CCNet DIGEST, 16 December 1998

    Andrea Boattini & Andrea Carusi <>

    Andrea Milani Comparetti <>

    Mike Rampino <>

    Tnu Pani <>

    NASA Science News <>

    George Zay <>

    Ron Baalke <>


    Andrew Yee <>


From Andrea Boattini & Andrea Carusi <>
Dear Benny,
the interesting debate that is arising around some recent discoveries,
including 1998 XB (which actually seems to be Aten with a = 0.90 AU and
the biggest of this class!!), demonstrates that we still don't know the
consistency of the NEA population very well for quite a few reasons.
Among them, we don't know which is the real fraction of Atens and
generally of all the objects with orbits inside that of the Earth.
The recent interest in NEA searching at smaller solar elongations is
opening a new scenario. LINEAR, NEAT and the programs in course at the
Xinglong and Mauna Kea Stations are giving us a hint of what can be
found in these portions of the sky.
Finally we want to present a study on Atens searching that we made at
the beginning of 1997 when the Aten population was basically half of
the present. The goal of this paper was not to come to final
conclusions but to open a wider discussion on this topic, especially on
the difficulties related to the follow-up process. Some of our results
are based on our experience with the italian CINEOS (Campo Imperatore
Near-Earth Objects Survey) program that has been active for a few
months in 1997 and concentrated its efforts at smaller solar
elongations. We will come back on CINEOS results soon.
Andrea Boattini
Andrea Carusi
Abstract: The class of Near-Earth Asteroids known as Atens are very
important search targets for two reasons: first, recent studies have
shown that they have the highest intrinsic frequency of close
encounters with the Earth, and second, they are probably undersampled
in the known NEA population, as searches have always concentrated
toward the opposition region. In order to remove this bias, we outline
a few search strategies to increase their discovery rate with the
available equipment, before an all-sky survey up to magnitude 22 is
implemented (the Spaceguard Survey). Searches should concentrate on two
regions located between 50 and 120 of elongation from the Sun. The
Campo Imperatore Near-Earth Object Survey (CINEOS) will be the first
specific search program to implement such a strategy.
Vistas in Astronomy, Vol. 41, No. 4, pp. 527-541, 1997

From Andrea Milani Comparetti <>

Dear OrbFitters and dear friends,
This message announces a new and significantly improved distribution
of the free software OrbFit.
The software can be obtained at
A README file to be found therein provides all the necessary
instruction for installation on all flavours of UNIX computers.
This software system has been developed by a consortium including the
groups led by A. Milani (Pisa University), M. Carpino (Astronomical
Observatory Milano/Brera), Z. Knezevic (Astronomical Observatory
Belgrade) and G. B. Valsecchi (CNR Rome). The consortium previously
included K. Muinonen (University of Helsinki), who is no longer
contributing; we anyway thank him for the impulse he originally gave
to our work.
The purpose of the software system we are distributing, maintaining
and continously upgrading, is to make available to observers of
asteroids an easy to use but accurate and reliable software to compute
preliminary orbits, ephemerides, improved orbits (by differential
corrections), identifications, and other auxiliary functions, to allow
the processing of astrometric observations and the planning of
observational campaigns (typically to recover lost objects).

Main improvements with respect to the previous distribution 1.7.0 are: 

1) Online help in fitobs; example files for orbfit
2) Output of elements from fitobs in standard format, reusable as input
3) Full removal of millennium bug in asteroid names, including 9
character temporary designations
4) New preliminary orbit algorithms, including Vaisala 3-observations
method and Gauss 3-observation method
5) Revision of headers
6) Elimination of the ephem main; its functions are now fully included
in orbfit
7) Automatic outlier rejection
Main limitations:
1) the online manual is still very incomplete.
2) the standardisation of the software has still a long way to go.
3) the DOS version is no longer supported, and the Windows95 version
is not yet ready.
We are presently working to several improvements, described in the
file README.workinprog which is enclosed with the distribution; the
most urgent one is to generate a native WINDOWS95 version, because we
do understand this is required by many potential users.
Copyright (C) 1997,1998 OrbFit Consortium
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.
    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    GNU General Public License for more details.
    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
    02111-1307, USA
To contact us:,,,


