CCNet DIGEST, 19 July 1999


    "I hope that [these hearings] will help create increasing awareness
    of this issue within the international astronomical community.
    Indeed, the problem of a potential large asteroid strike is not
    just a U.S.problem; it is a worldwide problem. I believe that all
    industrialized nations of the Earth should cooperate on a program
    to discover and track the large asteroids that can pose a serious
    threat to our home planet. [Today] the emerging scientific
    consensus seems to be that it is no longer a question "If the Earth
    will again be hit with a large asteroid?"; the question is now
    "When will the Earth again be hit by a large asteroid?" (George E.
    Brown [1920-1999], speaking at the US Congressional Hearings,
    24 March 1993)

    Gerhard Hahn <>

    Ron Baalke <>

(3) A DISCOURSE ON 1997 XF11
    The Journal of the British Interplanetary Society

    Luigi Foschini <>

    Andrew Yee <>

    John McCue <>


(8) GEORGE E. BROWN (1920 - 1999)
    David Morrison <>



From Gerhard Hahn <>

Dear Benny,

The following might be of interest for the readers of the CCNet.

With best wishes



After the obviously successful tests (as examplified with 1999 AN10) of
our plate archive search for precovery images of NEOs we would like to
announce the set up of a webpage for DANEOPS, the DLR-Archenhold
Near-Earth Objects Precovery Survey

Project, were a short description of the procedure and methods used can
be found. A continuously  updated progress report is intended, together
with some images of nice trails.

We plan to locate precovery images of newly discoverd NEOs, as soon as
reasonably reliable orbits become available. Currently we are using the
Digitized Sky Survey (DSS 1 & 2), but it is our intention to include
other plate archives in the future.


Gerhard Hahn, DLR
Andreas Doppler, Archenhold Observatory
Arno Gnaedig, Archenhold Observatory


From Ron Baalke <>

Finding 1999 AN10 Pre-discovery Observations with SkyMorph

'SkyMorph' is a currently available internet tool that can be used to
automatically identify transient objects in optical image catalogs
generated by the Near Earth Asteroid Tracking (NEAT) program as well as
those in the DSS and DSS2 Digitized Sky Surveys.

Developed jointly by teams at JPL (Steve Pravdo, Principal
Investigator)and Goddard Spaceflight Center (Thomas McGlynn),
the system can be used to search for and display "pre-discovery"
observations. That is, incidental recordings of asteroids that were not
noticed at the time, but may be of objects later "discovered."  Such
positional measurements extend the data arc and can greatly reduce
statistical uncertainties in the orbit solution.  A search routine
within SkyMorph takes advantage of the up-to-date database of
near-Earth objects maintained by the NASA Near-Earth Object Office at
JPL and the JPL Horizons on-line ephemeris systems developed by Jon
The 1999 AN10 case provided an example of the possible use of 
SkyMorph, also high-lighting some incidental bad luck in positioning. 
Initially discovered by the LINEAR observing program in New Mexico, an
initial search by SkyMorph found no pre-discovery images until the 1955
trailed image was separately identified by German amateur astronomers,
Gnadig and Doppler.

Commenting on the prototype system's functioning in the 1999 AN10 case,
Pravdo noted that initially SkyMorph was looking at the center of the
plate and a circle of radius 3 degrees around that center for the
position of the object. This left out the square corners of the plate
where the image of 1999 AN10 was located.  This problem was quickly
fixed and now the entire plate is included in the automatic search.

Interested users may access SkyMorph at:

Once the object 1999 AN10 is specified and a search requested for the
Palomar Sky Survey, users can call up the 1955 pre-discovery image via
this web interface.  This search engine will become increasing useful
as additional Near-Earth Objects are discovered.

Jon Giorgini and Don Yeomans
NASA Near-Earth Object Office (NASA/JPL)

(3) A DISCOURSE ON 1997 XF11

From The Journal of the British Interplanetary Society

Brian Marsden's ground-breaking research on asteroid 1997 XF11 and his
method of searching for "resonant return" impact possibilities,
first developed and presented on the CCNet (long before the
discovery of asteroids 1999 AN10 and 1998 OX4), is now accessible on
the website of the Journal of the British Interplanetary Society at:
Once on the page, just click on Marsden's name.

