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(meteorobs) meteorobs-digest V3 #323 -
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>>> "meteorobs@jovian.com" 03/22/00 19:57 >>>
meteorobs-digest Wednesday, March 22 2000 Volume 03 : Number 323
(meteorobs) Excerpts from "CCNet, 36/2000 - 21 March 2000"
Re: (meteorobs) Re: Iridium satellites' re-entry
(meteorobs) Electrophonic phenomena
Re: (meteorobs) Re: March 9th, 2000, Arkansas fireball
Re: (meteorobs) Re: Iridium satellites' re-entry
Re: (meteorobs) Re: Iridium satellites' re-entry
Re: (meteorobs) Electrophonic phenomena
Re: (meteorobs) Electrophonic phenomena
(meteorobs) Observations March 21/22-00
(meteorobs) Fwd: Update on March 19 New Jersey fireball sighting
(meteorobs) Excerpts from "CCNet, 37/2000 - 22 March 2000"
Re: (meteorobs) Electrophonic phenomena
(meteorobs) [ASTRO] NEAR-Shoemaker Science Update - March 22, 2000
----------------------------------------------------------------------
Date: Tue, 21 Mar 2000 16:41:58 -0500
From: Lew Gramer <dedalus@latrade.com>
Subject: (meteorobs) Excerpts from "CCNet, 36/2000 - 21 March 2000"
- ------- Forwarded Message
From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet, 21 March 2000
Date: Tue, 21 Mar 2000 10:33:28 -0500 (EST)
CCNet, 36/2000 - 21 March 2000
- ------------------------------
[...]
(5) VELOCITY OF LARGE COMETARY DUST PARTICLES
D.W. Hughes, UNIVERSITY OF SHEFFIELD
(6) CCD PHOTOMETRY OF ASTEROIDS 1982 TA & 1997 LY4
P. Pravec et al., ACADEMY OF SCIENCE OF THE CZECH REPUBLIC
[...]
========================================================================
(5) VELOCITY OF LARGE COMETARY DUST PARTICLES
D.W. Hughes: On the velocity of large cometary dust particles.=20
PLANETARY AND SPACE SCIENCE, 2000, Vol.48, No.1, pp.1-7
*) UNIVERSITY OF SHEFFIELD,DEPT PHYS & ASTRON,SHEFFIELD S3 7RH,S=20
YORKSHIRE,ENGLAND
The Whipple formula for the emission velocity of meteoroid dust from
the surface of a cometary nucleus is reviewed and it is concluded that,
in normal circumstances, the dust velocity is 'low', typically being
less than 20% the radial gas velocity. If, however, the dust particle
contains some embedded snows when it leaves the cometary nucleus, its
final velocity is considerably increased. (C) 1999 Elsevier Science
Ltd. All rights reserved.
========================================================================
(6) CCD PHOTOMETRY OF ASTEROIDS 1982 TA & 1997 LY4
P. Pravec*), L. Sarounova, M. Wolf, I.R.V. Ferrin, J. Zhu: CCD=20
photometry of asteroids (4197) 1982 TA and 1997 LY4. PLANETARY AND=20
SPACE SCIENCE, 2000, Vol.48, No.1, pp.59-65
*) ACADEMY OF SCIENCE OF THE CZECH REPUBLIC,INST ASTRON,CZ-25165=20
ONDREJOV,CZECH REPUBLIC
We present results of our photometric observations of the Apollo=20
asteroid (4197) 1982 TA and the Mars-crosser 1997 LY4. Their synodic=20
rotation periods (3.53802 +/- 0.00005) and (46.07 +/- 0.02) h,=20
respectively, have been derived. The fast rotation of (4197) suggests a =
lower limit of the bulk density of 1.1 g/cm(3). The mean diameter of=20
(4197) is likely in the range 3-6 km, The present knowledge does not=20
support a possibility that (4197) is an extinct cometary nucleus as=20
suggested from its orbit. The smaller (1.4-3 km), slowly-rotating=20
asteroid 1997 LY4 is an elongated object with the equatorial axis ratio =
greater than or equal to 1.8. (C) 1999 Elsevier Science Ltd. All rights =
reserved.
