Johns Hopkins Gazette: March 25 1996

Comet to Offer Good Time, Good Science

Emil Venere
Homewood News and Information

     The brightest comet in 20 years is streaking past Earth this
month, and astronomers are using the most powerful telescopes to
learn more about the enigmatic objects.

     Ultimately, insights from the encounter will help scientists
piece together mysteries surrounding the origins of life on
Earth: water and possibly other ingredients vital for life to
develop on the primordial planet are believed to have come from

     Comet Hyakutake (pronounced yah koo TAH key) promises to
provide a good show for amateur stargazers, while yielding
valuable data about its composition. Astronomers will use the
Hubble Space Telescope to look at Hyakutake this Tuesday, and
again April 1 through April 4.

     "This is a very good time for comet observers, and we have
some unusual instruments that have never been used before on a
comet this bright, so we're really expecting that the scientific
return will be very high, besides providing a very nice show to
the casual observer," said Paul Feldman, a professor of physics
and astronomy.

     Feldman is among about a dozen astronomers who plan to get a
closeup view of the comet's icy center. Hyakutake will come
within 9 million miles of Earth, a mere one-tenth the distance to
the Sun.

     "Because of that, with our telescopes, both on the ground
and in space, we can get an unprecedented view of the inner
workings of a comet," Feldman said. Astronomers hope to focus on
the comet's nucleus and measure its size. The only time that has
been done before was when European and Soviet spacecraft flew by
Halley's Comet in March 1986. 

     Of course, there was no Hubble telescope then. The space
telescope's high sensitivity and resolving power make it ideal
for observing comets as they approach the inner solar system.

     Comets are too small to be seen from large distances. They
populate a huge swarm of comets, called the Oort Cloud, a pool of
material left over from the birth of the solar system that
extends as far as one light-year, or 6 trillion miles, from the
Sun. That's one-fourth the distance to the nearest star.

     Occasionally, nearby stars exerting gravitational forces
kick one of these objects out of its distant orbit, and it comes
close to the Sun, Feldman said.

     As it gets closer to the inner solar system the Sun's warmth
heats up its frozen core, releasing various gases that brighten
the comet. Electrically charged particles from the solar wind
react with the cometary gases, forming a large tail that always
extends directly away from the Sun.

     By using a spectrometer to study the luminous gases,
astronomers can analyze what the core is made of.

     "We know that water is there, but there are also many other
molecules that are trapped in the ice, and these are the ones
that contain carbon and sulfur and various other elements that
are absolutely essential for life on Earth," Feldman said. "By
looking very close we will have a much better view of these

     When scientists view more distant comets they can't be
certain that the molecules they are seeing were originally in the
comet's ice, or whether they were produced subsequently by the
chemical reactions brought about by sunlight.

     "You want to try to understand exactly what's in these
comets in order to assess how important they really were for
bringing the chemical elements that were necessary for life on
Earth to arise." 

     Scientists believe the embryonic Earth had no oceans and
that its original atmosphere was blown off into space shortly
after the planets were formed. Well-accepted theories paint a
scenario in which the oceans and a permanent atmosphere were
generated later. Comets collided with Earth, bringing water; the
atmosphere was produced from gases venting from the interior of
the planet. But researchers can't be sure about this scenario
until they know which materials were present during the early
solar system. Comets are a throwback to those times, 4.5 billion
years ago, when the planets were born.

     "There are some very deep scientific questions, and every
time we have a new comet, we can make an incremental advance, and
learn a little bit more," Feldman said. 

     But, aside from the pure science, Hyakutake represents an
unusual opportunity for amateur astronomers: a comet visible to
the naked eye. It may be seen in the northeastern sky until
around mid-April.

     "We have to go back almost 20 years to find a naked-eye
object that was visible to many people," Feldman said. "That was
Comet West in 1976. Unfortunately, it was a morning object, and
not too many people rose early in the morning to see it."

     Hyakutake was named after amateur Japanese astronomer Yuji
Hyakutake, who discovered the comet in January with a pair of
high-powered binoculars. The comet makes its closest approach to
Earth the night of March 24. 

     "It should be a good show," Feldman said. But he noted that
people who intend to look for the comet must get away from the
city, where light pollution will prevent a clear view.

     "It's well-placed for people in Baltimore, but don't forget
to look for the darkest site you can and have a clear view to the
north and east," he said.

     The Maryland Space Grant Observatory, located on the roof of
the physics and astronomy building, will be open for public
viewing of the comet, weather permitting, beginning at sunset
this Monday and Tuesday. 

     For more information, see the Space Grant Consortium
Observatory homepage:
, or call the
consortium, at (410)516-7351.

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