Scientists reveal conditions at start of solar system – sciencedaily

Ever since scientists started looking at meteorites with microscopes, they’ve been intrigued – and fascinated – by what’s inside. Most meteorites are made of tiny glass balls that date back to the early days of the solar system, even before the planets formed.

Scientists at the University of Chicago have published an analysis explaining how these pearls, found in many meteorites, came to be – and what they can tell us about what happened at the start of the solar system .

“These are big questions,” said Nicole Xike Nie, former UChicago student, PhD’19, postdoctoral fellow at the Carnegie Institution for Science and first author of the study. “Meteorites are snapshots that can reveal the conditions this early dust went through, which has implications for the evolution of Earth and other planets.”

“This question goes back 50 years”

The glass balls inside these meteorites are called chondrules. Scientists believe they are chunks of rock left over from debris that floated billions of years ago, which eventually melted into the planets we know and love now. These are extremely useful to scientists, who can get their hands on pieces of the original stuff that made up the solar system – before the constant rolling of Earth’s volcanoes and tectonic plates changed all the rock we can. find on the planet itself.

But the exact cause of the formation of these chondrules remains uncertain.

“We have the same theories as 50 years ago,” said Timo Hopp, study co-author and postdoctoral researcher at UChicago. “While there has been progress in many other areas, this one has been stubborn.”

Scientists can find clues to the early days of the solar system by examining the types of a given element in a rock. The elements can come in many different forms, called isotopes, and the proportion in each rock varies depending on what happened when that rock was born – how hot it was, how slowly it cooled. or that it was frozen, what other items were around to interact with it. From there, scientists can piece together a history of probable events.

To try to figure out what happened to the chondrules, Nie, Hopp, and other scientists at the Dauphas Origins Lab at UChicago tried to apply a unique angle to the isotopes.

First, Nie took extremely rigorous and precise measurements of the concentrations and isotopes of two depleted elements in meteorites, potassium and rubidium, which reduced the possibilities of what might have happened in the beginning. of the solar system.

From this information, the team reconstructed what was to happen when the chondrules formed. The elements would have been part of a pile of dust hot enough to melt and then vaporize. Then, as the material cooled, some of this vapor melted back into chondrules.

“We can also tell you how quickly it cooled down, because it was fast enough that everything didn’t condense,” said Nicolas Dauphas, professor of geophysical sciences at UChicago. “This must mean that the temperature was dropping at a rate of about 500 degrees Celsius per hour, which is very fast.”

Based on these constraints, scientists can theorize what kind of event would have been sudden and violent enough to cause this extreme warming and cooling. A suitable scenario would be massive shock waves passing through the first nebula. “Large planetary bodies nearby can create shocks, which would have heated and then cooled the dust as it passed,” Dauphas said.

Over the past half-century, people have come up with different scenarios to explain the formation of chondrules – lightning strikes or collisions between rocks – but this new evidence tips the scales in favor of shock waves as an explanation.

This explanation may be the key to understanding a lingering discovery that has plagued scientists for decades, involving a category of “moderately volatile” elements including potassium and rubidium. Earth contains fewer of these elements than scientists would expect, based on their general understanding of how the solar system was formed. They knew the explanation could be traced to a complex chain of heating and cooling, but no one knows the exact sequence. “This is a huge question in the field of cosmochemistry.” said Dauphas.

Now, finally, the team is happy to have made a significant breach in the mystery.

“We know other processes have happened – this is only part of the story – but it really resolves a stage in the formation of the planets,” Hopp said.

Nie agrees: “It’s really cool to be able to say quantitatively, this is what happened.”

The other co-authors of the article were from the Carnegie Institution for Science and the University of Washington.


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Arline J. Mercier