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Crushed space rocks hint at the early atmospheric composition of exoplanets

The pieces of burnt meteorites on earth can tell scientists that the first atmospheres of exoplanets are formed.

A set of experiments firing the pulverized space rocks suggest that the rocky planets had early atmospheres filled with water, astrophysicist Maggie Thompson of the University of California, Santa Cruz reported Jan. 15 at the American Astronomical Society's virtual meeting. Air could also have carbon monoxide and carbon dioxide, with smaller amounts of hydrogen gas and hydrogen sulfide.

Astronomers have discovered thousands of planets orbiting other stars. Like the terrestrial planets of the solar system, many could have rocky surfaces under thin atmospheres. Existing and future space telescopes can peek into the starlight filter through the atmospheres of these exoplanets to find out what chemicals they contain and, if any, are hospitable to life (SN: 19/04/16).

Thompson and his colleagues are taking a different approach, working from the beginning. Instead of looking at the atmospheres themselves, you are examining the rocky blocks of planets to see what kind of atmospheres they can create (SN: 5/11/18).

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The researchers collected small samples, approximately three milligrams per experiment, of three different carbonaceous chondrite meteorites (SN: 27/08/20). These rocks are the first solids to condense from the disk of dust and gas that surrounded the new sun and eventually formed the planets, scientists say. Meteorites form “a record of the original components that formed planetesimals and planets in our solar system,” Thompson said in a talk at the AAS meeting. Exoplanets probably formed from similar things.

The researchers turned the meteorites into dust and then heated the dust in a special furnace connected to a mass spectrometer that can detect trace amounts of different gases. When the dust warmed, the researchers were able to measure the amount of each gas escaped.

That configuration is analogous to how rocky planets formed their initial atmospheres after they solidified billions of years ago. The planets warmed their original rocks with the disintegration of radioactive elements, collisions with asteroids or other planets and with the excess heat of their own formation. Heated rocks give off gas. “Measuring the degassing composition of meteorites can provide a number of atmospheric compositions for rocky exoplanets,” Thompson said.

The three meteorites mostly released water vapor, which accounted for 62 percent of the gas emitted on average. The next most common gases were carbon monoxide and carbon dioxide, followed by hydrogen, hydrogen sulfide, and some more complex gases that this first version of the experiment did not identify. Thompson says he hopes to identify those gases in future experimental tests.

The results indicate that astronomers should expect water-rich vapor atmospheres around new rocky exoplanets, at least as a first approximation. “Actually, the situation will be much more complicated,” Thompson said. Planets can be made of other types of rocks that would contribute other gases to their atmospheres, and geological activity changes a planet's atmosphere over time. After all, the Earth’s breathable atmosphere is very different from the thin, carbon-rich air of Mars or the thick, hot, sulfurous soup of Venus (SN: 14/09/20).

Still, “this experimental framework takes an important step forward in connecting the interiors of the rocky planet and its early atmospheres,” he said.

This type of basic research is useful because it "put a quantitative compositional framework on what those planets might look like as they evolve," says planetary scientist Kat Gardner-Vandy of Oklahoma State University in Stillwater, who did not participate in this new program. . work. She also studies meteorites and is often asked if they are worth experiments that crush ancient and rare rocks.

“People will inevitably ask me,‘ Why would you pick up a piece of meteorite and then ruin it? », Di. "The new knowledge of the study of meteorites is as priceless as the meteorite itself."

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