PLEASE NOTE:
*
CCNet, 82/2000 - 1 September 2000
-------------------------------
(1) "CLOSE CALL" WITH VERY LITTLE WARNING
Michael Paine <mpaine@tpgi.com.au>
(2) AMOR ASTEROID APPROACHES EARTH
The Cosmic Mirror, 31 August 2000
(3) A CLOSE ENCOUNTER WITH A SPACE ROCK
NASA Science News <nglist@lyris.msfc.nasa.gov>
(4) ASTEROID 2000 QW7: NO CAUSE FOR CONCERN
Benny J Peiser <b.j.peiser@livjm.ac.uk>
(5) METEOR SHOWERS EXPLOSIVE ON MARS
Discover.com, 30 August 2000
(6) NEW CLUES ABOUT MARTIAN METEORITES BAFFLE SCIENTISTS
Space.com, 30 August 2000
(7) NEA SURVEY STATUS
David Morrison <dmorrison@arc.nasa.gov>
(8) VARIOUS NEO & METEORITE ITEMS IN THE LATEST COSMIC MIRROR
Daniel Fischer <dfischer@astro.uni-bonn.de>
(9) RE: CO2 NOT MAIN CULPRIT OF GLOBAL WARMING
Michael Paine <mpaine@tpgi.com.au>
===============
(1) "CLOSE CALL" WITH VERY LITTLE WARNING
From Michael Paine <mpaine@tpgi.com.au>
Dear Benny,
NEA 2000QW7 comes within about 4.5 million km of the Earth
tomorrow (1
Sept). Found by NEAT on 26 August, this object is around 400m in
diameter (H=20.2). According to NEODys it will also make
"close"
approaches in 2019, 2038 & 2057.
URLs:
MPC http://cfa-www.harvard.edu/iau/lists/Dangerous.html
NEODys (search for 2000QW7)
http://newton.dm.unipi.it/cgi-bin/neodys/neoibo
MPEC http://cfa-www.harvard.edu/mpec/K00/K00Q32.html
regards
Michael Paine
===========
(2) AMOR ASTEROID APPROACHES EARTH
From The Cosmic Mirror, 31 August 2000
http://www.astro.uni-bonn.de/~dfischer/mirror/202.html
Amor asteroid approaches Earth, 12 mag possible!
2000 QW7 was at 13.6 magnitudes when the asteroid was found by
the
NEAT telescope on August 26, and it should brighten to around
12.7
mag at the end of the month when the object approaches Earth to
within 0.032 Astronomical Units or 4.7 million km or 12
Earth-Moon
distances. 2000 QW7 can be found in the constellation Aquarius
right now; see the links in the sidebar for an ephemeris..
Because
the object comes so close to Earth, being in different locations
can shift the asteroid's position markedly by the parallax
effect,
by the way.
The orbital elements show that 2000 QW7 belongs to the Amor
family
and follows an orbit inclined 4.2 degrees to the ecliptic. It
ranges as far out as the main belt of asteroids, but every 2.7
years it comes in to a point fairly close to the Earth's orbit.
As
far as is currently known, the object has not been detected by
astronomers before. Its brightness suggests it may be roughly 800
meters across. Several occultations of stars have already been
predicted, but only when radar data should become available will
the ground tracks be known with any precision.
============
(3) A CLOSE ENCOUNTER WITH A SPACE ROCK
From NASA Science News <nglist@lyris.msfc.nasa.gov>
NASA Science News for September 01, 2000
This morning a half-kilometer wide space rock is
zooming past Earth barely 12 times farther from
our planet than the Moon. In cosmic terms, it's a
near miss, but there is absolutely no danger of a
collision. Instead, the encounter offers
astronomers an unusually good opportunity to
study a near-Earth asteroid.
FULL STORY at
http://spacescience.com/headlines/y2000/ast01sep_1.htm?list
============
(4) ASTEROID 2000 QW7: NO CAUSE FOR CONCERN
From Benny J Peiser <b.j.peiser@livjm.ac.uk>
Asteroid 2000 QW7 is currently around 0.032 AU from the earth and
observable with a medium-sized telescope. At an absolute
magnitude
H = 20.2, it is indeed relatively small. The main point, however,
is
that its orbit is quite clearly and completely outside that of
the
earth. In short, there is absolutely no chance of an earth impact
in the
foreseeable future.
