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(meteorobs) Excerpts from "CCNet DIGEST, 24 May 1999"
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To: cambridge-conference@livjm.acdot uk
Subject: CCNet DIGEST, 24 May 1999
Date: Mon, 24 May 1999 10:33:04 -0400 (EDT)
CCNet DIGEST, 24 May 1999
==========================
[...]
(2) LEONID METEOR IMPACTS ON MOON CREATE CLOUD OF SODIUM GAS
Harvey Leifert <HLeifert@agu.org>
[...]
(4) SPACE ROCK HINTS AS EARLY ASTEROID FURNACE
INSCiGHT, 20 May 1999
[...]
(10) WHIPPLE'S NEW PAPER ON COMET NUCLEI
F.L. Whipple, CTR ASTROPHYSICS, CAMBRIDGE, MA
(11) COMETARY SPLITTING DUE TO THERMAL STRESSES
L.V. Tambovtseva & L.I. Shestakova, RUSSIAN ACADEMY OF SCIENCE
(12) PHOTOMETRIC OBSERVATIONS OF ASTEROID 85 IO
A. Erikson et al., DLR,INSTITUTE OF PLANETARY EXPLORATION
=========================================================
(2) LEONID METEOR IMPACTS ON MOON CREATE CLOUD OF SODIUM GAS
>From Harvey Leifert <HLeifert@agu.org>
PRESS CONFERENCE UPDATES FOR THE AGU SPRING MEETING
=20
May 21, 1999
AGU RELEASE NO. 99-17
FOR IMMEDIATE RELEASE=09
Contact: Harvey Leifert
(202) 939-3212
hleifert@agu.org
=20
Media Advisory
1999 Spring Meeting
Updated Press Conference Schedule
LEONID METEOR IMPACTS ON MOON CREATE CLOUD OF SODIUM GAS
=20
Leonid Meteors Create a Temporary Lunar Atmosphere
June 1, 10:00 A.M. - Room 111
The November 17, 1998, return of a strong Leonid meteor shower provided =
a boost to scientists studying the origins of the Moon's weak=20
atmosphere. Meteor impacts on the lunar surface created a cloud of=20
sodium gas that escaped from the Moon. Sodium atoms were pushed away by =
the pressure of sunlight, reaching the vicinity of the Earth on=20
November 19th. This cloud of lunar gas was "gravitationally focused"=20
into a narrow tail that was photographed using a sensitive camera at=20
the Boston University Station, McDonald Observatory, in Fort Davis,=20
Texas. Experimental results and computer animations will be presented=20
by researchers from the BU Center for Space Physics. (Relates to=20
Session P21A)
=20
Participants:
Michael Mendillo, Professor of Astronomy, Boston University,
Boston, MA (Overview)
Steven M. Smith, Research Associate, Boston University,
Boston, MA (Observational Results)
Jody K. Wilson, Research Associate, Boston University,
Boston, MA (Computer Simulations)
For more information, please contact Harvey Leifert <HLeifert@agu.org>
=========================================================
(4) SPACE ROCK HINTS AS EARLY ASTEROID FURNACE
=20
>From INSCiGHT, 20 May 1999
[http://www.academicpress.com/inscight/05201999/grapha.htm]
=20
Thursday, 20 May 1999, 5 pm PST
=20
Space Rock Hints at Early Asteroid Furnace =20
By Erik Stokstad
=20
Long before Earth or any other planet had formed around the sun, a vast =
cloud of dust began to coalesce into asteroids. Most of the drifting=20
chunks were the kind of stone-cold rubble that Han Solo had to weave=20
through in his clunky old spaceship in Star Wars, but others oozed=20
lava. After a decades-long search for what melted these large=20
asteroids, researchers report in tomorrow's issue of Science (20 May,=20
p.1348) that a once-molten 4.57-billion-year-old meteorite bears the=20
unmistakable signs of radioactive heat.
=20
Planetary scientists have long suspected that the radioactive isotope=20
aluminum-26 could have pumped out terrific amounts of heat in the early =
solar system. With a relatively short half-life of 730,000 years, the=20
plentiful isotope could have quickly melted early asteroids. But=20
researchers came up empty-handed when they looked for its decay=20
product, magnesium-26, in meteorites from parent asteroids that once=20
had molten interiors. Complicating the search, these so-called=20
differentiated meteorites make up fewer than 5% of those that hit=20
Earth.
=20
Luckily, just such a meteorite thundered into the desert state of=20
Rajasthan in western India on 20 June 1996. Called Piplia Kalan after a =
nearby village, the 42-kilogram meteorite seemed a prime hunting ground =
for evidence of 26Al. The grains of the aluminum-rich mineral=20
plagioclase contained little magnesium, leading planetary scientist=20
Gopalan Srinivasan of the Physical Research Laboratory in Ahmedabad,=20
India, and his colleagues to think they had a good shot at finding the=20
26Mg produced by 26Al decay. Indeed, 26Mg levels in four grains of=20
Piplia Kalan were up to 3% higher than the usual amount in terrestrial=20
plagioclase. By cosmic chemistry standards, says Srinivasan, "this=20
excess is very significant."
