Cosmic dust

Cosmic dust, also called extraterrestrial dust, space dust, or star dust, is tiny particles found in outer space or that have fallen to Earth. Most of these particles are very small, ranging from just a few molecules to about 0.1 mm across. Cosmic dust can be found in many places, such as between galaxies, inside stars systems, and around planets.

We can learn about dust far from our Solar System by watching the sky with special tools like photometry, polarimetry, and infrared spectroscopy. Closer to home, we can collect space dust directly. For example, the Stardust spacecraft gathered dust from a comet and brought samples back to Earth in 2006.

In our Solar System, dust from planets like Mars, moons like lunar regolith, and objects such as asteroids and comets creates the beautiful glow known as the zodiacal light. Every year, thousands of tons of cosmic dust reach Earth, with most grains being very tiny. Much of the dust in space comes from stars and contains minerals like silicates and graphite, as well as organic compounds that form naturally around stars.

Study and importance

Cosmic dust used to bother astronomers because it blocked their view of stars and other objects. But when scientists started using infrared light to look at the sky, they found that dust is very important for how stars and planets form. Dust helps stars lose mass when they are about to end their lives, assists in the early steps of creating new stars, and is part of what makes planets.

Studying cosmic dust connects many areas of science, like physics, chemistry, and astronomy. Dust particles go through changes in their chemical makeup, shape, and movement. This cycle is like how we recycle materials every day—making, storing, using, collecting, and throwing away. By observing dust in different places, such as around stars or in our Solar System, scientists can learn more about how the Universe recycles material. This helps us understand the journey of dust from its beginning to its end.

Detection methods

We can study cosmic dust in many ways. Scientists use tools that look at the light from dust, like measuring the Zodiacal light. They also collect dust directly from the air or from places like ice in Antarctica and the deep sea.

NASA uses special planes to catch dust particles in the atmosphere. We can also find clues in meteorites, which contain pieces from stars called stardust. Spacecraft carry instruments to study dust particles flying through space. These instruments measure what happens when dust hits them at high speeds.

Infrared light can pass through dust clouds, helping us see inside areas where stars are born. NASA’s Spitzer Space Telescope was good at seeing this kind of light before the James Webb Space Telescope was launched.

In 2019, scientists found dust from outside our solar system in Antarctica by looking for special materials in the samples.

Radiation properties

When dust particles meet light and other types of energy from stars, they react in special ways. How they react depends on the size of the dust, what it's made of, and the type of light or energy.

Dust can bounce or change the path of light. Light that moves only a little bit from its original path is called forward-scattered light. Light that bounces back toward its source is called back-scattered light. By studying how dust changes light, scientists can learn about the size and nature of the dust particles.

In pictures taken over long periods, the way dust scatters visible light can be clearly seen in special cloudy areas of space called reflection nebulae. Scientists also study how dust affects X-ray light from stars, which can help them understand more about the dust in space.

Presolar grains

Main article: Presolar grains

Presolar grains are tiny particles found inside meteorites. These grains are special because they were formed before the Earth existed. Scientists can study them in labs to learn about the stars and how elements were created.

These grains are made from strong materials that can survive very high temperatures, like silicon carbide and graphite. They have unique compositions that help scientists identify which stars they came from. Some grains even come from explosions of stars called supernovae. Studying these grains helps us understand how stars live and change over time.

Some bulk properties

Cosmic dust is made of tiny grains and clumps called particles. These particles have different shapes and can be fluffy or compact. Their makeup, size, and other traits depend on where they are found. For example, dust in dense clouds often has a layer of ice and is usually bigger than dust floating in open space. Particles called interplanetary dust are usually the largest of all.

Most of the space material that reaches Earth comes from small rocks called meteoroids, ranging from 50 to 500 micrometers across. These have an average density of 2.0 g/cm³ and contain about 40% empty space. In circumstellar dust, scientists have found traces of molecules like CO, silicon carbide, and water ice. Cometary dust differs from asteroidal dust, with cometary dust sharing traits with dust found between stars, including silicates and water ice. Recent studies show that cometary dust can vary in structure, from compact grains to loose clumps. In September 2020, scientists found evidence of solid water mixed with silicate grains in cosmic dust floating between stars. The makeup of cosmic dust can also change over time based on the available elements.

Dust grain formation

The large pieces of dust in space are likely made of complex materials. They start with cores that form inside stars and then gain layers as they move through cold clouds of gas and dust. These cores are mainly made from minerals that form in the atmospheres of cool, giant stars, a type of star that has changed from its earlier form. Some of these cores also form during powerful explosions called supernovae.

Scientists study these dust particles to learn where they come from. They look at special signals in infrared light to identify different types of dust, like silicate dust from oxygen-rich stars or silicon carbide dust from carbon-rich stars. Most dust in our solar system has been changed over time, formed from the material that made the solar system and then altered by collisions and other processes. Some dust, however, comes directly from stars and has not been changed much. Recent observations have even found dust in very early galaxies, showing that dust formed soon after the universe began.

From the solar nebula to Earth

The arrows in the diagram show how tiny particles from space can travel back to the early days of our solar system.

Some of these particles, called chondritic interplanetary dust particles, are grouped based on how much they have changed. They include carbon-rich particles, ordinary ones, and special ones called enstatite chondrites. The carbon-rich ones hold important elements and organic compounds, suggesting they formed early in the solar system's life. These particles have never been very hot, keeping their original material.

Scientists think that complex molecules needed for life might have formed around the sun before Earth existed. These molecules could have helped create life on our planet and maybe on others too. Studies show that certain chemicals can change into more complex ones under space-like conditions, which might be a step toward forming the building blocks of life.

Some "dusty" clouds in the universe

Our Solar System has its own interplanetary dust cloud, and other star systems do too. There are many types of cloudy areas in space, each with different reasons and ways they form. These include diffuse nebula, infrared (IR) reflection nebula, supernova remnant, molecular cloud, HII regions, photodissociation regions, and dark nebula.

These cloudy areas glow in different ways because of the kind of energy they give off. For example, H II regions, like the Orion Nebula, where many new stars are being born, shine with heat. Supernova remnants, such as the Crab Nebula, glow in a different way because of energy moving at very high speeds, called synchrotron radiation.

Some well-known dusty areas in space are found in the Messier catalog, including M1, M8, M16, M17, M20, M42, and M43.

Dust sample return

The Stardust mission was started on 7 February 1999. Its goal was to collect tiny pieces from the area around comet Wild 2, as well as bits of space dust. The mission brought these samples back to Earth on 15 January 2006. In 2007, scientists shared news that they had found pieces of dust from between the stars in these samples.

Dust particles on Earth

In 2017, scientists studied tiny pieces of space dust that land on Earth. They collected 500 of these tiny pieces from rooftops in cities like Oslo and Paris. These pieces are made mostly of a special kind of rock and change shape when they enter Earth’s atmosphere. In the UK, scientists also look for these pieces on cathedral rooftops, such as Canterbury Cathedral and Rochester Cathedral. About 40,000 tons of space dust falls to Earth every year.