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(meteorobs) Excerpts from "CCNet DIGEST, 26 May 1999"




------- Forwarded Message

From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet DIGEST, 26 May 1999
Date: Tue, 25 May 1999 11:05:55 -0400 (EDT)

CCNet DIGEST, 26 May 1999
--------------------------

[...]

(3) FIREWORKS IN THE SKY?
    Andy Nimmo <andy.nimmo@net.ntl.com

(4) GREAT BALLS OF ... DUST
    Duncan Steel <dis@star.arm.acdot uk>=20

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

(3) FIREWORKS IN THE SKY?

>From Andy Nimmo <andy.nimmo@net.ntl.com

Dear Dr Peiser,

I noted in the BBC OnLine excerpt in the CCNet Special of 20th May, it
says:-

"Astronomers at the Minor Planet Center at the US Smithsonian=20
Astrophysical Observatory used Zoltowski's work to work out an=20
estimated approach distance for AN10 of 56,500 kilometres from Earth.=20
The fly-by will occur on August 7, 2027. "

As the thickness of Earth's magnetosphere, at its thinest, is never=20
less than around 64,000 kilometres from Earth, I presume this means=20
there is a very good chance that on 7th August 2027, AN10 will come=20
well within Earth's magnetosphere.

When your CCNet Digest came in, I happened to be reading Professor Mike =
Baillie's interesting book, "Exodus to Arthur", in which, on page 178, he
enquired of Gerry McCormac "a colleague who had trained and worked = as an
atmospheric physicist" as to what would happen if a comet came very=20 close to
the earth? He replied, "If it came within the earth's=20 magnetosphere it would
probably be spectacular ...the sky would go=20 purple or green, particles from
the comet would spiral down the lines = of force and it is likely that you would
have amazing auroral displays and coloured streamers..."

Well, AN10 is an asteroid rather than a comet, but perhaps it may have=20 small
stones and/or dust in its wake. What chance do the CCNet experts=20 think there
may be that we'll have a spectacular display that night?

Andy Nimmo

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

(4) GREAT BALLS OF ... DUST

>From Duncan Steel <dis@star.arm.acdot uk>=20
=20
Dear Benny,
=20
A note has been passed to me from Andy Nimmo in which he very =
reasonably=20
asks about what sorts of things might be witnessed when (if) 1999 AN10=20
makes a very close fly-by of the Earth in 2027. Basically, he is=20
wondering whether we might see great balls of fire (copyright, Jerry =
Lee=20
Lewis).  I would suggest here that great balls of dust are more likely.
=20
My answer is based on the assumption that 1999 AN10 is indeed =
asteroidal=20
(i.e., no volatile component producing outgassing and hence auroral=20
effects etc. as Nimmo mentions).
=20
First, a simple prediction based upon its observed brightness indicates =

that it would be between magnitudes +3 and +4 as it passes from day- to =

night-side during the close approach. That is, brighter than all but a=20
handful of stars.
=20
Now, let me assume that it has a dusty regolith, and that it passes =
close=20
enough to penetrate the magnetosphere. I believe that under such=20
circumstances the individual dust grains (I am talking about sub-micron =
to
100 micron particles here) would charge to some thousands of volts.
Electrostatic repulsion would then make them fly off the asteroid. That =

is, a dust coma co-moving with the asteroid might be formed. This would =

perhaps scatter much more light than the solid body itself, and extend=20
over a large volume of space, gradually dispersing.
=20
Let me give a background reference which some others might find=20
interesting.  The dust detection instrument on board the HEOS-2 =
satellite=20
operated by the Heidelberg group during the 1970s found evidence for=20
bursts of impacts by dust grains only whilst the satellite was close to =

the Earth, as opposed to apogee out near the lunar distance.  Their=20
interpretation (see the item by Hugo Fechtig in Comets, ed. L. =
Wilkening,=20
Univ. of Arizona Press, 1982) was that dust balls/agglomerations of =
mass=20
of order 1 tonne were remaining intact in space until such time as they =

approached the Earth/magnetosphere, and consequent charging led to=20
electrostatic bursting of the mass, producing a cloud of co-moving dust =

particles. (I might mention in passing that at one stage I gave some=20
thought to whether this phenomenon, if it is real, might explain =
whatever=20
it is that Lou Frank claims to detect, the so-called dark atmospheric=20
holes, avoiding his preposterous explanation of substantial minicomets=20
depositing water as they break up.) =20
=20
What I am suggesting here is the possibility that, if 1999 AN10 has a=20
dusty regolith (surface layer), then the small dust grains might be=20
levitated through charging, producing a bright dust coma (*not* a gas=20
coma, the dominant factor in the brightness of a comet). If this does=20
happen, then we might see a celestial ghost in 2027.
=20
Duncan Steel
dis@star.arm.acdot uk=20

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Information circulated on this network is for scholarly and=20
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