PLEASE NOTE:
*
CCNet DIGEST, 3 December 1998
-----------------------------
(1) FIRST NEAR DISTANT IMAGE OF EROS
Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
(2) LEONIDS LIVE 1999
Chris Riley <chris.riley@bbc.co.uk>
(3) LEONIDS PROVIDE OPPORTUNITY FOR ATMOSPHERIC RESEARCH
Andrew Yee <ayee@nova.astro.utoronto.ca>
(4) THE COMPOSITION OF CENTAUR 5145 PHOLUS
D.P. Cruikshank et al., NASA, AMES RES CTR
(5) PRIMORDIAL COMETARY BELT BETWEEN URANUS AND NEPTUNE
A. Brunini & M.D. Melita, NATIONAL
UNIVERSITY OF LA PLATA
(6) COMAE AROUND KUIPER BELT & CENTAUR OBJECTS
W.R. Brown & J.X. Luu, HARVARD SMITHSONIAN
CTR ASTROPHYS
(7) A NEW INTERPRETATION OF THE MAIN-BELT ASTEROID SIZE
DISTRIBUTION
D.D. Durda, R. Greenberg, R. Jedicke,
UNIVERSITY OF ARIZONA
(8) SPECTROPHOTOMETRY OF NEAR-EARTH ASTEROIDS 2100 RA-SHALOM
& 1991 EE.
A.W. Harris et al., DLR, INST PLANETARY
EXPLORATION
(9) PHOTOMETRIC PROPERTIES OF ASTEROID 4179 TOUTATIS
R.S. Hudson*), S.J. Ostro, WASHINGTON
STATE UNIVERSITY
====================
(1) FIRST NEAR DISTANT IMAGE OF EROS
From Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
http://near.jhuapl.edu/IOD/index.html
This first image of the asteroid 433 Eros was acquired by the
multispectral imager on the Near Earth Asteroid Rendezvous (NEAR)
spacecraft on November 5, 1998, at a distance of 2.5 million
miles (4
million kilometers) from the asteroid. Eros, located at the
center of
the image and circled, appears against the star background in a
single
illuminated pixel. At the time of the image, NEAR was located 200
million miles (321 million kilometers) from Earth, and the radio
signal
which transmitted the image from the spacecraft took nearly 18
minutes
to reach Earth. The image is a part of a 5.3-hour sequence of
images
that show Eros over one full rotation of the asteroid. Repeated
imaging
of Eros through January will be used to refine knowledge of
NEAR's
trajectory relative to the asteroid, to plan firings of the
spacecraft's engines to slow the craft and place it into orbit.
Currently, NEAR is approaching Eros at a rate of 2100 miles per
hour
(945 meters per second). Three firings of NEAR's engines,
beginning on
December 20, 1998, will slow spacecraft velocity relative to the
asteroid to near 10 miles per hour (5 meters per second) at Eros
orbit
insertion on January 10, 1999.
Built and managed by The Johns Hopkins University Applied Physics
Laboratory, Laurel, Maryland, NEAR was the first spacecraft
launched in
NASA's Discovery Program of low-cost, small-scale planetary
missions.
=====================
(2) LEONIDS LIVE 1999
From Chris Riley <chris.riley@bbc.co.uk>
The BBC is currently putting plans together for a live broadcast
to
cover next years Leonid meteor storm. At this stage we were
looking
into the possibility of covering it in as global a way as
possible,
with cameras at strategic locations around the world and even in
the
odd aircraft. I hope you don't mind me writing to you all in this
way,
but I was looking for some advice and information in a couple of
areas.
1. I realise the intensity of these showers is very hard to
predict,
but is there any scientific evidence that the 99 Leonids will be
at
least as good as the 98 shower? Is there any evidence other than
historical patterns (1998 mimicking 1965 and possibly 1999
therefore
mimicking 1966) for 1999 to be better than 1998. I understand
that 1966
was a couple of hours late. Could 1999 be the same. If so why?
