CCNet, 003/2000 - 7 January 2000


     "Until Jan. 4th, 2000, the two big NEO movies of 1998 had made
     together 903 million dollars in worldwide theatrical box office
     sales alone (not even counting video rentals and TV rights) - an
     amount to ponder... Armageddon is now at # 11 of the all-time
     charts, with $ 554.4m, while Deep Impact is at # 50 with $ 348.6m,
     according to the list at
     Earlier impact movies like "Meteor" are not mentioned there, so
     the overall sum should be close to one billion dollars."
         -- Daniel Fischer, University of Bonn

    THE GUARDIAN, 6 January 2000

    Daniel Fischer <>

    Jon Richfield <>

    W. Benz*) & E. Asphaug, UNIVERSITY OF BERN

    K.R. Housen & K.A. Holsapple, BOEING CO


    D.D. Durda*) & G.J. Flynn, SW RES INST

    L.L. Kiss etal., JATE UNIVERSITY

    M.J. Lopez Gonzalez & E. Rodriguez, CSIC,INST ASTROFIS ANDALUCIA


From THE GUARDIAN, 6 January 2000

Why call an asteroid 1997 XF11 when you could call it Zappafrank?
Duncan Steel explains

Thursday January 06 2000
The Guardian (London/Manchester)

There is indeed a Mr Spock out there in space. Asteroid 2309 Mr. Spock.
It was called after a tabby cat. The feline itself was named for the
Vulcan in Star Trek, on the grounds that he (the cat) was also
"imperturbable, logical, intelligent and had pointed ears". 

Alongside such names as 1815 Beethoven, 2001 Einstein and 2985
Shakespeare a mere cat seems an unlikely addition. Since asteroid Spock
got its name a couple of decades back, the International Astronomical
Union - the IAU, the world-wide body which superintends such matters -
has tightened up its rules, specifically discouraging the application
of pets' names.  

A committee of about a dozen astronomers vet all suggested names. If
the discoverer declines to put forward an acceptable label then the
naming rights may be taken away. 

While some names are not allowed - like terms in bad taste, or people
best-known for military or political exploits unless they've been dead
for at least a century (Napoleon is all right, but not Margaret
Thatcher) - the committee is not humourless. 

Take 3142 Kilopi. Who was that? Well, think of the mathematical
constant p which relates the circumference of a circle to its diameter,
and multiply by a thousand (a kilo).

I was responsible for one little piece of mischief. In Bill Forsyth's
film Local Hero one character, Felix Happer, was desperate to have a
comet named for him. He'll just have to make do with asteroid 7345

After an asteroid is discovered (the IAU insists they should be called
minor planets) it will generally take a few years before its orbit
about the sun is well-enough determined to deserve adding to the
definitive list of asteroids. Then the discoverer can put forward a

Not their own name, though; any comet you find will get your surname
with no argument. But for asteroids the done thing is to propose some
other name. For one of my discoveries I suggested 9767 Midsomer Norton,
the Somerset town where I was born. 

The chairman of the asteroid naming committee is Brian Marsden, an
Englishman who directs the Minor Planet Center at Harvard university.
He is assisted by another Englishman, Gareth Williams. It was somewhat
incongruous when three pommies joined together to name 2472 Bradman for
the great Australian cricketer. It's only fair - think of  the South
African players Kepler Wessels and Herschelle Gibbs, each of whom have
names derived from great astronomers. 

And here's a little puzzle for the cricket buffs. One other asteroid is
named after a prominent cricketer. Like Sir Donald Bradman, this man is
also knighted, and played for South Australia. Who is he? (No, not Sir
Richard Hadlee, although you would be correct to think of Trent
Bridge.)  So much for the names, what about the numbers? The sequence
of minor planet names and numbers begins with 1 Ceres, discovered on
January 1, 1801. Ceres is a behemoth, at about 600 miles across the
largest of the asteroids. Mind you, that is still too small to see
clearly in any telescope except Hubble, because it's so far away. The
word "asteroid" means "star-like", because they look like stars through
a telescope: mere pinpricks of light.

In the following decades dozens of asteroids were discovered, and given
prosaic names derived from ancient mythologies. The Greek goddess of
victory, Nike, had her name on an asteroid long before running shoes and

All was not altruistic, however. British astronomers were still smarting
over the naming of the planet Uranus, discovered by Sir William
Herschel in 1781. To flatter the king they had wanted to call it
George's Star, but on the continent this name was rejected.
Consequently, no sooner had the twelfth asteroid been discovered than
it was named Victoria to less than universal acclaim. 