The object was discovered by NEAT on 26 August, and two days ago
the
Minor Planet Centre recognised prediscovery observations of the
object
by LINEAR on 3 August. The NEODYS website indicates further
approaches
to the earth in 2019, 2038 and 2087, but NEODYS may have greatly
underestimated the error factor in the orbital eccentricity. The
effect
of this inherent uncertainty on the 2019 and subsequent
"close
approaches" is enormous.
While the object could in September 2019 be as close as 0.03 AU,
it is
important to appreciate that it could just as easily be as far
away as
0.8 AU. In other words, the asteroid, though technically a PHA,
can
scarcely be classified as dangerous.
Benny J Peiser
=================
(5) METEOR SHOWERS EXPLOSIVE ON MARS
From Discover.com, 30 August 2000
http://www.discovery.com/news/briefs/20000830/sp_marsblast.html
By Larry O'Hanlon,
Discovery.com News
Aug. 30, 2000 -- Meteors that would be little more than a flash
in the
sky on Earth can cause massive explosions, vast dust storms and
giant
lightning bolts on Mars, say Russian scientists.
By adapting some classified Cold War equations created to predict
what
nuclear blasts would do in Earth's atmosphere, scientists from
the
Russian Academy of Sciences Institute for Dynamics of Geospheres
think
they have a way of predicting how meteors would behave when they
bust
through the thin martian atmosphere.
"The calculations are very complex," said researcher
Igor Kosarev, who
explained the research Tuesday at the meeting of the Meteoritical
Society in Chicago. Complex and so secret that only simplified
versions
are released for general scientific use, explains Christian
Koeberl, a
geochemist and impact specialist from the University of Vienna.
Most meteors are rocky chunks of space debris, as opposed to the
rarer
metallic meteors, which explode before reaching Earth's surface
because
of the intense heat of atmospheric entry. The same probably
happens to
meteors that drop onto Mars. But because Mars' atmosphere is 100
times
less dense than Earth's, meteors probably get closer to the
ground
before exploding, says Kosarev.
Add to that the dryness of the martian atmosphere and the dusty
conditions, and you get a situation where meteors probably leave
a
charged path of dusty air in their wake that flashes violently
with
electrical energy.
The Russian team tested these violent martian meteor events by
creating
miniature simulations of martian impacts in a laboratory, says
Kosarev.
Their simulations showed that when a meteor explosion occurs, the
shock
wave from the blast creates vortices of wind rolling along the
ground
away from the blast that stir up even more dust, triggering vast
dust
storms.
There is even a possibility that the electrical flashes
associated with
the meteors might be observable from Earth. If so, it could help
scientists remotely watch and learn what sorts of meteors are
hitting
the Red Planet, says Kosarev.
"They're doing good work," said Koeberl, who pointed
out that only a
few research facilities in the world have access to the equations
needed to describe such explosive events.
FULL STORY AT:
http://www.discovery.com/news/briefs/20000830/sp_marsblast.html
=============
(6) NEW CLUES ABOUT MARTIAN METEORITES BAFFLE SCIENTISTS
From Space.com, 30 August 2000
http://www.space.com/scienceastronomy/solarsystem/martian_meteorite_000830.html
By Greg Clark
CHICAGO -- Analysis of new Martian meteorites is confounding
planetary
scientists with clues that simply don't add up. Rather than
clearing up
existing questions about the Red Planet, results from the new
meteorites
seem to be opening up a Pandora's box of questions about Mars.
Evidence
from the rocks doesn't seem compatible with one of the most
trusted
scientific conclusions about the planet: that the vast majority
of the
Martian surface is billions of years old.
The puzzle came into sharp focus here this week at the annual
meeting
of the Meteoritical Society, as scientists announced their
findings
from three recently discovered Mars rocks.
The Los Angeles meteorite, which was discovered last fall by a
Los
Angeles rock hunter, was revealed to be only 175 million years
old --
contemporary in geologic terms. It is a volcanic rock that
crystallized
from magma near the Martian surface. Larry Nyquist and a research
team
at NASA's Johnson Space Center and Lockheed Martin in Houston
determined the age by measuring the state of certain weakly
radioactive
isotopes within the meteorite.
When a rock solidifies, a sort of internal stopwatch is turned
on.
Certain unstable isotopes are locked into the crystals of the
rock, and
they begin to decay. By carefully measuring just how much of
various
unstable isotopes have decayed away, scientists can determine how
long
it has been since the material crystallized to become rock. This
age is
called a rock's crystallization age, and is very important to
scientists who study meteorites.
While surprisingly young, the meteorite is not unique in its
youth.
