from
https://www.sciencenews.org/article/ryugu-asteroid-stardust-old-space

Ryugu asteroid samples are sprinkled with stardust older than the solar
system
These stellar ashes could illuminate the history of the solar system
A photo of a sample of the asteroid Ryugu, small black rocks, in a small
circular dish.
Samples of the asteroid Ryugu (pictured) contain bits of stardust
created before the solar system was born. That stardust could reveal
details of the solar system’s history.

T. YADA ET AL/NATURE 2021

By Lisa Grossman

JULY 14, 2023 AT 2:00 PM

Samples of the asteroid Ryugu contain bits of stardust that predate the
birth of our solar system.

Slivers of Ryugu material, snagged by the Japanese Hayabusa2 spacecraft,
appear to come from the solar system’s frozen fringes, rather than from
the asteroid itself, scientists report July 14 in Science Advances.
These foreign fragments could illuminate details of the solar system’s
history.

Finding these fragments “is really unique,” says cosmochemist Ann Nguyen
of NASA’s Johnson Space Center in Houston. “It’s showing us a new type
of material, but also telling us about the dynamics of material from the
outer solar system.”

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The Hayabusa2 spacecraft visited the asteroid in 2018 and 2019, then
returned to Earth with 5.4 grams of the space rock in 2020 (SN:
12/7/20). Scientists examined those samples in the lab in ways that
can’t be done with telescopes or even spacecraft, like getting detailed
measurements of chemical composition.

So far, those examinations have shown that Ryugu is rich in carbon, that
it’s made of the same material as some of the rarest meteorites found on
Earth, and that it was altered by water at some point in its past (SN:
6/9/22). Scientists think that Ryugu formed from the debris of a larger
asteroid, which broke up in a collision and re-formed into a loose pile
of rubble (SN: 3/20/19).

Nguyen, however, was searching for something different. “My focus of
research is presolar grains,” tiny specks of material that formed from
the ashes of dying stars, she says (SN: 1/13/20). “I was on the hunt for
them.” These delicate grains contain different isotopes — atoms of an
element that have different numbers of neutrons — than those formed by
the sun, giving away their alien origins.

Nguyen and her colleagues examined two samples of Ryugu, each less than
a millimeter in size. They then picked out tiny slivers of rock, 50 to
200 micrometers wide, called clasts, that stood out from the rest of the
Ryugu sample.

Using scanning electron microscopes and other imaging techniques, Nguyen
and colleagues found that two of the clasts are chemically different
from the rest of Ryugu, with lower oxygen, magnesium and silicon
contents, and greater amounts of iron and sulfur.

Electron microscope images of a sliver of solar system material
(outlined in white) in a sample of the asteroid Ryugu show that the
material is different from the rest of the asteroid. The different
colors highlight different elements in the sample: oxygen (magenta),
magnesium (green), silicon (light blue), iron (dark blue) and sulfur
(yellow). The slivers also contain grains of silicates (white arrows)
that come from outside the solar system.
Electron microscope images of a sliver of solar system material
(outlined in white) in a sample of the asteroid Ryugu show that the
material is different from the rest of the asteroid. The different
colors highlight different elements in the sample: oxygen (magenta),
magnesium (green), silicon (light blue), iron (dark blue) and sulfur
(yellow). The slivers also contain grains of silicates (white arrows)
that come from outside the solar system.
A. NGUYEN ET AL/SCIENCE ADVANCES 2023
The clasts also have much higher concentrations of presolar grains than
the rest of the Ryugu material. The grains contain silicon carbide,
which is easily destroyed by water, plus an extra abundance of organic
matter.

That means the grains could not have been part of Ryugu’s parent body,
which was extensively altered by water. The researchers think the grains
were bits of a comet that formed in the outer solar system’s Kuiper
belt, where the conditions were cool and dry. Then the grains sprinkled
onto the rubble that formed Ryugu sometime between the original
asteroid’s destruction and the rubble pile’s formation.

“Between these events, it kind of collected some other friends that came
from other bodies, from different parts of the solar system,” Nguyen
says. It’s not yet clear how material from the outer solar system found
its way to Ryugu. Perhaps the asteroid formed farther from the sun — and
hence, closer to the Kuiper belt — than it is today. “It’s interesting
to visualize how this asteroid came about and what it gathered along the
way.”

The discovery is “very exciting,” says cosmochemist Philipp Heck of the
Field Museum of Natural History in Chicago, who was not involved in the
new work. “These clasts that got incorporated into Ryugu after it
formed, they’re really valuable. I think they’re even more valuable than
the Ryugu sample itself.”

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The clasts can reveal what the unaltered ingredients that formed the
solar system were made of. Think of the disk that formed the planets as
bread dough, Heck says. Once the dough is well-mixed, it’s hard to tell
what went into it. Clasts like the ones in the Ryugu sample are like
bits of unmixed flour that survived intact in the final loaf, he says —
not delicious, but very informative.

