PLEASE NOTE:
*
CCNet, 019/2000 - 11 February 2000
----------------------------------
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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