From Mike Rampino <>
The Amazing Earth program will be aired again Saturday, December 19, at
2 p.m. and 8 p.m., and midnight, and on Sunday, December 27, at 3 p.m.
Mike Rampino

This world premiere reveals the catastrophic events that have changed
the face of our world and will ultimately change its face again. From
the heights of Mount Everest to the molten lava fields of Hawaii, from
the silence of space to the depths of the oceans, explore the
geological history of a planet whose wrenching transitions are far from
Patrick Stewart narrates these two special-effects-packed hours,
which tell the tumultuous geological history and future of the Earth.
AMAZING EARTH relates the Earth's incredible tale, including how
meteorite impacts, gigantic eruptions, continental shifts and an
unending string of geological events have created such famous global
features as the Himalayan peaks, India's ancient volcano flows,
evidence of an ice-age flood that ravaged parts of Washington State
with the force of 50 Amazon Rivers and California's San Andreas
Fault. Using 3D computer animation and digital compositing, the
program puts viewers in the middle of the largest volcanic explosion
the world has ever known. Breathtaking sequences show how a new Ice
Age would submerge everything from the Statue of Liberty to the city
of San Francisco, and specially created graphics take viewers on a
journey to the unseen center of the earth. 


From Tnu Pani <>

The following is about Nordic-Baltic Network for Impact Crater
Studies. The third summer-course will be held in 1999, in Kuressaare
(Estonia), near to the Kaali crater-field. Priority will be given to
the research-students.



It was only 80 years ago that the well-preserved Meteor Crater in 
Arizona was recognized as a cosmic collision structure - an impact 
crater. In 1928, Estonian mining engineer Ivan Reinwald proved that
the  ~100 m Kaali main crater and the surrounding smaller craters in
Saaremaa, western Estonia, were caused by a cosmic collision.
However, the first suggestions of meteoritic origin of the Kaali
crater were made within the correspondence between R. Meyer and
Alfred Wegener in 1921. In 1922, Estonian teacher Juhan Kalkun
supposed the meteoritic origin in his study book "General Geology".
After the Meteor Crater, Kaali was the second terrestrial object,
which extraterrestrial origin was recognized. It was the only known
impact structure in Europe for several decades. About 40 years later
similar structures were found all around the world and today about
150 such craters are known worldwide. The number increases for each
year. In the Baltic shield and its nearest surroundings, 16 impact
craters were recognized 1992 and since then another 5 structures have
been identified. As knowledge about impact generated lithologies is
increasing, also cases occur where coptogenic rocks are found but no
nearby crater structure. One of the largest impact events occurred 65
million years ago at what is now the Yucatan peninsula. This event
extincted a very large portion of terrestrial and marine life,
including most of the dinosaur species. The resulting crater is about
200 km in diameter. Catastrophes of this dimension may only occur
once every 30 million years, however smaller cosmic projectiles in
the 1 km size range collide more frequently with the earth - about
one every few million years. Their impact craters may have become
eroded away or covered under sedimentary sequences. Although still
relatively scarce, impact cratering has been recognized as an
important geological process also on earth.

Nordic-Baltic cooperation

A deeper knowledge of the impact cratering processes will increase
our understanding of the evolution of the earth and the solar system.
We are now in the beginning of this research field and it would thus
be of importance to inspire and to educate new researchers. On a
national basis, the competence profile is usually too narrow to cover
the topic, but by cooperation, a considerable widening of competence
may be achieved. Up to a few years ago, small groups within each
country have studied impact craters with a limited width in the
scientific approach. However, cooperation across the discipline
boundaries and between the different universities could take
advantage of the unique situation in the Baltic shield: Here many
crater structures have been detected, several more can be identified,
and a well developed infrastructure makes it possible to study them
in detail.

The Nordic-Baltic Network for Impact Crater Studies, funded by NorFA

The network was initiated in 1996 in order to promote this particular
field of geoscience, and especially to facilitate coordinated 
post-graduate courses in impact geology and -geophysics. Such courses
contain theoretical studies with lectures combined with field
practice in impact geology and geophysics. Since the start of the
network in 1997, two summer schools short courses have been
organized. The first in Delsbo within the 20 km diameter Dellen
crater, where 12 students and 5 teachers participated. The 10 days
studies concentrated on impact lithologies, like impact melt and
suevite, and geophysics of impact structures. The second course was
held 1998 in Nesbyen close to the 6 km diameter Gardnos crater, with
11 students and 5 teachers. That course concentrated on marine impact
craters and impact crater modeling and gave the unique opportunity to
study a large impact crater that has been obliquely eroded.