- ----------------------------------------
THE CAMBRIDGE-CONFERENCE NETWORK (CCNet)
- ----------------------------------------
The CCNet is a scholarly electronic network. To subscribe/unsubscribe,=20
please contact the moderator Benny J Peiser <b.j.peiser@livjm.acdot uk>.=20
Information circulated on this network is for scholarly and=20
educational use only. The attached information may not be copied or=20
reproduced for any other purposes without prior permission of the=20
copyright holders. The fully indexed archive of the CCNet, from=20
February 1997 on, can be found at:
http://abob.libs.ugadot edu/bobk/cccmenu.html
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------------------------------
Date: Tue, 21 Mar 2000 18:20:57 EST
From: RRash62@aol.com
Subject: Re: (meteorobs) Re: Iridium satellites' re-entry
Could someone please tell me what electrophonic phenomena is.
Thank you.
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------------------------------
Date: Tue, 21 Mar 2000 19:05:23 -0500
From: Lew Gramer <dedalus@latrade.com>
Subject: (meteorobs) Electrophonic phenomena
This was a thread discussed only late last year on our list... Basically, there
have been sounds recorded SIMULTANEOUSLY with bright fireballs for many years:
these are difficult to explain, as fireballs are witnessed anywhere from 30 to
1000 km distant, and so sound could NEVER travel fast enough from the meteor
itself to the hearer to appear simultaneous. So what are these "anomolous"
sounds? One possible mechanism is called "electrophonics". Here is a post from
last early December, which gives a short description of this theory:
http://www.tiacdot net/users/lewkaren/meteorobs/msg16436.html
Clear skies!
Lew Gramer
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------------------------------
Date: Tue, 21 Mar 2000 17:34:14 PST
From: "Roger Haler" <rhaler@hotmail.com>
Subject: Re: (meteorobs) Re: March 9th, 2000, Arkansas fireball
Thanks Kevin I was just getting mixed up with the double Re: again many
thanks for the info.
Roger
>From: KevTK@aol.com
>Reply-To: meteorobs@jovian.com
>To: meteorobs@jovian.com
>Subject: Re: (meteorobs) Re: March 9th, 2000, Arkansas fireball
>Date: Mon, 20 Mar 2000 20:54:15 EST
>
>In a message dated 3/19/00 7:46:40 PM Eastern Standard Time,
>rhaler@hotmail.com writes:
>
><< May I inquire as to which fireball is in reference here. I see two
>replies
> and do not know which one I am reading?? >>
>
>The two we are comparing is the alleged Arkansas meteorite that cause a
>brushfire a couple of weeks ago to a fall in Japan (unknown if it was
>named)about 1996 (more or less). The Japan meteorite was all over the news
>in
>southern California which is where I acquired the tapes.
>
>Kevin K
>
>"I'm all for individuality...just as long as everyone does it."
>To UNSUBSCRIBE from the 'meteorobs' email list, use the Web form at:
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______________________________________________________
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------------------------------
Date: Wed, 22 Mar 2000 02:43:36 GMT
From: Dejan Vinkovic <dejan@ccsdot ukydot edu>
Subject: Re: (meteorobs) Re: Iridium satellites' re-entry
> Could someone please tell me what electrophonic phenomena is.
Some details of the electrophonic phenomenon you can find here:
http://users.hunterlinkdot net.au/~ddcsk/
http://www.ticetboodot demon.codot uk/audible.htm
http://gefs.ccsdot ukydot edu/GEFS_Elec.html
The sound is produced by vibrations of some objects close to the
observer and these vibrations are induced by very low frequency (VLF) and
extremely low frequency (ELF) radio waves (30Hz - 30kHz).
