PLEASE NOTE:


*

CCNet, 23 November 1999
-----------------------



(1) THE LION ISN'T DEAD YET
    Jim Bedient <bedient@amsmeteors.org>

(2) LEONID STRIKES THE MOON
    BBC Online News, 23 November 1999

(3) NEODyS ANNOUNCEMENT
    NEO Dynamic Site <neodys@newton.dm.unipi.it>

(4) SIZE & PHYSICAL PROPERTIES OF COMET HALE-BOPP
    V.G. Kruchinenko & K.I. Churyumov, KYIV NATL UNIVERSITY

(5) NUCLEAR SIZE OF COMET HALE-BOPP
    Z. Sekanina, CALTECH,JET PROP LAB

(6) DETECTION OF A SATELLITE ORBITING THE NUCLEUS OF COMET
    HALE-BOPP
    Z. Sekanina, CALTECH,JET PROP LAB

(7) CHEMICAL ABUNDANCE IN COMETS
    W.F. Huebner & J. Benkhoff, SW RES INSTITUTE

(8) GAS AND DUST RELEASE FROM COMET HALE-BOPP
    D. Prialnik, TEL AVIV UNIVERSITY

(9) IS COMET HALE-BOPP A JUVENILE COMET?
    J. Benkhoff & H. Rauer, DLR,

(10) MONTE CARLO SIMULATIONS OF OORT CLOUD COMETS
     P. Nurmi et al., UNIVERSITY OF TURKU

==============
(1) THE LION ISN'T DEAD YET

From Jim Bedient <bedient@amsmeteors.org>

Dear Benny,

Amongst all the accounts of Leonid activity, I note many comments along
the line of "Well, that's it 'til 2033".  It is important to note that
there are several other storm-level returns of the Leonid meteor shower
possible during 2001-2002.

David J. Asher and Robert H. McNaught, whose model of the Leonid stream
was so spectacularly vindicated on November 18 also predict encounters
with additional filaments or trails in the Leonid stream.  The table
below shows some of their predictions:

     Time (UT)      Estimated ZHR           Visible from
2001 Nov 18, 10:01      1,500?       N. & Central America
2001 Nov 18, 17:31     15,000        Australia, E. Asia
2001 Nov 18, 18:19     15,000        W. Australia, E., SE & Central Asia
2002 Nov 19, 04:00     15,000        W. Africa, W. Europe, N. Canada, NE S.America
2002 Nov 19, 10:36     25,000        N. America

So the Lion is certainly not dead yet, and it won't be 33 years, but
hopefully less than two before we'll be showered again with Leonids.

Jim Bedient
American Meteor Society

==============
(2) LEONID STRIKES THE MOON

From The BBC Online News, 23 November 1999
http://news.bbc.co.uk/hi/english/sci/tech/newsid_532000/532448.stm

By BBC News Online Science Editor Dr David Whitehouse

Astronomers think they have witnessed a meteor striking the Moon. Brian
Cudnik from Houston, Texas, captured the event, which may be the first
such confirmed observation.

He was looking at the Moon during last week's Leonid meteor storm in
the hope that he might see something interesting. It had been suggested
that skywatchers might see a Leonid strike the lunar surface about
three hours after the storm's peak on Earth.

Cudnik saw a brief flash near the centre of the Moon's dark side at
about 0446 GMT.

Observing through a telescope, he estimated that the flash, lasting
only a fraction of a second, was at least as bright as some nearby
stars. It was also seen by astronomer David Dunham observing near
Washington DC, who made a video recording of the event.

Astronomers are now appealing for anyone else who may have seen the
event to come forward. According to Dunham, analysis of the images will
permit a reasonably good determination of the brightness and location
of the impact flash.

Impact site

The next step would be to use high-power telescopes to scrutinise the
impact site to see if there have been any changes. This is unlikely as
the impact must have been by a small meteor, probably less than a
kilogram in mass. But astronomers will want to look, nonetheless.

It would certainly help to establish if this is the first, confirmed
lunar impact observation. A probable lunar meteor impact was 
photographed on 15 November, 1953, but was not confirmed by other
observations.