"[The Los Angeles meteorite] is one of now seven meteorites
with ages
of about 175 million years old," Nyquist said.
This applies to nearly half of the 15 Martian meteorites with
known
ages. A 16th Martian meteorite, known as Dhofar 019, was
discovered by
a Russian expedition traveling in the desert of Oman earlier this
year.
It has yet to be dated conclusively, but some think it will end
up
being the eighth 175 million-year-old Mars rock. There is, of
course,
no agreement about that forecast.
"The Los Angeles meteorite's young age -- indicating that
Martian
volcanism has been active until very recently -- upports recent
interpretations of [Mars Global Surveyor] imagery," Nyquist
said.
The Mars Global Surveyor, which has been in orbit around Mars
since
1997, has recently sent back images that seem to suggest some
areas of
Mars have young volcanic deposits. But photo interpretation is a
subjective business, and scientists have been searching for other
evidence in the matter.
The speculation that Mars may remain volcanically active stands
in
dramatic contrast to older, more accepted theories about Mars,
which
hold that geological activity on the Red Planet ended billions of
years
ago.
FULL STORY at:
http://www.space.com/scienceastronomy/solarsystem/martian_meteorite_000830.html
===========
(7) NEA SURVEY STATUS
From David Morrison <dmorrison@arc.nasa.gov>
NEO News (8/30/00) NEA Survey Status
Dear Friends & Students of NEOs:
This edition of NEO News features a comprehensive summary from
Don
Yeomans of the current status of NEA surveys (aka The Spaceguard
Survey). In addition, you will find below a short report on
the UK
task group studying NEOs and the impact hazard, and a newspaper
account of a space telescope proposal being discussed in Canada
(taken from Benny Peiser's CCNet). It is interesting that a
number
of recent space mission proposals have suggested contributions to
NEO
searches as a justification, although in general these missions
have
other primary targets and seem to add the NEO role as an
afterthought.
David Morrison
==============================================
NEA SURVEY STATUS FROM DON YEOMANS
Minutes taken during the Near-Earth Object Observers meeting held
August 15, 2000 during the IAU General Assembly in Manchester
England
This gathering was the second meeting of the Near-Earth Object
(NEO)
observers to discuss efforts to maximize the NEO discovery rate
among
the entire international observing community. The first
meeting,
which included only the NASA supported search efforts, took place
September 20-21, 1999 at MIT's Lincoln Laboratory in Cambridge,
Massachusetts.
Don Yeomans opened the meeting at 11:00 and welcomed the
community of
NEO observers and several interested IAU attendees. Yeomans
noted
that the goal of this meeting was to discuss plans to maximize
the
discovery rate of NEOs among the international community of NEO
observers and to investigate the extent to which coordination
among
the various teams would help reach the Spaceguard goal. The
Spaceguard goal is to discover 90% of the near-Earth asteroids
(NEAs)
larger than one kilometer within 10 years. The assumption
is made
that a NEA with an absolute magnitude (H) less than 18.0 has a
diameter larger than one kilometer. Recent work by
Rabinowitz et al.
(2000), Bottke et al. (2000), and Harris (2000) suggest that the
total population of near-Earth asteroids (NEAs) larger that one
kilometer (H < 18.0) is about 700, 900, and 1000
respectively. In an
earlier session of the IAU Working Group on NEOs (D. Morrison,
Chair), Yeomans presented charts that showed a dramatic increase
in
the NEA discovery rate in recent years (over 400 NEAs larger than
one
km through July 2000). During the same WGNEO meeting, Al
Harris
presented his analysis suggesting that at the current rate of
discovery, the Spaceguard goal of discovering 90% of the NEAs
larger
than one kilometer in ten years, would be reached not in 2009 but
rather in about 2015. Harris noted that to achieve the
Spaceguard
Goal would require large NEA discoveries at roughly twice the
current
rate. Hence we may be 40 - 50 % of the way toward meeting
the
Spaceguard goal in terms of raw numbers, but certainly not in
terms
of the time interval required.
Short status reports (see Appendix) were given by representatives
of
the Japanese Spaceguard (S. Isobe), Catalina Sky Survey (S.
Larson),
LINEAR (G. Stokes), LONEOS (E. Bowell), NEAT (E. Helin), and
Spacewatch (R. McMillan). Brian Marsden and Gareth Williams
also
presented remarks from the perspective of the Minor Planet Center
(MPC).
After these short reports, the floor discussion began with
Yeomans
noting the conclusions resulting from the earlier meeting (Sept.