The open question about this phenomenon is how the meteors can produce such
a strong ELF/VLF radio emission, since the current Colin Keay's theory:
http://users.hunterlinkdot net.au/~ddcsk/solutio1.htm
has problems with some electrophonic fireballs.
cheers!
Dejan Vinkovic
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------------------------------
Date: Wed, 22 Mar 2000 02:29:47 EST
From: RRash62@aol.com
Subject: Re: (meteorobs) Re: Iridium satellites' re-entry
Thank you for the information.
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------------------------------
Date: Tue, 21 Mar 2000 23:39:10 -1000
From: Jim Bedient <bedient@amsmeteors.org>
Subject: Re: (meteorobs) Electrophonic phenomena
At 07:05 PM 3/21/00 -0500, Lew wrote:
>
>This was a thread discussed only late last year on our list... Basically,
there
>have been sounds recorded SIMULTANEOUSLY with bright fireballs for many
years:
Worth looking at are Colin Keay's pages on electrophonic effects:
http://www.users.hunterlinkdot net.au/~ddcsk/gelphonx.htm
http://www.users.hunterlinkdot net.au/~ddcsk/index.html
JB
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------------------------------
Date: Wed, 22 Mar 2000 06:51:39 -0800
From: Dave English <prospector@sd.znet.com>
Subject: Re: (meteorobs) Electrophonic phenomena
Hi lew,
This post more or less gets the researcher looking in December '99
for electronphoic posts, I would suggest for those interested to look at the
MONTHS list too in July 1999 where a thread ran over ten days mostly
under Fireballs & Sonic Booms. Lots of information and good ideas.
http://www.tiacdot net/users/lewkaren/meteorobs/maillist-months.html
The first post is the same repost you listed.
Dave English
Oceanside. California
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------------------------------
Date: Wed, 22 Mar 2000 23:08:42 -0500
From: Kim Youmans <ksyo@pinelanddot net>
Subject: (meteorobs) Observations March 21/22-00
- --------------8456A7A390872DB45896B512
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
I recieved a note from a certain friend in Sicily to keep an eye
out for any Camelopardalids that may come my way. I checked the dates
and and one source for maximum activity (which still would not be what
most folks would term "active") was given as March 21.
So I decided to go out and observe for the one dark hour that preceeded
moonrise. Besides, my hourly totals for March are terribly low, so I
figured I could at least begin to remedy that.
Wow, what activity -- two +3's, two 0's, and three -2's! Too bad
they were all satellites, aircraft and fireflies! I did see one single
bright flare at the bear's front paw that did not repeat.
Finally at 8:31, just a few minutes before moonrise, a fine -1
appeared and went between Procyon and Hydra's head. It WAS quite slow
and I gave it a speed of one. The wake/trail was visible in the meteors
glow, but I'd refrain from calling it a train given the slowness of the
meteor. The meteor head was plainly visible and it had about a ten
degree path. But the plot revealed it almost certainly was not a
possible CAM.
The moon rose, a deep, dark orange with a striking .5 degree orange
halo. I intend to monitor this possible fireball shower each night
before moonrise as long as the weather allows, and maybe bring my March
hourly totals back up to snuff.
********************************************************************
OBSERVER: Kim S. Youmans (YOUKI) DATE:03-21/22-00
BEGIN: 00:41UT END 00:41UT LOCATION: Treutlen Co, Ga.
