Recent observations on comet Hyakutake shed new light on the information of our solar system
RECENTLY, two groups of researchers
published their findings on comet
Hyakutake. They have detected certain
compounds in the comet which could
provide us with valuable information
about the composition of the nebula
from which our Sun and the planets
emerged. Comets are also believed to
have been a source of many of the
organic compounds seen on the terrestrial planets (Nature, Vol 383, No 6599).
In March 1996, the comet
Hyakutake (officially termed as comet
c/Hyakutake 1996 132) was at its perigee
or the closest distance to the earth. It
came as close as about 10 per cent of the
distance between the Sun and the earth.
This close range gave astronomers a
unique opportunity to observe the
comet with various instruments.
William Irvine from the Paris
Observatory, France, and his collaborators have detected hydrogen isocyanide
(HNC) molecule in comet Hyakutake. Using the Caltech Submillimeter
Observatory (cso), California, us, the
group detected and identified a spectral
line at a frequency of 362.630092 giga-
hertz, which is characteristic of the
compound.
The group has also measured the
abundance of another organic molecule, hydrogen cyanide (HCN) in the
comet. The surprising result is that the
abundance of HNc relative to HCN is very
similar to that seen in interstellar molecular clouds. Furthermore, the ratio is
very different from that expected in the
material in the outermost reaches of
our solar system, from which the
comets are thought to have been
formed.
A comet has a solid nucleus composed of ice mixed with micrometer-sized dust grains. As the nucleus
approaches the Sun, the temperature
rises and the ice evaporates. The resulting gas escapes with the dust particles
trailing in a gigantic tail, millions of km long.
The studies have lead the
researchers to conjecture that some of
the interstellar gases could have been
incorporated into the comet's nucleus
as ice on the interstellar grains. This
hypothesis, if verified by other data, will
provide an important clue to our understanding of the conditions prevalent in
the solar nebula at the time when the
planets and the comets formed.
Close on the heels of this comes
another report of the discovery of x-ray
and extreme ultraviolet emission from
Hyakutake. c m Lisse and his collaborators have studied the comet at its perigee
using the Roentgen x-ray satellite and
the Rossi x-ray Timing Explorer. Lisse
and his team's observations are significant as x-ray and ultraviolet emission
from comets had not been observed before.
The researchers believe that the
interaction between the comet and the
solar wind (the constant stream of energetic particle being emitted by the Sun)
or the solar magnetic field could be a
possible explanation of the emission.
They have also found x-ray emission
from three other comets as well as
Hyakutake in its post perihelion (the
closest distance to the Sun) phase. The
perigee of the comet Hale-Bopp will
provide another opportunity for scientists early next year to confirm these
findings.
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