PLEASE NOTE:
*
CCNet 3/2001 - 5 January 2001
-----------------------------
"Exploding meteors bombarding the Earth from space could be
mistaken
for nuclear bomb tests, say seismologists of the Royal
Netherlands
Meteorological Institute. This could present problems for
monitoring the
Comprehensive Nuclear Test Ban Treaty (CTBT), which aims to halt
the
testing of all nuclear weapons."
-- Philip Ball, Nature, 5 January 2001
"The beginning of the Dark Ages may have been literal, as
well as
figurative, as the result of a massive volcanic eruption in the
6th
century, according to a volcanologist at the Department of
Energy's Los
Alamos National Laboratory. Ken Wohletz said an eruption in the
Indonesian archipelago could have produced a 150-meter-thick
cloud layer
over the entire Earth, triggering a chain of climatic,
agricultural,
political and social changes that ushered in the Dark Ages."
-- John Webster, Los Alamos National Laboratory
"Hyper-hyperbole. It's massive!"-- article title in the
UK newspaper
The Observer, Feb. 27, criticizing news media which make
exaggerated claims
to bolster their arguments.
"It's apocalypse now as world boils over."-- headline
in the same
newspaper, same day.
-- Congratulations to the UK winner of The Dubious
Data 2000
Award!
(1) METEORS COME IN WITH A BANG
Andrew Yee <ayee@nova.astro.utoronto.ca>
(2) MILLENNIUM ASTEROID GREETS NEW YEAR
Ron Baalke <baalke@jpl.nasa.gov>
(3) NASA CONSIDERS DISCOVERY MISSION PROPOSALS: FLIGHTS TO CERES
& VESTA
UNDER CONSIDERATION
NASANews@hq.nasa.gov
(4) NEO NEWS/CERES BICENTENNIAL
David Morrison <dmorrison@arc.nasa.gov>
(5) ISO FINDS 'MISSING INGEDIENT' TO MAKE JUPITER-LIKE PLANETS
ESA News <sciweb@estec.esa.nl>
(6) THE DARK AGES MAY HAVE REALLY BEEN DIMMER
Los Alamos National Laboratory
(7) TOTAL LUNAR ECLIPSE ON TUESDAY JANUARY 9th
Duncan Steel <D.I.Steel@salford.ac.uk>
(8) SIZZLING SKIES
James Oberg <JamesOberg@aol.com>
(9) AVOIDING COLLISIONS: THE SPACEGUARD FOUNDATION
J. Tate
(10) CALCULATIONS OF ASTEROID IMPACTS INTO VENUSIAN ATMOSPHERE
D.G. Korycansky et al.
(11) METEOROID IMPACT FLASHES ON THE MOON
L.R.B. Rubio et al.
(12) HYPERVELOCITY IMPACTS FROM THE 1999 LUNAR LEONIDS
L.R.B. Rubio et al.
(13) SIMULATED DEGRADADTION OF LUNAR IMPACT CRATERS
R.A. Craddock & A.D. Howard
(14) TOPOGRAPHY OF VENUSIAN IMPACT CRATERS
R.R. Herrick & V.L. Sharpton
(15) DEGRADATION OF IMPACT CRATERS ON CALLSITO
A.T. Basilevsky et al.
(16) LONG-TERM RETENTION OF IMPACT CRATERS ON GANYMEDE
A.J. Dombard & W.B. McKinnon
(17) SEARCHING FOR SMALL SPACE DEBRIS
W. Flury et al.
(18) AND FINALLY: THE DUBIOUS DATA 2000 AWARDS
Statistical Assessment Service, 1
January 2001
===========
(1) METEORS COME IN WITH A BANG
From Andrew Yee <ayee@nova.astro.utoronto.ca>
From Nature Science Update, 5 January 2001
[ http://helix.nature.com/nsu/010104/010104-8.html
]
Friday, 5 January 2001
Meteors come in with a bang
By PHILIP BALL
Exploding meteors bombarding the Earth from space could be
mistaken for
nuclear bomb tests, say seismologists of the Royal Netherlands
Meteorological Institute. This could present problems for
monitoring the
Comprehensive Nuclear Test Ban Treaty (CTBT), which aims to halt
the testing
of all nuclear weapons.
