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(meteorobs) Excerpts from "CCNet DIGEST, 7 April 1999"
Sorry for the out-of-order forwarding... I missed this one!
Lew Gramer
------- Forwarded Message
From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet DIGEST, 07/04/99
Date: Wed, 7 Apr 1999 11:45:28 -0400 (EDT)
CCNet DIGEST, 7 April 1999
--------------------------
QUOTE OF THE DAY
Italian researchers discovered that the scarab at the center of
King Tut's pectoral, or necklace, found by Howard Carter in chest
n. 267, is not "greenish-yellow chalcedony," as Carter had said,
but Libyan desert silica glass, a natural glass that exists only
in the remote Great Sand Sea of Egypt -- the Western Desert. "Its
origin is probably celestial, caused by the impact on the sand of
a chondritic meteorite or comet," says De Michele. "The glass is
scattered over a 15-mile diameter area, but unfortunately, no
crater has been found yet." (Discovery Online News, 4 April)
[...]
(3) ARE THE LEONIDS METEORITES?
Ron Baalke <BAALKE@kelvin.jpl.nasadot gov>
[...]
(7) EVIDENCE FOR EXTRA-SOLAR COMETS
D. de Winter et al., INSTITUTE ASTROFIS CANARIAS
(8) INTERSTELLAR VOLATILE CONTENT OF COMETS
G.A. Blake et al., CALTECH
==================
(3) ARE THE LEONIDS METEORITES?
>From Ron Baalke <BAALKE@kelvin.jpl.nasadot gov>
Leonids Sample Return Mission Update
Marshall Space Flight Center
http://science.nasadot gov/newhome/headlines/ast01apr99_1.htm
NASA scientists will describe initial results from a program to catch
meteoroids in flight at the NASA/Ames Leonids Workshop April 12-15, 1999
Apr. 1, 1999: Later this month NASA scientists will present initial
results from an innovative program to catch meteoroids in flight
through Earth's atmosphere. The paper, to be presented at the NASA/Ames
Leonid Workshop on April 12-15, will describe tiny particles captured
20 km above Earth's surface during last year's Leonids meteor shower.
During the peak of the 1998 Leonids, Dr. David Noever and colleagues
from the NASA/Marshall Space Flight Center launched a 10m weather
balloon into the stratosphere where it hovered for nearly 2 hours above
98% of Earth's atmosphere. The payload included a digital video camera
and an xerogel micrometeorite collector, similar in some respects to
the cosmic dust collector on board the Stardust spacecraft now in route
to comet Wild-2.
"The 1998 balloon flight was really intended as an engineering test,"
says Noever. "We wanted to see if it was possible to sample meteoroids
- -- or any kind of dust -- in the stratosphere and to evaluate the
hardware in our payload before the 1999 Leonids."
As it turned out, the 1998 flight was more successful than anyone
expected. The video camera recorded a number of fireballs that were
broadcast live on the web to nearly 100,000 people. Over 1,000,000
people saw the replay the next day.
That's not all. After the balloon payload was recovered, Noever and his
colleagues used an Environmental Scanning Electron Microscope at NASA's
Marshall Space Flight Center to examine the xerogel dust collector.
They found 8 tiny craters created by impacts from particles measuring
20 to 50 microns in diameter.
"Are they Leonid meteoroids?" asks Noever. "We really don't know at
this point. The size of the particles is about what we would expect for
meteoroids in the stratosphere, but they may also be terrestrial."
The answer a least partly lies in the chemical composition of the
impactors. Particles like meteoroids that have entered the atmosphere
at high speeds tend to be enriched in elements that are not easily
vaporized by the extreme heat of atmospheric friction. The mass ratios
Mg/Si, Al/Si and Fe/Si along with isotopic abundances can usually be
used to distinguish terrestrial from extraterrestrial particles.
"The way the impactors look is important, too" continued Noever.
"Meteroids that have been partially melted by atmospheric friction
often have a translucent rim surrounding an unmelted, opaque core.
Right now we're studying both the appearance of the impactors and their
chemical makeup. Hopefully we'll have an answer soon."
Meanwhile, Noever and his colleagues plan to launch an identical
balloon this month, on April 10, to sample the dust environment of the
stratosphere when the Earth is not passing through a major meteoroid
debris stream like the Leonids. "During the first quarter of every year
there's a minimum of meteor activity," explains Dr. Tony Phillips, a
NASA astronomer. "Earth doesn't pass through any major cometary debris
fields from about Jan 15 until late April of each year. There's nothing
special about those months. The low meteor flux during that time is
just a result of the random distribution of comet debris trails in the
solar system."
