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From: djb@cbosgd.UUCP (David J. Bryant)
Newsgroups: net.space,net.astro
Subject: Re: fake comet
Message-ID: <529@cbosgd.UUCP>
Date: Fri, 30-Nov-84 10:34:05 EST
Article-I.D.: cbosgd.529
Posted: Fri Nov 30 10:34:05 1984
Date-Received: Sat, 1-Dec-84 19:45:05 EST
References: <1510@drutx.UUCP>
Organization: Bell Labs, Columbus
Lines: 74

> Apparently, on December 25th at about 4:00 a.m. an explosion of
> Barium at 70,000 feet above the Earth will produce a comet-like
> phenomenon.  Scientists plan to observe the ``comet'' and the
> effects that the Earth's electromagnetic field has on it.
> 
> I would like to know more
> detail about the experiment and am hoping this discussion can
> shed some light (np).  If you have any insight about the
> significance of the date, I'm interested in that too.
> 
> Thanks,
> rod
> drutx!rjs

I've seen (heard) several items that discuss this "fake comet", most
notably in the December issue of Sky & Telescope (page 516), and the
December issue of Science '84 (page 38).  Even the local radio stations
have had short news items about the "comet".

The comet is, as you mentioned, a cloud of ionized barium that will
be released as part of a three-nation, three satellite project called
AMPTE (Active Magnetoshperic Particle Tracer Explorers).  The three
probes (representing West Germany, the United Kingdom, and the U.S.)
were launched on Aug. 16th.  The way the experiment works is that
Germany's Ion Release Module (IRM) ejects clouds of barium and lithium,
and the other two satellites watch and see what happens.  The IRM, and
the United Kingdom Subsatellite (UKS) are in an orbit with a 70,000 mile
apogee, taking them out of the Earth's magnetosphere and into the solar
wind on the sunward side.  The released gasses quickly ionize and flow
back along the solar wind, much like dumping a tracer dye into a river.
While the UKS takes measurements near the gas cloud, the U.S Charge Composition
Explorer (CCE) will observe from a lower (30,700 mile apogee) orbit.

The purpose of the experiment is to determine what fraction of the particles
in the Earth's magnetosphere (including the Van Allen belts) come from the
solar wind, and how many are captured from the ionosphere.  Two releases
have already taken place, on Sept 11th, and again on Sept 20th.  These two
were from positions upstream in the solar wind, ahead of "bowshock" of the
Earth.  Although both releases were during periods of instability in the
magnetosphere, data indicates that less than 1% of the solar wind particles
are trapped in the magnetosphere.

The "Christmas Comet" will come from a release on the morning of December
24th (if the "weather" is bad in the magnetosphere, the backup date is
December 27th).  This time, the IRM will be inside the Earth's bowshock,
but outside the magnetopause.  Scheduled releast time for the 2kg of barium
is between 11:30 and 13:30 UT, just above the Galapagos Islands.  (The
Science '84 article pinpoints release time at 4:16am, Pacific Time,
which is 12:16 UT.)  Initially, the 100 mile-wide cloud will appear 
greenish, but will turn blue as the barium ionizes.  The appearance will 
be similar to a comet with a 5 degree tail.  Peak magnitude is expected to 
be about +2.5, making the comet visible to the naked eye for about 3-10 
minutes.  The release point is just west of Spica (the brightest star in
the constellation Virgo), althought the comet will move rather quickly to the
west north west.  To see the "comet", you must be in the dark at about this 
time, which means west of a line that runs through Mexico City, Houston, 
St. Louis, and Milwaukee, and Canada's Belcher Islands (where they make 
all that Canadian beer).

For more detailed updates, call NASA at (301) 344-0470 after December 1st.

By the way, there will be another release in the Spring of 1985.  This time, 
the IRM will be centered in the Earth's magnetic "tail" (downstream).

       *         * 
				David Bryant
				AT&T Bell Laboratories
               * 		Columbus, OH 43213
            *			(614) 860-4516
	 *  .
            :			djb@cbosgd.UUCP
                		cbosgd!djb@Berkeley.ARPA
       *         *