Baked meteorites give clues to planetary atmospheres

In a new laboratory investigation of the initial atmospheres of rocky Earth-like planets, researchers at UC Santa Cruz heated pristine meteorite samples in a high-temperature furnace and analyzed the gases .

Their results, published on April 15 in Nature astronomy, suggest that the initial atmospheres of terrestrial planets may differ considerably from many common assumptions used in theoretical models of planetary atmospheres.

“This information will be important when we begin to be able to observe the atmospheres of exoplanets with new telescopes and advanced instrumentation,” said first author Maggie Thompson, graduate student in astronomy and astrophysics at UC Santa Cruz.

It is believed that the first atmospheres of rocky planets are formed primarily from gases from the planet’s surface as a result of intense warming during the accretion of planetary building blocks and volcanic activity later in the onset of the development of the planet.

“When the building blocks of a planet come together, the material is heated and gases are produced, and if the planet is large enough, the gases will be retained as an atmosphere,” explained co-author Myriam Telus, assistant professor of earth and planetary sciences. at UC Santa Cruz. “We are trying to simulate in the laboratory this very early process during the formation of a planet’s atmosphere in order to be able to impose experimental constraints on this history.

The researchers analyzed three meteorites of a type known as CM-type carbonaceous chondrites, which have a composition believed to be representative of the material from which the sun and planets were formed.

“These meteorites have remained on the building block materials that served to form the planets in our solar system,” said Thompson. “Chondrites are different from other types of meteorites in that they did not heat up enough to melt, so they retained some of the more primitive components that can tell us about the make-up of the solar system at the time of formation. the planet. “

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Baked meteorites give clues to planetary atmospheres
Samples of three carbonaceous chondrite meteorites – Murchison, Jbilet Winselwan and Aguas Zarcas – were analyzed in the degassing experiments. Credit: M. Thompson

In collaboration with materials scientists from the physics department, the researchers set up a furnace connected to a mass spectrometer and a vacuum system. When the meteorite samples were heated to 1,200 degrees Celsius, the system analyzed the volatile gases produced from the minerals in the sample. Water vapor was the dominant gas, with significant amounts of carbon monoxide and carbon dioxide, and smaller amounts of hydrogen and hydrogen sulfide gas also being .

According to Telus, models of planetary atmospheres often assume solar abundances, that is, a composition similar to that of the sun and therefore dominated by hydrogen and helium.

“Based on the outgassing of the meteorites, however, one would expect water vapor to be the dominant gas, followed by carbon monoxide and carbon dioxide,” she said. “Using solar abundances is fine for large Jupiter-sized planets that acquire their atmosphere from the solar nebula, but smaller planets are believed to derive more of their atmosphere from outgassing.”

The researchers compared their results with the predictions of chemical equilibrium models based on the composition of meteorites. “Qualitatively, we’re getting pretty similar results to what chemical equilibrium models predict degassing should be degassed, but there are differences as well,” said Thompson. “You need experiences to see what is really going on in practice. We want to do this for a wide variety of meteorites to provide better constraints for theoretical models of exoplanetary atmospheres.

Other researchers have done heating experiments with meteorites, but these studies were for other purposes and used different methods. “A lot of people are interested in what happens when meteorites enter Earth’s atmosphere, so these kinds of studies were not done with that framework in mind to understand outgassing,” said Thompson. .

The three meteorites analyzed for this study were Murchison’s chondrite, which fell in Australia in 1969; Jbilet Winselwan, collected in Western Sahara in 2013; and Aguas Zarcas, who fell in Costa Rica in 2019.

“It may seem arbitrary to use meteorites from our solar system to understand exoplanets around other stars, but studies on other stars reveal that this type of material is actually quite common around other stars,” Telus noted.

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