Space is a big place. Astronomers refer to space as everything that lies beyond our Earth. The Moon, other planets, stars, and galaxies are in space. Astronomers and astrophysicists know that space is also the region between celestial bodies, which in reality is not empty but filled with particles or gas. Depending on where it is, it can be called an interplanetary, interstellar, or intergalactic medium, and the number of particles in each might vary. Regardless, this gas is so tenuous that it feels like a vacuum for us.
The interstellar medium is quite interesting because it is filled with atoms and molecules that, if concentrated in enough quantities, can absorb or deviate the light from the nearby stars and re-emit or reflect it in interesting structures that we call nebulae. Studying the light of these nebulae we can infer the composition of these particles (atoms and molecules), their temperature, the number of particles in a given volume of gas, how they are distributed if they are moving fast or slow, and if they originated from the nearby star or they were there before the star was born.
Interestingly, the interplanetary medium, besides atoms and molecules, also contains tiny particles called interstellar dust. This is known also as cosmic dust and it is created by a collection of molecules that come together to form a dust grain, much like water molecules come together to form a snowflake. These dust grains play an important role in galaxy physics, the chemical evolution of matter, and the absorption and re-emission of stellar light. Is this dust like the dust we see on Earth? Some of the Earth's dust, the small dust, is like cosmic dust. It consists of particles less than a few millimeters in diameter and can be made from different minerals or different mineral structures[1].
In space, its composition, structure, and form depend greatly on the surrounding environmental conditions. For example, in space dust can form around old stars that have ejected some of their material into space, and when it cools forms dust. It can also form in molecular clouds or be part of the leftover material after a star was formed. So studying cosmic dust can provide details of the environments in which they formed, like temperature, pressure, materials available, and heating and cooling rate, and can also tell what they have experienced since they were formed, such as exposure to water or heat around other stars and planetary systems or within molecular clouds. In our own solar system, interplanetary dust is primarily derived from comets and asteroids, and is responsible for a phenomenon observed from Earth called the zodiacal light – a faint, diffuse white glow that, in favorable observing conditions, can be seen to extend along the ecliptic [1]
The dust also affects the formation of new stars and planets. When a star forms, it condenses from molecular clouds and dust grains that are part of the interstellar medium where they are born[2]. Before a star is born, the dust acts as a shield that protects molecular clouds from the intense light from stars in the neighborhood. It allows the molecular cloud to stay cold and eventually collapse to form new stars. The dust around these clouds eventually gets destroyed and provides more material for the forming stars. Dust in the vicinity of a newborn star that does not get destroyed could eventually be the seeds of new planets forming from the leftover material from the star.
References:
1 Astronomy & Geophysics, Volume 58, Issue 1, 1 February 2017, Pages 1.35–1.40, https://doi.org/10.1093/astrogeo/atx027
2 Monthly Notices of the Royal Astronomical Society, Volume 513, Issue 1, June 2022, Pages 1531–1543, https://doi.org/10.1093/mnras/stac695