Läslo Evers and Hein Haak detected a sonic boom from a meteor
explosion with
an instrument similar to those currently under construction for
verification
of the CTBT.
The explosion released energy equivalent to 1.5 kilotons of TNT,
the
researchers calculate. This is as big a bang as was made by
several of the
US nuclear tests of the early 1960s, and at the lower end of the
estimated
size of the Pakistani tests of 1998.
The future of the CTBT has been under a cloud since the US Senate
decided
not to ratify it in 1999. But many other nations have already
done so, and
plans are afoot for global detection systems that will alert the
international community to secret nuclear weapons tests.
Underground tests send out shock waves that seismic monitoring
stations
designed for earthquake detection can pick up. And atmospheric
tests create
a kind of low-frequency ('infrasound') sonic
boom which highly sensitive air-pressure meters (microbarometers)
can
register. A worldwide network of 60 infrasound detectors is being
built for
this purpose.
Situated near the village of Deelen in the Netherlands, the
instrument Evers
and Haak used is not designated for CTBT verification -- it is
primarily a
meteorological device. But in November 1999, it registered a most
unusual
event.
At around four o'clock in the morning of the 8th November, a few
early
risers in Germany and the Netherlands saw a flash in the dark sky
above
northern Germany. A meteor -- a small chunk of space rock
plunging through
the atmosphere -- had exploded at a height of about 20
kilometres.
The event was similar to a better-documented one that occurred in
the middle
of the afternoon over New Zealand the previous July. On that
occasion,
observers reported "a bright light, exactly like a
flare", variously
described as blue, red, orange or yellow. It was followed by a
loud boom,
and left behind a puff of brown smoke.
About one meteor detonates in the atmosphere every week. Most go
unseen by
human eyes, as they break apart very high in the sky. Only rarely
does one
strike or explode close to the planet's surface, such as the
object that
levelled trees over hundreds of square kilometres in Tunguska,
Siberia, in
1908.
That event aside, the height of these explosions usually hides
their
tremendous ferocity. The explosion of November 1999 showed up on
the Deelen
microbarometer as an infrasound blip slightly greater than the
background
noise generated by ocean waves, which create a constant barrage
of small
atmospheric booms called microbaroms.
Reported in the journal Geophysical Research Letters [1], Evers
and Haak's
research highlights how crucial it will be for an infrasound
network to be
able to distinguish between meteor explosions and genuine nuclear
blasts.
[1] Evers, L. G. & Haak, H. W. Listening to sounds from an
exploding meteor
and oceanic waves. Geophysical Research Letters 28, 41-44 (2001).
© Macmillan Magazines Ltd 2000 - NATURE NEWS SERVICE
==================
(2) MILLENNIUM ASTEROID GREETS NEW YEAR
From Ron Baalke <baalke@jpl.nasa.gov>
Jet Propulsion Laboratory
January 3, 2001
Millennium Asteroid Greets New Year
NASA's Near Earth Asteroid Tracking System (NEAT), operated by
JPL,
discovered the first asteroid of the new millennium on Jan. 1.
This is 200
years after the discovery of Ceres, the first and largest
asteroid ever
discovered. NEAT scientists compare snapshots of the same parts
of the sky
to find moving objects, which may be small or faint.
Image of the asteroid available here:
http://www2.jpl.nasa.gov/files/images/browse/2001aar.jpg
--------------------------------------------------------------
From the NEAT home page (http://neat.jpl.nasa.gov/)
MILLENNIUM ASTEROID
2001 AA = MBTR3F
NEAT discovered the first asteroid of the new millennium on 1
January 2001.
