Volatile (astrogeology)

Some things turn into gas very easily. Scientists call these things volatiles. They can be found on moons and planets. Some are like ice. Others are like the air we breathe.

These things also live in hot, melted rock. This melted rock is called magma. When magma moves up, it makes bubbles. These bubbles can make a volcano explode.

It is a very powerful force. Volcanoes can even shoot out water vapor. They can also release other gases. This is how a volcano works.

Volatiles are things that turn into gas very easily. They include many items like water, oxygen, and nitrogen. Scientists study them on moons and planets. Some volatiles are gases. Others are ices, which are solids with low melting points. For example, Uranus and Neptune are called ice giants.

Volatiles also live inside magma. Magma is hot, melted rock. Most magma is just liquid rock. But it holds small amounts of gas. As magma rises, the pressure drops. This causes the gas to come out of the liquid. This step makes bubbles.

These bubbles can grow into a big network. This can make a volcano erupt in a big way. Some eruptions are very explosive. This happens when magma has a lot of silica. Silica is a part of the rock. Other eruptions are calm. They might look like a lava fountain.

Volcanoes release many things. They release water vapor and carbon dioxide. They also let out sulfur dioxide. This gas is often in certain rocks. Even tiny amounts of gas can make a big change. This is because gas takes up a lot of space when it expands.

Volatiles are a special group of chemical elements and compounds. These substances can turn into gas very easily. This is different from refractory substances, which do not vaporize easily. Scientists study volatiles in the crust or atmosphere of planets and moons. They include many things like hydrogen, nitrogen, and oxygen. Other examples are water, ammonia, methane, and carbon dioxide. Even noble gases are part of this group. Knowing about volatiles helps us understand how worlds work.

In space, scientists group these materials by their melting points. Volatiles with very low melting points are called gases. These include hydrogen and helium. Other volatiles with melting points above 100 K are called ices. This means they are below –173 °C or –280 °F. Even though we use these names, they can be solids, liquids, or gases. For example, Jupiter and Saturn are called gas giants. Uranus and Neptune are called ice giants. Inside these planets, the material is often a hot, dense fluid.

Volatiles are also very important inside volcanoes on Earth. Magma is mostly liquid rock, making up 95% to 99% of the mix. However, the small amount of gas inside can create a huge volume. As magma rises toward the surface, the pressure decreases. This causes the volatiles to come out of the liquid. They form bubbles that connect into a network. This can lead to an explosive eruption. Some magma has a high silica content, which makes eruptions more explosive. Other magma has low silica and can create lava fountains.

Many different gases come out of a volcano during an eruption. Water vapor and carbon dioxide are the main ones. Volcanoes also release sulfur dioxide, which is common in certain rocks. They can even release hydrogen chloride and hydrogen fluoride. The way these gases behave depends on three main factors. These are the pressure, the temperature, and the makeup of the magma. Pressure and the makeup of the magma are the most important. Scientists use math to figure out how much gas stays dissolved in the liquid.

Bubbles in the magma start through a process called nucleation. This happens when the magma becomes saturated with gas. Molecules can group together on their own in a way called homogeneous nucleation. Sometimes, they use solid crystals in the magma as a place to start. These crystals act as perfect sites for bubbles to grow. If the magma rises very quickly, it stays out of balance. This can make the bubbles form in a different way. Understanding these tiny bubbles helps us predict how a volcano will act.

In the study of astrogeology, scientists focus on a specific group of substances called volatiles. Volatiles are chemical elements and compounds that can be easily vaporized. This means they can turn into gas quite readily. This is the opposite of refractory substances, which are materials that do not vaporize easily. By studying volatiles, planetary scientists can learn about the crusts and atmospheres of various planets and moons. Common volatiles include hydrogen, nitrogen, oxygen, and water. Other examples are ammonia, methane, carbon dioxide, and noble gases. They also include substances like sulfur dioxide, phosphine, and various halogens.

Planetary scientists use specific categories to group these materials based on their melting points. Volatiles with exceptionally low melting points, such as helium and hydrogen, are classified as gases. Volatiles with melting points above 100 K (–173 °C or –280 °F) are referred to as ices. It is important to note that these terms can describe substances in solid, liquid, or gas forms. For example, Jupiter and Saturn are known as gas giants. Uranus and Neptune are called ice giants. Even in these giant planets, the interior material is often a hot, highly dense fluid. In Neptune, temperatures may even reach 5,100 °C.

On Earth, the term volatiles is used frequently in igneous petrology. This branch of science studies how volatiles behave within magma, which is molten rock. Magma is usually composed of 95% to 99% liquid rock. Even though the percentage of gas is very small, it represents a massive volume when it expands. This expansion is what generates explosive volcanic eruptions. The type of eruption depends on the viscosity, or thickness, of the magma. Felsic magma has a high silica (SiO2) content and high viscosity. This type of magma often produces explosive eruptions. In contrast, mafic magma has a lower silica content and lower viscosity. These tend to result in effusive eruptions or lava fountains.

Several factors control how volatiles disperse within magma. These factors include the temperature, the composition of the magma, and the confining pressure. Pressure and composition are considered the most important parameters. Scientists must understand solubility to predict how magma behaves. Solubility is the ability of a liquid to hold a dissolved substance. For example, water in rhyolite magma follows a specific mathematical relationship involving pressure. As magma rises toward the surface, the confining pressure decreases. This decrease in pressure causes volatiles to come out of solution. This process is known as exsolving. When volatiles exsolve, they create bubbles that circulate and connect into a network.

Magma can exist in different states of saturation regarding its volatiles. If a magma holds less water than the maximum amount possible, it is undersaturated. Most magma in the deep crust and mantle is undersaturated. When magma reaches the maximum amount of water it can hold, it is considered saturated. If the magma continues to rise and more water is dissolved, it becomes supersaturated. In a supersaturated state, the extra volatiles are ejected as bubbles or water vapor. Carbon dioxide behaves differently than water because it has much lower solubility. Because of this, carbon dioxide tends to exsolve at greater depths than water. This can cause carbon dioxide bubbles to leak through cracks in a caldera.

The formation of these bubbles begins with a process called nucleation. Nucleation occurs when a volatile becomes saturated. Molecules can group together spontaneously through a process called homogeneous nucleation. However, nucleation can also happen more easily if there are solid crystals present in the magma. These crystals act as perfect potential nucleation sites for the bubbles. If nucleation is delayed, the magma may become significantly supersaturated. This can cause bubbles to form much later and more suddenly. If magma rises rapidly to the surface, the system stays out of equilibrium. This rapid rise affects how the distance between bubbles is determined.

Understanding volatiles helps us connect many different scientific fields. It links the study of planetary atmospheres to the study of deep volcanic systems. By measuring the amount of hydrogen chloride, hydrogen fluoride, or sulfur dioxide released, scientists can learn about the magma's composition. The study of volatiles also touches on cometary activity. In the region inside Jupiter's orbit, the sublimation of water ice drives comets. Even far out in space, supervolatiles like carbon monoxide and carbon dioxide can generate cometary activity. This makes volatiles a central topic for understanding the history and behavior of our solar system.