TEM analyses of in situ presolar grains from unequilibrated ordinary chondrite LL3.0 Semarkona. (arXiv:2205.04372v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Singerling_S/0/1/0/all/0/1">Sheryl A. Singerling</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nittler_L/0/1/0/all/0/1">Larry R. Nittler</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Barosch_J/0/1/0/all/0/1">Jens Barosch</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dobrica_E/0/1/0/all/0/1">Elena Dobrica</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Brearley_A/0/1/0/all/0/1">Adrian J. Brearley</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Stroud_R/0/1/0/all/0/1">Rhonda M. Stroud</a>
We investigated six presolar grains from very primitive regions of the matrix
in the unequilibrated ordinary chondrite Semarkona with TEM. These grains
include one SiC, one oxide (Mg-Al spinel), and four silicates. Structural and
elemental compositional studies of presolar grains located within their
meteorite hosts have the potential to provide information on conditions and
processes throughout the grains’ histories. Our analyses show that the SiC and
spinel grains are stoichiometric and well crystallized. In contrast, the
majority of the silicate grains are non-stoichiometric and poorly crystallized.
These findings are consistent with previous TEM studies of presolar grains from
interplanetary dust particles and chondritic meteorites. We interpret the
poorly crystalline nature, non-stoichiometry, more Fe- rather than Mg-rich
compositions, and/or compositional heterogeneities as features of the formation
by condensation under non-equilibrium conditions. Evidence for parent body
alteration includes rims with mobile elements (S or Fe) on the SiC grain and
one silicate grain. Other features characteristic of secondary processing in
the interstellar medium, the solar nebula, and/or on parent bodies, were not
observed or are better explained by processes operating in circumstellar
envelopes. In general, there was very little overprinting of primary features
of the presolar grains by secondary processes (e.g., ion irradiation,
grain-grain collisions, thermal metamorphism, aqueous alteration). This finding
underlines the need for additional TEM studies of presolar grains located in
the primitive matrix regions of Semarkona, to address gaps in our knowledge of
presolar grain populations accreted to ordinary chondrites.
We investigated six presolar grains from very primitive regions of the matrix
in the unequilibrated ordinary chondrite Semarkona with TEM. These grains
include one SiC, one oxide (Mg-Al spinel), and four silicates. Structural and
elemental compositional studies of presolar grains located within their
meteorite hosts have the potential to provide information on conditions and
processes throughout the grains’ histories. Our analyses show that the SiC and
spinel grains are stoichiometric and well crystallized. In contrast, the
majority of the silicate grains are non-stoichiometric and poorly crystallized.
These findings are consistent with previous TEM studies of presolar grains from
interplanetary dust particles and chondritic meteorites. We interpret the
poorly crystalline nature, non-stoichiometry, more Fe- rather than Mg-rich
compositions, and/or compositional heterogeneities as features of the formation
by condensation under non-equilibrium conditions. Evidence for parent body
alteration includes rims with mobile elements (S or Fe) on the SiC grain and
one silicate grain. Other features characteristic of secondary processing in
the interstellar medium, the solar nebula, and/or on parent bodies, were not
observed or are better explained by processes operating in circumstellar
envelopes. In general, there was very little overprinting of primary features
of the presolar grains by secondary processes (e.g., ion irradiation,
grain-grain collisions, thermal metamorphism, aqueous alteration). This finding
underlines the need for additional TEM studies of presolar grains located in
the primitive matrix regions of Semarkona, to address gaps in our knowledge of
presolar grain populations accreted to ordinary chondrites.
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