Arguments over celestial names continue. A couple of years back we
could see the number 10,000 approaching, and the suggestion was made
that Pluto should be allotted to that number. Although this provoked a
furore in the media - some people felt that Pluto was being downgraded
from a major to a minor planet - the logic was plain. Pluto had been
spotted in 1930, but no other objects were found beyond Neptune until,
in 1992, another lump was found in these distant reaches of the solar

Since then a couple of hundred other rocky and icy bodies ranging up to
300 miles in size have been identified slowly circuiting in this frigid
region. Given that Pluto is only about 1,400 miles across, one could
question why it should be classed as a major planet, and the others as
minor planets. Pluto is rather smaller than Mars or Mercury, or even
our Moon. Where does one draw the line?  

The solution seemed to be to add it to the list of minor planets in a
special place, as number 10,000. But this provoked such public outrage
that astronomers had to backtrack. In the end asteroid 10,000 was
called Myriostos (myriad actually means numbering in the tens of

But what about 1997 XF11 or 1999 AN10? These are "preliminary
designations". The first four numbers show the year of discovery.  

The first letter shows the half-month the object was found. Letter A
implies January 1-15 inclusive. The order is alphabetical, the letter I
not being used, to avoid confusion with the number one. This means that
December 16-31 has the letter Y. Why not also skip the letter O as it may
be confused with zero? Because then Z would be used which could perhaps
be mistaken for a number two.  

The second letter indicates the ordering within the half-month. The
first asteroid of the year is 1999 AA, the second is 1999 AB, and so on
except that I again is not used, producing 25 possibilities.  

When asteroid discoveries were few that was fine, but once the number
found per fortnight exceeded 25 there was a problem. The fix was to
employ numbers after the second letter (and to be strictly correct
these are supposed to be subscripted).  

This means that 1997 XF11 was the 281st asteroid spotted in the first
half of December 1997. It became famous because for a short while we
thought it might hit the Earth in 2028. We now are sure it won't. And
soon 1997 XF11 will be given a permanent number and name. Perhaps
Nearmiss would be appropriate. 

There's a real Starr out there, and a Lennon, McCartney and Harrison
too, not to mention 3834 Zappafrank and 4305 Clapton: for Eric, not the
London suburb. There is no London in the sky, whereas Paris, Roma and
Moskva have been up there for aeons. Check them all out on

Some readers may say they've bought star names for friends and family,
so what's all the fuss about asteroid names? Sorry, trying to slap your
name on a star has no greater effect than saying you've re-named the
street or village for yourself. The post office and map makers will pay
no attention.  

Neither does the IAU recognise names for stars. Save your money. Anyone
can print up a gilt certificate saying a star is named for you. It
simply has no effect.

And the answer to the cricket question? 6581 Sobers. Even Adelaide
residents tend to forget Sir Garfield played for their state for a

Duncan Steel is a space researcher at the university of Salford, and
minor planet 4713 Steel

Copyright Guardian Media Group plc.


From Daniel Fischer <>

Dear Benny,

until Jan. 4th, 2000, the two big NEO movies of 1998 had made together
903 million dollars in worldwide theatrical box office sales alone (not
even counting video rentals and TV rights) - an amount to ponder...

Armageddon is now at # 11 of the all-time charts, with $ 554.4m, while
Deep Impact is at # 50 with $ 348.6m, according to the list at Earlier impact movies like
"Meteor" are not mentioned there, so the overall sum should be close
to one billion dollars.

Daniel Fischer


From Jon Richfield <>


A Ms is not nearly as good as a Miss, but may be better than a Mr.

I am worried about some aspects of the discussions on acceptable
options for dealing with possible impactors. No one could doubt that if
we have the time and the resources to react, the intelligent choice is
to deal with a direct threat by nudging it gently, safely and
economically into a harmless orbit (and preferably an orbit that will
not tempt the media into orgies of speculation at every subsequent
thrilling near miss.) However, we have no guarantee that every
dinosaur-killer will give us a twenty-year warning. So suppose that we
are lucky and get just a five-year warning of some billion-ton stray
from the Oort cloud. That would be hopelessly too little time to
deflect it unless it had been aiming for the merest graze. 

