Featured in this image from the NASA/ESA Hubble Space Telescope is a lenticular galaxy called NGC 4753 with intricate cosmic dust structures. Here on Earth, dust is a collection of small particles originating from geological sources, such as rocks, as well as other materials like pollen, dirt, bacteria, or pollutants. In space, dust wouldn’t consist of pollen or bacteria. For decades, astronomers assumed space dust to be a sparse collection of specks of rock and carbon, like tiny billiard balls. It’s a simple idea, and according to a new study, it’s probably wrong.

Cosmic dust, it turns out, isn’t made of miniature rocks. It’s fluff.

A comprehensive analysis of data from space missions, advanced computer simulations, and innovative laboratory experiments argues that primordial dust particles are porous, complex, and fractal, resembling delicate snowflakes more than solid grains.

Dusty Secrets

Cosmic dust was once purely an annoyance to astronomers, an obstacle that hid some of the objects they wanted to observe. When infrared astronomy began and more wavelengths were used, scientists realized that dust can also be useful. They discovered that the energy dust absorbs from starlight is released as a faint glow at infrared wavelengths. This emission turned out to be a powerful tool, allowing astronomers to trace the total mass of both gas and dust within the dense, dark clouds where new stars and planets are born.

But its usefulness goes far beyond being a simple tracer. Scientists now understand that this dust is one of the most crucial ingredients in the cosmos. Cosmic dust is more than just random grit. These grains are the fundamental building blocks of rocky planets, the cores of gas giants, and smaller bodies like comets and asteroids. In some cases, the dust even speeds these processes up, acting as a catalyst.

This is a scanning electron microscope image of an interplanetary dust particle. Image credits: University of Washington/Seattle. But as it turns out, we still have plenty to learn about cosmic dust.

The case for porous dust isn’t built on a single discovery but on a trail of clues gathered from across the solar system and deep into space. The first and most compelling clue is the dust we can actually touch. In the past couple of years, with the Stardust mission and the Rosetta mission, researchers have had access to primordial dust samples. These samples showed very diverse types of grains, many of which were “fluffy aggregates”: porous, low-density clumps of particles.

Separately, scientists have also managed to recreate the birth of dust in their labs. In sophisticated vacuum chambers, they use high-powered lasers to vaporize targets of graphite or silicon-based materials, mimicking the outflows of dying stars where dust is born. As the vaporized atoms cool and condense in a low-pressure gas, they don’t form solid little spheres. Instead, they first form nanometer-sized seeds which then collide and stick, growing into porous, random-shaped aggregates with up to 90% empty space—a near-perfect match for the fluffy particles found on comets.

Why This Matters

Dr. Alexey Potapov from the Friedrich Schiller University Jena, the lead author of the review, explains:

“If these grains are porous, that means they have a far greater surface area than we thought. That could radically change our understanding of how molecules form and evolve in space.”

Cosmic dust of the Horsehead Nebula as revealed by the Hubble Space Telescope. Image credits: NASA. Quite a few cosmic models in use today involve cosmic dust. The formation of many molecules, including molecular hydrogen, is thought to be linked to cosmic dust. Some models even suggest the grain surfaces themselves, with their unusual atomic arrangements, could act as powerful catalysts, actively driving the formation of complex organic molecules needed to seed life. If the dust is more porous than we thought, this models could be finessed.

Secondly, this fluffiness could solve a major headache in planet formation theory: how to get things started. For planets to grow, tiny dust grains must stick together when they collide. For decades, models struggled to explain how solid, rocky grains could do this without simply bouncing off each other or shattering. But laboratory experiments and simulations show that fluffy, porous aggregates are much stickier. Their open structures can deform and interlock upon impact, dissipating the collision’s energy and making it far more likely that they merge rather than break apart. This would offer a much better explanation as to how planets can start growing in their early phases.

Professor Martin McCoustra, from Heriot-Watt’s School of Engineering and Physical Sciences, explained, “Spongy grains could be more easily destroyed by shocks and radiation as they travel through interstellar space.”

But perhaps the most important implication is for water.

Could Earth’s Water Come From Dust?

Earth formed inside our solar system’s “snowline,” the region where it was too warm for water to freeze into solid ice. The dust here should have been bone-dry. So, where did our oceans come from? The leading theory has long been that Earth was born dry and had its water delivered much later by a barrage of icy comets and asteroids flung in from the outer solar system.

Porous cosmic dust offers an alternative.

Porous silicate grains act like powerful desiccants, capable of trapping water molecules within their intricate structures. These water molecules become so strongly bound that they can remain locked to the dust grain even at high temperatures. This means that the dust grains in the hot, inner region of the solar nebula were not dry after all. They were sponges, carrying a hidden reservoir of water.

Earth could have been built from this water-rich dust from the very beginning. Perhaps, Earth inherited its oceans not from a chance celestial bombardment, but from the very fabric of its formation. Recent analysis of JWST observations has already provided tantalizing evidence for trapped water inside the snowline of a distant planet-forming disk. If this holds true, it suggests that rocky, Earth-like planets across the galaxy may be born with their own water, making potentially habitable worlds far more common than we ever thought.

This is all a bit speculative. We don’t know if this actually happened. But this is one of the intriguing possibilities opened up by out new understanding of cosmic dust. This fluffy, sponge-like material may just hold some key clues to how planets are formed and how they get seeded with water.