The next course

For 1999, the third short course is planned to be held mainly in
Kuressaare, close to the post-glacial Kaali crater field. The 9 day
course will concentrate on the study of post-glacial crater
morphology and -geophysics, thermal evolution of impact craters and
the dating of impact events, among other topics as listed below.
Eight teachers have been invited to present their specialities and
there will be frequent opportunities for field studies. Research
students and students within geosciences from the Nordic-Baltic
region (Iceland, Denmark, Norway, Sweden, Finland, NW Russia,
Estonia, Latvia and Lithuania) are invited to participate. Travel
costs, housing and living costs are covered by the network funding.
Priority will be given to research students. In case of remaining
capacity, undergraduate students and students from outside the
Nordic-Baltic region can participate. Non-Nordic-Baltic participants
would need to bring their own financing for travel costs and a fee of
500 USD. Within EU, grants may be applied for from ESF.

The research course Post-glacial impact craters and physical-chemical
aspects of impact structures - will be held at Kuressaare and
Viitna in Estonia from June 14 to 22, 1999, - can host 20 students,
- has the following topics included:

The environment of impact cratering in Fennoscandia,
impact related phenomena in sedimentation,
dating of impact events,
geochemistry of impactites,
thermal evolution of impact craters,
hydrothermal alteration of impact rocks,
electrical and electromagnetic methods in impact crater studies,
field work at the Kaali crater and Neugrund structure.

The following teachers have been invited:

Prof. Christian Koeberl, Vienna
Prof. Alexander Deutsch, Muenster
Herbert Henkel, Stockholm
Dr. Bo Olofsson, Stockholm
Prof. Vino Puura,Tallinn
Prof. Anto Raukas, Tallinn
Dr. Tonu Meidla, Tartu
Mrs. Reet Tiirmaa, Tallinn 
Mr. Kalle Suuroja, Tallinn.

Applications for participation are sent before March 31, 1999 to:

Dr V Puura, Institute of Geology, University of Tartu, Vanemuise 46,
51014 TARTU, Estonia. Tel: +372 7 375 834. Fax: +372 7 375 836. Email:

An application should contain a curriculum vitae, the applicants =
scientific background and a motivation for participation. For
undergraduate students, a letter of recommendation from their
university department or professor is required.


From NASA Science News < >

NASA Space Science News -- 15 December 1998
Bunches and Bunches of Geminids -- Last weekend sky watchers around
the globe were treated to one of the strongest Geminid meteor showers
ever. Next year could be even better when the source of the Geminids,
the mysterious asteroid 3200 Phaethon, visits the inner solar system.
This article includes a video clip of Geminid and Leonid meteors
streaking through the constellation Orion. FULL STORY at

From George Zay < >
Before you call the 1998 Meteor Shower Season over, you might want to
give the Ursids a try. If there is any shower that is in need of
serious observations, it would probably be this one. It is seldom
watched mainly because of the winter season, near Christmas and not as
active as the two biggies that surrounds it....Geminids and
Quadrantids. The moon should be a minor problem. Here are some
particulars for you.
Ursids - These meteors are weakly visible for one week prior to
Christmas. Although the radiant is circumpolar for most northern
hemisphere locations, it's activity will mainly be noted after midnight
on the morning of Dec 21/22. Actually I find the best activity near 3
am to dawn. A waxing crescent moon will give relatively dark skies for
observations almost all night on Dec 22. The parent source for the
Ursids is comet 8P/Tuttle, which last reached perihelion in 1994. A
short but strong display has been seen three times while comet Tuttle
was near aphelion. The last burst of activity occurred in 1986. Thus
the year 2000 may provide the next possible strong display of Ursid
Meteors. This shower is difficult to photograph due to the low numbers
and faintness of it's meteors. Thus a fast 50 mm lens aimed at the bowl
of the little dipper would be my preference. This shower is invisible
in the southern hemisphere. Max. Dec 21/22, 1998 at 18hr UT; ZHR: 10
(occasionally variable up to 50); Vel. 33 km/s (Medium); Duration: Dec
17-26; Population Index: 3.0; Radiant: RA 14h28m, Dec +76; Three Letter
Shower Code: URS
George Zay