82. 24' 25" W; 32. 24' 45" N METHOD: Tape
Elev 240 ft Facing East
1 periods, sky 0% obscured, No breaks
Period 1 00:41 - 01:41 UT SPO(1)
Dead time =2 min Teff = 0.97 F= 1.00
SolarLong. 001.726x Avg LM = 6.28
Limiting Magnitudes
00:52 UT (IMO 4)+6.37 (IMO 17)+6.09
01:23 UT (IMO 4)+6.54 (IMO 17)+6.11
Center FOV - Midperiod (UT)
Period 1 9hrsx +45x
Showers Observed
VIR(0) 190x -1x
SPO(1)
Mag Distribution
Period 1
SPO(1) -1(1)
Meteor Data
Period 1
(Time UT, Shower, Mag, Speed, Accuracy/plot #)
01 01:31 SPO -1 1 3 A
Accuracy scale(1-3) 1/best 2/medium 3/worst
- --------------8456A7A390872DB45896B512
Content-Type: text/html; charset=us-ascii
Content-Transfer-Encoding: 7bit
<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
<html>
<tt> I recieved a note from a certain friend in
Sicily to keep an eye out for any Camelopardalids that may come my way.
I checked the dates and and one source for maximum activity (which still
would not be what most folks would term "active") was given as March 21.</tt>
<br><tt>So I decided to go out and observe for the one dark hour that preceeded
moonrise. Besides, my hourly totals for March are terribly low, so
I figured I could at least begin to remedy that.</tt>
<br><tt> Wow, what activity -- two +3's, two 0's,
and three -2's! Too bad they were all satellites, aircraft and fireflies!
I did see one single bright flare at the bear's front paw that did not
repeat.</tt>
<br><tt> Finally at 8:31, just a few minutes before
moonrise, a fine -1 appeared and went between Procyon and Hydra's head.
It WAS quite slow and I gave it a speed of one. The wake/trail was
visible in the meteors glow, but I'd refrain from calling it a train given
the slowness of the meteor. The meteor head was plainly visible and
it had about a ten degree path. But the plot revealed it almost certainly
was not a possible CAM.</tt>
<br><tt> The moon rose, a deep, dark orange with a striking
.5 degree orange halo. I intend to monitor this possible fireball
shower each night before moonrise as long as the weather allows, and maybe
bring my March hourly totals back up to snuff.</tt>
<br><tt>********************************************************************</tt><tt></tt>
<p><tt>OBSERVER: Kim S. Youmans (YOUKI) DATE:03-21/22-00</tt>
<br><tt>BEGIN: 00:41UT END 00:41UT LOCATION: Treutlen
Co, Ga.</tt>
<br><tt>82. 24' 25" W; 32. 24' 45" N METHOD: Tape</tt>
<br><tt>Elev 240 ft Facing East</tt>
<br><tt>1 periods, sky 0% obscured, No breaks</tt>
<p><tt>Period 1 00:41 - 01:41 UT SPO(1)</tt>
<br><tt>Dead time =2 min Teff = 0.97 F= 1.00</tt>
<br><tt>SolarLong. 001.726x Avg LM = 6.28</tt>
<p><tt>Limiting Magnitudes</tt>
<br><tt>00:52 UT (IMO 4)+6.37 (IMO 17)+6.09</tt>
<br><tt>01:23 UT (IMO 4)+6.54 (IMO 17)+6.11</tt>
<p><tt>Center FOV - Midperiod (UT)</tt>
<br><tt>Period 1 9hrsx +45x</tt>
<p><tt>Showers Observed</tt>
<br><tt>VIR(0) 190x -1x</tt>
<br><tt>SPO(1)</tt>
<p><tt>Mag Distribution</tt>
<br><tt>Period 1</tt>
<br><tt>SPO(1) -1(1)</tt>
<p><tt>Meteor Data</tt>
<br><tt>Period 1</tt>
<br><tt>(Time UT, Shower, Mag, Speed, Accuracy/plot #)</tt>
<br><tt>01 01:31 SPO -1
1 3 A</tt>
<br><tt></tt> <tt></tt>
<p><tt>Accuracy scale(1-3) 1/best 2/medium 3/worst</tt>
<br> </html>
- --------------8456A7A390872DB45896B512--
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------------------------------
Date: Wed, 22 Mar 2000 12:49:06 -0500
From: Larry Klaes <lklaes@bbn.com> (via Lew Gramer)
Subject: (meteorobs) Fwd: Update on March 19 New Jersey fireball sighting
NOTE: Neither Larry nor Bob are current 'meteorobs' subscribers. If you follow
up, please MANUALLY put 'lklaes@bbn.com' in the "CC:" line of your reply!