Benny J Peiser


From Luigi Foschini <>

The expedition has left Krasnoyarsk on July 16 at 10:00 local time (see
photo attached). They have flown over an auriferous land and some zones
with fires, travelling on board of helicopter Mi-26 at 250 km/h. The
helicopter landed on a small village Culymba for refuelling: in this
village there is a lot of oil, but they have not money to extract it.

The expedition arrived at the Ceko lake while it was raining. The
helicopter tossed a little, but it landed well. The members of the
expedition were tired and, after a swim in the river Stony Tunguska,
they go to bed.

Yesterday they mounted the base camp on the Ceko lake. It is a hot
summer there: 36 degrees Celsius on July 18. There are less mosquitos
than during the previous expedition (1991), but many more horse-flies.
In any case, there is a lot of insects!

Today, 18 July, the katamaran "Kulik" made the first run on the lake
and it is all right. Marine geologists recorded the first profile of
the bottom of the Ceko lake: at a first sight, it looks very
interesting. There are several features that must be investigated in

More informations and photos are available at the Tunguska Home Page,
that will be continuously updated also during the expedition, with
reports from the field:

For the Tunguska99 Press Office:
Luigi Foschini (


From Andrew Yee <>

News Service
Cornell University

Contact: David Brand
Office: (607) 255-3651

FOR RELEASE: July 14, 1999

Potential hazard of Earth-asteroid collisions to be discussed at
international space conference at Cornell July 26

ITHACA, N.Y. -- The possibility of the Earth being struck by comets or
asteroids is being given more and more attention by researchers,
according to Paul Chodas of NASA's Jet Propulsion Laboratory (JPL).
Chodas will discuss this potential threat to the planet when he
moderates one of the daily press conferences that will provide
important new insights into the latest space research at the seventh
International Asteroids, Comets and Meteors Conference at Cornell
University July 26-July 30.

A schedule of the press conferences is available on the ACM media web
site The site
provides the latest press releases on research to be reported at the
conference, as well as a list of researchers from around the world who
will be attending the meeting.

Chodas's press conference (Tuesday, July 27, 10 a.m., 305 Ives Hall)
will cover asteroids and meteors collectively known as near-Earth
objects (NEO's). Other participants will include David Rabinowitz of
JPL, Richard Binzel of the Massachusetts Institute of Technology, Alan
Harris of the Jet Propulsion Laboratory (JPL) and Andrea Milani of the
University of Pisa, Italy.

In recent movies, asteroids and comets are shown threatening to collide
with the Earth, only to be destroyed at the last minute by astronaut
heroics. But Chodas believes that the hazards of collisions with comets
or asteroids are more than a topic for fiction. Chodas and Milani will
discuss their independent efforts to predict close-Earth approaches and
impact probabilities further into the future than has been previously

It has been estimated that only 15 to 20 percent of NEO's larger than
one kilometer have been detected to date. Several telescopic discovery
programs are actively searching for these large NEO's, and the
discovery rate is increasing. However, Chodas believes, it may be at
least 10 years before 90 percent of the total population is revealed.

A new analysis by Rabinowitz shows that there may be only half as many
large hazardous objects as previously estimated. Harris will present
new evidence to refute a controversial theory that the Earth is
continually bombarded by a population of house-sized comets.

What is the nature of these seemingly "loose cannons" that might be
posing a threat? A new view has evolved, suggesting that many large
asteroids are "rubble-piles," according to William Bottke, a research
associate in Cornell's Department of Astronomy, who will moderate the
press session (Friday, July 30, 10 a.m., Princeton-Yale Room, Statler
Hotel) on asteroid moons and spins. Other participants will include
Petr Pravec of Ondrejov Astronomy Institute, Czech Republic, and JPL's

Until recently, most planetary scientists considered asteroids to be
little more than beat-up rocks in space, with solid interiors and
lunar-like surfaces. It is difficult to prove or disprove this theory
since remote sensing techniques can only probe the top layers of an
asteroid's surface, says Bottke. But data taken from spacecraft
fly-bys, ground-based observations and computer modeling indicate that
large asteroids are no more than piles of rubble held together not by
physical strength but by the gravitational attraction of the pieces of

Although Pravec's research, based on an extensive study of near-Earth
asteroid (NEA) rotation rates, is consistent with the "rubble-pile"
scenario, his new results suggest that some small asteroids are solid.
At the conference he will discuss two asteroids, 1996 KY26 and 1995 HM,
both smaller than 100 meters, that are spinning so fast that they have
to be solid objects -- weakly bound rubble piles fly apart if spun too
fast. These two bodies are small enough that they provide the "missing
link" to the rubble-pile theory that astronomers have been looking for
-- filling the gap between between kilometer-size asteroids that cannot
spin overly fast and fast-spinning meter-sized meteorites that are known
to be solid.

