Satgen299      Comets and Meteors  by GM4IHJ                       17Dec94
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In July 94 Comet Shoemaker-Levy demonstrated very clearly what happens
when a moderate sized asteroid or comet hits a planet. It did not take a
big telescope to see the enormous earth sized clouds of dust which each
piece of the comet raised in Jupiters atmosphere, and from that display,
it is easy to follow the suggestion of the late Luis Alvarez - that a 
similar hit on the earth 65 million years ago blacked out and ended the
long reign of the dinosaurs.
As Radio Amateurs we are uniquely placed to follow some of these comets by
monitoring their annual meteor showers , as the earth crosses the trail of
tiny particles the comets spew out in great loops around the Solar system.
This week the Geminids meteor shower has provided meteor scatter
communications each morning and evening, and , coming shortly on the night
of 3rd/4th Jan 95 between 2300 and 0200 utc approx, is the regular
Quadrantids shower which only lasts for a couple of hours but can be the
most intense shower of the whole year.
These two meteor showers offer a complete contrast in styles. THe Geminids
were sow by an ancient Comet which has now lost all its main features and
circles the Solar System as a burnt out cinder like small asteroid, whose
old meteor dust trail is spread out wide producing a shower lasting
several days. By contrast the comet of the Quadrantids shower may be
a recent newcomer to the inner Solar system and has not yet been
identified. Its trail has simply not had time to spread out very far so
the shower is short duration and very intense at times.
Meanwhile the much bigger Comet Swift Tuttle the progenitor of the summer
Perseids meteor shower caused a fuss recently when it came rather close to
the Earth and produced strong meteor shower activity. Careful study by
Astronomers has suggested that contrary to press hysteria , Swift Tuttle
is not likely to hit the Earth on its next visit in 2126 AD. But the sting
in the tail of their report says that Swift Tuttles orbit period is locked
in resonance exactly 11 times Jupiters orbit period . Which means Swift
Tuttle is going to keep coming back until it eventually hits something.
It is no surprise therefore that organisations like Spacewatch have begun
to receive political support for their efforts to monitor wayward Comets
and Asteroids. Just what we do about one if it seems to be likely to hit
the Earth is not clear. But a recent suggestion which appears to have more
merit than most, is that if we get enough warning, we should not try to
blow it apart, we should dig it up. This is in fact not as crazy as it
sounds. If we can develope the techniques to dismantle these wanderers the
rewards could be enormous. Noting that in a big body like the earth most
of the heavy precious metals sink into the centre. But evidence from some
meteors which reach the Earth intact, suggests this does not happen in
smaller solar system bodies. There the precious metals stay in reach near
the surface. So Comet or Asteroid mining could be the Klondike of the
future.
If however the Quadrantids meteor which lands on your front lawn early am
4th Jan95, does not have much expensive metal content, do not despair. The
young lady in New York whose ancient Chevy was recently bashed by a meteor
is reported to have sold the car and the meteor for a rumoured $69,000 .
Happy Xmas de John GM4IHJ @ GB7SAN