spin, which also creates centrifugal forces. Combined, these forces often shape the spherules into aerodynamic forms. These forms include oblate (flattened) or prolate (elongated) spherules. Spin along multiple axes, combined with simultaneous crystallization, may form more complex forms.

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The gravitational and centrifugal forces also affect metal beads and vesicles present in the spherules, with high-density beads being forced outward and low-density vesicles being forced inward. Thus, oblate spherules may contain a ring of beads around the perimeter and a large vesicle at the center. Prolate spherules with their spin axis parallel to the direction of flight often lack vesicles, which were likely lost from their tail. Hollow spherules with large inner voids are believed to form by rapid and complex spin, which traps large vesicles at the center. These particles are believed to have only been recently released from their parent body and their spin hasn’t yet been slowed by magnetic damping. See also Genge (2016).