Computer modeling suggests the transition size for solid objects to
turn into rubble piles is roughly a few hundred meters in diameter.
More support for the rubble-pile theory also comes from Pravec: He will
report that many NEO's have small moons. These moons are most likely to
be a by-product of close encounters between rubble-pile asteroids and
planets. When a rubble-pile asteroid passes too close to a planet like
Earth, tidal forces can pull it apart, leaving some of the fragments to
orbit one another.

Related World Wide Web sites: The following sites provide additional
information on this news release. Some might not be part of the Cornell
University community, and Cornell has no control over their content or

* ACM "virtual pressroom"

* ACM conference site


From John McCue <>

I am grateful to Michael Paine (CCNet 12 April, 1999) for drawing
attention to the Scientific American article (March, 1999) by Mark A.
Bullock and David H. Grinspoon describing evidence of "a
geological event of global proportions (that) wiped out all the old
craters some 800 million years ago". The colliding object responsible
is quoted to be "hundreds of kilometres in diameter" It is not beyond
the bounds of possibility for a collision of this magnitude to have had
an effect on the rotation of Venus.

Calculations performed by Dr. John Dormand and myself from the
University of Teesside, UK, (Journal of the British Astron. Assn., vol
98, no.1) showed that an object 2000 km in diameter in collision with
Venus could have halted the latter's rotation, given a Venusian
prograde spin period of about 30 hours at the time. Such a massive
impact would obviously have planet-splitting potential but if the
collision happened in the very early history of the solar system there
would be time for the Venusian fragments to reform in Miranda fashion.
However, Bullock and Grinspoon's object is only, say, 500 km. in
diameter and so would only be able to halt, or even reverse, Venus, and
explain its current retrograde rotation, if the planet was rotating
much more slowly; a rough pro-rata calculation giving a figure of about
80 terrestrial days.

If this collision occurred only 800 million years ago, what does this
imply about Venus' primitive rotation? Evolutionary sequences of the
rotation of Venus under the action of atmospheric and body tidal
torques from the Sun (published again by Dr. Dormand and myself: Earth,
Moon and Planets, 63, 209-225, 1993) suggest that Venus, in the
beginning would have been spinning in a prograde sense in a time of
about 50 days, giving it time to slow down to about 80 days. This is a
very slow primitive rotation compared with the other terrestrial
planets. Could Venus have been unlucky enough to have been hit twice!!

Dr. John McCue, FRAS
40, Bradbury Rd.
TS20 1LE



Chicken Little was right: The sky is falling

By Michael Paine for

On a clear, dark night away from the city lights you might be lucky
enough to glimpse a grain of sand colliding with the Earth at 15 miles
per second. To our primitive ancestors, these "shooting stars" must
have been the most interesting objects in the night sky - brief flashes
of light to break the monotony of the fixed stars.

Of more practical concern to the ancients, however, was the passing of
the seasons. The science of astronomy became a respected means of
timing the planting of crops and hunting migrating herds. The elite
practitioners of this science probably dismissed shooting stars as
unimportant and this attitude persisted until just a few decades ago.

From time to time, the peace and tranquillity was broken by violent
events - collisions with large chunks of rocks from space. Most of
these collisions were destructive. Some may have pushed the human
species close to extinction, but sometimes they brought a blessing,
such as mysterious metals that could be pounded into weapons and tools.

