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(meteorobs) Remaining Excerpts from "CCNet DIGEST, 5 July 1999"
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From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
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Subject: CCNet DIGEST, 5 JULY 1999
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Date: Mon, 5 Jul 1999 10:36:30 -0400 (EDT)
CCNet DIGEST, 5 July 1999
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[...]
(4) A DUSTY SOURCE FOR METEORIC WATER VAPOR
Harvey Leifert <HLeifert@agu.org>
(5) THE SEARCH FOR SMALL COMETS
S. Knowles et al., USN, RES LAB
(6) KUIPER BELT OBJECTS
D. Jewitt, INSTITUTE FOR ASTRONOMY
(7) INFRARED KUIPER BELT CONSTRAINTS
V.L. Teplitz et al., SO METHODIST UNIVERSITY
(8) AN OVERVIEW ON THE JUIPER BELT
A. Morbidelli, NICE OBSERVATORY
(9) COMPOSITIONAL SURFACE VARIETY AMONG THE CENTAURS
M. A. Barucci et al., PARIS OBSERVATORY
(10) DYNAMICAL CONSTRAINTS TO THE MASSES OF LARGE PLANETESIMALS
M.G. Parisi & A. Brunini, OBSERV ASTRON LA PLATA,ARGENTINA
=======================
(4) A DUSTY SOURCE FOR METEORIC WATER VAPOR
>From Harvey Leifert <HLeifert@agu.org>
Geophysical Research Letters
Highlights of this issue - July 1, 1999
A dusty source for meteoric water vapor
The presence of a narrow H2O layer centered near 70 km altitude and
restricted to latitudes within 30 degrees of the equator cannot be
explained by conventional chemical or dynamical processes. An
extraterrestrial source (influx of small comets) has been suggested
as a possibility (see GRL, 1 Oct. 1997). Summers and Siskind
["Surface recombination of O and H2 on meteoric dust as a source of
mesospheric water vapor"] propose a terrestrial mechanism for the
production of the observed mesospheric H2O layer: the reaction O + H2
- --> H2O on the surface of meteoric dust. Noting that depleted H2 must
coincide with the observed layer of mesospheric water vapor, they
suggest that coincident observations of H2 and H2O in the mesosphere
will help answer whether the observed water vapor layer has a
terrestrial or extraterrestrial source.
Michael E. Summers, David E. Suskind, E.O. Hulburt Center for Space
Research, Naval Research Laboratory, Washington, DC.
Journalists and public information officers of educational and
scientific institutions (only) may receive one or more of the papers
cited in the Highlights; send a message to Daryl Tate
[dtate@agu.org], indicating which one(s). Include your fax number. If
you did not receive this message directly from AGU, please provide
your full name, title, organization, address, and phone as well.
Harvey Leifert
Public Information Manager
American Geophysical Union
2000 Florida Avenue, N.W.
Washington, DC 20009
Phone (direct): +1 (202) 777-7507
Phone (toll-free in North America): (800) 966-2481 x507
Fax: +1 (202) 328-0566
Email: hleifert@agu.org
================
(5) THE SEARCH FOR SMALL COMETS
S. Knowles*), R.R. Meier, B.A.S. Gustafson, F.J. Giovane: A search for
small comets with the Naval Space Command radar
JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, 1999, Vol.104, No.A6,
pp.12637-12643
*) USN,RES LAB,EO HULBURT CTR SPACE RES,CODE 7604,WASHINGTON,DC,20375
We have searched for the hypothetical small comets proposed by Frank et
al. [1986a, b] and Frank and Sigwarth [1993] using the world's most
powerful radar in terms of gain-aperture product. The Naval Space
Surveillance System can detect most space objects in low Earth orbit
with radar cross sections (RCSs) of 0.1 m(2) or larger; at higher
altitudes of the order of 10,000-20,000 km the radar can detect objects
with RCSs of 1 m(2). We carried out detailed first-principle
calculations of the RCS of spherical comet using the properties
proposed by Frank and Sigwarth [1993]. We find that 8-12 m diameter
comets have an average cross section of 0.4 m(2) at the radar frequency
(217 MHz), with peaks reaching 1 m. Therefore the Naval radar system
has sufficient sensitivity to detect many small comets, especially as
they approach low Earth orbit. We estimate that at least 800-5000 small
comets should have been detected by the radar during the 37 day search
period during fall 1997. None of the more than 12,000 unidentified
detections can be explained by small comets. The lack of detection of
small comets by the radar can be explained only if small comets have
RCSs <0.1% of their assumed physical size,(which is unrealistic, given
that human technology can match this value only by tailoring a design
for a specific radar) or if their impact rate with Earth is some 4
orders of magnitude less than proposed by Frank et al. [1986a] and
Frank and Sigwarth [1993]. Copyright 1999, Institute for Scientific
Information Inc.
