Iron-rich meteorites show record of core crystallization in system's
oldest planetesimals

Date:
August 3, 2020
Source:
Carnegie Institution for Science
Summary:
New work uncovers new details about our Solar System's oldest
planetary objects, which broke apart in long-ago collisions
to form iron-rich meteorites. Their findings reveal that the
distinct chemical signatures of these meteorites can be explained
by the process of core crystallization in their parent bodies,
deepening our understanding of the geochemistry occurring in the
Solar System's youth.



FULL STORY ==========================================================================
New work led by Carnegie's Peng Ni and Anat Shahar uncovers new details
about our Solar System's oldest planetary objects, which broke apart
in long-ago collisions to form iron-rich meteorites. Their findings
reveal that the distinct chemical signatures of these meteorites can be explained by the process of core crystallization in their parent bodies, deepening our understanding of the geochemistry occurring in the Solar
System's youth. They are published by Nature Geoscience.


==========================================================================
Many of the meteorites that shot through our planet's atmosphere and
crashed on its surface were once part of larger objects that broke up
at some point in our Solar System's history. The similarity of their
chemical compositions tells scientists that they originated as part of
common parent bodies, even if they arrived here centuries apart and in
vastly different locations.

Deciphering the geologic processes that shaped these parent bodies could
teach us more about our Solar System's history and Earth's formative
years. To truly understand what makes our planet capable of sustaining
life, and to look for habitable worlds elsewhere, it is crucial to
understand its interior -- past and present.

"Like our Solar System's rocky planets, these planetesimals accreted from
the disk of dust and gas that surrounded our Sun in its youth," explained
lead author Ni. "And like on Earth, eventually, the densest material
sank toward the center, forming distinct layers." Iron meteorites were
thought to be the remnants of the cores of their ancient, broken-apart
parent bodies.

"A history of how their layers differentiated is recorded in their
chemical makeup, if we can read it," said Shahar.

There are four stable isotopes of iron. (Each element contains a
unique number of protons, but its isotopes have varying numbers of
neutrons.) This means that each iron isotope has a slightly different
mass than the others. As a result, some isotopes are preferred by certain chemical reactions -- which, in turn, affects the proportion of that
isotope in the reaction's end products.

The traces of this favoritism can be found in rock samples and can help elucidate the processes that forged these meteorite parent bodies.

Previous research on the ratios of iron isotopes in iron meteorites
led to a puzzling observation: compared to the raw material from which
their parent bodies were constructed, they are enriched in heavy isotopes
of iron.

Together with Nancy Chabot and Caillin Ryan of the Johns Hopkins
University Applied Physics Laboratory, Ni and Shahar determined that
this enrichment can be explained entirely by the crystallization of a
parent object's core.

The researchers use lab-based mimicry to simulate the temperatures of core crystallization in iron meteorite parent bodies. Sophisticated models
of the crystallization process including other elemental concentrations
-- for example, of gold and iridium, as well as isotopes of iron --
confirmed their findings.

"This improved understanding of core crystallization adds to our knowledge about our Solar System's formative period," Ni concluded.


========================================================================== Story Source: Materials provided by
Carnegie_Institution_for_Science. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Peng Ni, Nancy L. Chabot, Caillin J. Ryan, Anat Shahar. Heavy iron
isotope composition of iron meteorites explained by core
crystallization.

Nature Geoscience, 2020; DOI: 10.1038/s41561-020-0617-y ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200803120152.htm

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