By Jason Matthews

Four and a half billion years ago, our solar system formed from a vast nebular of Stella dust and gases. This material condensed and collapsed to form the planets and our sun. Venus, Earth, and Mars, being rocky planets, were super-heated from the friction caused by this process and the constant bombardment of meteor impacts from leftover material.

An artist’s impression of a protoplanetary disk, our solar system might have looked something like this during its very early beginnings - Image Credit: Elen11 via iStock/Getty Images

The intense heat released gases trapped within the rock that eventually formed their early atmospheres. Over time, as the planets cooled and became more geologically stable, other processes slowly transformed those atmospheres into what we know today.

Co-author of a recent laboratory study, Myriam Telus, who is an assistant professor of Earth and planetary sciences at UC Santa Cruz, explained, "When the building blocks of a planet are coming together, the material is heated, and gases are produced, and if the planet is large enough the gases will be retained as an atmosphere. We're trying to simulate in the laboratory this very early process when a planet's atmosphere is forming so we can put some experimental constraints on that story."

The assumption was that Earth's early atmosphere had the same composition as the gases that formed our sun and the other planets in our solar system. It was believed Hydrogen and helium were the dominant gases, and this seems accurate with regards to our gas giants like Jupiter. However, the process that releases gases on rocky worlds [called outgassing] is different, so the researchers at UC Santa Cruz decided to determine what composition likely made up these early atmospheres.

The early atmospheres of rocky planets are thought to form mostly from gases released from the surface of the planet as a result of the intense heating during the accretion of planetary building blocks and later volcanic activity early in the planet… — The early atmospheres of rocky planets are thought to form mostly from gases released from the surface of the planet as a result of the intense heating during the accretion of planetary building blocks and later volcanic activity early in the planet's development. - Image Credit: Dan Durda/Southwest Research Institute via Eurekalert

The team collected three special meteorites called CM-type carbonaceous Chondrites. One landed in Australia in 1969, another in Western Sahara in 2013, and the third struck near Costa Rica in 2019. Chondrites are leftover building blocks from the early formation of the solar system, which have avoided melting. Their unchanged condition makes them perfect for this study, as their composition should give an accurate representation of the same materials that later became the rocky worlds orbiting our sun.

With the help of materials scientists, the team heated the samples to 1200 degrees Celsius. Released gases were collected and passed through a spectrometer to measure their types and quantities. Most of the released gases were water vapour, with high levels of carbon monoxide and CO2. The results showed the release of only small amounts of hydrogen and hydrogen sulphide.

The three carbonaceous chondrite meteorites that were analysed - Image courtesy of M. Thompson via Eurekalert

These levels mostly fit the predictions of planetary atmospheres coming from outgassing but with some differences. The first author of the study, Maggie Thompson, explained why this is important, "You need experiments to see what actually happens in practice. We want to do this for a wide variety of meteorites to provide better constraints for the theoretical models of exoplanetary atmospheres."

The data collected will be invaluable when we study distant exoplanets' atmospheres. It will allow scientist a better understanding of what the compositions of those atmospheres mean. Among other things, it will enable more accurate predictions about how an exoplanet has developed in the time it has taken for the light to reach us.

Telus concluded, "It may seem arbitrary to use meteorites from our solar system to understand exoplanets around other stars, but studies of other stars are finding that this type of material is actually pretty common around other stars."

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