================
(6) KUIPER BELT OBJECTS
D. Jewitt: Kuiper belt objects. ANNUAL REVIEW OF EARTH AND PLANETARY
SCIENCES, 1999, Vol.27, pp.287-312
INST ASTRON,2680 WOODLAWN DR,HONOLULU,HI,96822
The region of the solar system immediately beyond Neptune's orbit is
densely populated with small bodies. This region, known as the Kuiper
Belt, consists of objects that may predate Neptune, the orbits of which
provide a fossil record of processes operative in the young solar
system. The Kuiper Belt contains some of the Solar System's most
primitive, least thermally processed matter. It is probably the source
of the short-period comets and Centaurs, and may also supply
collisionally generated interplanetary dust. I discuss the properties
of the Kuiper Belt and provide an overview of the outstanding
scientific issues. Copyright 1999, Institute for Scientific Information
Inc.
===============
(7) INFRARED KUIPER BELT CONSTRAINTS
V.L. Teplitz*), S.A. Stern, J.D. Anderson, D. Rosenbaum, R.J. Scalise,
P. Wentzler: Infrared Kuiper belt constraints. ASTROPHYSICAL JOURNAL,
1999, Vol.516, No.1 Pt1, pp.425-435
*) SO METHODIST UNIV,DEPT PHYS,DALLAS,TX,75275
We compute the temperature and IR signal of particles of radius a and
albedo a at heliocentric distance R, taking into account the emissivity
effect, and give are interpolating formula for the result. We compare
with analyses of COBE DIRBE data by others (including recent detection
of the cosmic IR background) for various values of heliocentric
distance R, particle radius a, and particle albedo a. We then apply
these results to a recently developed picture of the Kuiper belt as a
two-sector disk with a nearby, low-density sector (40 < R < 50-90 AU)
and a more distant sector with a, higher density. We consider the case
in which passage through a molecular cloud essentially cleans the solar
system of dust. We apply a simple model of dust production by comet
collisions and removal by the Poynting-Robertson effect to find limits
on total and dust masses in the near and far sectors as a function of
time since such a passage. Finally, we compare Kuiper belt IR spectra
for various parameter values. Results of this work include: (1)
numerical limits on Kuiper belt dust as a function of (R, a, alpha) on
the basis of four alternative sets of constraints, including those
following from recent discovery of the cosmic IR background by Hauser
et al.; (2) application to the two-sector Kuiper belt model, finding
mass limits and spectrum shape for different values of relevant
parameters including dependence on time elapsed since last passage
through a molecular cloud cleared the outer solar system of dust; and
(3) potential use of spectral information to determine time since last
passage of the Sun through a giant molecular cloud. Copyright 1999,
Institute for Scientific Information Inc.
==================
(8) AN OVERVIEW ON THE JUIPER BELT
A. Morbidelli: An overview on the Kuiper belt and on the origin of
Jupiter-family comets. CELESTIAL MECHANICS & DYNAMICAL ASTRONOMY, 1998,
Vol.72, No.1-2, pp.129-156
OBSERV NICE,CNRS,UMR 6529,OCA,BP 4229,F-06304 NICE 4,FRANCE
The present paper reviews our current understanding of the dynamical
structure of the Kuiper belt and of the origin of Jupiter-family
comets. It also discusses the evolutionary scenarios that have been
proposed so far to explain the observed structure of the Kuiper belt
population. Copyright 1999, Institute for Scientific Information
Inc.
