Hubble and IUE Hale-Bopp Observations Surprise Astronomers

From: Jan Wee <>
Subject: Hubble and IUE Hale-Bopp Observations Surprise Astronomers
Date: Thu, 27 Mar 1997 16:17:14 -0600

Dear discuss-lfm members,

For all the Hale-Bopp lovers out there.  I saw the comet
last night and it was quite an exciting sight!

Jan Wee, moderator



       Completing an unprecedented year-long study of Comet Hale-
Bopp using two NASA observatories, the Hubble Space Telescope and 
the International Ultraviolet Explorer, astronomers report that 
they are surprised to find that the different ices in the nucleus 
seem to be isolated from each other.  They also report seeing 
unexpectedly brief and intense bursts of activity from the nucleus 
during the monitoring period.  The Hubble observations suggest that 
the nucleus is huge, 19 to 25 miles across.

       The findings, by a team of scientists led by Johns Hopkins 
astrophysicist Dr. Harold Weaver, are being published in the March 
28 issue of the journal Science.  

       "Hale-Bopp will probably provide the most revealing portrait 
of the workings of a cometary nucleus since the spacecraft missions 
to comet Halley in 1986," said Weaver.  "This is a unique 
opportunity; we have never had the chance to examine a comet in 
this much detail, over this large a range of distance from the 

The key results:

Violent Eruptions on the Comet's Surface

       During the course of long-term observations, which began in 
August 1995, astronomers unexpectedly caught the comet going 
through a sudden brief outburst, where, in little more than an 
hour, the amount of dust being spewed from the nucleus increased at 
least eight-fold.  "The surface of Hale-Bopp's nucleus must be an 
incredibly dynamic place, with 'vents' being turned on and off as 
new patches of icy material are rotated into sunlight for the first 
time," Weaver said.

A Complex, Mottled Nucleus 

       To their surprise, astronomers found that water ice 
sublimates (turns directly from a frozen solid into a gas) at a 
different rate than the trace ices, implying that those components 
are not contained within the water on the comet.  This conclusion 
is further supported by Hubble data showing that the rate at which 
dust left the nucleus was much different than the sublimation rate 
of water.  This result is contrary to previous models for a comet's 
nucleus, which suggest that the trace components, such as carbon 
disulfide ice, are contained inside of the most abundant ice on the 
comet, frozen water.  As water sublimates, the trace components and 
dust should be released at similar rates, but this is not what 
Hubble observed.

A Monstrous Nucleus

       By studying Hubble Space Telescope images, the astronomers 
have estimated that its nucleus may be about 19 to 25 miles in 
diameter.  The average comet is thought to have a nucleus of about 
three miles in diameter, or even smaller.  The comet or asteroid 
that struck the Earth 65 million years ago, possibly causing the 
extinction of the dinosaurs, was probably about six to nine miles 

       Because Hale-Bopp was unusually bright when it was still a 
great distance away, well outside the orbit of Jupiter, it has 
given scientists their best view ever of the changes in a comet's 
nucleus as it gets closer to, and is progressively heated by, the 
Sun.  Those changes, in turn, provide information about the 
composition and structure of comets, which are believed to be 
remnants from the formation of the solar system, about 4.6 billion 
years ago.  Learning more about comets can provide important 
information about the materials and processes that formed the solar 

     The Space Telescope Science Institute is operated by the 
Association of Universities for Research in Astronomy, Inc. (AURA), 
for NASA, under contract with the Goddard Space Flight Center, 
Greenbelt, MD.  The Hubble Space Telescope is a project of 
international cooperation between NASA and the European Space 
Agency (ESA).

                          - end -

EDITOR'S NOTE:  An image to accompany this release is available to 
news media representatives by calling the Headquarters Imaging 
Branch on 202/358-1900.  Photo numbers are:

HST Hale-Bopp       (Color) 97-HC-163           (B&W) 97-H-163

Image files in GIF and JPEG format and captions may be accessed on 
Internet via anonymous ftp from in /pubinfo.

                            GIF                  JPEG
PRC97-08      Hale-Bopp  gif/hb9596.gif         jpeg/hb9596.jpg

Higher resolution digital versions (300 dpi JPEG) of the release 
photograph are available in /pubinfo/hrtemp: 97-08.jpg (color) and 
97-08bw.jpg (black & white).

GIF and JPEG images, captions and press release text are available 
via the World Wide Web at and via links in or