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(meteorobs) Excerpts from "CCNet, 1 September 1999"
------- Forwarded Message
From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet, 1 September 1999
Date: Wed, 1 Sep 1999 09:49:26 -0400 (EDT)
CCNet, 1 September 1999
-----------------------
[...]
(5) REMOTE SENSING ANALYSIS OF ASTEROIDS
J.L. Hinrichs et al., UNIVERSITY OF HAWAII
(6) LARGE METEOROIDS IN THE LYRID STREAM
M. Beech & S. Nikolova, UNIVERSITY OF REGINA
(7) INTERNAL STRUCTURES AND DENSITIES OF ASTEROIDS
L. Wilson et al., UNIVERSITY OF HAWAII MANOA
==============================================
(5) REMOTE SENSING ANALYSIS OF ASTEROIDS
J.L. Hinrichs*), P.G. Lucey, M.S. Robinson, A. Meibom, A.N. Krot:=20
Implications of temperature-dependent near-IR spectral properties of=20
common minerals and meteorites for remote sensing of asteroids.=20
GEOPHYSICAL RESEARCH LETTERS, 1999, Vol.26, No.12, pp.1661-1664
*) UNIVERSITY OF HAWAII,HAWAII INST GEOPHYS & PLANETOL,2525 CORREA=20
RD,HONOLULU,HI,96822
=20
Remote sensing analysis of common mafic silicates on bodies like=20
asteroid 433 Eros may be in error unless temperature effects are=20
considered. In this paper, spectral sensitivity to temperature as a=20
function of wavelength from 0.4 to 2.5 microns is quantified using new=20
measurements of reflectance spectra of olivine and two ordinary=20
chondrites. The new data were obtained at higher temperature resolution =
and with greater accuracy than previous measurements. We use a simple=20
thermal model to show that the temperature difference between=20
terrestrial ambient conditions and those prevailing on main belt=20
asteroids, as well as the temperature variations expected on the=20
surfaces of individual asteroids during observations by spacecraft, are =
large enough to cause easily detectable spectral differences.=20
Therefore, interpretations of asteroid spectra using spectra of=20
minerals and meteorites obtained at terrestrial ambient conditions are=20
suspect. Copyright 1999, Institute for Scientific Information Inc.
==============================================
(6) LARGE METEOROIDS IN THE LYRID STREAM
M. Beech*) & S. Nikolova: Large meteoroids in the Lyrid stream. MONTHLY =
NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 1999, Vol.305, No.2,=20
pp.253-258
*) UNIVERSITY OF REGINA,CAMPION COLL,REGINA,SK S4S 0A2,CANADA
The outburst of the Lyrid meteor shower in 1803 was remarkable for=20
being rich in bright fireballs and the generation of electrophonic=20
sounds. The implications implicit to the detection of electrophonic=20
sounds are studied in this paper. We present estimates for the=20
minimum-sized Lyrid meteoroid capable of generating electrophonic=20
sounds, and compare these lower limits with the largest meteoroid that=20
might reasonably be ejected from a cometary nucleus through coupling=20
with the sublimation gas outflow. A difference of a factor of order 30=20
is found between the two limiting sizes. A minimum diameter of order Im =
is required for a Lyrid meteoroid to satisfy the conditions necessary=20
for generating electrophonic sounds. The mechanisms responsible for the =
placement of large, metre-sized meteoroids into the Lyrid stream are=20
not well defined, but they possibly relate to surface ageing effects of =
the parent comet, Comet C/1861 G1 Thatcher, and to a history of nuclear =
fragmentation. Copyright 1999, Institute for Scientific Information=20
Inc.
==============================================
(7) INTERNAL STRUCTURES AND DENSITIES OF ASTEROIDS
L. Wilson*), K. Keil, S.J. Love: The internal structures and densities=20
of asteroids. METEORITICS & PLANETARY SCIENCE, 1999, Vol.34, No.3,=20
pp.479-483
*) UNIVERSITY OF HAWAII MANOA,HAWAII INST GEOPHYS & PLANETOL,=20
HONOLULU,HI,96822
=20
Four asteroidal bodies (the Martian satellites Phobos and Deimos and=20
the main-belt asteroids 243 Ida and 253 Mathilde) have now been the=20
subjects of sufficiently close encounters by spacecraft that the masses =
and sizes and, hence, the densities of these bodies can be estimated to =
similar to 10%. All of these asteroids are significantly less dense=20
than most members of the classes of meteorites identified as being=20
compositionally most nearly similar to them on the basis of spectral=20
characteristics. We show that two processes can act, independently or=20
in concert, during the evolutionary histories of asteroids to produce a =
low bulk density. One of these processes is the result of one or more=20
impact events and can affect any asteroid type, whereas the other can=20
occur only for certain types of small asteroids that have undergone=20
aqueous alteration. Copyright 1999, Institute for Scientific=20
Information Inc.
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