This is 200 years to the day after the discovery of Ceres, the
first and
largest asteroid. 2001 AA is a Mars-approaching asteroid, about
1.5 km (1
mile) in size. A visualization is provided from a preliminary
orbital
solution (K. Lawrence, JPL):
http://skys.gsfc.nasa.gov/cgi-bin/skymorph/neo.pl?Name=2001AA&Epoch=20001230.0&M=4.71018&e=0.2886571&a=2.1090046&Peri=275.47466&Node=162.50763&Incl=13.09239&Eqnx=2000.0
===============
(3) NASA CONSIDERS DISCOVERY MISSION PROPOSALS: FLIGHTS TO CERES
& VESTA
UNDER CONSIDERATION
From NASANews@hq.nasa.gov
Don Savage
Headquarters, Washington,
DC
January 4, 2001
(Phone: 202/358-1727)
RELEASE: 01-01
NASA CONSIDERS DISCOVERY MISSION PROPOSALS
It's a difficult decision: With about $300 million to spend,
should NASA buy
a spacecraft that could find Earth-sized planets around nearby
stars? What
about a mission that could peer deep
inside Jupiter's gaseous atmosphere? Or should the agency go with
a mission
to orbit the two largest asteroids in the solar system?
The answer to that question will have to wait about a year. In
the first
step of a two-step process, NASA's Office of Space Science
selected three
proposals for detailed study as candidates for the next mission
in the
agency's Discovery Program of lower cost, highly focused,
rapid-development
scientific spacecraft.
"The diversity of science represented in these three mission
proposals is
outstanding. NASA will have its hands full picking only one for
flight,"
said Dr. Jay Bergstralh, acting Director of Solar System
Exploration at NASA
Headquarters, Washington, DC.
The selected proposals were judged to have the best science value
among 26
proposals submitted to NASA last August. Each selected team will
receive
$450,000 to conduct a four-month implementation-feasibility study
focused on
cost, management and technical plans, including educational
outreach and
small business involvement.
Following detailed mission concept studies, NASA intends to
select one of
the three proposals late in 2001 for full development. The
mission should be
launched around 2005 or 2006.
NASA has also decided to fund American participation in a mission
to Mars
being flown by another nation. In this "Mission of
Opportunity" NASA will
contribute to seismology, meteorology and
geodesy (to measure the size and shape of the planet) experiments
on the
French-led NetLander Mission, scheduled for launch in 2007. The
Mission of
Opportunity team will receive $250,000 to conduct its feasibility
study.
The selected Discovery and Mission of Opportunity proposals are:
* The Kepler mission is a space telescope specifically
designed to detect
Earth-sized planets around stars in the Sun's neighborhood of the
galaxy. By
monitoring 100,000 stars over a
four-year mission, Kepler could detect up to 500 Earth-sized
planets and up
to 1000 Jupiter-sized planets. Dr. William Borucki of NASA's Ames
Research
Center at Moffet Field, CA, would lead Kepler at a total cost to
NASA of
$286 million.
* The Interior Structure and Internal Dynamical Evolution
of Jupiter
(INSIDE Jupiter) mission is a Jupiter orbiter designed to observe
and
measure processes occurring within the Jovian magnetosphere and
atmosphere.
INSIDE Jupiter would determine the internal structure of the
planet by
obtaining high resolution maps of the magnetic and gravity
fields. Dr.
Edward J. Smith of the Jet Propulsion Laboratory in Pasadena, CA,
would lead
INSIDE Jupiter at a total cost to NASA of $296 million.
* The Dawn mission intends to orbit Vesta and Ceres, two of
the largest
asteroids in the solar system. According to current theories, the
very
different properties of Vesta and Ceres are the result of the
asteroids
being formed and evolving in different parts of the solar system.
By
observing both asteroids with the same set of instruments, Dawn
would probe
the early solar system as well as determine in detail the
properties of each
asteroid. Dr. Christopher T. Russell of the University of
California at Los
Angeles would lead Dawn at a total cost to NASA of $271 million.
* A U.S. contribution to the French-led NetLander mission
will add unique
capabilities to each of the four landers and the orbiter which
comprise the
mission. In 2007, NetLander will create the first science network
on Mars to
study the planet's internal structure. The American contribution
includes
short period seismometers and wind sensors on the landers, and a
high-resolution geodesy instrument on the orbiter. Dr. W. Bruce
Banerdt of
the Jet Propulsion Laboratory will lead the U.S. contribution to
NetLander
at a total cost to NASA of $35 million.