We know very well that if such a mass strikes practically anywhere on
the planet, our technological infrastructure is pretty well doomed and
our prospects for following in the tracks of the dinosaurs are

We also know that we can neglect the physical strength of the visitor.
Whether the impact comes from a gigatonne cloud of density 0.5 or a
gigatonne rock of density 2.5 will not make much difference. So people
have pointed out that nuking an incoming mass is a pretty iffy
expedient.  It may not do any useful deflection and to exchange a hit
by a rock or snowball for a hit by a compact cloud or even a shotgun
burst of large fragments might do little more than spread the pleasure.

And yet I am moved to reflect on the difference between being hit by a
hammer and being hit by a pillow.  How relevant the difference would
be, I am not sure, because the largest bomb we ever have built would
not vaporise a really large body, say of the order of a gigatonne.  But
all the same, let us consider a few scenarios.

Start by unrealistically supposing that we could reduce our incoming
cubic km to a cloud of gas or gravel  spread roughly evenly over a
diameter of some 10000km.  An impact from a rock with a cross section
of 1km^2 would be a disaster. However, if we first converted it to a
roughly 80000000km^2 spray, it should reach the ground only as dust. On
a planetary scale that shouldn't be too much worse than many a sizeable
volcanic eruption in terms of suspending dust in the atmosphere, and
the impact would be spread over at least many minutes, so the problem
of flash burns or shock waves should reduce to triviality. 

To be sure, the gross amount of heat deposited in the atmosphere should
not be much affected, in fact it would be greatly increased, because
normally most of the heat would wind up in the crust, while now it
would all stop in the atmosphere. However, it would be almost all in
the upper atmosphere. There would be negligible downward transport by
conduction or convection, and a great deal of the radiation would be
back into space. 

All right, so a scenario of a benign dust impact is not plausible, but
then what are the alternatives?  Here are a few:

Suppose the body breaks into a lot of dangerous lumps plus small
debris. The debris would be not much of a problem, and it is quite
conceivable that the big lumps would drift apart and miss the planet
altogether. Another triumph for Rock Budgers! Alternatively suppose
that now just one or a few of the large lumps hit the planet. Cool
comfort, if we may be permitted the term in such a hot context, but it
is comfort all the same. We should prefer a few city busters to one
dino killer any day! In fact, suppose we do in fact split the dino
killer into a shotgun-blast of city killers, and all of them then hit
the planet; that might have some embarrassing effects, but frankly I
think that our infrastructure (and therefore our civilisation) would
survive them a lot better than we could survive the dino killer. For
one thing they would not cause significant focussing of shock waves at
the other end of the planet. For another they should cause less
destructive quakes and tsunamis. 

Now, would anyone care to tell me why we should prefer to stand still
for the dino killer instead of having a go at nuking it, always assuming
that we have no time to deflect it gradually? 




W. Benz*) & E. Asphaug: Catastrophic disruptions revisited. ICARUS,
1999, Vol.142, No.1, pp.5-20


We use a smooth particle hydrodynamics method to simulate colliding
rocky and icy bodies from centimeter scale to hundreds of kilometers in
diameter in an effort to define self-consistently the threshold for
catastrophic disruption. Unlike previous efforts, this analysis
incorporates the combined effects of material strength (using a brittle
fragmentation model) and self-gravitation, thereby providing results in
the ''strength regime'' and the ''gravity regime,'' and in between.
In each case, the structural properties of the largest remnant
are examined. Our main result is that gravity plays a dominant role in
determining the outcome of collisions even involving relatively small
targets. In the size range considered here, the enhanced role of
gravity is not due to fracture prevention by gravitational compression,
but rather to the difficulty of the fragments to escape their mutual
gravitational attraction. Owing to the low efficiency of momentum
transfer in collisions, the velocity of larger fragments tends to be
small, and more energetic collisions are needed to disperse them. We
find that the weakest bodies in the Solar System, as far as impact
disruption is concerned, are about 300 m in diameter. Beyond this size,
objects become more difficult to disperse even though they are still
easily shattered. Thus, larger remnants of collisions involving targets
larger than about 1 km in radius should essentially be self-gravitating
aggregates of smaller fragments. (C) 1999 Academic Press.


