Planetary degassing is the process by which gases trapped inside a planet are released to the surface and atmosphere. This usually happens through volcanic eruptions or other natural events that let gases escape from deep underground. When a planet first forms, some gases get stuck inside it. Over time, heat and pressure inside the planet push these gases out, especially through volcanoes. The gases that come out can include water vapor, carbon dioxide, sulfur dioxide, methane, and nitrogen. This process is very important because it helps form the planet’s atmosphere, especially in the early part of its history.^[1][2][3]

Planetary degassing happens in several ways. One of the main ways is through volcanic eruptions, which bring hot, melted rock (called magma) and gas from deep underground up to the surface. Tectonic activity, which means the movement of large pieces of a planet’s outer layer, can also let gases escape. As a planet cools down over time, its inside separates into different layers. This change can push gases upward toward the surface. Even if there are no big eruptions, gases can slowly leak out through cracks in the ground or from the bottom of the ocean. Sometimes, asteroids or comets hit a planet and cause quick bursts of degassing. The force of the impact can heat up the surface, release gases trapped in rocks, or even melt parts of the crust.^[4][5]

Degassing has played an important role in shaping the atmospheres of planets. On early Earth, it was one of the main ways that gases like carbon dioxide, nitrogen, and water vapor got into the air. These gases helped create clouds, rain, and even oceans. Similar things may have happened on other planets, like Venus and Mars, but with different results. Venus ended up with a thick, super-hot atmosphere, while Mars lost most of its atmosphere and became cold and dry.^[6][7] Degassing still happens on some moons today. For example, Io, one of Jupiter’s moons, has active volcanoes that release gas into space all the time. This shows that degassing is an important part of how planets and moons change over time.^[1][8]

This process is closely connected to whether a planet can support life. The gases released during degassing can change the planet’s climate. For example, carbon dioxide can trap heat, and water vapor can help form oceans. These gases, called volatiles because they easily turn into gas, are very important for life. Without degassing, a planet might stay dry, have no air, and not be able to support life. By studying how degassing works, scientists can learn more about how life may have started on Earth and where life might be possible on other planets.^[9][10]

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