The Discovery Program is designed to provide frequent, low-cost
access to
space for planetary missions and missions to search for planets
around other
stars. The selected science missions must be ready for launch
before
September 30, 2006, within the Discovery Program's cap on each
mission's
cost to NASA of $299 million.
The Discovery Program is managed at NASA's Jet Propulsion
Laboratory, a
division of the California Institute of Technology, Pasadena, for
the Office
of Space Science, Washington, DC. More information on the
Discovery Program
is available at:
http://discovery.nasa.gov/
================
(4) NEO NEWS/CERES BICENTENNIAL
From David Morrison <dmorrison@arc.nasa.gov>
CERES BICENTENNIAL
by Richard P. Binzel (MIT)
I wanted to share with you that I had the opportunity to raise a
toast of
Sicilian wine to Giuseppe Piazzi at 8 pm Palermo time on the
evening of
January 1. The location of the toast was inside the dome of the
Palermo
Observatory where the refurbished transit circle was recently
re-installed.
All parts of the transit circle are original to the time of
Ceres'
discovery, exactly 200 years earlier, except for the eyepiece
which was
apparently discarded when it was replaced in the mid-nineteenth
century.
Attendance at the commemorative talks included members of the
Piazzi family
still living in the same house in Ponte Valtellina (northern
Italy) where
Giuseppe Piazzi was born in 1746. The mayor of Ponte Valtellina
was also in
attendance and conveyed his greetings. The post office of Palermo
issued a
special "Centenario Della Scoperta di Cerere" postmark
dated 1.1.2001.
Invited talks included a description of the design and
acquisition of the
Palermo transit circle, given by Professor Giorgia Fodera' Serio
(U.
Palermo), an account of Piazzi and his Paris colleagues by
Suzanne Debarbat
(Obs. Paris), and a description of Jesse Ramsden's London
workshop - where
the Palermo circle was made - given by Anita McConnell (U. K.).
The final
talk of the evening was my own "Asteroids Coming of
Age" (see Science 289,
2065) revealing how asteroids had come to earn their current
level of
scientific respect (with great credit to T. Gehrels and G.
Shoemaker).
The Palermo Observatory Director, Professor Salvatore Serio,
presented to
the members of the Piazzi family copies of the original
congratulatory medal
offered to Giuseppe Piazzi following his discovery.
Interestingly, Giuseppe
Piazzi turned down the original medal so that those funds be used
to
purchase additional instrumentation for the Observatory. It was a
thrill and
an honor for the current generation of the Piazzi family to
finally accept
the medal on behalf of their distant relative.
=================
(5) ISO FINDS 'MISSING INGEDIENT' TO MAKE JUPITER-LIKE PLANETS
From ESA News <sciweb@estec.esa.nl>
Astronomers have so far detected about 50 planets orbiting other
stars. They
are all giant, Jupiter-like planets, made mostly of gas, and
their formation
process is still unclear. ESA's Infrared Space Observatory, ISO,
now sheds
some light on this problem.
More at:
http://sci.esa.int/content/news/index.cfm?aid=1&cid=1&oid=25688
==========
(6) THE DARK AGES MAY HAVE REALLY BEEN DIMMER
From Los Alamos National Laboratory
http://www.lanl.gov/worldview/news/releases/archive/00-165.html
CONTACT: John Webster, webster@lanl.gov,
505-667-5543 (00-165)
The dark ages may have really been dimmer
LOS ALAMOS, N.M., Dec. 17, 2000 -- The beginning of the Dark Ages
may have
been literal, as well as figurative, as the result of a massive
volcanic
eruption in the 6th century, according to a volcanologist at the
Department
of Energy's Los Alamos National Laboratory.
Ken Wohletz said an eruption in the Indonesian archipelago could
have
produced a 150-meter-thick cloud layer over the entire Earth,
triggering a
chain of climatic, agricultural, political and social changes
that ushered
in the Dark Ages.
