PLEASE NOTE:


*

CCNet, 019/2000 - 11 February 2000
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     QUOTES OF THE DAY


     "SOHO is seeing fragments from the gradual breakup of a great
     comet, perhaps the one that the Greek astronomer Ephorus saw in
     372 BC," said Dr. Brian Marsden of the Center for Astrophysics in
     Cambridge, MA. "Ephorus reported that the comet split in two. This
     fits with my calculation that two comets on similar orbits
     revisited the Sun around AD 1100. They split again and again,
     producing the sungrazer family, all still coming from the same
     direction."  Their ancestor must have been enormous by cometary
     standards. "The rate at which we've discovered comets with LASCO
     is beyond anything we ever expected," said Biesecker.
           --- Space Science News, 10 February 2000


    "We need detectors in Space, whether they have military bearings or
    not. Comet debris trails might just be the most difficult encounter
    situation to mitigate and we don't know much about them except that
    they are hard to detect from the ground."
         -- Bob Kobres, 11 February 2000 



(1) WHEN BIG COMETS COME UNGLUED
    Bob Kobres <bkobres@uga.edu>

(2) KAMIKAZE COMETS
    Space Science News, 10 February 2000

(3) KAMIKAZE COMETS DON'T STAND A SNOWBALL'S CHANCE IN HELL
    Space.com, 9 February 2000

(4) RISK FROM SMALL NEOS - THE WORDEN-DEBATE
    Michael Paine <mpaine@tpgi.com.au>

(5) DANIEL WAS RIGHT: METEORITE IMPACT ON MOON WAS OPTICAL
    ARTEFACT
    Sirko Molau <molau@informatik.rwth-aachen.de>

(6) NEAR TO ASTEROIDS
    SPACEDAILY, 11 February 2000

(7) THE TOP FACTOIDS ABOUT ASTEROIDS
    MSNBC, Space News, 10 February 2000


===============
(1) WHEN BIG COMETS COME UNGLUED

From Bob Kobres <bkobres@uga.edu>

From:
http://spacescience.com/headlines/y2000/ast10feb_1.htm

"SOHO is seeing fragments from the gradual breakup of a great comet,
perhaps the one that the Greek astronomer Ephorus saw in 372 BC," said
Dr. Brian Marsden of the Center for Astrophysics in Cambridge, MA.
"Ephorus reported that the comet split in two. This fits with my
calculation that two comets on similar orbits revisited the Sun around
AD 1100. They split again and again, producing the sungrazer family,
all still coming from the same direction." 

Their ancestor must have been enormous by cometary standards. "The rate
at which we've discovered comets with LASCO is beyond anything we ever
expected," said Biesecker. "We've increased the number of known
sungrazing comets by a factor of four. This implies that there could be
as many as 20,000 fragments."
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

I wonder what the actual large fragment count of the Taurid Complex
progenitor might be? 
http://abob.libs.uga.edu/bobk/taurid.html 

We need detectors in Space whether they have military bearings or not. 
Comet debris trails might just be the most difficult encounter
situation to mitigate and we don't know much about them except that
they are hard to detect from the ground. 
http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?1988ApJ...334L..55S

Later
Bob Kobres

=================
(2) KAMIKAZE COMETS

From Space Science News, 10 February 2000
http://spacescience.com/headlines/y2000/ast10feb_1.htm

Ninety-two sungrazing comets discovered by SOHO appear to have
come from the breakup of a single gigantic comet more than 2000
years ago.

February 10, 2000 -- In just four years of operation, the Solar and
Heliospheric Observatory (SOHO) spacecraft has found 102 comets, making
it by far the most successful comet-hunter in history. Most of this
amazing number are suicidal comets that vaporize as they plunge into
the solar atmosphere.

One hundred years ago Heinrich Kreutz in Kiel, Germany, realized that
several comets seen buzzing the Sun seemed to have a common origin,
because they came from the same direction among the stars. These comets
are now called the Kreutz sungrazers. A whopping 92 of SOHO's 102 comet
discoveries belong to that class.

Nearly all of SOHO's comet discoveries have showed up in images from
the Large Angle and Spectrometric Coronagraph (LASCO) instrument. This
is a set of coronagraphs that view the space around the Sun out to 12.5
million miles, while blotting out the bright solar disk with masks.
LASCO watches for ejections of electrically charged gas from the Sun
that threaten to disturb the Earth's space environment. As a bonus of
unanticipated size, it also proved ideal for capturing objects falling
to the Sun.

"SOHO is seeing fragments from the gradual breakup of a great comet,
perhaps the one that the Greek astronomer Ephorus saw in 372 BC," said
Dr. Brian Marsden of the Center for Astrophysics in Cambridge, MA. 
"Ephorus reported that the comet split in two. This fits with my
calculation that two comets on similar orbits revisited the Sun around
AD 1100. They split again and again, producing the sungrazer family,
all still coming from the same direction."

