PLEASE NOTE:


*
Date sent:        Mon, 12 Jan 1998 13:54:08 -0500 (EST)
From:             Benny J Peiser B.J.PEISER@livjm.ac.uk
Subject:          CC DIGEST, 12/01/98
To:               cambridge-conference@livjm.ac.uk
Priority:         NORMAL

CAMBRIDGE-CONFERENCE DIGEST, 12 January 1998
--------------------------------------------

   "Only a threat from beyond the Earth can
   unify the quarrelsome human species"
   (Sir Arthur C Clarke)

New grounds for optimism? Are we on our way from Space-Race to
planetary defense co-operartion? Let's hope that Russia's new
democracy is stable enough and that China will also eventually
open up & join the free world. That would be even better than the
British-American-Chinese co-operation in the last James Bond movie
- and we could still use the same title: "Tomorrow never dies".

Benny J Peiser
=======================================================================

(1) RUSSIAN SCIENTISTS ASSESS PLANETARY DEFENSE: EFFECTS OF NUCLEAR
    EXPLOSION ON ASTEROIDS

(2) AMERICAN SCIENTISTS ASSESS PLANETARY DEFENSE: OPTIMAL LOW-THRUST
    INTERCEPTION OF EARTH-CROSSING ASTEROIDS

(3) WHAT DOES IT TAKE TO DISPERSE AN ASTEROID?

(4) WHAT WAS THE QAQORTOQ EVENT?

(5) NEW ASTEROID ENCOUNTER STATISTICS

(6) IS THERE EVIDENCE FOR ASTEROIDS FROM THE OORT CLOUD?

(7) MARIA'S FAMILY: STRUCTURE & IMPLICATIONS FOR GIANT NEOS

(8) DISCOVERY & PHYSICAL CHARACTERISTIC OF 1998 JA (1)
 

===============================================================
(1) RUSSIAN SCIENTISTS ASSESS PLANETRAY DEFENSE: EFFECTS OF NUCLEAR
EXPLOSION ON ASTEROIDS

V. Fortov*), V. Kondaurov & I. Lomov: Investigation of the nuclear
explosion effect on asteroids. INTERNATIONAL JOURNAL OF IMPACT
ENGINEERING, 1997, Vol.20, No.1-5, pp.265-269

*) RUSSIAN ACADADEMY OF SCIENCE, HIGH ENERGY DENS RES CTR,
13-19 IZHORSKAYA, MOSCOW 127412, RUSSIA

Impact of an asteroid on the Earth could be catastrophic. Deflection
and fragmentation of such asteroids by surface and underground nuclear
explosives has been proposed. The aim of this investigation is the
optimization of explosive effects by varying of the explosive depth and
charge. The study is based on nonlinear thermomechanics of an
elastoviscoplastic damaged medium. For numerical simulation Godunov's type
scheme on unstructured grid is used. The deflecting impulse depends on the
power and depth of the charge, and the physical and strength properties of
asteroid material. The process of dynamical vaporization and disintegration
of asteroid material around the burst point as well as the generation of
intensive jet is also investigated.

============================================================================
(2) OPTIMAL LOW-THRUST INTERCEPTION OF EARTH-CROSSING ASTEROIDS

B. A. Conway: Optimal low-thrust interception of earth-crossing
asteroids. JOURNAL OF GUIDANCE CONTROL AND DYNAMICS, 1997, Vol.20,
No.5, pp. 995-1002

UNIVERSITY OF ILLINOIS, DEPT AERONAUT & ASTRONAUT ENGN, URBANA,IL,61801

The spectacular collision of the Shoemaker-Levy 9 asteroid with Jupiter in
July 1994 was a dramatic reminder of the inevitability of such catastrophes
in the Earth's future unless steps are taken to develop methods far
Earth-approaching object detection and possible interdiction. In this work,
optimal (minimum-time) trajectories are determined for the interception of
asteroids that pose a threat of collision with the Earth. An
impulsive-thrust escape from the Earth is used initially to reduce flight
time but is followed with continuous low-thrust propulsion using values of
thrust and specific impulse representative of electric motors. The
continuous optimization problem is formulated as a nonlinear programming
problem using the collocation method in which the differential equations of
motion are included as nonlinear constraint equations.. The use of
low-thrust propulsion after Earth escape is shown to dramatically decrease
the mass of the interceptor vehicle at launch.

==========================================================================
(3) WHAT DOES IT TAKE TO DISPERSE AN ASTEROID?

H. J. Melosh*) & E. V. Ryan: Asteroids: Shattered but not dispersed
ICARUS, 1997, Vol.129, No.2, pp.562-564

*) UNIVERSITY OF ARIZONA, LUNAR & PLANETARY LAB, TUCSON, AZ, 85721

We use a combination of scaling laws and direct hydrocode computations that
include material strength to show that the impact energy needed to disperse
an asteroid is greater than that to thoroughly shatter it for asteroids
larger than about 400 m in radius. Thus, asteroids larger than this size
should probably be considered to be gravitationally bound, but otherwise
strengthless, rubble piles.