Could
1999 also be 13 hours early like this year. What's everyone's
best
guess and what science is it based on?
2. To ensure we catch something on film in 1999 where would you
place a
network of say 10 cameras? Is anyone planning to set
up there own web
cam stuff from anywhere around the world, which we could perhaps
take a
feed from? Realistically how many camera positions do you think
we'd
need to cover the shower/storm properly?
Do let me know if any of you can help.
Best wishes,
Chris
Dr Christopher Riley, LEONIDS LIVE '99
Room 4104, BBC Science, 201 Wood Lane, White City, London W12 7TS
tel: +44 181 752 6627 fax: +44 181 752 6789 mobile: +44 956 359
810
chris.riley@bbc.co.uk
====================
(3) LEONIDS PROVIDE OPPORTUNITY FOR ATMOSPHERIC RESEARCH
From Andrew Yee <ayee@nova.astro.utoronto.ca>
Air Force Research Laboratory
Office of Public Affairs
3550 Aberdeen Avenue S.E.
Kirtland AFB, NM 87117-5776
(505) 846-1911; Fax (505) 846-0423
INTERNET: http://www.de.afrl.af.mil/pa/
CONTACT: Sandra-Carol
PHONE: (505) 846-6315
November 25, 1998
PL RELEASE NO. 98-65
Leonid Meteors Provide Test Opportunities For SOR
KIRTLAND AIR FORCE BASE, N. M. -- More than one hundred and fifty
years
ago when the earth passed through the long tail of the Comet
Tempel-Tuttle, many observing the meteor storm that followed
thought
the world was ending.
Today, the scientific community at the Air Force Research
Laboratory's
Starfire Optical Range, here, greeted that same meteor storm with
eager
anticipation.
Those famous "shooting stars," which in the past,
rained down on the
earth by the thousands, were expected to assist in yielding
valuable
information about this planet's upper atmosphere.
The purpose of the experiments, using a laser radar system
(LIDAR), was
to measure sodium about 60 miles above the earth in the upper
atmosphere. It is hoped that the data will provide more
information
about the chemistry and physics at that level of the atmosphere.
Results of this information, in turn, might allow future adaptive
optics to produce higher resolution images of space objects and
satellites.
In the past, scientists, wanting to know more about the upper
atmosphere, have had to depend on expensive methods of data
collection
including rockets to the upper atmosphere..
In this case, nature has provided the Leonid meteors that are
known to
create rare contrails. It was those contrails the experimenters
targeted in mid-November.
Dr. Jack Drummond, a Directed Energy Directorate astronomer, said
in
the past, meteor trails have only been caught accidentally and
the
whole sum of past data equates to about 10 or 12 minutes of
material.
"This is the first time anyone has every tried to chase the
meteors. We
were able to capture more than an hour of data from ten meteors
over
two nights," he said.
The crystal clear sky created a perfect backdrop for the light
show
that peaked during the early morning hours before dawn. Above the
"oohs" and "aahs" of the group, as the
meteors streaked across the sky,
was the voice of the spotter, Dr. Drummond, providing azimuth and
altitude to the telescope operator.
Not every meteor created a contrail. When a contrail did appear,
the
spotter guided the 3.5-meter telescope across the darkened sky
until
the laser picked it up.
Drummond said the longest previous measurement of a meteor trail
was
only about a minute or two. "We had two contrails that
lasted more than
a half hour each. It was spectacular," he said
enthusiastically.
During the experiment, the LIDAR was used to excite the neutral
sodium
atoms.
"We shot the LIDAR at a certain frequency and it pumped up
an electron
one level. When that one electron dropped back one level, it
emitted
that same frequency of light and that is what we were
seeing," Drummond
explained.
What they were able to see will help the scientists understand
wind
velocity, wind shear, diffusion, temperature and density in the
upper
atmosphere.