There is also a very old historical account that could also be
explained by a meteor hitting the Moon. This was recorded by Gervase of
Canterbury who, in 1178, along with five other monks, saw a very bright
flash on the Moon:

"There was a bright New Moon, and as usual in that phase its horns were
tilted towards the east. Suddenly, the upper horn split in two. From
the midpoint of the division, a flaming torch sprang up, spewing out
fire, hot coals and sparks."

Some astronomers believe that the crater Bruno, one of the youngest on
the lunar surface, may have been formed in this event.

Copyright 1999, BBC

===============
(3) NEODyS ANNOUNCEMENT

From NEO Dynamic Site <neodys@newton.dm.unipi.it>

The Near-Earth Object Dynamics Site (NEODyS) has been significantly
improved and expanded.

NEODyS is an online information service for near-Earth asteroids
(NEA's), available since March 1999. At its core, NEODyS is a database
of orbital and observational information for each NEA; however, the
distinguishing feature of the system is the degree to which the
information is made accessible and searchable. NEODyS can be accessed
via the WWW at <http://newton.dm.unipi.it/neodys/>.

In NEODyS every NEA has its own "home page" containing sections devoted
to the object's orbit, observations, planetary close encounters,
additional services, and physical information. Also every observatory
has its own page with links to tables of all NEA observations from that
station.

One of the most valuable features is the database query facility. One
may of course look up an asteroid by name or number, but it is also
possible to search for all NEA's possessing some desired orbital or
observational characteristics, or to search for close approaches
within a given distance.

The new features available since 20 November 1999 are the following:

1) There is now a daily ephemeris (position on the sky) for each object
in the database, and the ephemerides are also searchable. This allows
an observer to search for NEA follow up targets based on observability
and other factors such as brightness, uncertainty, arc length, or the
number of days unobserved. Alternatively one can search for all NEODyS
objects in a particular region.

2) Radar observations are now incorporated into our orbital solutions.
For those objects with radar observations, this results in
substantially improved orbits, with far less uncertainty.

3) The orbits are now computed with statistical weighting of optical
astrometry according to the historical performance of the observatory.
Radar observations are also weighted in a rigorous way. The information
used to compute the weights are available on the page of each
observatory.

4) We are now using simpler and constant URL's. This means that you can
put a link on your own web pages to your favorite asteroid or
observatory, for example,

1999 AN10:
<http://newton.dm.unipi.it/cgi-bin/neodys/neoibo?objects:1999AN10;main>
(433) Eros: <http://newton.dm.unipi.it/cgi-bin/neodys/neoibo?objects:Eros;main>
Catalina Sky Survey: <http://newton.dm.unipi.it/cgi-bin/neodys/neoibo?sites:703;main>.

5) We have significantly improved the close approach table for each
object, adding calendar date (most users are unfamiliar with the
previous Modified Julian Day) and the minimum possible distance of
approach according to the linear theory (which is less than the nominal
approach distance, computed on the basis of the best fit orbit), and
other parameters useful to assess the circumstances of the encounter.

6) Another feature, which is not new now but was added after the first
announcement of NEODyS, is the Impact Risk Page, available at

http://newton.dm.unipi.it/neodys/risk.html

In this page we list all the asteroids for which possible impact
solutions, compatible with the existing observations, are known. In
all these cases we have been able to compute a very small, but
definitely non-zero, probability of collision.  Only one rogue asteroid
is currently listed on this page (and the probability of impact are
extremely low).

The database is automatically updated on a daily basis as new
observations are released from the Minor Planet Center. All of the data
files needed to reproduce the NEODyS results are freely available, even
the OrbFit software used for orbit determination
<http://newton.dm.unipi.it/~asteroid/orbfit>.

The system is being upgraded and improved continuously, comments and
suggestions are welcome. Among the improvement we are working on that
we can mention are

A) Availability of NEA proper elements (in table and graphical
form)

B) Complete list of all *possible* close approaches until 2050 (This
data is presently maintained privately as part of our recently
implemented automatic monitoring of the impact risk for all NEA's, but
we hope to put it in a publishable form soon.)

C) Qualitative study of the orbit-to-orbit distance with respect to the
Earth

D) Inclusion in the database of the asteroids which are not NEA
according to the nominal, best fit orbit, but nevertheless could be
NEA.

