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(meteorobs) Excerpts from "CCNet, 21 October 1999"


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From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet, 21 October 1999
Date: Thu, 21 Oct 1999 10:09:44 -0400 (EDT)

CCNet, 21 October 1999
------------------------

[...]

(7) A PHYSICAL MODEL OF ASTEROID GEOGRAPHOS
    R.S. Hudson & S.J. Ostro, WASHINGTON STATE UNIVERSITY

(8) RADAR OBSERVATIONS OF 37 MAINBELT ASTEROIDS
    C. Magri, et.al.,  UNIVERSITY OF MAINE

[...]

(10) COMETARY TRAVEL: FROM INTERSTELLAR SPACE TO EARTH'S OCEANS
     D. Laufer et al.,TEL AVIV UNIVERSITY

(11) COMETS, ICE & ORGANIC MOLECULES
     R.L. Hudson, ECKERD COLLEGE

(12) ORBITAL HISTORY OF COMET P/LAGERKVIST (1996 R2)
     G. Hahn & C.I. Lagerkvist, DLR BERLIN

(13) POLARIMETRY OF ASTEROID 2100 RA-SHALOM
     N.N. Kiselev ET AL., KHARKOV AM GORKII STATE UNIVERSITY

================================================

(7) A PHYSICAL MODEL OF ASTEROID GEOGRAPHOS

R.S. Hudson*), S.J. Ostro: Physical model of asteroid 1620 Geographos 
from radar and optical data. ICARUS, 1999, Vol.140, No.2, pp.369-378

*) WASHINGTON STATE UNIVERSITY,SCH ELECT ENGN & COMP 
   SCI,PULLMAN,WA,99164

We develop a physical model of asteroid 1620 Geographos using Goldstone 
delay-Doppler radar images obtained August 1994 (Ostro et al. 1996, 
Icarus 121., 46-66) with resolution as fine as 75 m, and optical 
lightcurves obtained in 1969, 1983, and 1993-1994 (Magnusson et al. 
1996, Icarus 123, 227-244). The data set admits a geometric ambiguity 
that precludes a unique model. Within this constraint, our model has 
maximum dimensions of (5.0, 2.0, 2.1) +/- 0.15 km and a volume of less 
than or equal to 8.8 km(3), equivalent to a sphere of less than or 
equal to 2.56 km diameter. The radar equivalent spherical albedo is 
greater than or equal to 0.12. The photometric solution provides Hapke 
parameters w greater than or equal to 0.22, g = -0.34 +/- 0.10, and 
<(theta)over bar> = 25 +/- 10 degrees with assumed values h = 0.02 and 
B-0 = 1.32. The spin state solution does not differ significantly from 
that of Magnusson et al, having lambda = 55 +/- 6 degrees, beta = -46 
+/- 4 degrees, and P = 5.2233270 +/- 0.00000072 h. We identify seven 
main features in the delay-Doppler images and their corresponding 
locations on the model. (C) 1999 Academic Press.

=================
(8) RADAR OBSERVATIONS OF 37 MAINBELT ASTEROIDS

C. Magri*), S.J. Ostro, K.D. Rosema, M.L. Thomas, D.L. Mitchell, 
D.B. Campbell, J.F. Chandler, I.I. Shapiro, J.D. Giorgini, D.K. 
Yeomans: Mainbelt asteroids: Results of Arecibo and Goldstone radar 
observations of 37 objects during 1980-1995. ICARUS, 1999, Vol.140, 
No.2, pp.379-407

*) UNIVERSITY OF MAINE,39 HIGH ST,PREBLE HALL,FARMINGTON,ME,04938

We report detailed results of Arecibo and Goldstone radar observations 
of 30 mainbelt asteroids (MBAs) during 1980-1995, In addition to 
estimates of radar cross section, radar albedo, and circular 
polarization ratio, we obtain new constraints on pole direction for 
several asteroids, with those for 21 Lutetia being particularly 
restrictive. We carry out statistical analyses of disk-integrated 
properties (radar albedo and polarization ratio) of all 37 
radar-observed MBAs. M asteroids seem to have higher radar albedos and 
a wider range of albedos than do asteroids from the other taxonomic 
classes; there is no evidence that C and S MBAs have different albedo 
distributions; and there is some suggestion, worthy of future study, 
that primitive B, F, G, and P asteroids are not as radar-bright as C
and S objects. There is no statistically significant evidence that 
different taxonomic classes have different polarization ratio 
distributions, despite suggestions to the contrary based on visual 
inspection of these distributions. The similarity between the C and S 
albedo distributions implies similar near-surface regolith bulk 
densities. The hypothesis of ordinary chondritic composition for the 
S-class asteroids is reasonably consistent with the radar data, 
provided that these asteroids have typical lunar porosities. 
Nevertheless, it is possible that some of these targets have 
high-porosity regoliths of stony-iron composition. Our M-class sample 
presumably contains both metallic objects (such as 216 Kleopatra and, 
probably, 16 Psyche) and less metallic objects. (C) 1999 Academic 
Press.