From Ron Baalke < >

SpaceDev Places JPL On Contract To Support NEAP Mission Planning

Commercial Deep-Space Mission-Support Contract is a First for NASA and JPL

SAN DIEGO--(BUSINESS WIRE)--Dec. 15, 1998--SpaceDev, Inc. (OTC
BB:SPDV - news), the world's first commercial space exploration
company, has placed NASA's Jet Propulsion Laboratory (JPL) under
contract to provide various analysis and planning services for
SpaceDev's first deep-space science mission, the Near Earth Asteroid
Prospector (NEAP).

The NEAP spacecraft is planned to launch in 2001 and by mid-2002
should brendezvous with the asteroid 4660 Nereus for a two-month
primary mission.

Starting immediately, engineers in JPL's Telecommunications and
Mission Operations Directorate (TMOD) will initiate the process for
allocating its world-wide DSN resources to support tracking,
commanding and telemetry reception for NEAP in 2002, principally
during the spacecraft's cruise to Nereus and during operations in
close proximity to the approximately 1-kilometer-(0.6-mile-) diameter

``To meet our NEAP launch readiness date of early 2001 and Nereus
rendezvous date of mid-2002, we have to get the DSN tracking
pass-allocation process started now,'' said Rex Ridenoure, SpaceDev's
Chief Mission Architect. ``The 34-meter DSN dishes we'll need for
communicating with NEAP also supports other numerous deep-space
missions, so now is the time to make our needs known to JPL and get
into the queue,'' he added.

The SpaceDev contract marks a first for NASA and JPL; never before in
the 40-year history of the DSN has a commercial company requested
tracking time and analysis support for a deep-space mission. ``The
Jet Propulsion Laboratory has accepted a request by SpaceDev to study
the feasibility of tracking NEAP using NASA's Deep Space Network,''
said Gael Squibb, JPL's Assistant Laboratory Director for TMOD.
``This is the first time a commercial enterprise has attempted to
build and fly a scientific mission into deep space, and we're looking
forward to working with SpaceDev on its NEAP mission,'' he added.

In coming months and through fall next year, JPL will also assess
NEAP's telecommunication system design for compatibility with the DSN
and will assist SpaceDev in defining and pricing selected
JPL-supplied mission-operations services, software tools and other
engineering support required for the mission. Demands placed by the
NEAP mission on JPL's Deep Space Mission System -- comprising the
world-wide DSN and JPL-based Advanced Multi-Mission Operations System
-- are expected to be quite modest. The JPL work follows a
well-defined process applied to all missions using the DSN.

SpaceDev is providing the funds for this work to JPL via JPL's
Technology Affiliates Program which covers the first of several
phases of expected JPL support activity. SpaceDev is also in the
process of negotiating with NASA on the possibility of providing
radio science data in exchange for certain DSN services, however the
parties have not entered into any formal agreement at this time.

SpaceDev, the world's first commercial space exploration and
development company, intends to launch the first privately financed
spacecraft to visit and land on another planetary body. SpaceDev is
selling rides for scientific instruments to governments and companies
to transport their instruments and experiments through deep space to
a near Earth asteroid. SpaceDev intends to sell the data acquired by
its instruments as commercial products. Colorado-based SpaceDev has
offices in San Diego, CA and Washington, DC.

SpaceDev also announced that its consolidated Revenue for the 1998
year will be lower than expected due to the timing of SpaceDev's
acquisition of its second wholly owned subsidiary and other delays
associated with NASA's funding cycle.

Pasadena-based JPL is a division of the California Institute of
Technology. It defines and conducts most deep-space missions for NASA
and also manages and operates the Deep Space Network (DSN).