NEODyS has been created by A. Milani and S. Chesley, Department of
Mathematics, University of Pisa, Italy.

===============
(4) SIZE & PHYSICAL PROPERTIES OF COMET HALE-BOPP

V.G. Kruchinenko*) & K.I. Churyumov: Size and physical properties of
the comet Hale-Bopp (C/1995 O1)nucleus. EARTH MOON AND PLANETS, 1999,
Vol.77, No.3, pp.141-146

*) KYIV NATL UNIV, ASTRON OBSERV, STR OBSERV 3, UA-254053 KIEV
   53,UKRAINE

It is possible to estimate the real size of the nucleus from the
equation of the energy balance, using some parameters obtained through
space experiments tied with the exploration of comet Halley. We have
also taken the albedo value 0.04 (for that part of the nucleus surface
which is covered with mineral crust and does not sublimate).
Representing the nucleus of comet Halley as a triaxial ellipsoid a.b.c
= 15.8.7.5 km we can calculate the parameter of its shape B = RequSF/V
= 3.20, where R-equ = (a.b.c)(1/3), S-F - the total surface of the
ellipsoid, V - its volume. Parameter B was also used for comet
Hale-Bopp's nucleus. The equation of the energy balance for comet Hale-
Bopp's nucleus is analyzed for the moment when the comet passed
perihelion and the sublimation rate (for water) was 10(31) molecules .
s(-1) approximate to 3.10(8)g.s(-1). The energy balance equation
contains the following components: energy coming from the Sun and
absorbed by the comet nucleus, sublimation energy and energy of heat
radiation of that part (1 - gamma) of the nucleus surface which does
not sublimate and iscovered with mineral crust; the mean temperature of
the nucleus surface (of the mineral crust) at perihelion according to
our calculations is 330 K. As a result the dependence of the value
R(e)qu on gamma, the fraction of the nucleus surface which is a source
of sublimation, was obtained. The minimal value of the nuclear radius
R-equ (for gamma = 1.0, i.e., the total surface sublimation) equals
14.6 km; for gamma = 0.5 the value R-equ = 20.7 km. For gamma = 0.1
(comet Halley's nucleus had approximately this value of gamma) R(e)qu =
46.3 km.; the thickness of the mineral crust equals approximate to 1 cm
for the heat conductivity coefficient lambda approximate to 2.10(4)
erg.cm(-1). s(-1).K-1. Copyright 1999, Institute for Scientific
Information Inc.

===================
(5) NUCLEAR SIZE OF COMET HALE-BOPP

Z. Sekanina: A determination of the nuclear size of comet Hale-Bopp
(C/1995 O1). EARTH MOON AND PLANETS, 1999, Vol.77, No.3, pp.147-153

CALTECH,JET PROP LAB,4800 OAK GROVE DR,PASADENA,CA,91125

The signal of the nucleus was digitally extracted from six images of
the innermost coma of this comet, obtained with the Hubble Space
Telescope's Wide-Field Planetary Camera 2 in the planetary mode between
October 23, 1995 and October 17, 1996. Two different anisotropic,
power-type laws were used to filter out the contribution from the dust
coma: one peaking at the center of the elliptical surface brightness
distribution (law A), the other peaking at its focus (law B). The
nuclear R magnitudes in the Cousins system, reduced to a zero phase
angle and to 1 AU from Earth and the Sun with a phase coefficient of
0.035 mag/deg and an inverse square distance power law, are found to
average 9.46 +/- 0.07 and 9.48 +/- 0.18 when law A and law B are
applied, respectively. These results become 9.49 +/- 0.07 and 9.51 +/-
0.17, when the nucleus signal on the October 1995 image is assumed to
consist of a sum of the contributions from two unresolved nuclear
components. In either scenario, no systematic variations are apparent
in the nuclear brightness with time, which suggests the absence of any
significant contamination of the extracted nuclear signal by the coma.
Assuming a geometric albedo of 4 percent, the corresponding effective
nuclear diameter amounts to 71 +/- 4 km (formal error). This result
substantially exceeds the size estimates published by Weaver et al.,
which are based only on the October 1995 observation and which were
obtained with the help of a different reduction method. Runs in which a
power-type law fitting the contribution from the coma was assumed to
hold all the way to a small fraction of a pixel from the nucleus led to
distinctly inferior solutions and yielded spurious values much less
than 70 km for the nuclear diameter. Copyright 1999, Institute for
Scientific Information Inc.

