Ask a Scientist

What is cosmic dust?

CorrespondentDecember 30, 2012 

Dr. Davide Lazzati is an astrophysicist and assistant professor of physics at N.C. State.

Dr. Davide Lazzati is an astrophysicist and assistant professor of physics at N.C. State. Here he gives his unique view of the cosmos. Questions and answers have been edited.

Q: What is cosmic dust?

Cosmic dust consists of microscopic particles of solid materials floating in space between stars. It is a mixture of small particles with size ranging from a few nanometers to a few microns. In technical terms, the smallest cosmic dust grains are nanoclusters, containing just a few to several hundred atoms each. However, cosmic dust also contains bigger particles with size analogous to fine sand on a beach. The materials that make cosmic dust – silicates, graphite, hydrocarbons, and oxides – are found also on Earth, where they can be classified as pollutants. However, they are not harmful in the interstellar space.

Q: What does cosmic dust have to do with everyday phenomena like the formation of nanopollutants in the atmosphere or the accumulation of raindrops in a cloud?

While cosmic dust does not have a direct impact on the formation of raindrops and some pollutants in the atmosphere, it shares the same formation processes. Understanding how rain is formed can help us understand how cosmic dust forms, and vice versa.

Q: How do you study cosmic dust?

Cosmic dust can be studied in many ways. We can collect cosmic dust with space missions, we can observe it absorbing and emitting light in distant stars, and we can reproduce its properties in computer simulations. In addition, we can exploit the similarity of the dust physics in the universe and on Earth to carry out laboratory experiments. All these techniques are complementary and help us form a complete theory of dust formation and its effects on the surrounding gas.

Q: What can these studies tell us about big issues like cosmology – the origins of the universe – and climate change?

Dust plays important roles in cosmology. It is on the surfaces of dust particles that chemical reactions take place in the universe, it can obscure distant stars and it can signal the presence of an infant galaxy through its thermal emission. Dust particles are also the building blocks of planets like Earth that are formed by coagulation of very many tiny grains around a young star. In our atmosphere, dust particles are the only cooling effect that is a consequence of human activity. Humans produce greenhouse gases that warm the atmosphere but they also create nanoparticles that cool it. Even though the net effect is that of heating and causing global warming, the effect would be even stronger and more dramatic without the cooling effect of dust particles or, as the climatologists call them, aerosols.

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