Olivine settling in cosmic spherules during atmospheric deceleration: An indicator of the orbital eccentricity of interplanetary dustOPEN ACCESS 

Matthew J. Genge, Martin Suttl

Geophysical Research Letters 43
DOI: 10.1002/2016GL070874
First published: 19 October 2016


Key Points

* Antarctic cosmic spherules with cumulate textures are reported
* Numerical simulation shows that settling of relict olivine is possible at entry velocities of 16 km s−1 relating to dust eccentricities of 0.35
* The relative abundance of cumulate olivine spherules provides a proxy for variations in the orbital properties of dust over time

“A new type of cosmic spherule is reported with textures suggesting settling of olivine during atmospheric deceleration. Numerical simulations of entry heating reveal that relict forsterite, which survives melting, can settle over the 1–2 s of flight at high entry angles and entry velocities up to 16 km s−1. Enhanced crystallization of phenocrysts by heterogeneous nucleation on accumulated relict forsterites is the most likely origin of the observed cumulate textures in cosmic spherules. Such textures in cosmic spherules reveal interplanetary dust with higher encounter velocity with the Earth that correspond to orbital eccentricities >0.3. The relative abundance of cumulate spherules suggests that 14% of ordinary chondrite-related, S(IV)-type asteroid dust over the last 800 kyr had relatively high orbital eccentricity owing to secular and planetary perturbations. The textures of cosmic spherules collected from sediments can therefore be used to trace dust orbital variations with time, which may influence terrestrial climate.”