1999) of the observers at MIT's Lincoln Lab could be summarized
as
follows:
A. Effective coordination requires knowledge of each search
program's
capability and capacity.
B. Each program needs to optimize and understand their own
efforts
before attempting an inter-survey optimization.
C. Each survey program's sky coverage and limiting magnitude
needs to
be well understood.
D. As a metric for gauging progress among the survey efforts,
each
survey team needs to compute their search volume covered per unit
time.
E. Once each separate survey is internally optimized and once
metrics
have been established for each survey, then monthly sky coverage
could be effectively divided up among the various surveys.
The following remarks represent the impressions of the
undersigned as
a result of this meeting. These comments do not necessarily
represent a consensus view of the meeting participants.
Current survey efforts are posting the sky areas that they
covered
the night before and this seems to be helping the plan to
coordinate
the total effort. Because of the vagaries of weather,
equipment,
personnel support, etc., this a posteriori posting of "where
we've
been" is considerably easier to provide than an accurate a
priori
posting of "where we'll look tonight." A
truly integrated and
coordinated international program of a priori postings of planned
search areas will be difficult and, in any case, not realistic
until
the above-mentioned points A-E are properly addressed. As
the
separate survey efforts optimize their own techniques, and total
accessible sky coverage goes to deeper limiting magnitudes, the
issue
of follow-up observations becomes more important. The
search efforts
may soon evolve to a point where targeted follow up (most by
relatively small aperture telescopes) will be replaced by
relatively
automatic inter survey follow-up as the same regions of sky are
searched more and more frequently by the various surveys.
Gareth
Williams noted in his remarks that, to some extent, this
automatic
follow-up between the various surveys is already taking place.
Don Yeomans
Manager, NASA Near-Earth Object Program Office
References:
Bottke, W.F. et al. (2000). Science, 288:2190.
Harris, A.W. (2000). Personnal communication.
Manuscript by Werner,
Harris, Ivanov, and Harris in prep. for
Icarus.
Rabinowitz, D.L. et al. (2000). Nature, 403:165.
---------------------------------------------------
Appendix: Short summaries of the status of the survey
efforts.
Japanese Spaceguard (S. Isobe):
Located at Bisei town Japan, the Japanese Spaceguard program will
consist of two optical telescopes for the detection of near-Earth
objects and space debris in Earth orbit. The 0.5 m
telescope, in
operation since February 2000, has a field of view of 2 square
degrees (f/1.9) and uses a CCD array consisting of two 2K x 4K
CCDs.
The one meter telescope, scheduled for operation in September
2000,
has a field of view of 3 square degrees (f/3) and will use a
mosaic
of ten 2K x 4K CCDs.
Catalina Sky Survey (S. Larson):
The Catalina program consists of both a northern and southern
hemisphere search and follow up capability. In the north,
the
Catalina Schmidt 0.7m (f/1.6) telescope is used for search while
the
Mt. Lemmon 1.5 m (f/2.0) is used for follow up
observations. In the
south, the Siding Spring Uppsala Schmidt 0.6 m (f/3) is currently
being used for search while the co-located 1.0 m (f/8) telescope
is
used for follow up. Upgrades are in progress for the
Catalina
Schmidt (corrector plate, new computers, dome control), the
Uppsala
Schmidt (declination drive and control room), and Mt. Lemmon
(declination drive, computer controls, coma corrector). Proposed
upgrades include a thinned 4K x 4K chip for the Catalina Schmidt,
a
0.9 m (f/1.7) optical system redesign for the Uppsala Schmidt and
a
larger 4K x 4K chip for the Mt. Lemmon telescope.
LINEAR (G. Stokes):
While efforts to utilize the U.S. Air Force one meter aperture
Ground-based Electro-Optical Deep Space Surveillance (GEODSS)
telescopes for discovering NEAs go back several years, it was in
March 1998 that the LINEAR program began routine operations using
a
special 1960 x 2560 CCD camera. This CCD is a thinned, back
side
illuminated, frame transfer device that allows very fast
readouts.
In October 1999, a second co-located GEODSS telescope was added
to
the LINEAR survey and the combination of these two telescopes now
accounts for roughly 70% of all NEA discoveries.