Drummond said one thing they noted during the experiment was
there
doesn't seem to be a uniform wind velocity field in the upper
atmosphere. "One meteor contrail moved in a southeast
direction," he
said. "We expected the next one to do the same. Instead, the
next
contrail moved north."
Another area of interest was an inexplicable enhancement of the
amount
of sodium deposited in comparison to the size of the particle.
"Something is happening in physics and chemistry at that
altitude that
we don't fully understand," he added.
Drummond said the laboratory is involved in a cooperative
agreement
with two universities. The University of Illinois and Cornell
University are providing equipment and expertise for special
observation projects over a three-year period. Together the group
decided to study the Leonid meteor contrails using a LIDAR, on
loan
from the University of Illinois.
According to Drummond, "We increased the amount of data
available by an
order of magnitude -- by a factor of ten." The directorate
scientist
speculated that enough data was collected in one night to
provided
dissertation material for three graduate students.
Drummond also said he is not aware that anyone else has ever
video
taped an evolving meteor trail. He explained that there were two
different types of trails recorded.
One type was evanescent, expanded quickly, and was optically
thin. "You
could see right through it," he explained.
The other example was optically thick, did not evolve very fast,
and
was much brighter. There was also no detection of sodium
enhancement in
this trail.
Drummond said PhD candidates from the two universities would be
analyzing the data. He said 1999 might be an even better year for
gathering data on the Leonid meteors.
=================
(4) THE COMPOSITION OF CENTAUR 5145 PHOLUS
D.P. Cruikshank*), T.L. Roush, M.J. Bartholomew, T.R. Geballe,
Y.J.
Pendleton, S.M. White, J.F. Bell, J.K. Davies, T.C. Owen, C.
deBergh,
D.J. Tholen, M.P. Bernstein, R.H. Brown, K.A. Tryka, C.M.
DalleOre: The
composition of Centaur 5145 Pholus. ICARUS, 1998, Vol.135, No.2,
pp.389-407
*) NASA, AMES RES CTR, MS 245-6, MOFFETT FIELD, CA, 94035
We present a new spectrum of the Centaur object 5145 Pholus
between
1.15 and 2.4 Gem. We model this, and the previously published
(0.4- to
1.0-mu m) spectrum, using Hapke scattering theory. Seen in
absorption
are the 2.04-mu m band of H2O ice and a strong band at 2.27 mu m,
interpreted as frozen methanol and/or a photolytic product of
methanol
having small molecular weight. The presence of small molecules is
indicative of a chemically primitive surface, since heating and
other
processes remove the light hydrocarbons in favor of
macromolecular
carbon of the kind found in carbonaceous meteorites. The
unusually red
slope of Pholus' spectrum is matched by fine grains of a
refractory
organic solid (tholin), as found previously by M. Hoffmann et al,
(1993, J. Geophys. Res. 98, 7403-7407) and P. D. Wilson et al.
(1994,
Icarus 107, 288-303). Olivine (which we model with Fo 82) also
appears
to be present on Pholus. We present a live-component model for
the
composite spectrum of all spectroscopic and photometric data
available
for 5145 Pholus and conclude that this is a primitive object
which hips
not yet been substantially processed by solar heat. The
properties of
Pholus are those of the nucleus of a large comet that has never
been
active. (C) 1998 Academic Press.
==========================
(5) PRIMORDIAL COMETARY BELT BETWEEN URANUS AND NEPTUNE
A. Brunini & M.D. Melita: On the existence of a primordial
cometary
belt between Uranus and Neptune. ICARUS, 1998, Vol.135, No.2,
pp.408-414
NATIONAL UNIVERSITY OF LA PLATA, FAC CIENCIAS ASTRON &
GEOFIS, PASEO
BOSQUE,RA-1900 LA PLATA,ARGENTINA
The existence of stable orbits in the interplanetary region
between
Uranus and Neptune over the lifetime of the Solar System has been
reported by Holman (1997, Nature 387, 785-788). A long-term
integration
of test particles in that zone resulted in a number of surviving
bodies
with semimajor axis roughly between 24 and 27 AU, and
eccentricities
and inclinations smaller than 10(-2) and 1 degrees, respectively.