Lew Gramer <owner-meteorobs@jovian.com>
- ------- Forwarded Message
Date: Wed, 22 Mar 2000 11:34:33 -0500
To: astro@lists.mindspring.com, shallow-sky@listsdot best.com
From: Larry Klaes <lklaes@bbn.com>
Subject: Update on March 19 New Jersey fireball sighting
Cc: dedalus@latrade.com, jonee@epixdot net,
Benny J Peiser <b.j.peiser@livjm.acdot uk>,
Donald Bellunduno <ghostriderman@excite.com>
This is the e-mail I received from my brother-in-law on
his observation of a bright fireball over northern New
Jersey on the evening of March 19, 2000:
From: scanlinr@squared.com
X-Lotus-FromDomain: AMERICAS
To: Larry Klaes <lklaes@bbn.com>
Date: Tue, 21 Mar 2000 11:34:22 -0500
Subject: Re: Bob, tell me more about the fireball you saw!
Larry,
Answers to your questions:
1. In terms of brightness and color it was very bright, so bright that it
appeared that it was travelling through the clouds. It may have been my
imagination, but I saw the flames as it burned up. I believe that if it
fell during the daylight hours I still would have seen it. The reason I
say that is because the night sky was bright due to a full moon. It was
very big. Big enough to keep on burning as it fell out of sight behind
some trees. I almost expected to here a boom from impact.
2. There were no sounds associated with it, since I was travelling in
my car and I had the windows rolled up.
3. As for smoke trails, it was too cloudy and dark to tell.
4. It was visible for a good second, like I said above, it was burning
up from about the 10 o clock position and it fell out of view behing
some trees.
5. I was facing east and I caught sight of it at about 10 o clock in
the sky and it appeared to fall straight down from there.
6. No one else was with me.
7. I was in my car travelling east on Interstate 80 in New Jersey
around exit 24.
Hopefully this helps out and I will talk to you later.
Bob
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------------------------------
Date: Wed, 22 Mar 2000 13:01:13 -0500
From: Lew Gramer <dedalus@latrade.com>
Subject: (meteorobs) Excerpts from "CCNet, 37/2000 - 22 March 2000"
The first item is particularly interesting. Curious this team should use earth
collected meteorite classes as the basis for classifying meteoroid debris: I
naively expect the bulk of meteoroid strikes in higher orbits would be from
cometary debris, which is completely unrepresented in earth-bound samples.
Clear skies,
Lew Gramer <owner-meteorobs@jovian.com>
- ------- Forwarded Message
From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet, 22 March 2000
Date: Wed, 22 Mar 2000 13:06:28 -0500 (EST)
CCNet, 37/2000 - 22 March 2000
- ------------------------------
[...]