The foregoing press release includes numerous forward-looking
statements concerning the company's business and future prospects and
other similar statements that do not concern matters of historical
fact. The federal securities laws provide a limited ``safe harbor''
for certain forward-looking statements. Forward-looking statements in
this press release relating to product development, business
prospects and development of a commercial market for technological
advances are based on the company's current expectations. The
company's current expectations are subject to all of the
uncertainties and risks customarily associated with new business
ventures including, but not limited to market conditions, successful
product development and acceptance, competition and overall economic
conditions, as well as the risk of adverse regulatory actions. The
company's actual results may differ materially from current
expectations. Readers are cautioned not to put undue reliance on
forward-looking statements. The company disclaims any intent or
obligation to update publicly these forward-looking statements,
whether as a result of new information, future events or for any other

NOTE: News releases and other information on SpaceDev can be accessed
at .



From Correspondent Garrick Utley

NEW YORK (CNN) -- The wonder of a science-fiction view of a space
station docking was depicted in the 1968 film "2001: A Space Odyssey."

Last week, we saw the reality of a space docking on the current mission
to build the International Space Station.

How well do fiction and reality meet in space?

Look at the vision of artist Chesley Bonestell in 1952, long before the
first man went into space. He depicted the shuttle with wings,
astronauts on spacewalks ... and an orbiting space station.

Vincent Di Fate, a leading illustrator of space, understands the
purpose of science fiction in words and images. "Whether they were
accurate or not, and many of them proved not to be accurate, they
created a credible vision for a time when people needed some means to
accept ideas about the future and the possibilities of space
development," Di Fate says.

Space is fascinating. It is also infinite, and that can make it
difficult for mere mortals to grasp. Not only those of us who are only
occasionally interested in space exploration but also those who devote
their lives to it.

They too need inspiration, that jolt of a new idea. Jules Verne
provided the first jolt in 1865, describing a rocket fired from
a cannon that goes to the moon.

The pioneers of rockets, including Robert Goddard, read Verne, H.G.
Wells, and others as they developed rockets that would eventually take
man to the moon.

More than a decade before the launch of the first satellite, science
fiction writer Arthur Clarke predicted how a few communications
satellites could link the entire planet.

At NASA, researcher John Mankins thinks like a science-fiction writer,
imagining new programs and concepts. His plan for a magnetic levitation
launch system, he says, is remarkably similar to one that appeared in
the 1951 movie "When Worlds Collide." "A lot of what we do ... is
influenced by what we see in science fiction,"
Mankins says.

And why not? Science, like fiction, begins with imagination. And in
space, as in fiction, there are no limits to where imagination can take

Copyright 1998, CNN


From Andrew Yee < >

News Services
University of Arizona


William V. Boynton, 520-621-6941
Samuel 'Hop' Bailey, 520-621-8637
Jazbir Bhangoo / Irina Mikheeva, 520-626-2712 / 520-621-2883

December 14, 1998

UA scientist is among the NEAR mission scientists about to get historic
long, close-up look at an asteroid

On Sunday, Dec. 20, the NEAR (Near Earth Asteroid Rendezvous)
spacecraft will initiate a series of rocket engine firings that
accelerate it toward a rendezvous with a faster-moving asteroid, 433
Eros. NEAR will reach Eros next month to begin the first close-up and
comprehensive study of an asteroid in space history.

"This is the first time ever a spacecraft will orbit an asteroid," said
Professor William V. Boynton of the Lunar and Planetary Laboratory at
The University of Arizona in Tucson. "There have been flybys and
snapshots, but not much in the way of quantitative scientific data."

Boynton is on one of six science teams that will study 433 Eros on the
year-long NEAR mission that begins on Jan. 10 and is scheduled to end
Feb. 6, 2000. The asteroid, which measures 24 miles in length and 10
miles in diameter (40 kilometers x 17 kilometers) was the first
near-Earth asteroid (those whose orbits come close to or cross the
orbit of Earth) spotted by astronomers.

Boynton is a scientist on the X-Ray/Gamma Ray Spectrometer, or XGRS,
experiment. It is the primary experiment for determining the elemental
composition of the surface and layers just beneath the surface. The
instrument will begin taking data next spring while NEAR is orbiting
above the asteroid's surface, coming as close as 9 miles (15

The XGRS was designed and built by the Johns Hopkins University Applied
Physics Laboratory in Laurel, Md., which also built the NEAR spacecraft
and manages the NEAR mission. Boynton and his group at the UA Lunar and
Planetary Laboratory will process XGRS data and manage the data base
for all XGRS data, as well as work on the scientific interpretation of
results. Boynton's UA colleagues on the NEAR mission include Samuel
(Hop) Bailey, project manager, and software specialists Jazbir (Jesse)
Bhangoo and Irina Mikheeva.

