Burning pieces of meteorite can tell scientists what the early atmospheres of exoplanets are made of.
A series of experiments on baking the powdered space rocks suggest that rocky planets had an early atmosphere full of water, astrophysicist Maggie Thompson of the University of California at Santa Cruz reported at the American Astronomical Society’s virtual meeting on Jan. 15. The air could also have contained carbon monoxide and carbon dioxide with lesser amounts of hydrogen gas and hydrogen sulfide.
Astronomers have discovered thousands of planets orbiting other stars. Like the terrestrial planets in the solar system, many could have rocky surfaces under thin atmospheres. Existing and future space telescopes can take a look at the filtering of starlight by the atmosphere of these exoplanets to find out what chemicals they contain and whether they are hospitable to life (SN: 04/19/16).
Thompson and her colleagues take a different approach and work from the ground up. Instead of looking at the atmospheres themselves, she examines the rocky building blocks of planets to see what kind of atmospheres they can create (SN: 5/11/18).
The researchers collected small samples of about three milligrams per experiment from three different carbonaceous chondrite meteorites (SN: 08/27/20). These rocks are the first solids to condense from the disk of dust and gas that surrounded the young sun and ultimately formed the planets, scientists say. The meteorites form “a record of the original components that formed planetesimals and planets in our solar system,” Thompson said in a presentation at the AAS meeting. Exoplanets likely formed from similar substances.
The researchers grind the meteorites into powder and then heated the powder in a special oven connected to a mass spectrometer that can detect trace amounts of various gases. As the powder warmed up, the researchers were able to measure how much of each gas was escaping.
This structure is analogous to how rocky planets formed their original atmosphere after they solidified billions of years ago. Planets heated their original rocks from the decay of radioactive elements, collisions with asteroids or other planets, and from the heat left over from their own formation. The heated stones released gas. “Measuring the outgassing composition of meteorites can provide a range of atmospheric compositions for rocky exoplanets,” Thompson said.
Most of the three meteorites released water vapor, which averaged 62 percent of the gas emitted. The second most common gases were carbon monoxide and carbon dioxide, followed by hydrogen, hydrogen sulfide, and some more complex gases that were not identified in this early version of the experiment. Thompson says she hopes to identify these gases in future trials.
The results show that astronomers should expect water-rich steam atmospheres around young rocky exoplanets, at least as a first approximation. “In reality, the situation will be far more complicated,” said Thompson. Planets can be made up of different types of rock that introduce different gases into their atmosphere, and geological activity changes a planet’s atmosphere over time. After all, Earth’s breathable atmosphere is very different from the thin, carbon dioxide-rich air of Mars or the thick, hot, sulphurous soup of Venus (SN: 9/14/20).
Still, “this experimental framework takes an important step forward in connecting the interiors of rocky planets and their early atmospheres,” she said.
This type of basic research is useful because it “created a quantitative compositional framework for what these planets might have looked like during their evolution,” says Kat Gardner-Vandy of Oklahoma State University in Stillwater, who was not involved in this new research was involved work. She also studies meteorites and is often asked whether it is worth doing experiments that crush the ancient, rare rocks.
“People will inevitably ask me, ‘Why would you take a piece of a meteorite and then ruin it? “She says.” New knowledge from studying meteorites is just as priceless as the meteorite itself. “