Violent cosmic collisions are inevitable events on a time scale of
thousands of years, but not on a time scale of a human lifetime.
Without firsthand accounts of impacts there was no reason to suspect
that a hazard existed. This changed in the 1960s. Robotic spacecraft
sent back pictures of thousands of impact craters on most of the
airless moons of our solar system and on the planets Mercury, Venus and
Mars, where craters are not obscured by plant growth or oceans.
Hundreds of impact craters have since been discovered on the surface
of the Earth. The scientific study of asteroids and comets became

Our neighbours in space

The Earth and the other planets orbit the Sun in near-circular paths
and stay well away from one another in their respective "running
lanes." Many asteroids and comets also orbit the Sun in near circular
orbits well away from the Earth. However, some of these objects are
occasionally sent into elongated orbits and they venture into our region
of the solar system. If their running lanes cross Earth's they become a

Comet Halley circles the Sun every 76years and spends most of its time
out beyond the orbit of Saturn. But every year the Earth crosses
Halley's running lane and collides with tiny bits of the comet. The
results are the Eta Aquarid and Orionid meteor showers. If Halley's
orbit stays the same then eventually, perhaps after hundreds of
millions of years, the Earth and Comet Halley will collide at more than
100,000 mph. A "dirty snowball" ten miles across can make quite a
mess at this speed - just ask the dinosaurs.

Comets, however, are not the greatest hazard to the Earth. We share our
running lane around the Sun with millions of chunks of rock. Most of
these asteroids are less than 50 yards across and, if they collide with
the Earth, will burn up in the upper atmosphere.

Asteroids between 50 and 200 yards across will typically explode
several milesup in an "airburst" much like an H-bomb. One such event
devastated 800 square miles of Siberian forest in 1908. Larger
asteroids will reach the Earth's surface and, if they hit land, will
form an impact crater. Asteroids and comets with orbits that come close
to the Earth are known as Near Earth Objects (rather a dull name!).

The odds of an impact

Based on estimates of the number of objects out there, astronomers
expect an asteroid 1 kilometer (1000 yards) in diameter to collide with
the Earth about once every 100,000 years, on average. Such an impact
is thought to be at the threshold of global catastrophe. 100 million
people could die, mainly from starvation due to global crop failures. It
is likely that the fragile global economy would collapse. Impacts by
small asteroids occur more frequently but do much less damage. An
asteroid 50 yards in diameter could easily devastate a city. With
asteroids more than 200 yards in diameter there is an additional risk
to coastal cities from tsunami (tidal waves) caused by ocean impacts.

Looking out for NEOs

The chances of an impact by a large asteroid or comet are very small,
but the consequences for our civilisation are very grave. After
watching the movie "Deep Impact" or "Armageddon" you might have come
away thinking that dozens of telescopes and hundreds of scientists are
busy searching for "a big one with our name on it." But only a handful
of professional searches are underway, and none of these cover the
skies in the Southern Hemisphere.

If a large asteroid is on a collision course with the Earth then the
[current] odds are 7 to 1 against that astronomers will detect it
beforehand. In 1992 the "Spaceguard Survey" was proposed as an
international search for large asteroids. The worldwide, ten-year
budget was less than Americans spent watching "Armageddon," but
Spaceguard is notyet underway. We seem to be facing the dilemma of the
ancient skywatchers -- those in power dismiss the issue as unimportant.

Saving the future

If an object is discovered to be on a collision course, we should have
several decades warning (provided that the full Spaceguard Survey gets
underway soon). We have the capability to send spacecraft to rendezvous
with an asteroid or comet and nudge it into a safe orbit. Current
technology is certainly closer to the task than that available to NASA
when President Kennedy announced the Moon landing goal in 1961.

On this theme of historic events another U.S. politician, Congressman
George Brown Jr, had this to say at the opening of a 1993 Congressional
hearing into the asteroid threat: "If some day in the future we
discover well in advance that an asteroid that is big enough to cause a
mass extinction is going to hit the Earth, and then we alter thecourse
of that asteroid so that it does not hit us, it will be one of the most
important accomplishments in all of human history."

c1999 Explorezone


Sadly I have just learnt that Congressman Brown died last week.

Since writing the article I have read "Mining the Sky" by John Lewis.
It will provide very useful as a reference for further Explorezone
articles. It shows, in practical ways, how space colonies such as those
envisioned by Asimov and Clark can become a reality through mining
resource rich astoroids (how do you chop up a 1 kilometre chunk of
stainless steel?). He even shows that a space elevator should be
feasible for reaching the surface of Mars.

