The Stuff Between The Stars

The role cosmic dust plays in planet and star formation is only one of many reasons astronomers are interested in better understanding its properties.

Dust also plays a role in crafting some of the most beautiful features of the cosmos: planetary rings (like those around Saturn), the long tails of comets and the spectacular, colourful clouds of nebulae.

Saturn's rings are marked by strange dark radial features called spokes. Since they have been observed on both sides of the ring plane, spokes are thought to be microscopic dust grains that have become charged and are levitating away from the ring plane. Another possibility is that a meteoroid punched through Saturn's rings, lifting dust particles away from the plane of the rings. When the Voyager spacecraft first observed these spokes, their movements seemed to defy gravity and had the scientists very perplexed. Since the spokes rotate at the same rate as Saturn's magnetic field, it is likely that electromagnetic forces are at work. This is still an unsolved puzzle.

Comet tails also contain a large amount of dust expelled by gases released when the comet passes close to the Sun. Because comets are composed mainly of dust and ice, studying the properties of cosmic dust will help scientists understand comets better, says Venturini.

Interstellar nebulae are laced with dust, too. The percentage of dust in nebulae is much less than in comets - less than 1 percent - but still the dust has important effects on the properties of the cloud.

For example, dust influences the way the cloud reflects, absorbs or emits light.

Understanding the optical properties of dust is especially important when an interstellar cloud upstages some other astronomical object that scientists are trying to study.

Dark nebulae completely block light coming from stars behind them, creating a dark patch in the sky. Some nebulae shine with reflected light from nearby stars (like clouds in Earth's atmosphere illuminated by the Sun), while other nebulae emit their own radiation in the form of infrared light.

"Most of the infrared light observed from the sky results from space dust," said Dr. James Spann, a DPL principal investigator. "Many times astronomers wish it was not there, but it is. They have to remove the contribution of the dust so that they can study other objects they are interested in."