Six papers on Comet LINEAR (C/1999 S4) are published
in the 18 May 2001 issue of Science magazine.
Here we list the authors and titles of those papers and
provide brief descriptions of the material they present.
The papers can be downloaded from
Science Online,
although note you must have a subscription to Science to obtain
access to the full articles.
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D. Bockelèe-Morvan, N. Biver, R. Moreno, P. Colom,
J. Crovisier, E. Gerard,
F. Henry, D. C. Lis, H. Matthews,
H. A. Weaver, M. Womack, M. C. Festou,
Outgassing Behavior and Composition of Comet C/1999 S4 (LINEAR)
during its Disruption.
Radio observations of HCN (hydrogen cyanide), HNC,
formaldehyde (H2CO),
hydrogen sulfide (H2S),
and CS (carbon monosulfide), and searches for
CO (carbon monoxide) and CH3OH (methanol), using the NRAO 12-meter
telescope at Kitt Peak, the Caltech Submillimeter Observatory (10.4
meter) at Mauna Kea, the James Clerk Maxwell Telescope (15 meter) at
Mauna Kea, and the Institut de Radio
Astronomie Milimètrique (IRAM) 30
meter telescope in Spain.
Results:
The team monitored the gas production from C/LINEAR before, during and
after the late-July breakup, found that the composition of C/LINEAR
before the breakup was similar to the composition
after the breakup, and measured a deficiency of methanol and
carbon monoxide. Based on mass budget considerations (i.e., a
comparison of masses before and after the breakup), the team also
concluded that the original nucleus was small (with a diameter between
200 and 600 meters), it had been shedding debris for weeks preceding
the late-July disruption, and much of the debris created after the
final disruption consisted of small (less than 40 cm across) pieces.
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T. L. Farnham, D. G. Schleicher, L. M. Woodney, P. V. Birch,
C. A. Eberhardy, L. Levy,
Imaging and Photometry of Comet C/1999 S4 (LINEAR) before
Perihelion and after Breakup.
Optical filter photometry of OH, NH, CN, C2,
and C3 using the Perkins
(1.8 meter) and Hall (1.1 meter) telescopes at the Lowell Observatory.
Optical CCD imaging observations from the Lowell, McDonald, and Perth
observatories.
Results:
The team estimated that the original nucleus was at least 880 meters across
(about 1/2 mile), which implies that its mass was about
200 billion kilograms, while the total mass of small dust in the tail
was about 3 billion kilograms. Since the size distribution of
the dust was more heavily weighted towards larger pieces compared
to most other comets, the team concluded that most of the
debris created after the disruption of C/LINEAR was ``hidden''
in pieces between 1 millimeter and 50 meters in size.
(See the
missing mass problem
for further discussion.)
The team also found that the amount of C2 in the
coma was depleted, unlike any other Oort Cloud comet they have
previously observed but similar to the depletion observed in
about 1/2 of the ``Jupiter-family'' comets. Despite their name,
``Jupiter-family'' comets are thought to have formed in the
Kuiper Belt region, not near Jupiter, so
this result seems to be at odds with the conclusion reached by
Mumma et al. (see below).
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C. M. Lisse, D. J. Christian, K. Dennerl, K. J. Meech,
R. Petre, H. A. Weaver, S. J. Wolk,
Charge Exchange Emission X-rays from Comet C/1999 S4 (LINEAR).
Chandra and Extreme Ultraviolet Explorer (EUVE) observations
during mid-July and early-August 2000.
Results:
The x-ray spectrum of C/LINEAR showed at least 6 different spectral
lines, which were probably produced by charge exchange between
highly ionized solar wind ions and neutral gases in the comet's coma.
The team also observed a strong increase in x-ray emission from the
comet coincident with a strong solar flare on 14-15 July 2000.
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J. Makinen, J.-L. Bertaux, M. R. Combi, E. Quemerais,
Water Production of Comet C/1999 S4 (LINEAR) Observed with
the SWAN Instrument.
Observations were made using the Solar Wind
ANisotropies (SWAN)
Hydrogen Lyman-alpha camera on the SOlar and
Heliospheric Observatory (SOHO).
Results:
The team measured the total amount of ice in the
original nucleus (about 3 billion kilograms, which is about 3 million tons),
the amount of ice outgassed during the final disruption event
(about 300 million kilograms, which is about 300 thousand tons),
determined the size distribution of the icy particles produced
during the disruption event, and observed four major outburst events
during the course of systematic monitoring of the comet between
the end of May and mid-August 2000. The amount of ice contained
in the nucleus is about 100 times smaller than the total mass of the nucleus
(see the paper by Farnham et al.), which suggests that the
comet was more like a ``snowy dirtball'' than a ``dirty snowball'',
i.e., there was much more ``dirt'' (meteoritic material) in the
comet than ice.
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M. J. Mumma, N. Dello Russo, M. A. DiSanti, K. Magee-Sauer,
R. E. Novak, S. Brittain, T. Rettig, I. S. McLean, D. C. Reuter,
L.-H. Xu,
Organic Composition of C/1999 S4 (LINEAR) : a Comet Formed
near Jupiter?
High resolution near-infrared spectroscopic observations
of water, carbon monoxide, methane, ethane, hydrogen cyanide,
NH2, hydroxyl, and searches for
methanol and acetylene during the first-half of July 2000
using the Keck Observatory and the NASA
InfRared
Telescope
Facility (IRTF), both on Mauna Kea.
Results:
The team measured strong depletions of carbon monoxide, methane,
ethane, methanol, and acetylene, which suggest that C/LINEAR formed in
a warmer environment than most comets, perhaps in the region near
Jupiter. If so, the amount of heavy water in C/LINEAR might also be
lower than in other comets and might be consistent with the amount of
heavy water currently found in Earth's oceans. Thus, comets having a
composition similar to that of C/LINEAR might be responsible for
supplying most of Earth's water. On the other hand, the depletion of
the organic (i.e., carbon-bearing) molecules in C/LINEAR may require a
re-evaluation of models in which comets supplied most of Earth's
inventory of organic material.
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H. A. Weaver,
Z. Sekanina,
I. Toth,
C. E. Delahodde,
O. R. Hainaut,
P. L. Lamy,
J. M. Bauer,
M. F. A'Hearn,
C. Arpigny,
M. R. Combi,
J. K. Davies,
P. D. Feldman,
M. C. Festou,
R. Hook,
L. Jorda,
M. S. W. Keesey,
C. M. Lisse,
B. G. Marsden,
K. J. Meech,
G. P. Tozzi,
R. West,
HST and VLT Investigations of the Fragments of
Comet C/1999 S4 (LINEAR).
Observations using HST in early-July and early-August 2000,
VLT observations in early-August from Chile, and observations
in early-August using the University of Hawaii 2.2 meter telescope
at Mauna Kea.
Results:
The team measured at least 16 large fragments in early August 2000,
determined that the largest fragments were roughly 100 meters (110
yards) across, estimated the total mass of 10 large fragments (about 2
billion kilograms, which is 2 million tons), estimated the total mass
of small dust particles in the tail (about 400 million kilograms, which
is 400 thousand tons), and measured a large depletion in the amount of
CO ice in the nucleus. The total mass recovered after the breakup
during these observations is almost 100 times smaller than the
mass of the original nucleus estimated by Farnham et al., which
suggests that the majority of the debris created after the breakup
may have ended up in objects between about 1 cm and 50 meters in
size, which are essentially invisible to optical telescopes.
See the
missing mass problem
for further discussion.
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