(8) COLLECTION OF MICROMETEOROID REMNANTS FROM LOW EARTH ORBIT
G. A. Graham et al., OPEN UNIVERSITY
(9) IN-SITU DETECTION OF MICROMETEOROIDS AND ORBITAL DEBRIS
J.C. Mandeville et al., OFF NATL ETUD & RECH AEROSP
(10) A COMMENT ON GOLD DUST
Larry Klaes <lklaes@bbn.com>
=================================================================
(8) COLLECTION OF MICROMETEOROID REMNANTS FROM LOW EARTH ORBIT
G. A. Graham*), A.T. Kearsley, M.M. Grady, I.P. Wright,
J.A.M. McDonnell: The collection of micrometeoroid remnants from low
earth orbit. ADVANCES IN SPACE RESEARCH, 1999, Vol.25, No.2, pp.303-307
*) OPEN UNIVERSITY,PSRI,MILTON KEYNES MK7 6AA,BUCKS,ENGLAND
The solar array panel returned from the Hubble Space Telescope after
3.62 years of space exposure offered the opportunity to study
individual solar cells for hypervelocity impact damage and residue. A
detailed electron microscope investigation of impact craters (100-1000
mu m diameters) has identified that most are residue-rich and by
digitised x-ray elemental mapping and semi-quantitative micro-spot
analysis the original precursor composition of the impactor can almost
unambiguously be identified. The residues contain diverse elemental
compositions that can be associated with known meteorite mineralogies
and directly compared with interplanetary dust particles and
micrometeorites, possibly the most likely source object. The
observation of a magnesium-rich residue with (Mg+Fe) / Si ratio similar
to that of forsterite (end-member Mg-olivine identified in meteorites),
indicates that it is possible in favourable conditions to define
clearly the compositional nature of the impactor. The identification of
near-intact calcium-rich fragments, that are neither artefacts nor
contamination, indicates that volatile chemistries can survive
hypervelocity impacts in brittle glass substrates. The abundance of
micrometeoroid residues in the individual solar cells has highlighted
that valuable information can be retained from impact craters in
returned space hardware which are essentially not designed as a dust
collectors. (C) 1999 COSPAR. Published by Elsevier Science Ltd.
=================================================================
(9) IN-SITU DETECTION OF MICROMETEOROIDS AND ORBITAL DEBRIS
J.C. Mandeville*), C.R. Maag, C. Durin: In-situ detection of
micrometeoroids and orbital debris: The PIE experiment on MIR.
ADVANCES IN SPACE RESEARCH, 1999, Vol.25, No.2, pp.329-334
*) OFF NATL ETUD & RECH AEROSP,DESP,2 AV E BELIN,TOULOUSE,FRANCE
During the last few years, investigation of impact features found on
material retrieved after exposure to space for a long period of time,
in low earth orbits, has provided us with a great deal of data on the
particulate environment, either natural or man-made. The PIE detection
device presented here has been deployed outside the Kvant-2 module
attached to the Russian MIR station, between June 1996 and April 1997.
Part of the experiment uses a detection technique similar to the one
used in previous experiments flown on LDEF and MIR. Passive sensors are
composed primarly of stacked thin metal foils (gold and aluminium).
According to the size of the particles, they are either decelerated or
fragmented upon high velocity impact. The size of holes or impact
craters give information on the size or shape of the impacting
particles. Samples have been retrieved for laboratory analysis.
Comparison with data from LDEF, EuReCa, I-IST and previous experiments
on MIR provides insight in the long term evolution rf small particle
population and in the debris environment of a permanently manned
station. Some of the samples show evidence of secondary impact
cratering: an attempt is made to locate the origin of the primary
impact site. Some results about the possible origin of the impactors
are provided by the chemical identification of particle remnants inside
the craters. (C) 1999 COSPAR. Published by Elsevier Science Ltd.
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please contact the moderator Benny J Peiser <b.j.peiser@livjm.acdot uk>.
Information circulated on this network is for scholarly and
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------------------------------
Date: Wed, 22 Mar 2000 13:16:05 -0500
From: Lew Gramer <dedalus@latrade.com>
Subject: Re: (meteorobs) Electrophonic phenomena
> http://www.tiacdot net/users/lewkaren/meteorobs/maillist-months.html
Thanks for the reminder, Dave - I've not updated the maillist-months
index with February's and March's posts so far! Coming this week...