===========================================================================

(4) WHAT WAS THE QAQORTOQ EVENT?

from: Jonathan TATE fr77@dial.pipex.com

IMPACT
Issue 2
January 1998

WHAT WAS THE QAQORTOQ EVENT?
J.R. Tate,  Spaceguard UK

Introduction

There is no doubt that at 08:11 UT on Tuesday 9th December 1997
something unusual happened about 50 kilometres north east of Narsarsuaq
airport in southern Greenland.  Word began to filter out to the world on the
11th and 12th of December that it was likely that there had been a
substantial meteorite fall in the region, but, since then, controversy has
surrounded the whole affair. Indeed, echoes of the Tunguska event in 1908
are already very much in evidence.

Eyewitness Accounts

Interest was first kindled by numerous eyewitness accounts of a bright
fireball, which was seen by a number of individuals, including the crews of
at least four trawlers, police officers and a storekeeper. In addition, a
bright flash lasting for about two seconds, and the bolide itself appear on
a videotape taken in a Nuuk car park by a surveillance camera, though only
reflected in a car bonnet!

The skipper of the Danish trawler Timmarut reported that his position
was 60d 30' N, 46d 43' W, and his heading was 290-300 degrees when he
observed a bright fireball to port.  The fireball crossed his heading
and disappeared at the horizon to his front, and starboard. The
first mate on the same vessel reported a bright fireball that crossed
the sky at high altitude from roughly 270-290 degrees to 90 degrees.
The path was curved, and there was no terminal flash. The event
lasted for about five seconds, and the colour of the fireball was
observed to be reddish.

The captain of the trawler Halten Traal, located at 62.05N, 41.10W was
travelling north east at about 0810 UT when he observed a large fireball
travelling in a south-westerly direction until it disappeared over the
horizon at a bearing of 230-240 degrees. He described the colour as bluish,
and there was a bright flash as the bolide disappeared. The whole event took
place in silence, and there was no electrical disturbance.

At about 08:10 UT the trawler Nicoline C was off Fiskenaesset in south
Greenland (62.55N, 51.35W) under a clear sky.  Although he did not observe
the fireball directly his wheelhouse and the mountains ashore were strongly
illuminated by a yellow-red light.  Shadow movement indicated that the
phenomenon was moving in a southerly direction, and it seemed to brighten as
it passed.  Again the whole event was silent, and no electrical disturbances
were observed.

The trawler Regina C was, at about 08:10 UT, positioned at 60.55N,
42.15W. The first mate saw a large fireball coming from the north.
It passed approximately 10 degrees above the horizon before
disappearing behind mountains at about 320-330 degrees.  The
mountains were silhouetted b the light, and then there was a powerful
flash. He described the colour as being pale green at the centre of
the fireball, and pieces fell onto the mountains from the glowing
trail. There was no sound from the event, and no disturbance of
electronic instruments. From this description it has been calculated
that the end of the track lies behind and between the mountains of
Kap Olfert Fischer og Nuk.

The captain of the cutter Tasiilaq was sailing on a southerly course,
and at approximately 08:10 UT was at 62.01N, 41.13W when he noticed a
bright white flash on the horizon.  The cutter and its surroundings
were lit up "like daylight" by the event, and the captain observed a
jagged column of fire, or tail stretching about 10 degrees above a
point in the mountains. He obtained an accurate bearing of 285 degrees true
to the column, which persisted for a few seconds.

Two police officers on patrol in Nuussuaq observed a fireball "about
the size of the moon" at between 08:10 and 08:15 UT. They estimated
that it passed to the west of them at an elevation of about 70-75
degrees. The colour of the fireball was described as orange-yellow,
and there was no sound.

==========================================================================
(4) NEW ASTEROID ENCOUNTER STATISTICS

A. DellOro*) & P. Paolicchi: A new way to estimate the distribution of
encounter velocity among the asteroids. PLANETARY AND SPACE SCIENCE, 1997,
Vol.45, No.7, pp.779-784

*)UNIVERSITY OF PISA, DEPARTMENT OF PHYSICS, PIAZZA TORRICELLI 2,
I-56127 PISA,ITALY

The statistics of asteroid mutual encounters has been studied by
several authors, mainly with the purpose of estimating collisional
rates (and thus mean collisional lifetimes) and the distribution of
encounter velocities. A new approach to this problem, very simple and
fast in terms of computer time is presented. Not-withstanding these
properties, and in spite of its heuristic nature, the method proved to give
results similar to those obtained by means of more sophisticated and
time-consuming techniques. Moreover, the method is particularly suitable for
undertaking more detailed analyses, including the distribution of impact
directions for a given target, and an evaluation of the quantitative
relevance of a number of possible effects, not taken into account in
previous studies.

