'Curious and curiouser!'

January 28, 2020

An unusual chunk in a meteorite may contain a surprising bit of space history, based on new research from Washington University in St. Louis.

Presolar grains -- tiny bits of solid interstellar material formed before the sun was born -- are sometimes found in primitive meteorites. But a new analysis reveals evidence of presolar grains in part of a meteorite where they are not expected to be found.

"What is surprising is the fact that presolar grains are present," said Olga Pravdivtseva, research associate professor of physics in Arts & Sciences and lead author of a new paper in Nature Astronomy. "Following our current understanding of solar system formation, presolar grains could not survive in the environment where these inclusions are formed."

Curious Marie is a notable example of an "inclusion," or a chunk within a meteorite, called a calcium-aluminum-rich inclusion (CAI). These objects, some of the first to have condensed in the solar nebula, help cosmochemists define the age of the solar system. This particular chunk of meteorite -- from the collection of the Robert A. Pritzker Center for Meteoritics and Polar Studies at the Chicago Field Museum -- was in the news once before, when scientists from the University of Chicago gave it its name to honor chemist Marie Curie.

For the new work, Pravdivtseva and her co-authors, including Sachiko Amari, research professor of physics at Washington University, used noble gas isotopic signatures to show that presolar silicon carbide (SiC) grains are present in Curious Marie.

That's important because presolar grains are generally thought to be too fragile to have endured the high-temperature conditions that existed near the birth of our sun.

But not all CAIs were formed in quite the same way.

"The fact that SiC is present in refractory inclusions tells us about the environment in the solar nebula at the condensation of the first solid materials," said Pravdivtseva, who is part of Washington University's McDonnell Center for the Space Sciences. "The fact that SiC was not completely destroyed in Curious Marie can help us to understand this environment a little bit better.

"Many refractory inclusions were melted and lost all textural evidence of their condensation. But not all."

Like solving a mystery

Pravdivtseva and her collaborators used two mass spectrometers built in-house at Washington University to make their observations. The university has a long history of noble gas work and is home to one of the best-equipped noble gas laboratories in the world. Still, this work was uniquely challenging.

The researchers had 20 mg of Curious Marie to work with, which is a relatively large sample from a cosmochemistry perspective. They heated it up incrementally, increasing temperature and measuring the composition of four different noble gases released at each of 17 temperature steps.

"Experimentally, it is an elegant work," Pravdivtseva said. "And then we had a puzzle of noble gas isotopic signatures to untangle. For me, it is like solving a mystery."

Others have looked for evidence of SiC in such calcium-aluminum-rich inclusions in meteorites using noble gases before, but Pravdivtseva's team is the first to find it.

"It was beautiful when all noble gases pointed to the same source of the anomalies -- SiC," she said.

"Not only do we see SiC in the fine-grained CAIs, we see a population of small grains that formed at special conditions," Pravdivtseva said. "This finding forces us to revise how we see the conditions in the early solar nebula."
-end-


Washington University in St. Louis

Related Solar System Articles from Brightsurf:

Ultraviolet shines light on origins of the solar system
In the search to discover the origins of our solar system, an international team of researchers, including planetary scientist and cosmochemist James Lyons of Arizona State University, has compared the composition of the sun to the composition of the most ancient materials that formed in our solar system: refractory inclusions in unmetamorphosed meteorites.

Second alignment plane of solar system discovered
A study of comet motions indicates that the Solar System has a second alignment plane.

Pressure runs high at edge of solar system
Out at the boundary of our solar system, pressure runs high.

What a dying star's ashes tell us about the birth of our solar system
A UA-led team of researchers discovered a dust grain forged in a stellar explosion before our solar system was born.

What scientists found after sifting through dust in the solar system
Two recent studies report discoveries of dust rings in the inner solar system: a dust ring at Mercury's orbit, and a group of never-before-detected asteroids co-orbiting with Venus, supplying the dust in Venus' orbit.

Discovered: The most-distant solar system object ever observed
A team of astronomers has discovered the most-distant body ever observed in our solar system.

Discovery of the first body in the Solar System with an extrasolar origin
Asteroid 2015 BZ509 is the very first object in the Solar System shown to have an extrasolar origin.

First interstellar immigrant discovered in the solar system
A new study has discovered the first known permanent immigrant to our solar system.

A star disturbed the comets of the solar system in prehistory
About 70,000 years ago, when the human species was already on Earth, a small reddish star approached our solar system and gravitationally disturbed comets and asteroids.

Scientists detect comets outside our solar system
Scientists from MIT and other institutions, working closely with amateur astronomers, have spotted the dusty tails of six exocomets -- comets outside our solar system -- orbiting a faint star 800 light years from Earth.

Read More: Solar System News and Solar System Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.