XGRS results are basic to solving such mysteries as the source of
meteorites and their relationship to asteroids.

"Eros is a very important asteroid because it is a member of a class
called 'S' asteroids, which appear to be similar to a rare type of
meteorite on Earth called 'stony-irons,'which have 50 percent metal and
50 percent silicate. Though the S-asteroids are very common in space,
they do not seem to match many of the meteorites that fall to Earth,"
Boynton said.

"The other half of this problem is that the most common meteorites
found on Earth, called ordinary chondrites, are very common on Earth
but appear to be rare in space. Some people think that ordinary
chondrites might come from S-asteroids and that S-asteroids actually
might have a lower metal content than ground-based astronomical data
suggest. This mission should really answer this question."

It's possible that the composition of Eros might turn out to be
different from any of the known meteorites, Boynton added. It's also
possible that Eros, a highly irregularly shaped object, is "possibly a
chip off some larger, pre-existing asteroid that was smashed up,"
richer in silicates on one side and richer in metal on another, Boynton
said. "This might allow us to learn something about the processes that
go on in asteroids."

NEAR is the first in NASA's Discovery Program for "faster, better,
cheaper" planetary missions. It was launched Feb. 17, 1996, from Cape
Canaveral, Fl., 9 months sooner than its 36-month schedule and $41.6
million under the $150 million budget. The other NEAR instruments
include a multispectral imager, a laser rangefinder, a near-infrared
spectrometer, a magnetometer and a radio science package.

NEAR is the first spacecraft powered by solar cells to operate beyond
the orbit of Mars. It returned 500 images of asteroid 253 Mathilde when
it flew within 750 miles of that object on June 27, 1997. Last January
NEAR returned to the Earth's vicinity for a "slingshot" gravity assist
toward Eros' orbital plane.

Next month, Boynton will travel from Cape Canaveral, site of the Jan. 3
launch of the Mars Polar Lander, to the Johns Hopkins lab to witness
NEAR's Jan. 10 arrival at Eros. On the Mars mission, Boynton heads an
experiment in the Mars Volatiles and Climate Surveyor integrated
payload. That experiment, TEGA, or the Thermal and Evolved Gas
Analyzer, is to discover how much water and carbon dioxide is in soil
at the south pole landing site on Mars, and what minerals make up that

(EDITORS NOTE: Press packets, an 11-minute broadcast-quality video,
"NEAR - The Journey Continues" (Feb 1998) and a 10-minute
broadcast-quality video, "NEAR Spacecraft's Encounter with Asteroid 433
Eros" (Nov 1998) is available to news media from Helen Worth, media
contact at the Johns Hopkins University Applied Physics Laboratory,
phone 240-228-5113. Lori Stiles in UA News Services, phone
520-621-1877, has copies of the press packet and Beta-format videos.
NASA will televise a news conference on the NEAR mission from NASA
headquarters, Washington D.C., at 1 p.m. EST Wednesday, Dec. 16.
NASA-TV will also carry live briefings on NEAR held at the Johns
Hopkins University at noon EST, Sunday, Jan. 10, 1999, and at 1 p.m.
EST Thursday, Jan. 14, 1999..)

[NOTE: A 25-page press kit issued by the Applied Physics Laboratory,
Johns Hopkins University, is available as a PDF file (1.3 MB) at]

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From Alasdair Beal <>

Dear Benny,

For various reasons (most of them non-scientific) 1999 is likely to
see a great deal of speculation about the danger from Near Earth
Objects. It is an uncomfortable fact that when it comes to the
possible dangers from this source in 1999, potentially the greatest
risk we face comes from a man-made NEO: the Cassini space probe which
is planned to pass close to the Earth next summer. If its radio
communications or its guidance rockets fail, it could re-enter the
Earth's atmosphere - with 30kg of plutonium on board. If this were to
happen, the consequences could be pretty nasty.

I know that discussing this may be uncomfortable for some of the
people involved but it is a timely reminder that it is not only
natural impacts which can cause a threat to humanity - man-made
objects can be every bit as big a problem.

Alasdair Beal

CCCMENU CCC for 1998