K.R. Housen*) & K.A. Holsapple: Scale effects in strength-dominated
collisions of rocky asteroids. ICARUS, 1999, Vol.142, No.1, pp.21-33


The application of laboratory collision experimental results to the
larger scales of asteroid impacts is complicated by the fact that the
dynamic strength of rock typically decreases as the loading duration
increases. Because loading times increase with the size scale of a
collision, large bodies are effectively weaker than small ones. While
this effect has been postulated for over a decade, it has never been
verified in actual collision experiments. This paper summarizes
collision tests performed under the conditions required to examine
scale effects, i.e., increasing the size scale of the experiment while
holding the impact velocity and impact kinetic energy per target mass
constant. Granite targets are used, with a diameter variation of a
factor of 18, The larger targets experienced significantly more
collisional damage than small ones, confirming a decrease in dynamic
strength with increasing size scale. The results are compared to a
scaling model based on the concept that fragmentation is accomplished
through the growth and coalescence of preexisting flaws. Measurements
of the actual flaw-size distribution are used to validate the model.
Field observations of flaw and fault sizes at scales to 10 km are used
to construct a scaling model that is believed to apply to the
shattering of a wide range of rock types. The results show that
kilometer-sized rocky bodies may be significantly weaker than indicated
by previous estimates, (C) 1999 Academic


M. Arakawa: Collisional disruption of ice by high-velocity impact
ICARUS, 1999, Vol.142, No.1, pp.34-45


High-velocity impact among icy planetesimals is a physical phenomenon
important to the planetary evolution process in the outer Solar System.
In order to study this phenomenon, impact experiments on water ice were
made by using a two-stage light gas gun installed in a cold room(-10
degrees C) to clarify the elementary processes of collisional
disruption and to study the reaccumulation and the escape conditions of
the impact fragments. Cubic ice targets ranging in size from 15 to 100
mm were impacted by a nylon projectile of 7 mg with an impact velocity
(v(i)) from 2.3 to 4.7 km/s. The corresponding mass ratio of the
projectile to the target (m(p)/M-t) ranged from 10(-3) to 10(-6), which
is two orders of magnitude lower than that used in previous studies
(Arakawa et al. 1995, Icarus 118, 341-354). As a result, we obtained
data on elementary processes such as attenuation of the shock wave and
fragmentation dynamics. We found that the shock pressure attenuates in
the ice target according to the relation of P proportional to
(L-p/r)(2), irrespective of the mass ratio between 10(-3) and 10(-
5), where L-p is the projectile size and r is a propagation distance.
The largest fragment mass (m(l)) normalized by the original target mass
has a good relationship to a nondimensional impact stress (P-I, NDIS)
defined as the ratio of the antipodal pressure to the material
strength. This relationship is described as m(l)/M(t)proportional to
P-I(-1.7) for a wide range of impact conditions (50 m/s < v(i) < 4 km/s
and 10(-1) < m(l)/M-t, < 10(-6)), and shows the utility of NDIS. Using
a measured shock wave decay constant of 2, the reaccumulation and the
escape conditions of icy bodies in high-velocity collisions were
estimated. As a result, it was clarified that a rubble pile could be
formed when large icy bodies (radius > 20 km) reaccumulated. On the
other hand, when smaller icy bodies (radius < 2 km) disrupted
catastrophically, all fragments escaped and a rubble pile was never
formed. (C) 1999 Academic Press.


D.D. Durda*) & G.J. Flynn: Experimental study of the impact disruption
of a porous, inhomogeneous target. ICARUS, 1999, Vol.142, No.1,