============
(6) DETECTION OF A SATELLITE ORBITING THE NUCLEUS OF COMET
    HALE-BOPP

Z. Sekanina: Detection of a satellite orbiting the nucleus of comet
Hale-Bopp (C/1995 O1). EARTH MOON AND PLANETS, 1999, Vol.77, No.3,
pp.155-163

CALTECH,JET PROP LAB,4800 OAK GROVE DR,PASADENA,CA,91125

This paper reports on the detection of a satellite around the principal
nucleus of comet Hale-Bopp. As shown elsewhere, a successful
morphological model for the comet's dust coma necessitates the
postulation of overlapping jet activity from a comet pair. The
satellite has been detected digitally on images taken with the Hubble
Space Telescope's Wide Field Planetary Camera 2 in the planetary mode
on five days in May-October 1996. An average satellite-to-primary
signal ratio is 0.21 +/- 0.03, which implies that the satellite is
similar to 30 km in diameter, assuming the main nucleus is similar to
70 km across. To avoid collision, the separation distance must exceed
50-60 km at all times. The satellite's projected distances on the
images vary from 160 to 210 km, or 0.06 to 0.10 arcsec. The satellite
was not detected in October 1995, presumably because of its subpixel
separation from the primary. The radius of the gravitational sphere of
action of the principal nucleus 70 km in diameter is 370-540 km at
perihelion, increasing linearly with the Sun's distance: the satellite
appears to be in a fairly stable orbit. Its orbital period at similar
to 180 km is expected to be similar to 2-3 days, much shorter than the
intervals between the HST observations. If the main nucleus should be
no more than 42 km across, Weaver et al.'s upper limit, the satellite's
orbit could become unstable, with the object drifting away from the
main nucleus after perihelion. Potentially relevant ground-based
detections of close companions are reported. Efforts to determine the
satellite's orbit and the total mass of the system will get under way
in the near future. Copyright 1999, Institute for Scientific
Information Inc.

===========
(7) CHEMICAL ABUNDANCE IN COMETS

W.F. Huebner*) & J. Benkhoff: On the relationship of chemical
abundances in the nucleus to those in the coma. EARTH MOON AND PLANETS,
1999, Vol.77, No.3, pp.217-222

*) SW RES INST,PO DRAWER 28510,SAN ANTONIO,TX,78228

One of the goals of comet research is the determination of the chemical
composition of the nucleus because it provides us with the clues about
the composition of the nebula in which comet nuclei formed. It is well
accepted that photo-chemical reactions must be considered to establish
the abundances of mother molecules in the coma as they are released
from the comet nucleus or from distributed dust sources in the coma.
However, the mixing ratios of mother molecules in the coma changes with
heliocentric distance. To obtain the abundances in the nucleus relative
to those in the coma, we must turn our attention to the release rates
of mother molecules from the nucleus as a function of heliocentric
distance. For this purpose, we assume three sources for the coma gas:
the surface of the nucleus (releasing mostly water vapor), the dust in
the coma (the distributed source of several species released from dust
particles), and the interior of the porous nucleus (the source of many
species more volatile than water). The species diffusing from the
interior of the nucleus are released by heat transported into the
interior. Thus, the ratio of volatiles relative to water in the coma is
a function of the heliocentric distance and provides important
information about the chemical composition and structure of the
nucleus. Our goal is to determine the abundance ratios of various
mother molecules relative to water from many remote-sensing
observations of the coma as a function of heliocentric distance. Comet
Hale-Bopp is ideal for this purpose since it has been observed using
instruments in many different wavelength regions over large ranges of
heliocentric distances. The ratios of release rates of species into the
coma are than modeled assuming various chemical compositions of the
spinning nucleus as it moves from large heliocentric distance through
perihelion. Since the heat flow into the nucleus will be different
after perihelion from that before perihelion, we can also expect
different gas release rates after perihelion compared to those observed
before perihelion. Since not all the data are available yet, we report
on progress of these calculations. Copyright 1999, Institute for
Scientific Information Inc.

