Comets are icy masses that appeared in the outer regions of the solar system when it was formed, 4.5 billion years ago. Their distance from the sun has resulted in comets being heated only minimally, preserving frozen gases that may give scientists clues about what materials existed in space when the solar system formed.

The compound is the only known molecule in comets that contains both nitrogen and sulfur. The molecule is a "radical," which means that chemically, it is highly reactive.

The discovery raises the question of whether the NS in comet Hale-Bopp (pictured here in a timed exposure with the moon) has existed since the start of the solar system, or if it was produced as a result of other compounds in the comet breaking apart.

Scientists will be able to determine that, Irvine said, by examining exactly where in comets the NS lies. An abundance in the head, or nucleus, would suggest original material, but the amount cannot be measured from Earth.

The way in which the abundance of NS varies in the comet's atmosphere -- or coma -- would indicate whether the molecule is the result of other compounds breaking apart due to the effect of sunlight, or whether it was produced by chemical reactions. To make such a determination, the NS molecule must be found in other comets.

The discovery is further intriguing because scientists have long suspected that many molecules on Earth were brought here by comets. "Could comets have provided molecules that became part of the oceans and the atmosphere?" Irvine asks. "Could this material perhaps even be relevant to the origin of life?"