Evidence supporting the catastrophe includes tree-ring and
ice-core
measurements, indications of a huge underwater caldera, and ash
and pumice
in the same area, said Wohletz, who discusses his work modeling
such an
eruption today (Dec. 17) at the fall meeting of the American
Geophysical
Union.
The 6th century was a turbulent, unsettling period in human
history. The
Roman Empire began to fall; nomads of central Asia migrated to
Europe and
the Near East; civilizations in Persia, Indonesia and South
America
collapsed; major religions experienced considerable change as
natural events
were viewed as omens.
Many of these social transformations resulted from widespread
crop failures
and the explosion of plague around the globe, which in turn were
caused by
major climatic changes, Wohletz said. Beginning in about the year
535,
according to historical and archeological records, the weather
was colder
and drier, sunlight diminished, snow fell in summer and regions
of
persistent drought suffered floods.
Wohletz was a resource for a book postulating that the climate
changes
resulted from a huge volcanic eruption. The book,
"Catastrophe: A Quest for
the Origins of the Modern World" by David Keys, was
published earlier this
year.
Wohletz said he worked with Keys to try to identify a volcano
that could
produce such dramatic climate change. "We came up with an
eruption that
would certainly be the largest in recorded history, some four or
five times
bigger than the (1815) eruption of Tambora, which is usually
considered the
biggest eruption in the past few millennia," he said.
Such an explosion, he said, would eject some 200 cubic kilometers
of
material, and one-third to one-half of it would be lofted into
the
stratosphere, where it would remain suspended for months to years
while
being carried around the globe.
"It would have produced enough dust and water vapor (in the
form of ice
crystals) to form a cloud layer 150 meters thick over the entire
globe, and
that's a conservative estimate," he said, adding that a
cloud of particles
that thick may have diminished the transmission of sunlight by as
much as 50
percent.
Wohletz said tree-ring data collected around the world and
ice-core
measurements in Greenland and Antarctica support the possibility
of a huge
eruption in the 6th century. Ocean depth measurements between
Sumatra and
Java where Krakatoa exploded in a well known 1883 eruption
indicate the
presence of a caldera up to 50 kilometers in diameter, and a
recent survey
uncovered evidence of ash and pumice layers formed in the area
during the
appropriate time frame.
Under a likely scenario, a large volcano, which Wohletz calls
proto-Krakatoa, connected the islands of Sumatra and Java. When
it erupted
and then subsided, it created the Sundra Strait and left a ring
of smaller
volcanoes, including the present day Krakatoa. The ash, dust and
water vapor
blown into the stratosphere would disperse across both the
Northern and
Southern Hemispheres.
"This volcano would have had the potential to be a major
player in
destabilizing the climate around the world," he said.
"An eruption that
could produce a caldera 50 kilometers across would have been big
enough."
Although definitive evidence for such a catastrophic eruption has
not been
discovered, the possibility deserves a full-scale field study,
Wohletz said,
in part because of the potential impact on the world if another
such
catastrophe happens.
"(Key's book) is the first detailed account of how closely
humanity is
linked to the natural world," he said. "If the natural
world goes through
some large upheaval, we'll all be affected."
Los Alamos National Laboratory is operated by the University of
California
for the U.S. Department of Energy.
===========
(7) TOTAL LUNAR ECLIPSE ON TUESDAY JANUARY 9th
From Duncan Steel <D.I.Steel@salford.ac.uk>
Total Lunar Eclipse on Tuesday January 9th
Essential points:
Moon enters the Earth's shadow at 18:42
Totality begins at 19:49
Totality ends at 20:51
Moon leaves the Earth's shadow at 21:59
The entire eclipse sequence is visible from throughout the U.K.
This is the
last such event to be seen from the U.K. until November 2003
See my book Eclipse (*paperback* edition of July 2000), p.54 in
particular.
