University of Massachusetts-Amherst
Contact: Elizabeth Luciano
Release: June 10, 1998
UMass Astronomers Look at Whether Comet Chemistry Can Reveal
Clues About the Early Solar System
Details will be published in prestigious journal Nature
AMHERST, Mass. -- A chemical in comets thought to reveal
secrets of the early days of the solar system may be only the
result of a chemical reaction caused by the sun's radiation. A
report by University of Massachusetts astronomer William
Irvine cautions that materials in the atmosphere of a comet
could have been caused by chemical reactions related to heat
from the sun, and may have little direct bearing on what
happened when the sun and planets were formed. Details will be
published in tomorrow's issue of the prestigious journal
Nature. Besides Irvine, co-authors include UMass astronomy
professor Peter Schloerb; former UMass graduate student Edwin
Bergin; postdoctoral researcher Matthew Senay; doctoral
candidates James Dickens and Amy Lovell; and University of
Hawaii astronomers David Jewitt and Henry Matthews.
The report expands on the researchers' previous discovery of
the chemical hydrogen isocyanide (HNC) in the Comet Hyakutake,
which passed by the Earth in 1996. HNC is too unstable to
exist on Earth, but is commonly found in interstellar space,
Irvine said. The discovery raised the question of whether the
chemical was interstellar matter that was preserved when the
solar system was first formed. "If so, that would suggest that
the formation was cooler and gentler than many astronomers
currently theorize. The traditional view is that, during
formation of a solar system, everything gets so hot that any
existing molecules are destroyed," Irvine said. But another
possibility, according to Irvine, is that HNC is produced by
chemical reactions in a comet's atmosphere, which astronomers
call its "coma."
The more recent findings, reported in tomorrow's Nature, focus
on Comet Hale-Bopp, which passed by the Earth last year. The
team tracked levels of HNC as Hale-Bopp neared the sun.
Researchers determined that HNC was being formed photochemically
in the comet's coma, Irvine said.
Irvine adds an intriguing caveat: not all comets are the same.
Some comets, such as Hale-Bopp, are quite active chemically;
others are less so. Comet Hyakutake produced too little gas to
allow the chemical reactions that are necessary to produce HNC
as it approached the sun. "We don't know why there are these
differences among comets," Irvine said. "The HNC in Hyakutake
may be primordial."