Their ancestor must have been enormous by cometary standards. "The rate
at which we've discovered comets with LASCO is beyond anything we ever
expected," said Biesecker. "We've increased the number of known
sungrazing comets by a factor of four. This implies that there could be
as many as 20,000 fragments."

Life is perilous for a sungrazer. The mixture of ice and dust that
makes up a comet's nucleus is heated like the proverbial snowball in
hell, and it can survive its visit to the Sun only if it is quite
large. What's more, the strong tidal effect of the Sun's gravity can
tear the loosely glued nucleus apart. The disruption that created the
many SOHO sungrazers was similar to the fate of Comet Shoemaker-Levy 9,
which went too close to Jupiter and broke up into many pieces that
eventually fell into the massive planet in 1994.

The history of splitting gives clues to the strength of comets, which
will be of practical importance if ever a comet seems likely to hit the
Earth. Also, the fragments seen as SOHO comets reveal the internal
composition of comets, freshly exposed, in contrast to the much-altered
surfaces of objects like Halley's Comet that have visited the Sun many
times.

The count of SOHO's comet discoveries would be one fewer without a late
bonus from SOHO's Solar Wind Anisotropies (SWAN) instrument, which
looks away from the Sun to survey atomic hydrogen in the Solar System.
In December 1999, the International Astronomical Union retrospectively
credited SOHO with finding Comet 1997 K2 (SOHO # 93) in SWAN full-sky
images from May to July 1997. It remained outside the orbit of the
Earth even at its closest approach to the Sun, and thus did not
vaporize entirely.

SOHO (the Solar and Heliospheric Observatory) is a mission of
international cooperation between NASA and the European Space Agency.
It is managed by the Goddard Space Flight Center for the NASA HQ office
of Space Science.

=================
(3) KAMIKAZE COMETS DON'T STAND A SNOWBALL'S CHANCE IN HELL

From Space.com, 9 February 2000
http://www.space.com/science/astronomy/soho_comet_000209.html

By Robert Roy Britt
Senior Science Writer

If you are a comet, then you live a precarious life, alternately being
boiled by the sun and then zooming out for a deep freeze in the outer
reaches of the solar system.

=================
(4) RISK FROM SMALL NEOS - THE WORDEN-DEBATE

From Michael Paine <mpaine@tpgi.com.au>

Dear Benny

The results of my simulation, using John Lewis's Hazards software,
reveal the risk of fatal impacts by small NEOs. This takes into account
the estimated NEO population and the population distribution on Earth.

NEO Dia (m)      Annual Risk of fatal impact      Average fatalities per
  fatal event

25-99            1 in 400                         100000
100-199          1 in 1400                        300000
200-499          1 in 3400                        2 million
500-999          1 in 23000                      14 million

See http://www1.tpgi.com.au/users/tps-seti/sta1046.htm for more results.
This suggests, as expected, that there is a high risk of a localised
fatal event of the Tunguska size.

In his book accompanying the software, John Lewis evaluates the
*economics of search and tracking* and concludes a program to find 90%
of NEOs down to 100m diameter *is clearly a worthwhile investment*.
Below 100m the benefits to costs drop off rapidly.

regards
Michael Paine

================
(5) DANIEL WAS RIGHT: METEORITE IMPACT ON MOON WAS OPTICAL
    ARTEFACT

From Sirko Molau <molau@informatik.rwth-aachen.de>

Hello friends,

after new pictures of the possible meteorite impact on the moon have
been examined at DLR it seems quite clear now that all photographs in
question show indeed only optical artefacts, as many amateurs have
suspected before. In addition, the visual TLP observation turned out to
be carried out at a different time.

Best regards,
Sirko Molau

================
(6) NEAR TO ASTEROIDS

From SPACEDAILY, 11 February 2000
http://www.spacedaily.com/spacecast/news/near-00n.html

Arizonian Scientists Ready To Map Asteroid's Minerals

Tucson - February 10, 2000 - Monday could be a special Valentine's Day
for University of Arizona planetary scientists planning not just a
brief fling, but a year long rendezvous with Eros where they will find
either riches or tears.

FULL STORY AT
http://www.spacedaily.com/spacecast/news/near-00n.html

==============
(7) THE TOP FACTOIDS ABOUT ASTEROIDS

From MSNBC, Space News, 10 February 2000
http://msnbc.com/news/368661.asp?cp1=1

Space rocks can provide insights about Planet Earth’s origins

By David Ropeik
MSNBC CONTRIBUTOR
              
Feb. 10 —  A Valentine’s Day “rendezvous” with an asteroid named for
the Greek god of love? We’re sure this is coincidence. But the
yearlong study of Eros is no accident. Asteroids have a lot to teach
us about where we came from.

FULL STORY AT
http://msnbc.com/news/368661.asp?cp1=1


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