The diagram given there comes from:
http://sunearth.gsfc.nasa.gov/eclipse/LEplot/LE2001Jan09T.gif
Duncan Steel
=============
(8) SIZZLING SKIES
From James Oberg <JamesOberg@aol.com>
Re CCNet 1/4/01: SIZZLING SKIES: << And there are even
unconfirmed reports
that the space shuttle returns to Earth with an electrophonic
crackle. >>
"Unconfirmed" indeed! I collected dozens of eyewitness
accounts from shuttle
entries over Texas in 1984-5 and forwarded them to Keay. We
even went out
during one fireball fly-over with antennas to record the EM
pulse. There are
fewer opportunities now because the required orbit (28 degrees)
and landing
site (KSC in Florida) are rarely used together since most
missions are to
the northerly orbit of the Mir or International Space Station, so
the flyovers
are either across the American midwest or across the Yucatan
penninsula,
where we don't have any experienced observers.
Jim Oberg
============
(9) AVOIDING COLLISIONS: THE SPACEGUARD FOUNDATION
J. Tate: Avoiding collisions: the Spaceguard Foundation. SPACE
POLICY 16:
(4) 261-265 NOV 2000
The Earth has a long and violent history of collisions with
extraterrestrial
bodies such as asteroids and comet nuclei. Several of these
impacts have
been large enough to produce major environmental changes, causing
mass
extinctions and severe alterations to weather patterns and
geography. There
is no reason to suppose that the likelihood of such collisions
will be any
less in the future and the spread of human settlement,
civilisation, and
particularly urbanisation, makes it much more likely that a
future impact,
even relatively small, could result in the massive loss of human
life and
property. Despite the fact that the technology exists to predict
and to some
extent prevent such events, there is currently no co-ordinated
international
response to this threat. This article presents a realistic
assessment of the
threat to Earth from NEOs, describes the (underfunded) efforts so
far made
to counter it and makes a plea for further action to produce a
fully
functioning Spaceguard Foundation. (C) 2000 Published by Elsevier
Science
Ltd.
Addresses:
Tate J, Spaceguard UK, Cygnus Lodge, High St, Salisbury SP4 8JT,
Wilts,
England.
Spaceguard UK, Salisbury SP4 8JT, Wilts, England.
Copyright © 2001 Institute for Scientific Information
==============
(10) CALCULATIONS OF ASTEROID IMPACTS INTO VENUSIAN ATMOSPHERE
Korycansky DG, Zahnle KJ, Law MMM: High-resolution calculations
of asteroid
impacts into the venusian atmosphere
ICARUS 146: (2) 387-403 AUG 2000
We present results from a number of 2D high-resolution
hydrodynamical
simulations of asteroids striking the atmosphere of Venus. These
cover a
wide range of impact parameters (velocity, size, and incidence
angle), but
the focus is on 2-3 km diameter asteroids, as these are
responsible for most
of the impact craters on Venus. Asteroids in this size range are
disintegrated, ablated, and significantly decelerated by the
atmosphere, yet
they retain enough impetus to make large craters when they meet
the surface.
We find that smaller impacters (diameter <1-2 km) are better
described by a
"pancaking" model in which the impactor is compressed
and distorted, while
for larger impacters (>2-3 km) fragmentation by mechanical
ablation is
preferred. The pancaking model has been modified to take into
account
effects of hydrodynamical instabilities. The general observation
that most
larger impacters disintegrate by shedding fragments generated
from
hydrodynamic instabilities spurs us to develop a simple heuristic
model of
the mechanical ablation of fragments based on the growth rates of
Rayleigh-Taylor instabilities. Although in principle the model
has many free
parameters, most of these have little effect provided that they
are chosen
reasonably. In practice the range of model behavior can be
described with
one free parameter. The resulting model reproduces the mass and
momentum
fluxes rather well, doing so with reasonable values of all
physical
parameters. (C) 2000 Academic Press.
Addresses:
Korycansky DG, Univ Calif Santa Cruz, Univ Calif Observ, Lick
Observ, Santa
Cruz, CA 95064 USA.
Univ Calif Santa Cruz, Univ Calif Observ, Lick Observ, Santa
Cruz, CA 95064
USA.
