AMHERST, Mass. -- The brightest comet of 1996 -- Comet Hyakutake -- may have shed some new light on a question that astronomers have asked for centuries, "what is a comet made of?" Many scientists believe that the volatile components of comets are the nearest things we know to material untouched since the time of the formation of the Solar System, and so provide a record of the conditions that prevailed in our primitive solar nebula.
Writing in the latest issue of the journal Nature (Oct. 3, 1996), University of Massachusetts radio astronomer William Irvine and colleagues suggest, based on recent observations of Comet Hyakutake, that comets consist of the same material that made the stars themselves, and these dramatic celestial objects may have been a source of some organic materials on Earth. Irvine, along with UMass colleague Peter Schloerb and UMass doctoral candidate Amy Lovell, help organize an international team that used radio telescopes to observe Comet Hyakutake when it blazed across the sky in the spring of 1996. Millions of non-scientists also viewed Comet Hyakutake with only binoculars or the unaided eye, as it made a spectacular pass near planet Earth.
Comets are small celestial bodies that orbit the sun and thought to consist mostly of dust particles and icy materials -- what some astronomers informally refer to as "dirty snowballs."
Irvine says that the observational evidence from viewing Hyakutake by several powerful radio telescopes positioned around the world -- including the 14 meter Five College Radio Astronomy Observatory located near Amherst -- suggests that it contains some of the same material found deep in interstellar space.
"The detection of hydrogen isocyanide (HNC) in Comet Hyakutake supports the idea that interstellar gases were incorporated into the nucleus of this and other comets," says Irvine. Interestingly, the hydrogen isocyanide was found in the same ratio to another molecule -- hydrogen cyanide (HCN) -- as that observed in interstellar clouds.
This measurement supports the idea that interstellar gases were incorporated into the nucleus of this and other comets, perhaps as ices frozen onto interstellar grains.
Scientists know that material found in interstellar clouds -- such as hydrogen, carbon, nitrogen, and oxygen -- form the basic chemistry of life as we know it. Some astronomers have theorized that comets could have been a delivery mechanism for pre-biological organic matter that ultimately helped develop, or even triggered life on Earth.
Irvine and Schloerb explain that organic molecules might have congregated into comets in interstellar space billions of years ago. Identifying the exotic gases and solid particles found in comets could tell us much about the conditions under which the solar system, and especially Earth, were formed.
Irvine says that most astronomers believe the chemical and physical processes that helped set the stage for the origin of life on earth occurred over some ten billion years before the formation of the Earth.
"Chemical and physical processes relevant to the origin of life have been taking place ever since the beginning of the universe, roughly 15 billion years ago," says Irvine. "It's interesting to note that with the exception of phosphorus, the chemical elements of which we are made -- hydrogen, carbon, oxygen, nitrogen, and sulfur -- are among the most abundant in the universe."
Irvine says that largely as a result of extensive observations using radio telescopes, a rich and complex chemistry is known to exist in dense interstellar space.
Does the presence of organic materials in comets make it likely that life also formed in other parts of the universe? The answer isn't clear.
Irvine believes that the nature of the Earth might have been much more influenced by interstellar material than has been believed.
"The basic building blocks of life are out there," Irvine says, "and at least some of the organic matter in comets and meteorites has reached, and continues to reach, the surface of the Earth relatively unaltered."