According to up-to-date surveys, the total mass of this putative
belt
has been estimated as less than or equal to 10(-3) M+ and it
would
be composed of objects with radius smaller than 50 km. In this
work we
assess the plausibility of the existence of a real population of
objects in such a belt. Time-reversal arguments rule out the
possibility of capture in such long-term stable orbits, for
example, of
objects escaped from the Kuiper belt. So if a real population
exists
nowadays, it should have undergone the conditions of planetesimal
accretion in the region. Hence, we have studied the orbital
evolution
of test particles under different kinds of plausible primordial
scenarios. The conditions considered were mutual collisions and
gravitational encounters, planetary migration and the presence of
an
adjacent Pluto-sized object. Under none of these conditions have
we
obtained a surviving substantial population on the reported belt
region, from which it is concluded that, at present time, it
would be
very unlikely to find a subtantial number of primordial objects
in
those long-term stable orbits. (C) 1998 Academic Press.
=====================
(6) COMAE AROUND KUIPER BELT & CENTAUR OBJECTS
W.R. Brown & J.X. Luu: Properties of model comae around
Kuiper Belt and
Centaur objects. ICARUS, 1998, Vol.135, No.2, pp.415-430
HARVARD SMITHSONIAN CTR ASTROPHYS, 60 GARDEN ST, CAMBRIDGE, MA,
02138
The cometary activity of Chiron inspires us to investigate
observable
lifetimes of hypothetical dust particles around large, distant
Centaur
and Kuiper Belt objects (KBOs). Our model computes dust particle
trajectories assuming comet nucleus gravity, solar gravity, and
solar
radiation pressure. We find that particle lifetimes are extremely
sensitive to the magnitude of the initial velocity. Long-lived
orbits
require an exact combination of nucleus size, heliocentric
distance,
particle size, and initial velocity. Estimating ejection
velocities due
to CO sublimation, we find that particles escape >50,000 km
from
Centaurs in 6 days and from KBOs in less than or similar to 10
days.
Assuming optimal ejection velocities < nu(escape) upper limits
to bound
coma lifetimes are 50-75 days for Centaurs with Chiron-like
activity.
Thus Chiron's long-lived coma cannot be a result of an outburst.
To
observe a KBO coma requires a massive similar to 5 x 10(9)-kg
dust
coma, and its lifetime varies from <2 months to similar to 1
year
depending on object size and heliocentric distance. (C) 1998
Academic Press.
=======================
(7) A NEW INTERPRETATION OF THE MAIN-BELT ASTEROID SIZE
DISTRIBUTION
D.D. Durda, R. Greenberg, R. Jedicke: Collisional models and
scaling
laws: A new interpretation of the shape of the main-belt asteroid
size
distribution. ICARUS, 1998, Vol.135, No.2, pp.431-440
UNIVERSITY OF ARIZONA, LUNAR & PLANETARY LAB, TUCSON, AZ,
85721
Numerical models of the collisional evolution of the main-belt
asteroids lead to a new interpretation of the shape of the
observed
size distribution. Using recent hydrocode predictions of
shattering and
disruption criteria as starting points, we adjust the
size-strength
scaling relation for asteroidal strengths within our collisional
model
until a best least-squares fit to the observed size distribution
is
obtained. We show for the first time general agreement between
the
predictions of hydrocodes, results of numerical collisional
models, and
the observed size distribution of the main-belt population. (C)
1998
Academic Press.
================
(8) SPECTROPHOTOMETRY OF NEAR-EARTH ASTEROIDS 2100 RA-SHALOM
& 1991 EE.