===============
(8) GAS AND DUST RELEASE FROM COMET HALE-BOPP

D. Prialnik: Modelling gas and dust release from comet Hale-Bopp. EARTH
MOON AND PLANETS, 1999, Vol.77, No.3, pp.223-230

TEL AVIV UNIV,DEPT GEOPHYS & PLANETARY SCI,IL-69978 RAMAT AVIV,ISRAEL

Numerical simulations of the evolving activity of comet Hale-Bopp are
presented, assuming a porous, spherical nucleus, 20 km in radius, made
of dust and gas-laden amorphous ice. The main effects included are:
crystallization of amorphous ice and release of occluded gas,
condensation, sublimation and flow of gases through the pores, changing
pore sizes, and flow of dust grains. The model parameters, such as
initial pore size and porosity, emissivity, dust grain size, are varied
in order to match the observed activity. In all cases, a sharp rise in
the activity of the nucleus occurs at a large heliocentric distance
pre-perihelion, marked by a few orders of magnitude increase in the CO
and the CO2 fluxes and in the rate of dust emission. This is due to the
onset of crystallization, advancing down to a few meters below the
surface, accompanied by release of the trapped gases. A period of
sustained, but variable, activity ensues. The emission of water
molecules is found to surpass that of CO at a heliocentric distance of
3 AU. Thereafter the activity is largely determined by the behaviour of
the dust. If a dust mantle is allowed to build up, the water production
rate does not increase dramatically towards perihelion; if most of the
dust is ejected, the surface activity increases rapidly, producing a
very bright comet. Copyright 1999, Institute for Scientific Information
Inc.

============
(9) IS COMET HALE-BOPP A JUVENILE COMET?

J. Benkhoff*) & H. Rauer: Is Hale-Bopp a 'juvenile' comet? Study of the
energy balance to explain the vapor flux of volatiles from the surface.
EARTH MOON AND PLANETS, 1999, Vol.77, No.3, pp.231-236

*) DLR,INST PLANETENERKUNDUNG,RUDOWER CHAUSSEE 5,D-12484 BERLIN,GERMANY

Sublimation of minor gases from ices inside of a porous comet nucleus
strongly depends on the effective energy input. Our model meant to
describe the gas flux inside and out of the porous nucleus has been
used to study the influence of physical and structural parameters on
the effective energy input. We solve the conservation equations for H2O
and CO as the most abundant minor component of higher volatility under
appropriate boundary conditions. From the calculations we obtain the
gas flux from volatile, icy components inside the porous nucleus,
temperature profiles, changes in relative chemical abundances, and the
gas flux into the coma for each of the volatiles. We will show results
from our calculations for a model comet in the orbit of Hale-Bopp
(C/1995 O1). In this paper we focus on the energy balance at the
surface. We will also relate measurements of molecule fluxes to
available energies and try to provide hints about the evolutionary
status of the comet. Copyright 1999, Institute for Scientific
Information Inc.

============
(10) MONTE CARLO SIMULATIONS OF OORT CLOUD COMETS

P. Nurmi*), M.J. Valtonen, J.Q. Zheng, S. Mikkola, H. Rickman: Monte
Carlo simulations of oort cloud comets: The influence of mantle
blow-off on the inclination distribution of Jupiter family. EARTH MOON
AND PLANETS, 1999, Vol.77, No.3, pp.239-244

*) UNIV TURKU,TUORLA OBSERV,PIIKKIO 21500,FINLAND

We have developed an efficient Monte Carlo method by which we can
evaluate the evolution of comets. There are many poorly known
evolutional parameters, and we have investigated the influence of these
parameters on the final populations and the inclination distributions
of short-period comets. We compare the observed and calculated
inclination distributions of different comet populations and obtain a
good fit for the inclinations of the Jupiter family comets by assuming
a mantle blow-off and a sudden brightening of the comet when its
perihelion distance is lowered in a major jump. Copyright 1999,
Institute for Scientific Information Inc.

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