“If we want to understand the ingredients from which the solar system
formed, the original ingredients, we need to find these very rare,
unaltered clasts,” Heck says. “This is one of them.”

Questions or comments on this article? E-mail us at
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CITATIONS
A. Nguyen et al. Abundant presolar grains and primordial organics
preserved in carbon-rich exogenous clasts in asteroid Ryugu. Science
Advances. Published online July 14, 2023. doi: 10.1126/sciadv.adh1003.

Lisa Grossman
About Lisa Grossman
E-mail
Twitter
Lisa Grossman is the astronomy writer. She has a degree in astronomy
from Cornell University and a graduate certificate in science writing
from University of California, Santa Cruz. She lives near Boston.

On 7/18/23 11:54, a425couple wrote:
> from
> https://www.sciencenews.org/article/ryugu-asteroid-stardust-old-space
>
> Ryugu asteroid samples are sprinkled with stardust older than the solar
> system

also, from
https://www.npr.org/2023/07/14/1187815750/ryugu-hayabusa-stardust-sprinkled-asteroid

Researchers discover stardust sprinkled on a nearby asteroid
July 14, 20233:51 PM ET
Heard on All Things Considered
Geoff Brumfiel, photographed for NPR, 17 January 2019, in Washington DC.
Geoff Brumfiel

2-Minute Listen
Download
Transcript

A small sample of asteroid collected by Japan's Hayabusa-2 probe streaks
back to Earth in 2020. Researchers now say the sample contains tiny
grains of dust from other stars.
MORGAN SETTE/AFP via Getty Images
Scientists have made a surprising discovery in a sample returned from an
asteroid: Embedded in its rocks are grains of stardust.

The dust, which came from distant stars and drifted through space for
millions or billions of years, could provide clues about how the solar
system formed, according to Ann Nguyen, a cosmochemist at NASA's Johnson
Space Center in Houston, Texas.

"It was definitely not something I expected to find," she says. "I
cannot tell you the excitement I felt."

Stellar Forges
Stars forged nearly all of the elements of the Universe. Many of the
atoms that make up our bodies were themselves made inside of the core of
a star somewhere else. That's because the high pressures and
temperatures can fuse lightweight atomic nuclei into heavier elements.

Japan's Hayabusa2 Spacecraft Arrives At Its Asteroid Destination
SPACE
Japan's Hayabusa2 Spacecraft Arrives At Its Asteroid Destination
"The core is extremely hot, and then you go out in the atmosphere, it's
cool enough so that gas can form and aggregate into tiny grains," Nguyen
says.

Think of these little grains as cosmic dust motes. Sometimes the star
that formed these grains would explode, blowing them across the galaxy
like dandelion seeds. Other times they would drift away on their own —
traveling on the stellar wind into deep space.

Ryugu is a near-Earth asteroid. Researchers think it picked up the
stardust when it was previously residing at the edge of the solar
system, possibly in a collision with another comet or asteroid.
JAXA/ISAS
"Probably a lot of them do get destroyed," Nguyen says, "but some of
them survive and they make it to our region of the universe where our
solar system formed."

The stardust swirled and clumped and eventually became part of the sun,
and the planets, and even us. That idea led the astronomer Carl Sagan to
famously remark that "We're made of star-stuff."

Cosmic Dust Motes
The problem is, the original dust grains were fragile — and so when they
became part of this new solar system, they were broken up, and blended.
Their origins were lost, and learning more about where they came from
"is one of the big questions in cosmochemistry," Nguyen says.

Fast-forward a couple billion years: In 2019, a Japanese spacecraft
visited a little asteroid called Ryugu. It scooped up a tiny sample, and
an even tinier portion of that sample found its way to Nguyen's lab. She
fired up her best dust analyzers, ready to nerd out on some asteroid grit.

"I kind of thought the results I would get would be run-of-the-mill,"
she recalls.

Nasa scientists received a tiny sample from the asteroid Ryugu in 2021.
Their new analysis suggests it contains stardust.
ROBERT MARKOWITZ/ NASA-JSC
But as her team writes in the journal Science Advances, the samples
contained organic molecules from deep space, pieces of ancient rock from
the very edge of the solar system, and many tiny grains of perfectly
preserved stardust.

Nguyen says the grains look different than the material from our own
solar system, because different stars leave different nuclear signatures
in the atoms.

"It kind of lights up like a Christmas tree light," she says. "Their
isotopic signatures are just so different than the material that formed
in our solar system or got homogenized in the solar system."

Nguyen says that the stardust grains provide some clues about the types
of stars that contributed to our solar system. It also shows that
exploding stars, or supernovae, probably contributed more of the dust
than researchers had previously believed.

But above all, she says, these tiny grains are a reminder of the way in
which we fit into the vast cosmos.

"It just shows us how rich our Universe is," she says. "These materials
all played a part in our life here on Earth."

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