Sculpted by starlight: A meteorite witness to the solar system's birth
Researchers use unusual meteorite to gain insight into our solar system's past, present

Date:
July 6, 2021
Source:
Washington University in St. Louis
Summary:
Scientists knew a burst of UV light left its mark on our solar
system.

Now they know the source of that light.



FULL STORY ==========================================================================
In 2011, scientists confirmed a suspicion: There was a split in the local cosmos. Samples of the solar wind brought back to Earth by the Genesis
mission definitively determined oxygen isotopes in the sun differ from
those found on Earth, the moon and the other planets and satellites in
the solar system.


========================================================================== Early in the solar system's history, material that would later coalesce
into planets had been hit with a hefty dose of ultraviolet light, which
can explain this difference. Where did it come from? Two theories emerged: Either the ultraviolet light came from our then-young sun, or it came
from a large nearby star in the sun's stellar nursery.

Now, researchers from the lab of Ryan Ogliore, assistant professor of
physics in Arts & Sciences at Washington University in St. Louis, have determined which was responsible for the split. It was most likely light
from a long-dead massive star that left this impression on the rocky
bodies of the solar system.

The study was led by Lionel Vacher, a postdoctoral research associate
in the physics department's Laboratory for Space Sciences.

Their results are published in the journal Geochimica et Cosmochimica
Acta.

"We knew that we were born of stardust: that is, dust created by other
stars in our galactic neighborhood were part of the building blocks of
the solar system," Ogliore said.

"But this study showed that starlight had a profound effect on our
origins as well." *Tiny time capsule


==========================================================================
All of that profundity was packed into a mere 85 grams of rock, a piece
of an asteroid found as a meteorite in Algeria in 1990, named Acfer
094. Asteroids and planets formed from the same presolar material,
but they've been influenced by different natural processes. The rocky
building blocks that coalesced to form asteroids and planets were broken
up and battered; vaporized and recombined; and compressed and heated. But
the asteroid that Acfer 094 came from managed to survive for 4.6 billion
years mostly unscathed.

"This is one of the most primitive meteorites in our collection,"
Vacher said.

"It was not heated significantly. It contains porous regions and tiny
grains that formed around other stars. It is a reliable witness to the
solar system's formation." Acfer 094 is also the only meteorite that
contains cosmic symplectite, an intergrowth of iron-oxide and iron-sulfide
with extremely heavy oxygen isotopes -- a significant finding.

The sun contains about 6% more of the lightest oxygen isotope compared
with the rest of the solar system. That can be explained by ultraviolet
light shining on the solar system's building blocks, selectively breaking
apart carbon monoxide gas into its constituent atoms. That process
also creates a reservoir of much heavier oxygen isotopes. Until cosmic symplectite, however, no one had found this heavy isotope signature in
samples of solar system materials.

With only three isotopes, however, simply finding the heavy oxygen
isotopes wasn't enough to answer the question of the origin of the
light. Different ultraviolet spectra could have created the same result.



========================================================================== "That's when Ryan came up with the idea of sulfur isotopes," Vacher said.

Sulfur's four isotopes would leave their marks in different ratios
depending on the spectrum of ultraviolet light that irradiated hydrogen
sulfide gas in the proto-solar system. A massive star and a young sun-like
star have different ultraviolet spectra.

Cosmic symplectite formed when ices on the asteroid melted and reacted
with small pieces of iron-nickel metal. In addition to oxygen, cosmic symplectite contains sulfur in iron sulfide. If its oxygen witnessed this ancient astrophysical process -- which led to the heavy oxygen isotopes -- perhaps its sulfur did, too.

"We developed a model," Ogliore said. "If I had a massive star,
what isotope anomalies would be created? What about for a young,
sun-like star? The precision of the model depends on the experimental
data. Fortunately, other scientists have done great experiments on
what happens to isotope ratios when hydrogen sulfide is irradiated
by ultraviolet light." Sulfur and oxygen isotope measurements of
cosmic symplectite in Acfer 094 proved another challenge. The grains,
tens of micrometers in size and a mixture of minerals, required new
techniques on two different in-situ secondary-ion mass spectrometers:
the NanoSIMS in the physics department (with assistance from Nan Liu,
research assistant professor in physics) and the 7f-GEO in the Department
of Earth and Planetary Sciences, also in Arts & Sciences.

*Putting the puzzle together It helped to have friends in earth and
planetary sciences, particularly David Fike, professor of earth and
planetary sciences and director of Environmental Studies in Arts &
Sciences, and Clive Jones, research scientist in earth and planetary
sciences.

"They are experts in high-precision in-situ sulfur isotope measurements
for biogeochemistry," Ogliore said. "Without this collaboration, we would
not have achieved the precision we needed to differentiate between the
young sun and massive star scenarios." The sulfur isotope measurements
of cosmic symplectite were consistent with ultraviolet irradiation from
a massive star, but did not fit the UV spectrum from the young sun. The
results give a unique perspective on the astrophysical environment of the
sun's birth 4.6 billion years ago. Neighboring massive stars were likely
close enough that their light affected the solar system's formation. Such
a nearby massive star in the night sky would appear brighter than the
full moon.

Today, we can look to the skies and see a similar origin story play out elsewhere in the galaxy.

"We see nascent planetary systems, called proplyds, in the Orion nebula
that are being photoevaporated by ultraviolet light from nearby massive
O and B stars," Vacher said.

"If the proplyds are too close to these stars, they can be
torn apart, and planets never form. We now know our own solar
system at its birth was close enough to be affected by the
light of these stars," he said. "But thankfully, not too close." ========================================================================== Story Source: Materials provided by
Washington_University_in_St._Louis. Original written by Brandie
Jefferson. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Lionel G. Vacher, Ryan C. Ogliore, Clive Jones, Nan Liu, David
A. Fike.

Cosmic symplectite recorded irradiation by nearby massive stars
in the solar system's parent molecular cloud. Geochimica et
Cosmochimica Acta, 2021; DOI: 10.1016/j.gca.2021.06.026 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/07/210706115405.htm

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