=============
(9) COMPOSITIONAL SURFACE VARIETY AMONG THE CENTAURS
M. A. Barucci*), M. Lazzarin, G.P. Tozzi: Compositional surface variety
among the Centaurs. ASTRONOMICAL JOURNAL, 1999, Vol.117, No.4,
pp.1929-1932
*) OBSERV PARIS,PL JULES HUSSIEU 5,F-92195 MEUDON,FRANCE
The Centaurs are a particular family of objects with orbits whose
semimajor axes fall between those of Jupiter and Neptune. They are
likely the transition objects between the Kuiper belt population and
short-period comets. To investigate the nature of these particular
objects, we have performed optical spectroscopic observations of five
Centaurs. The results show a great diversity among the reflectances of
the five Centaurs. The colors do not seem to be related to the
perihelion distance of the objects. We looked for weak cometary
emission features, in particular the CN-band emission at 3880 Angstrom,
but no CN emission feature has been detected within 3 sigma in any of
the investigated spectra. Copyright 1999, Institute for Scientific
Information Inc.
===============
(10) DYNAMICAL CONSTRAINTS TO THE MASSES OF LARGE PLANETESIMALS
M.G. Parisi*) & A. Brunini: Dynamical constraints to the masses of
large planetesimals. PLANETARY AND SPACE SCIENCE, 1999, Vol.47, No.5,
pp.607-617
*) OBSERV ASTRON,PASEO BOSQUE S-N,LA PLATA,ARGENTINA
The mean square momentum accumulated by a planet as a result of
collisions and encounters with planetesimals during the accretionary
epoch was computed. It is assumed that the present mean square
eccentricity and inclination of the planetary orbits were determined by
this process. The encounters resulted the dominant effect, especially
for Saturn, Uranus and Neptune, where using the current upper limit of
the mass distribution of planetesimals m(1)/M inferred from the
obliquities and spin periods of the planets (Safronov, 1969. Evolution
of the Protoplanetary Cloud and Formation of the Earth and the Planets.
NASA TTF-677, Nauka, Moscow; Lissauer and Safronov, 1991. Icarus 93,
288), the resulting orbital parameters would be higher than their
present values. For this reason, a new upper limit to the power law
mass distribution of planetesimals in the outer solar system,
consistent with the present orbital parameters is obtained, which is
one or two orders lower than the previous estimates cited above. In the
case of the Earth and Venus we obtain a high upper limit of the mass
distribution, since the present eccentricity and inclination of their
orbits are probably determined mainly by the gravitational
perturbations and not by the process of accumulation. Our results of
m(1)/M in the inner and outer solar system are in good agreement with
those obtained by Harris and Ward (1982. Annu. Rev. Earth Planet. Sci.
10, 61). They carried out a somewhat different calculation of the
random impulses than the one presented in this work, obtaining that the
present eccentricity and inclination of the giant planets' orbits
demand a very small mass ratio. On one hand we have calculated m(1)/M
considering that the total mass of the planets is due to the accretion
of planetesimals. On the other hand, in the case of the giant planets,
we considered the accretion of planetesimals to form a core of solid
material which accreted prior to gas accumulation. The inclusion of the
gas component leads to a higher value of the mass ratio for Jupiter and
Saturn, while for Uranus and Neptune the results remain the same
neglecting the gas component. Even when the gas is taken into account,
the present eccentricity and inclination of the planetary orbits in the
outer solar system demand much smaller values of m(1)/M than most of
the previous estimates. This is consistent with the runaway accretion
scenario, where the largest planetesimals rapidly grow becoming
detached from the distribution while the rest of the mass remains in
smaller bodies. We also constrain the masses of the largest
planetesimals which are probably out of the continuous mass
distribution, studying the increase in the eccentricity of the
planetary orbits caused by a single close encounter and a single impact
with these large bodies. Previous estimates of the largest planetesimal
masses at the end of the accretionary epoch have been obtained assuming
that the inclination of the spin axes of the planets were caused by
off-center impacts (Safronov, 1969. Evolution of the Protoplanetary
Cloud and Formation of the Earth and Planets. NASA TTF-677, Nauka,
Moscow; Lissauer and Safronov, 1991. Icarus 93, 288; Parisi and
Brunini, 1996a. Muzzio, J.C., Ferraz-Mello, S., Henrard, J. (Eds.),
Proceedings of the Workshop: Chaos in Gravitational N-Body Systems, p.
291; Parisi and Brunini, 1997. Planet. Space Sci. 45, 181). In the case
of the giant planets our results of the maximum allowed masses of the
largest bodies are, generally speaking, in good agreement with those
previous estimates, although we obtain masses for the Earth and Venus
which are much higher. (C) 1999 Elsevier Science Ltd. All rights
reserved.
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