The scientists working on this project hope that the balloon flight
scheduled for April 10 will provide valuable information about the
background environment of dust and meteoroids in the stratosphere for
comparison with their Leonids sample. Next week Science@NASA will
provide more details about the upcoming launch and offer readers an
opportunity to participate in this research by counting visual meteors
on the night of the flight.
=====================
(7) EVIDENCE FOR EXTRA-SOLAR COMETS
D. de Winter*), C.A. Grady, M.E. vanden Ancker, M.R. Perez, C. Eiroa:
Episodic accretion around the Herbig Ae star BF orionis - Evidence for
the presence of extra-solar comets. ASTRONOMY AND ASTROPHYSICS, 1999,
Vol.343, No.1, pp.137-150
*) INSTITUTE ASTROFIS CANARIAS,C VIA LACTEA S-N,E-38200 LA
LAGUNA,TENERIFE,SPAIN
The results of a monitoring programme of high and intermediate
resolution spectra covering He I 5876 Angstrom, Na I D-2,D-1 and H
alpha of the isolated Herbig Ae star BF Ori are presented. We detect
the presence of blue and redshifted emission and absorption components
of these lines which vary from day-today with correlated changes
suggesting a similar origin. The appearance, strength and variations of
the redshifted Na I D absorption component on a time scale of days show
variable accretion activity similar to that seen toward the Herbig Ae
star UX Ori and beta Pic, suggesting evaporation of star-grazing
bodies. We estimate for one event that such a body is kilometer sized,
evaporates at a distance of about 0.4 AU from the central star and has
a mass comparable to comets in the solar system. A dependence was found
of the H alpha line profile on the photometric brightness of BF Ori
similar to that observed for UX Ori. It is evidence for obscuration of
a dense dusty body located in the outer disk regions as no extra
absorption components from a gaseous content and no direct influences
on the cometary activity were observed. More complex variations of the
H alpha profile could be explained in part by absorption of star-grazer
material, equal to the absorption at the sodium lines, and in part by
obscuration of its Line forming region by the cometesimal. More
evidences for detections of revolving clumpy material are: observed
changes in the velocity direction of the very strong Na I D-2,D-1 low
velocity absorption components and the observed flip over of the
relative strength of the blue and red peak of H alpha simultaneous with
the change of blue to redshifted absorption components in both the
Na I D-2,D-1 and He I lines. In case of orbiting bodies, the estimated
period lies between 60 and 100 days with a distance from 0.35 to 0.57
AU, respectively. The detection of possible orbiting and comet-like
objects in the disk of BF Ori, a 3(-1)(+2) Myr old pre-main sequence
A5-6 IIIe star, making it a possible progenitor of the HR 4796
(protoplanetary) disk system, suggests the existence of structures
similar to those probably present in the solar system at a time of
formation of planetesimals. The estimated much higher than cosmic
abundances of refractory (Na) over volatile (H, He) gases for the
detected bodies supports this suggestion. Copyright 1999, Institute for
Scientific Information Inc.
===============
(8) INTERSTELLAR VOLATILE CONTENT OF COMETS
G.A. Blake*), C. Qi, M.R. Hogerheijde, M.A. Gurwell, D.O. Muhleman:
Sublimation from icy jets as a probe of the interstellar
volatile content of comets. NATURE, 1999, Vol.398, No.6724, pp.213-216
*) CALTECH 150 21,DIV GEOL & PLANETARY SCI,PASADENA,CA,91125
Comets are some of the most primitive bodies left over from the Solar
System's early history. They may preserve both interstellar material
and material from the proto-solar nebula, and so studies of their
volatile components can provide dues about the evolution of gases and
ices, as a collapsing molecular cloud transforms into a mature
planetary system(1,2). Previous observations of emission from
rotational transitions in molecules have averaged over large areas of
the inner coma, and therefore include both molecules that sublimed from
the nucleus and those that result from subsequent chemical processes in
the coma. Here we present high-resolution observations of emission from
the molecules HNC, DCN and HDO associated with comet Hale-Bopp. Our
data reveal are-like structures-icy jets-offset from (but close to) the
nucleus. The measured abundance ratios on 1-3'' scales are
substantially different from those on larger scales(3-5), and cannot be
accounted for by models of chemical processes in the coma(2,6,7); they
are, however, similar to the values observed in the cores of dense
interstellar clouds and young stellar objects. We therefore propose
that sublimation from millimetre-sized icy grains ejected from the
nucleus provides access to relatively unaltered volatiles. The D/H
ratios inferred from our data suggest that, by mass, Hale-Bopp (and by
inference the outer regions of the early solar nebula) consists of
greater than or equal to 15-40% of largely unprocessed interstellar
material. Copyright 1999, Institute for Scientific Information Inc.
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