LONEOS (E. Bowell):
The LONEOS 0.6 m Schmidt telescope (f/1.9) is currently making
about
15,000 asteroid detections per lunation. With the recent
improvements in computer software (Sextractor) and the new camera
(two 2K x 4K thinned backside illuminated CCDs), the current
detection rate is about twice what it once was. Ted Bowell
noted
that while an improvement to the current thermal environment
might
increase the system efficiency somewhat, the current system has
gone
about as far as it can so that plans are underway to investigate
the
use of the USNO 1.5 m telescope in Flagstaff for future NEA
searches.
NEAT (E. Helin):
NEAT began operations with the 1.0 m GEODSS telescope at
Haleakala,
Maui, Hi in 1995. In 1999, NEAT was moved to the use of the
MSSS 1.2
m telescope at the same location and began operations there in
February 2000. The current telescope not only has a larger
aperture
but is available 18 nights per month whereas the GEODSS telescope
was
only available about 6 nights/month. In addition, upgrades
are
already in progress to convert the Palomar 1.2 m Schmidt
telescope
into a NEA search instrument with operations expected to begin in
October 2000. The Maui MSSS 1.2 m telescope uses a 4Kx4K
CCD with a
field of view of 2.6 sq. degrees whereas the Palomar Schmidt will
utilize an array of three 4Kx4K CCDs for a field of view of 3.9
sq.
degrees.
Spacewatch (R. McMillan)
The Spacewatch telescopes include the 0.9 m and the 1.8 m.
When used
with the 4 x (4.6K x 2K) mosaic CCD, the 0.9 m has a field of
view of
2.9 sq. degrees. When brought on line at the end of 2000,
the 1.8 m
telescope will have a field of view of 0.32 sq. degrees and
utilize a
2K x 2K CCD. The average rate of discovery of NEAs with H
< 18.0 has
been about 7 per year since 1995. The Spacewatch telescopes
are used
primarily for deep searches in limited areas for NEAs and
Kuiper-belt
objects (KBOs) rather than the wide area NEA searches provided by
the
other search programs. As a result, Spacewatch finds many
of the
smaller NEAs, some KBOs and recently, the 17th satellite of
Jupiter.
MPC (G. Williams)
Until Oct. 1998, most of the data processing of incoming
observations
and orbit improvements were performed on one VAX workstation.
Starting in Oct. 1998, the first of the Alpha workstations were
brought on line for doing the orbit improvements while the VAX
still
processed the observations. In early 1999, four clustered
Alpha
workstations were brought on line to process the observations,
compute orbits and prepare the MPCs for export. The porting
of the
entire MPC operations from the VAX to the Alpha systems has been
very
time consuming and is still ongoing. Since late 1999,
several
batches of MPCs have contained over 300,000 observations and the
expectation is that one of the 2000 MPC batches will break the
500,000 observation mark. Gareth noted a "follow up
rating" that was
defined as the percentage of submitted observations made in a
specified period that can now be identified with previously known
objects or linked with other objects. For the first few
months of
2000, these follow up ratings were about 95% for NEAT, 70% for
Spacewatch, 85% for LONEOS and 90% for Catalina and LINEAR.
================================================
UK NEO TASK GROUP
At the International Astronomical Union meeting in Manchester UK,
David Williams gave a brief background on a report expected to be
released by the UK government in mid-September on their proposed
program for Near-Earth objects. No details were available at this
time, but we all look forward to this official government
assessment
of the NEO risk and of ways that might be appropriate for the UK
to
participate in the worldwide Spaceguard effort. Stay tuned.
--------
MODERATOR'S NOTE: The UK Government is expected to publish
the NEO Task Force's report on 18 September. I understand that it
will
be
also made available on the web and plan to provide further
details
(and URL) as soon as possible.
==================
(8) VARIOUS NEO & METEORITE ITEMS IN THE LATEST COSMIC MIRROR
From Daniel Fischer <dfischer@astro.uni-bonn.de>
Hi Benny,
your readers might find several articles in
http://www.astro.uni-bonn.de/~dfischer/mirror/202.html
interesting.
Regards, Daniel
==================
(9) RE: CO2 NOT MAIN CULPRIT OF GLOBAL WARMING
From Michael Paine <mpaine@tpgi.com.au>
Dear Benny,
I think the title ('Greenhouse Gases not responsible for Global
Warming') you used was inappropriate. The article expresses the
view that
'non-CO2 greenhouse gases ... have been more significant in
climate
change'. This is not surprising since, per kilogram, methane has
about
20 times the greenhouse effect of CO2. The figure for N2O is
about 300
times that of CO2. The point is that all greenhouse-related
emissions
need to be taken into consideration in understanding global
climate
change.
regards
Michael Paine
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