Carbon’s interstellar journey to Earth

star dust

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The saying goes that we are made of stellar dust, and some studies that include research from the University of Michigan may be more true than we previously thought.

The first study, led by UM researcher Jie (Jackie) Li, and published in Scientific progress, finds that most carbon on Earth is likely to come from the interstellar medium, the material that exists in the space between stars in a galaxy. This probably happened well after the protoplanetary disk, the cloud of dust and gas that surrounded our young sun and contained the building blocks of the planets, formed and warmed up.

Carbon was probably sequestered in solids within one million years after the sun’s birth – meaning that carbon, the backbone of life on earth, survived an interstellar journey to our planet.

Previously, researchers thought that carbon in the earth came from molecules that were initially present in new gas, which then accrued on a rocky planet when the gases were cool enough to precipitate the molecules. Li and her team, which includes UM astronomer Edwin Bergin, Geoffrey Blake of the California Institute of Technology, Fred Ciesla of the University of Chicago and Marc Hirschmann of the University of Minnesota, point out in this study that the gas molecules that carry carbon , not The earth can not be built, because once it evaporates carbon, it does not condense back to a solid.

“The condensation model has been widely used for decades. It assumes that during the formation of the sun all the elements of the planet evaporated, and as the disk cooled, some of these gases condensed and supplied chemical constituents to solids. does not work for carbon, ‘said Li, a professor in the UM Department of Earth and Environmental Sciences.

Much of the carbon was delivered to the disk in the form of organic molecules. However, when carbon evaporates, it produces much more volatile species that require very low temperatures to form solids. More importantly, carbon does not condense back into an organic form. As a result, Li and her team deduced that most of Earth’s carbon was probably inherited directly from the interstellar medium, avoiding evaporation altogether.

To better understand how the earth obtained its carbon, Li estimates the maximum amount of carbon the earth can contain. To do this, she compared how fast a seismic wave travels through the nucleus with the known sound velocities of the nucleus. It told the researchers that carbon probably makes up less than half a percent of the earth’s mass. Understanding the upper limits of how much carbon the earth may contain, the researchers tell information about when the carbon was possibly delivered here.

“We asked another question: we asked how much carbon you can put in the earth’s core and still be in compliance with all the constraints,” said Bergin, professor and chairman of the Department of Astronomy at UM. “There’s uncertainty here. Let’s embrace the uncertainty of asking what the real limit is for how much carbon is very deep in the earth, and that will tell us the true landscape we are in.”

The carbon of a planet must exist in the right proportions to support life as we know it. Too much carbon and the Earth’s atmosphere would be like Venus, which traps the heat of the sun and maintains a temperature of about 880 degrees Fahrenheit. Too little carbon, and the earth will look like Mars: an inhospitable place that can not support life on water, with a temperature of minus 60.

In a second study by the same group of authors, but led by Hirschmann of the University of Minnesota, the researchers looked at how carbon is processed when the small precursors of planets, known as planetesimals, retain carbon during their early formation. By examining the metal cores of these bodies, which are now preserved as iron meteorites, they found that much of the carbon must be lost during this important step of planetary origin if the planetary animals melt, core form and lose gas. It enhances the previous thinking, says Hirschmann.

“Most models have the carbon and other vital materials like water and nitrogen that go from the nebula into primitive rock bodies, and are then delivered to growing planets like Earth or Mars,” said Hirschmann, professor of earth and environmental sciences. . . “But it skips an important step in which the planetary animals lose much of their carbon before they accidentally hit the planets.”

Hirschmann’s study was recently published in Proceedings of the National Academy of Sciences.

“The planet needs carbon to regulate its climate and make life exist, but it’s a very delicate thing,” Bergin said. “You do not want too little, but you do not want too much.”

Bergin says the two studies both describe two different aspects of carbon loss – and suggest that carbon loss appears to be a central aspect in the construction of the earth as a habitable planet.

“To answer whether or not terrestrial planets exist elsewhere can only be achieved by working at the intersection of disciplines such as astronomy and geochemistry,” said Ciesla, professor of geophysical sciences. “While approaches and the specific questions that researchers work to answer differ across disciplines, it is necessary to compile a coherent story to identify topics of mutual interest and find ways to bridge the intellectual gaps between them. It’s challenging, but the effort is stimulating and rewarding. ‘

Blake, a co-author of both studies and a professor of cosmochemistry and planetary science and chemistry at Caltech, says this kind of interdisciplinary work is critical.

“Over the history of our galaxy alone, rocky planets like the earth or a little bigger have been composed hundreds of millions of times around stars like the sun,” he said. “Can we expand this work to investigate carbon loss in planetary systems more widely? Such research would require a diverse community of scholars.”


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More information:
“Earth’s carbon shortage caused by early loss due to irreversible sublimation” Scientific progress (2021). advances.sciencemag.org/lookup …. .1126 / sciadv.abd3632

Provided by the University of Michigan

Quotation: From star dust to light blue spot: Carbon’s interstellar journey to Earth (2021, 2 April) detected on 3 April 2021 from https://phys.org/news/2021-04-stardust-pale-blue-dot-carbon. html

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