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(meteorobs) Excerpts from "CCNet DIGEST, 8 June 1999"


------- Forwarded Message

From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet DIGEST, 8 June 1999
Date: Tue, 8 Jun 1999 12:06:35 -0400 (EDT)

CCNet DIGEST, 8 June 1999
--------------------------

[...]

(4) FAST ROTATING ASTEROIDS
    Petr Pravec <ppravec@asudot cas.cz> 

[...]

(10) IS THERE A 100 KRY PERIODICITY IN THE ACCRETION OF INTERPLANETARY DUST?
    D.B. Patterson and K.A. Farley, CALTECH

(11) DICARBOXYLIC ACIDS IN K-T BOUNDARY SEDIMENTS
     H. Mita et al., UNIVERSITY OF TSUKUBA

(12) ON THE EXTRATERRESTRIAL DELIVERY OF ORGANIC MATTER
     V.A. Basiuk and J. Douda, UNIV NACL AUTONOMA MEXICO

[...]

===========

(4) FAST ROTATING ASTEROIDS

>From Petr Pravec <ppravec@asudot cas.cz> 
 
Benny,
 
Reading a press release about the Mark Hammergren's work in the June 
7 issue of the CCNet Digest, I think that you and others could be 
interested in my review talk on Fast Rotating Asteroids that I will 
give on the Asteroids, Comets, Meteors 1999 conference to be held at 
the Cornell University during July 26-30.  See an abstract of my talk 
at the ACM99 abstract web page
http://scorpio.tn.cornelldot edu/ACM/web_abs.html
(Although I am drawing your attention to my talk, I believe also many 
of the other abstracts on the page would be interesting for you and 
others.)
 
It was nice to meet you at the IMPACT workshop.
 
Best wishes,
 
Petr Pravec
Astronomical Institute
Ondrejov
Czech Republic

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

(10) IS THERE A 100 KRY PERIODICITY IN THE ACCRETION OF INTERPLANETARY DUST?
 
D.B. Patterson*) and K.A. Farley: Extraterrestrial He-3 in seafloor 
sediments: Evidence for correlated 100 kyr periodicity in the accretion 
rate of interplanetary dust, orbital parameters, and Quaternary 
climate. GEOCHIMICA ET COSMOCHIMICA ACTA, 1998, Vol.62, No.23-24, 
pp.3669-3682
 
*) CALTECH,DIV GEOL & PLANETARY SCI,PASADENA,CA,91125
 
We have determined the helium abundance and isotopic composition of 
seafloor carbonate sediments from the flanks of the Ontong Java 
Plateau, western equatorial Pacific Ocean (ODP Site 806). These results 
provide a two million year record of the burial flux of 
extraterrestrial He-3, which we believe is a proxy for the 
terrestrial accretion rate of interplanetary dust particles. The He-3 
burial flux prior to similar to 700 ka was relatively low, similar to 
0.5 pcc cm(-2) kyr(-1), but from 700 ka to the present, the burial 
flux gradually increased to a value of similar to 1.0 pcc cm(-2) 
kyr(-1). 100 kyr periodicity in the He-3 burial flux is apparent over 
the last 700 kyr and correlates with the oxygen isotope record of 
global climate, with high He-3 burial fluxes associated with 
interglacial periods. This periodicity and phase are consistent with 
previous He-3 measurements in North Atlantic sediments. Although 100 
kyr periodicity in He-3 burial flux is in agreement with recent 
predictions of the accretion rate of interplanetary dust based on a 
model of the orbital evolution of asteroidal debris, the measurements 
and predictions differ by one half cycle in phase. Nevertheless, our 
observations suggest the terrestrial accretion rate of interplanetary 
dust is controlled by orbital eccentricity and/or inclination 
relative to the solar-system invariable plane. Such control is a 
necessary but not sufficient condition for the hypothesis of Muller 
and MacDonald (1995) that variations in extraterrestrial dust 
accretion modulates terrestrial climate with a 100 kyr period. We 
also identify several brief (<25 kyr) intervals of strongly enhanced 
He-3 burial, possibly related to random and transient fluctuations in 
the accretion rate of asteroidal or cometary dust particles. 
Copyright (C) 1998 Elsevier Science Ltd.
 
====================

(12) ON THE EXTRATERRESTRIAL DELIVERY OF ORGANIC MATTER
 
V.A. Basiuk*) and J. Douda: Pyrolysis of simple amino acids and 
nucleobases: survivability limits and implications for 
extra-terrestrial delivery. PLANETARY AND SPACE SCIENCE, 1999, 
Vol.47, No.3-4, pp.577-584
 
*) UNIV NACL AUTONOMA MEXICO,LAB QUIM PLASMAS & ESTUDIOS 
PLANETARIOS,INST CIENCIAS NUCL,MEXICO CITY 04510,DF,MEXICO
 
The idea of extraterrestrial delivery of organic matter to the early 
Earth is strongly supported by the detection of a large variety of 
organic compounds in the interstellar medium, comets: and 
carbonaceous chondrites. Whether organic compounds essential for the 
emergence and evolution of life, particularly amino acids and nucleic 
acid bases found in the meteorites, can be efficiently delivered by 
other space bodies is unclear and depends primarily on capability of 
the biomolecules to survive high temperatures during atmospheric 
deceleration and impacts to the terrestrial surface. In the present 
study we estimated survivability of simple amino acids glycine, 
L-alanine, alpha-aminoisobutyric acid, L-valine and L-leucine), 
purines (adenine and guanine) and pyrimidines (uracil and cytosine) 
under rapid heating to temperatures of 400-1000 degrees C under N-2 
or CO2 atmosphere. We have found that most of the compounds studied 
cannot survive the temperatures substantially higher than 700 degrees 
C; however at 500-600 degrees C, the recovery can be at a percent 
level (or even l0%-level for adenine: uracil, alanine, and valine). 
The final fate of amino acids and nucleobases during the atmospheric 
deceleration and surface impacts is discussed depending on such 
factors as size of the space body, nature and altitude of the 
heating, chemical composition of the space body and of the 
atmosphere. (C) 1999 Elsevier Science Ltd. All rights reserved.

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