A.W. Harris*), J.K. Davies, S.F. Green: Thermal infrared
spectrophotometry of the near-Earth asteroids 2100 Ra-Shalom and
1991
EE. ICARUS, 1998, Vol.135, No.2, pp.441-450
*) DLR, INST PLANETARY EXPLORAT, RUDOWER CHAUSSEE 5, D-12489
BERLIN, GERMANY
Thermal infrared observations of the near-Earth asteroids 2100
Ra-Shalom and 1991 EE are presented and interpreted with the aid
of
published asteroid thermal models. The broad wavelength range
covered
allows the best fitting of a family of model spectra to be
selected,
eliminating the ambiguity associated with deriving model
parameters
from observations at just one or two thermal wavelengths. Neither
the
''standard'' thermal model nor the ''fast rotating'' model
provide good
fits to the thermal spectra. Much improved fits are obtained with
a
modified standard thermal model with values of the model
''beaming''
parameter, eta, significantly higher than normally assumed in the
standard thermal model. The results for the Aten asteroid 2100
Ra-Shalom provide convincing confirmation that this object has an
unusually high surface thermal inertia. The resulting optical
albedos
(on the H, G magnitude system) and effective diameters are 0.13
+/-
0.04 and 2.48 +/- 0.35 km for 2100 Ra-Shalom (near lightcurve
maximum)
and 0.30 +/- 0.10 and 1.01 +/- 0.15 km for 1991 EE (referred to
the
lightcurve mean magnitude). The derived size for 2100 Ra-Shalom
is
consistent with previous estimates but the moderate albedo,
coupled
with infrared colors more typical of S-types, leads us to
question
its classification as C-type. These are the first size and albedo
determinations for the Apollo asteroid 1991 EE. The near infrared
colors and albedo of 1991 EE suggest an S-type classification.
(C) 1998
Academic Press.
=================
(9) PHOTOMETRIC PROPERTIES OF ASTEROID 4179 TOUTATIS
R.S. Hudson*), S.J. Ostro: Photometric properties of Asteroid
4179
Toutatis from lightcurves and a radar-derived physical model.
ICARUS,
1998, Vol.135, No.2, pp.451-457
*) WASHINGTON STATE UNIVERSITY, SCH ELECT ENGN & COMP
SCI, PULLMAN, WA, 99164
Optical lightcurves reported by J. R. Spencer et al. (1995,
Icarus 117,
71-89) and a radar-derived shape and spin-state model (R. S.
Hudson and
S. J. Ostro, 1995, Science 270, 84-86) are used to estimate the
Hapke
parameters of the Earth-crossing Asteroid 4179 Toutatis. We find
a
particle single-scattering albedo w = 0.261 +/- 0.019, opposition
surge
width h = 0.036 +/- 0.023 and amplitude B-0 = 1.20 +/- 0.32,
particle
phase function asymmetry factor g = -0.29 +/- 0.06, and
macroscopic
roughness parameter <(theta)over bar> = 32 +/- 8 degrees.
The synthetic
lightcurves generated with this model provide a good fit (rms
residual
= 0.12 mag) to the optical data which span phase angles from 0.2
degrees to 121.4 degrees. The addition of optical data in the
modeling
process results in a slight refinement of the radar-derived
estimate of
the parameters that describe Toutatis's non-principal-axis spin
state.
Analysis of the opposition surge width in light of recent radar
results
supports the hypothesis that a significant fraction of Toutatis's
surface is covered by a fine particulate regolith. (C) 1998
Academic
Press.
----------------------------------------
THE CAMBRIDGE-CONFERENCE NETWORK (CCNet)
----------------------------------------
The CCNet is a scholarly electronic network. To subscribe, please
contact the moderator Benny J Peiser at <b.j.peiser@livjm.ac.uk>.
Information circulated on this network is for scholarly and
educational
use only. The attached information may not be copied or
reproduced for
any other purposes without prior permission of the copyright
holders.
The electronic archive of the CCNet can be found at
http://abob.libs.uga.edu/bobk/cccmenu.html