How stony-iron meteorites form
SAPHiR multi-anvil press solves mystery of the solar system

Date:
July 29, 2020
Source:
Technical University of Munich (TUM)
Summary:
Meteorites give us insight into the early development of the solar
system. A scientific team has for the first time simulated the
formation of a class of stony-iron meteorites, so-called pallasites,
on a purely experimental basis.



FULL STORY ========================================================================== Meteorites give us insight into the early development of the solar system.

Using the SAPHiR instrument at the Research Neutron Source Heinz
Maier-Leibnitz (FRM II) at the Technical University of Munich (TUM),
a scientific team has for the first time simulated the formation of
a class of stony-iron meteorites, so- called pallasites, on a purely experimental basis.


========================================================================== "Pallasites are the optically most beautiful and unusual meteorites,"
says Dr.

Nicolas Walte, the first author of the study, in an enthusiastic
voice. They belong to the group of stony-iron meteorites and comprise
green olivine crystals embedded in nickel and iron. Despite decades of research, their exact origins remained shrouded in mystery.

To solve this puzzle, Dr. Nicolas Walte, an instrument scientist at the
Heinz Maier-Leibnitz Zentrum (MLZ) in Garching, together with colleagues
from the Bavarian Geoinstitute at the University of Bayreuth and the
Royal Holloway University of London, investigated the pallasite formation process. In a first, they succeeded in experimentally reproducing the structures of all types of pallasites.

Deployment of the SAPHiR instrument For its experiments, the team used the SAPHiR multi-anvil press which was set up under the lead of Prof. Hans
Keppler of the Bavarian Geoinstitute at the MLZ and the similar MAVO
press in Bayreuth. Although neutrons from the FRM II have not yet been
fed into SAPHiR, experiments under high pressures and at high temperatures
can already be performed.

"With a press force of 2400 tons, SAPHiR can exert a pressure of 15
gigapascals (GPa) on samples at over 2000 DEGC," explains Walte. "That
is double the pressures needed to convert graphite into diamond." To
simulate the collision of two celestial bodies, the research team required
a pressure of merely 1 GPa at 1300 DEGC.



==========================================================================
How are pallasites formed? Until recently, pallasites were believed to
form at the boundary between the metallic core and the rocky mantle of asteroids. According to an alternative scenario, pallasites form closer
to the surface after the collision with another celestial body. During
the impact molten iron from the core of the impactor mingles with the olivine-rich mantle of the parent body.

The experiments carried out have now confirmed this impact
hypothesis. Another prerequisite for the formation of pallasites is that
the iron core and rocky mantle of the asteroid have partially separated beforehand.

All this happened shortly after their formation about 4.5 billion
years ago.

During this phase, the asteroids heated up until the denser metallic
components melted and sank to the center of the celestial bodies.

The key finding of the study is that both processes -- the partial
separation of core and mantle, and the subsequent impact of another
celestial body -- are required for pallasites to form.

Insights into the origins of the solar system "Generally, meteorites are
the oldest directly accessible constituents of our solar system. The
age of the solar system and its early history are inferred primarily
from the investigation of meteorites," explains Walte.

"Like many asteroids, the Earth and moon are stratified into multiple
layers, consisting of core, mantle and crust," says Nicolas Walte. "In
this way, complex worlds were created through the agglomeration of cosmic debris. In the case of the Earth, this ultimately laid the foundations
for the emergence of life." The high-pressure experiments and the
comparison with pallasites highlight significant processes that occurred
in the early solar system. The team's experiments provide new insights
into the collision and material mixing of two celestial bodies and the subsequent rapid cooling down together. This will be investigated in
more detail in future studies.


========================================================================== Story Source: Materials provided by
Technical_University_of_Munich_(TUM). Note: Content may be edited for
style and length.


========================================================================== Journal Reference:
1. Nicolas P. Walte, Giulio F.D. Solferino, Gregor J. Golabek, Danielle
Silva Souza, Audrey Bouvier. Two-stage formation of pallasites
and the evolution of their parent bodies revealed by deformation
experiments.

Earth and Planetary Science Letters, 2020; 546: 116419 DOI:
10.1016/ j.epsl.2020.116419 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200729114723.htm

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