=20
The finding "strengthens implications that 26Al was the heat source" at =
the heart of asteroids, says Glenn MacPherson, a geochemist at the=20
Smithsonian Institution in Washington, D.C. For connoisseurs of=20
asteroid history, it also suggests that the massive parent body of=20
Piplia Kalan melted and cooled within 5 million years of the solar=20
system's birth. This time span jibes with computer models of the=20
process, providing "a real shot in the arm for theoretical work," says=20
geochemist Richard Carlson of the Carnegie Institution in Washington,=20
D.C.
=20
=A9 1999 The American Association for the Advancement of Science
=20
[Extracted from INSCiGHT, Academic Press.]
=========================================================
(10) WHIPPLE'S NEW PAPER ON COMET NUCLEI
F.L. Whipple: Note on the structure of comet nuclei. PLANETARY AND=20
SPACE SCIENCE, 1999, Vol.47, No.3-4, pp.301-304
=20
CTR ASTROPHYSICS, CAMBRIDGE, MA, 02138
=20
The recent developments in cometary studies suggest rather low mean=20
densities and weak structures for the nuclei. They appear to be=20
accumulations of fairly discrete units loosely bound together, as=20
deduced from the observations of Comet Shoemaker-Levy 9 during its=20
encounter with Jupiter. The compressive strengths deduced from comet=20
splitting by Opik and Sekanina are extremely low. These values are=20
confirmed by theory developed here, assuming that Comet P/Holmes had a=20
companion that collided with it in 1892. There follows a short=20
discussion that suggests that the mean densities of comets should=20
increase with comet dimensions. The place of origin of short-period=20
comets may relate to these properties. (C) 1999 Elsevier Science Ltd.=20
All rights reserved.
=========================================================
(11) COMETARY SPLITTING DUE TO THERMAL STRESSES
=20
L.V. Tambovtseva*) & L.I. Shestakova: Cometary splitting due to thermal =
stresses. PLANETARY AND SPACE SCIENCE, 1999, Vol.47, No.3-4, pp.319-326
=20
*) RUSSIAN ACADEMY OF SCIENCE,CENT ASTRON OBSERV,PULKOVSKOE SHOSSE=20
65-1,ST PETERSBURG 196140,RUSSIA
=20
We consider the thermal evolution of icy solids moving on the highly=20
eccentric orbits on the base of the numerical solution of the=20
non-linear heat diffusion equation. Thermal stresses which arise inside =
of solids and at their surface can exceed the tidal stresses by several =
orders of magnitude in the neighborhood of the Sun and play an=20
important and, perhaps, a crucial role in the evolution of comets.
A possible disintegration scenario of a distant icy solid due to=20
thermal stresses is presented. (C) 1999 Elsevier Science Ltd. All=20
rights reserved.
=20
=========================================================
(12) PHOTOMETRIC OBSERVATIONS OF ASTEROID 85 IO
=20
A. Erikson*), J. Berthier, P.V. Denchev, A.W. Harris, Z. Ioannou,
A. Kryszczynska, C.I. Lagerkvist, P. Magnusson, T. Michalowski,=20
A. Nathues, J. Piironen, P. Pravec, L. Sarounova, F. Velichko:=20
Photometric observations and modelling of the asteroid 85 Io in
conjunction with data from an occultation event during the 1995-96=20
apparition. PLANETARY AND SPACE SCIENCE, 1999, Vol.47, No.3-4,=20
pp.327-330
=20
*) DLR,INSTITUTE OF PLANETARY EXPLORATION,RUDOWER CHAUSSEE 5,D-12489=20
BERLIN,GERMANY
=20
The asteroid 85 Io has been observed using CCD and photoelectric=20
photometry on 18 nights during its 1995-96 and 1997 apparitions. We=20
present the observed lightcurves, determined colour indices and=20
modelling of the asteroid spin vector and shape. The colour indices=20
(U-B =3D 0.35 +/- 0.02, B-V =3D 0.66 +/- 0.02, V-R =3D 0.34 +/- 0.02, =
R-I =3D=20
0.36 0.02) are as expected for a C-type asteroid. The allowed spin=20
vector solutions have the pole co-ordinates lambda(0) =3D 285 +/- 4=20
degrees, beta(0) =3D -52+/-9 degrees or beta(0), =3D 108 +/- 10 =
degrees,=20
beta(0) =3D -46 +/- 10 degrees and lambda(0) =3D 290 +/- 10 degrees,=20
beta(0) =3D - 16 +/- 10 degrees with a retrograde sense of rotation and =
a=20
sidereal period P-sid =3D 0(d).286463 +/- 0(d).000001. During the =
1995-96=20
apparition the International Occultation Time Association (IOTA)=20
observed an occultation event by 85 Io. The observations and modelling=20
presented here were analysed together with the occultation data to=20
develop improved constraints on the size of the asteroid. The derived=20
value of 164 km is about 5% larger than the IRAS diameter. (C) 1999=20
Elsevier Science Ltd. All rights reserved.
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