Lew Gramer
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------------------------------
Date: Wed, 22 Mar 2000 20:54:22 -0500
From: Lew Gramer <dedalus@latrade.com>
Subject: (meteorobs) [ASTRO] NEAR-Shoemaker Science Update - March 22, 2000
- ------- Forwarded Message
From: Ron Baalke <BAALKE@KELVIN.JPL.NASAdot gov>
Date: Thu, 23 Mar 2000 0:43:38 GMT
Subject: [ASTRO] NEAR-Shoemaker Science Update - March 22, 2000
NEAR-Shoemaker Science Update
March 22, 2000
http://near.jhuapldot edu/news/sci_updates/00mar22.html
Last week the NEAR spacecraft was renamed "NEAR
Shoemaker," in honor of the late Eugene M. Shoemaker, a
pioneer in the study of asteroid and comet impacts on
Earth and other planets. It is largely because of Gene's
work that we know that the famous Meteor Crater in
Arizona (also called Barringer Crater) was indeed
created by the impact of a 15-meter iron-rich meteoroid
and not by a volcano. While many scientists suspected an
impact origin, including Barringer himself, it was
Shoemaker and his colleague Chao's discovery of the high
pressure silicate mineral coesite that finally convinced
skeptics.
Gene was also heavily involved in the Apollo missions
that resolved one of the leading scientific
controversies of our time, whether the craters on the
Moon were formed by volcanoes or by impacts. We now know
that the surface of the Moon is actually saturated with
impact craters and that even the largest features we
see, those that make up the "man in the moon", lie
within the scars of giant impacts. These features are
dark because, later in the moon's history, the giant
impact scars were filled with volcanic lavas. The Moon's
surface records a period of violent bombardment in the
early history of the solar system, a bombardment which
the Earth itself did not escape. Of course, on Earth the
record of ancient giant impacts has been mostly erased
by the actions of weather and plate tectonics. Gene was
among the first to recognize the importance of large
impacts for the geologic history of the Earth and for
the evolution of life on Earth.
Since the projectiles that bombarded the Moon, the
Earth, and other terrestrial planets were asteroids and
comets, Gene initiated telescopic observing programs to
search for such objects in orbits close to Earth's orbit
(that is, near-Earth asteroids and comets) as well as in
more distant orbits. He and David Levy discovered the
comet Shoemaker-Levy 9 that plunged into Jupiter in
1994, after splitting into more than 20 fragments,
temporarily creating dark spots in Jupiter's clouds
larger than the Earth.
NEAR Shoemaker is now orbiting one of the largest of the
near-Earth asteroids, 433 Eros. Gene always thought of
the near-Earth asteroids as "roadcuts in the heavens",
which would have fascinating and important stories to
tell about the formation of the planets. We all have the
experience of driving through a roadcut on the highway
and looking at exposed layers of sediment or rock on
either side, which would reveal something of the
geologic history of that particular site. How
appropriate it is that we now see fantastic systems of
linear features - ridges, grooves, and chains of craters
or pits - all around the surface of Eros. Were the
linear features formed by ancient geologic activity on
the parent body of Eros, making Eros possibly a
'roadcut' through the parent body from which it was
derived? Or were the linear features formed by later
processes? Our task is now to find the evidence that
would indicate which of these possibilities may be
correct.
One important line of evidence will come from NEAR's
x-ray and gamma-ray spectrometers, which will measure
the elemental compositions of surface materials. Last
week, NEAR recorded the first detections of x-ray
emissions from an asteroid. NEAR's x-ray spectrometer
was able to identify emission from the elements silicon,
aluminum, magnesium, calcium and iron during a large
solar flare on March 2, 2000. The flare bombarded the
asteroid's surface with an unusually high intensity of
x-rays, enabling NEAR's x-ray spectrometer to detect the
asteroid emissions at a range of more than 200
kilometers from the surface. From that one observation,
we were not able to determine quantitative abundances of
these elements, which is the information that might tell
us whether Eros is from a differentiated parent body
(one large enough to have melted in the interior and
separated into heavier and lighter constituents) or from
a more primitive parent body. We'll have to be patient
and await more observations, especially from the lower
orbits where the x-ray and gamma ray spectrometers were
designed to operate. Gene would have had difficulty with
the notion of being patient at Eros - he wanted to go
there and bang on it with a hammer - but he would have
understood.
Andrew Cheng
NEAR Project Scientist
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