Measurements of the densities of interplanetary dust particles and
unweathered stone meteorites indicate that both have significant
porosity on the microscopic scale, In addition, the chondritic stone
meteorites are generally inhomogeneous, typically consisting of strong,
millimeter-size, olivine chondrules embedded in a weaker, fine-grained
matrix, Since target porosity is known to influence energy partitioning
in cratering and disruption, we have begun a series of experiments to
study the impact disruption of inhomogeneous assemblages of two
materials of different strengths and which exhibit significant
porosity, Experiments were performed on three similar to 300-g targets
of porphyritic olivine basalt, consisting of millimeter-size olivine
phenocrysts in a fine-grained vesicular matrix (simulating a stone
meteorite). Using the NASA Ames Vertical Gun, each target was impacted
by a 1/4-in. diameter aluminum sphere at a speed of similar to 5 km s(-
1). To avoid measuring the secondary effects of fragmentation caused by
material impacting on the walls of the gun chamber, we monitored
primary debris using passive detectors. We measured the size-frequency
distribution of the small fragments using thin foils. Most foils showed
only small depressions, sometimes containing fragments of debris,
indicating relatively low velocity debris. One foil showed similar to
300 puncture holes from high-speed particles, presumably a localized
jet or cone of target or projectile ejecta, The size-frequency
distribution was quite steep down to the similar to 10- to 20-mu m
limit where particle size was comparable to foil thickness. Aerogel
cells were employed to capture dust-size primary debris. Using an in
situ chemical analysis technique, we distinguished matrix from olivine
and determined that fragments <100 mu m in size were matrix while the
majority of the largest fragments (> 200 mu m in size) were olivine, We
also collected the debris from the floor of the gun chamber, The
largest fragments (significantly bigger than individual olivine
phenocrysts) were representative of bulk target material, In the
millimeter-size range we found a large number of isolated olivine
crystals, indicating the target experienced preferential failure along
the phenocryst-matrix boundaries. All three shots showed distinct
changes in the slopes of the mass-frequency distribution near 0.4 g,
the size of typical olivine phenocrysts. This suggests that the
mechanical failure of the material was affected by the presence of the
phenocrysts. If our results are directly applicable to chondritic
meteorites, then impact cratering and disruption of chondritic
asteroids may overproduce olivine-rich material from chondrules in the
millimeter-size range and olivine might be underrepresented at smaller
sizes in the primary debris. (C) 1999 Academic Press.


L.L. Kiss*), G. Szabo, K. Sarneczky: CCD photometry and new models of 5
Vol.140, No.1, pp.21-28


We present new R filtered CCD observations of 5 faint and moderately
faint asteroids carried out between October, 1998 and January, 1999.
The achieved accuracy is between 0.01-0.03 mag, depending mainly on the
target brightness. The obtained sinodic periods and amplitudes: 683
Lanzia - 4(h).6 +/- 0(h).2, 0.13 mag; 725 Amanda > 3(h).0, greater than
or equal to 0.40 mag; 852 Wladilena - 4(h).62 +/- 0(h).01; 0.32 mag
(December, 1998) and 0.27 mag (January; 1999); 1627 Ivar - 4(h).80 +/-
0(h).01; 0.77 mag (December, 1998) and 0.92 mag (January. 1999). The
Near Earth Object 1998 PG unambiguously showed doubly-periodic
lightcurve, suggesting the possibility of a relatively fast precession
(P-1 = 1(h).3: P-2 = 5(h).3). Collecting all data from the literature,
we determined new models for 3 minor planets. The resulting spin
vectors and triaxial ellipsoids hare been calculated by an amplitude-
method. Sidereal periods and senses of rotation were calculated
for two asteroids (683 and 1627) by a modified epoch-method. The
results are: 683 - lambda(P) 15/195 +/- 25 degrees, beta(P) = 52 +/- 15
degrees; a/b = 1.15 +/- 0.05, b/c = 1.05 +/- 0.05, P-sid = 0(d).1964156
+/- 0(d).0000001; retrograde; 852 - lambda(P) = 30/210 +/- 200, beta(P)
= 30 +/- 10 degrees, a/b = 2.3 =/- 0.3, b/c = 1.2 +/- 0.2; 1627 -
lambda(P) = 145/325 =/- 8 degrees, beta(P) = 34 +/- 6 degrees, a/b =
2.0 +/- 0.1, b/c = 1.09 +/- 0.05, P-sid = 0(d).1999154 +/-
0(d).0000003; retrograde. The obtained shape of: 1627 is in good
agreement with radar images by Ostro et al. (1990).
Copyright 2000, Institute for Scientific Information Inc.


M.J. Lopez Gonzalez*) & E. Rodriguez: Stromgren photometry of 40
Harmonia, 45 Eugenia and 52 Europa.ASTRONOMY & ASTROPHYSICS SUPPLEMENT
SERIES, 1999, Vol.139, No.3, pp.565-574


The Asteroids 40 Harmonia, 45 Eugenia and 52 Europa have been studied
photometrically. From their lightcurves synodic periods of
8(h)54(m)36(s), 5(h)42(m)00(s) and 5(h)37(m)46(s), and maximum
amplitudes of 0.(m)15, 0.(m)12 and 0.(m)20, have been deduced for 40
Harmonia, 45 Eugenia and 52 Europa, respectively. Improved solutions
for the sense of rotation, sidereal period, pole orientation and shape
properties are proposed. Copyright 2000, Institute for Scientific
Information Inc.

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