===============================

(10) COMETARY TRAVEL: FROM INTERSTELLAR SPACE TO EARTH'S OCEANS

D. Laufer*), G. Notesco, A. Bar Nun: From the interstellar medium to 
Earth's oceans via comets - An isotopic study of HDO/H2O. ICARUS, 1999, 
Vol.140, No.2, pp.446-450

*) TEL AVIV UNIVERSITY,DEPT GEOPHYS & PLANETARY SCI,IL-69978 TEL 
   AVIV,ISRAEL

The isotopic enrichment of HDO over H2O when water vapor freezes into 
ice at 60-170 K was studied experimentally. No such enrichment was 
detected (1.003-1.007 in the 95% confidence interval). Thus HDO cannot 
be enriched when ice is formed by freezing of water vapor. The very 
similar D/H ratio in the water of Comets Halley, Hyakutake, and 
Hale-Bopp(similar to 3 x 10(-4)) is 10-20 times larger then the D/H 
ratio in the solar nebula. Therefore the cometary water had to 
originate in a giant molecular cloud, where the HDO is enriched by ion-
molecule reactions. We cannot determine whether the ice grains which 
agglomerated into these comets were formed in a similar to 50 K warm 
clump in the giant molecular cloud and settled intact to the solar 
nebula or sublimated and refroze in the similar to 50 K Uranus-Neptune 
region. The HDO/H2O ratio in Earth's oceans suggests that the water was 
delivered by both comets and rocky material formed in Earth's region of 
the solar nebula. (C) 1999 Academic Press.
 
========================================================

(11) COMETS, ICE & ORGANIC MOLECULES

R.L. Hudson: Laboratory studies of the formation of methanol and other 
organic molecules by water plus carbon monoxide radiolysis: Relevance 
to comets, icy satellites, and interstellar ices. ICARUS, 1999, 
Vol.140, No.2, pp.451-461

ECKERD COLLEGE,DEPT CHEM,ST PETERSBURG,FL,33733

Radiation processing of cometary, planetary, and interstellar ices has 
been investigated by irradiating mixtures of H2O and CO near 16 K with 
0.8-MeV protons. IR spectroscopy and isotopic substitution showed that 
H and OH, from H2O, added to CO to form HCO, H2CO, HCOOH, and CH3OH. A 
values (integrated spectral absorbances) for HCOOH and HCO trapped in 
H2O ice were measured for the first time. These new values, along with 
published A's for H2CO and CH3OH, were used to calculate radiation 
yields (G values) and conventional percentage yields. Significantly 
higher percentage yields of HCOOH and CH3OH were observed, compared to 
previous solid-state H2O + CO experiments. This suggests that radiation 
processing may help explain the discrepancy between the observed 
gas-phase abundances of small organic molecules and the abundances 
predicted by current theoretical models and previous laboratory 
experiments. In contrast to previous experiments on one-component ices, 
no spectral evidence for long-chain molecules was found in the present 
work. This demonstrates that ice composition is a critical factor in 
applying laboratory results to cometary, icy satellite, and 
interstellar ices. (C) 1999 Academic Press.

========================================

(12) ORBITAL HISTORY OF COMET P/LAGERKVIST (1996 R2)

G. Hahn*) & C.I. Lagerkvist: The recent orbital history of periodic 
Comet P/Lagerkvist (1996 R2). ICARUS, 1999, Vol.140, No.2, pp.462-463

*) DLR,INST PLANETARY EXPLORAT,RUDOWER CHAUSSEE 5,D-12489 
   BERLIN,GERMANY

Numerical integrations of 99 orbits centered on that of Comet 
P/Lagerkvist (P/1996R2) and of the original orbit were made 70 
years backward in time and 200 years into the future. The 
integrations show that this comet, belonging to the quasi-
Hildas (G. Tancredi et al., 1990, Astron. Astrophys. 239, 375-
380), most likely has been transferred into its present orbit 
as recently as 1990, ending a phase of temporary satellite 
capture by Jupiter. The future orbital evolution indicates a 
stable period for about 100 years, when another close encounter
with Jupiter may Lead to further drastic changes. (C) 1999 
Academic Press.

================================================

(13) POLARIMETRY OF ASTEROID 2100 RA-SHALOM

N.N. Kiselev*), V.K. Rosenbush, K. Jockers: Polarimetry of asteroid 
2100 Ra-Shalom at large phase angle. ICARUS, 1999, Vol.140, No.2, 
pp.464-466

*) KHARKOV AM GORKII STATE UNIVERSITY, ASTRON OBSERV,UA-310077 
   KHARKOV, UKRAINE

Two-color polarimetric observations of C-type asteroid 2100 Ra-Shalom 
were conducted when its phase angle was 59.7 degrees. No other C-type 
asteroid has so far been observed at such a large phase angle. We 
relate the new data point to the available data on C-type asteroids and 
on Phobos and Deimos and compare the phase curve of these objects with 
the phase curve of dusty comets. The observed polarization of Ra-Shalom 
is slightly lower than expected from a common curve of the other C-type 
asteroids and the martian moons. We conclude that this may be caused by 
the immature regolith on the surface of this small asteroid. (C) 1999 
Academic Press.

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