======================================================================== (5)
IS THERE EVIDENCE FOR ASTEROIDS FROM THE OORT CLOUD?

P. R. Weissman*) & H. F. Levison: Origin and evolution of the unusual
object 1996 PW: Asteroids from the Oort cloud? ASTROPHYSICAL JOURNAL,
1997, Vol.488, No.2 Pt2, pp.L133-L136

*)CALTECH,JET PROP LAB,DIV EARTH & SPACE SCI,MAIL STOP 183-601,4800 OAK
GROVE DR,PASADENA,CA,91109

The unusual object 1996 PW was discovered on 1996 August 9 by the
Near-Earth Asteroid Tracking automated search camera operating from
Haleakala in Hawaii. Although asteroidal in appearance, it was soon
determined that the object is in a near-parabolic orbit similar to that of a
long-period comet. No object that was not an active comet has ever been
discovered on such an eccentric orbit. The discovery of 1996 PW prompted us
to examine and evaluate its possible origins, including the intriguing
possibility that it is an asteroid from the Oort cloud. Current models for
the formation of the Oort cloud argue that most of the material there should
be from the Uranus-Neptune region and thus cometary, not asteroidal, in
composition. We better quantify these models and show that similar to 1% of
the Oort cloud population should be asteroids. We find that 1996 PW has
almost certainly been a resident of the Oort cloud. However we find it
equally likely that 1996 PW is an extinct comet or an asteroid. Although not
conclusive, our results represent a significant change in our understanding
of the Oort cloud, because they suggest that the ejection process sampled
(1) material from as close to the Sun as the asteroid belt in the primordial
solar nebula and hence (2) much warmer formation temperatures than
previously thought. This diverse sample is preserved in the Oort cloud.

====================================================================
(7) MARIA'S FAMILY: STRUCTURE & IMPLICATIONS FOR GIANT NEOS

V. Zappala*), A. Cellino, M. DiMartino, F. Migliorini, P. Paolicchi:
Maria's family: Physical structure and possible implications
for the origin of giant NEAs. ICARUS, 1997, Vol.129, No.1, pp.1-20

*)OSSERVATORIO ASTRONOMICO TORINO,I-10025 PINO TORINESE,TO,ITALY

An extensive analysis of the Maria family is presented. A
reconstruction of the original ejection velocity field of the fragments
suggests that a substantial number of relatively large fragments may have
been injected into the neighboring 3/1 mean motion resonance with Jupiter.
This also agrees with an analysis of the size distribution of the family,
suggesting that about 10 objects in the size range 15-30 km have probably
been lost. As a consequence, Maria's family can be seen as one of the most
promising candidates for the source of the 'giant' near-Earth asteroids 433
Eros and 1036 Ganymed. This is also supported by an extensive spectroscopic
survey of the family members in the spectral range 5000-10000 Angstrom. The
spectra obtained are very similar and are consistent with the known spectra
of Eros and Ganymed.

=========================================================================
(8) DISCOVERY & PHYSICAL CHARACTERISTIC OF 1998 JA (1)

T.B. Spahr*), C.W. Hergenrother, S.M. Larson, M. Hicks, B.G. Marsden,
G.V.Williams, D.J. Tholen, R.J. Whiteley & D.J. Osip: The discovery and
physical characteristics of 1998 JA(1). ICARUS, 1997, Vol.129, No.2,
pp.415-420

*) UNIVERSITY OF FLORIDA, DEPT ASTRON, GAINESVILLE, FL, 32611

1996 JA(1), which approached to 0.003 AU of the Earth on 1996 May 19.7 UT,
was discovered on films exposed 5 days earlier during the course of the
high-ecliptic-latitude Bigelow Sky Survey. The utility of high-latitude
surveying for near-Earth objects is demonstrated by the fact that 1996 JA(1)
traveled through the usual ecliptic survey region at a rate of 5 degrees
hr(-1), and would likely have escaped detection even at V = 11. Rapid
astrometry and communication through the Minor Planet Center and the World
Wide Web facilitated follow-up observations that indicate 1996 JA(1) has a
mean diameter of 170 m, a rotational period of 5.23 hr, and an albedo of
0.30, With a spectrum consistent with the V class, it is possible that 1996
JA(1) shares the same source as the HED meteorites.



CCCMENU CCC for 1998

The content and opinions expressed on this Web page do not necessarily reflect the views of nor are they endorsed by the University of

The content and opinions expressed on this Web page do not necessarily reflect the views of nor are they endorsed by the University of Georgia or the University System of Georgia.