Michael Paine

(8) GEORGE E. BROWN (1920 - 1999)

From David Morrison <>

NEO News (7/17/99) George Brown

Dear friends and students of NEOs:

It is with sadness that I report the death of George E. Brown of the U.S.
House of Representatives, the strongest supporter of Spaceguard within the
Congress. Representative Brown died in Washington on July 15 of
complications following heart surgery.

George Brown was first elected to the Congress in 1962. For many years
he chaired the Committee on Science and Technology in the House, and at
the time of his death he was the ranking Democrat on the Committee. He
held a degree in physics from the University of California at Los
Angeles, and he often described himself as a scientist (one of very few
in the Congress).

In addition to his broad support over many years of scientific research
and space exploration, George Brown took a very real personal interest
in the NEO impact hazard. Under his leadership, the Congress first
asked NASA to study this issue in 1991, leading to the Spaceguard
Report of 1992. After the 1994 impact of Comet Shoemaker-Levy 9 into
Jupiter, his Committee challenged NASA to accelerarate plans for
Spaceguard and to develop a program plan to find 90% of NEOs larger
than 1 km within a decade. We will all miss his support and friendship.

Following are the remarks made by Mr. Brown at the 1993 Congressional
hearings on the NEO impact hazard, as well as the key language from his
Committee that defined the program that we now call Spaceguard.

David Morrison


Congressional Hearings, March 24 1993

Introductory statement by Mr. Brown:

For Members [of Congress] who are hearing about this subject [the
impact threat] for the first time, I know that the tendency is to be
somewhat skeptical. And, one could certainly ask why this subject
should be of interest to the Congress? None of our friends, relatives,
or constituents have ever been killed by an asteroid. It has probably
been hundreds of thousands of years since the last time a really big
asteroid hit the Earth.

I think it is the duty of the Congress to provide periodic oversight of
all matters that relate to the health and welfare of the citizens of
this country. This is particularly true for issues where Congressional
oversight might spur the Administration forward to taking some
appropriate action. I believe that the topic of Earth-threatening
asteroids is just such an issue.

I hope that [these hearings] will help create increasing awareness of
this issue within the international astronomical community. Indeed, the
problem of a potential large asteroid strike is not just a U.S.problem;
it is a worldwide problem. I believe that all industrialized nations of
the Earth should cooperate on a program to discover and track the large
asteroids that can pose a serious threat to our home planet.

[Today] the emerging scientific consensus seems to be that it is no
longer a question "If the Earth will again be hit with a large
asteroid?"; the question is now "When will the Earth again be hit by a
large asteroid?"

If we invest the time and resources to find these things, we can remove
the guesswork. We will know ahead of time when we are at risk, so that
we can take appropriate actions to deflect the threatening asteroids
years in advance.

I believe that the initiatives we are now getting underway to deal with
this issue in a thorough and scientific manner have the potential for
being one of the most important things that mankind has ever done.

If some day in the future we discover well in advance that an asteroid
that is big enough to cause a mass extinction is going to hit the
Earth, and then we alter the course of that asteroid so that it does
not hit us, it will be one of the most important accomplishments in all
of human history.


1991 statement from the House Committee on Science and Technology as
enacted in the NASA Authorization Bill:

The chances of the Earth being struck by a large asteroid are extremely
small, but since the consequences of such a collision are extremely
large, the Committee believes it is only prudent to assess the nature
of the threat and prepare to deal with it. We have the technology to
detect such asteroids and to prevent their collision with the Earth.

The Committee therefore directs that NASA undertake two workshop
studies. The first would define a program for dramatically increasing
the detection rate of Earth-orbit-crossing asteroids; this study would
address the costs, schedule, technology, and equipment required for
precise definition of the orbits of such bodies. The second study would
define systems and technologies to alter the orbits of such asteroids
or to destroy them if they should pose a danger to life on Earth. The
Committee recommends international participation in these studies and
suggests that they be conducted within a year of the passage of this


1994 statement from the House Committee on Science and Technology
passed as an amendment to the House version of the NASA Authorization

Catalogue of Earth-Threatening Comets and Asteroids

(a) Requirement -- To the extent practicable, the National Aeronautics
and Space Administration, in coordination with the Department of
Defense and the space agencies of other countries, shall identify and
catalogue within 10 years the orbital characteristics of all comets and
asteroids that are greater than 1 km in diameter and are in an orbit
around the sun that crosses the orbit of the Earth.

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