NASA, Ames Res Ctr, Moffett Field, CA 94035 USA.
Amer Museum Nat Hist, Dept Astrophys, New York, NY 10024 USA.
============
(11) METEOROID IMPACT FLASHES ON THE MOON
Rubio LRB, Ortiz JL, Sada PV: Observation and interpretation of
meteoroid
impact flashes on the moon
EARTH MOON AND PLANETS 82-3: 575-598 2000
The first unambiguous detection of meteoroids impacting the night
side of
the Moon was obtained during the 1999 Leonid storm. Up to eight
optical
flashes were recorded with CCD video cameras attached to small
telescopes on
November 18, 1999. Six impacts were videotaped by at least two
independent
observers at the same times and lunar locations, which is perhaps
the
strongest evidence for their collisional nature. The flashes were
clearly
above the noise and lasted for less than 0.02 s. Although
previous
observational efforts did not succeed in detecting impact
flashes,
additional candidates have been reported in the literature. The
evidence
accumulated so far implies that small telescopes equipped with
high speed
cameras can be used as a new tool for studying meteoroid streams,
sporadic
meteoroids, and hypervelocity collisions. In this review we
discuss the
various intervening parameters for detectability of flashes on
the night
side of the Moon (geometrical effects, contamination by scattered
light from
the day side, and properties of the meteoroids such as speed and
flux of
particles). Particular emphasis is placed on the analysis of the
observations in order to derive relevant physical parameters such
as
luminous efficiencies, impactor masses, and crater sizes. Some of
these
parameters are of interest for constraining theoretical impact
models. From
a simple analysis, it is possible to derive the mass distribution
of the
impactors in the kg range. A more elaborate analysis of the data
permits an
estimate of the fraction of kinetic energy converted to radiation
(luminous
efficiency) if the meteoroid flux on the Moon is known. Applied
to the 1999
lunar Leonids, these methods yield a mass index of 1.6 +/- 0.1
and luminous
efficiencies of 2 x 10(-3) with an uncertainty of about one order
of
magnitude. Predictions of visibility of the major annual meteor
showers are
given for the next few years. These include the forthcoming 2001
Leonid
return, for which we estimate detection rates in the visible.
Addresses:
Rubio LRB, Inst Astrofis Canarias, Tenerife, Spain.
Inst Astrofis Canarias, Tenerife, Spain.
CSIC, Inst Astrofis Andalucia, Granada, Spain.
Univ Monterrey, Monterrey, Mexico.
Copyright © 2001 Institute for Scientific Information
=============
(12) HYPERVELOCITY IMPACTS FROM THE 1999 LUNAR LEONIDS
Rubio LRB, Ortiz JL, Sada RV: Luminous efficiency in
hypervelocity impacts
from the 1999 lunar Leonids
ASTROPHYSICAL JOURNAL 542: (1) L65-L68, Part 2 OCT 10 2000
An analysis of the optical flashes produced by Leonid meteoroids
impacting
the Moon in 1999 November is carried out in order to estimate the
fraction
of kinetic energy converted into radiation, the so-called
luminous
efficiency eta. It is shown that the observational data are
consistent with
luminous efficiencies of 2 x 10(-3) in the wavelength range of
400-900 nm
with an uncertainty of about 1 order of magnitude. This
experimental value
of eta is significantly larger than previous estimates for
meteoroids of
asteroidal composition based on numerical calculations and
scaling laws from
laboratory collisions. According to our results, the luminous
efficiency
might vary with mass, i.e., the smaller impactors converting less
kinetic
energy into light and vice versa. A comparison with recent
numerical
simulations for meteoroids of cometary composition is also
carried out.
Addresses:
Rubio LRB, Inst Astrofis Canarias, Via Lactea, E-38200 La Laguna,
Canary
Islands, Spain.
Inst Astrofis Canarias, E-38200 La Laguna, Canary Islands, Spain.
CSIC, Inst Astrofis Andalucia, E-18080 Granada, Spain.
Univ Monterrey, Dept Fis & Matemat, Monterrey 66238, Nuevo
Leon, Mexico.
Copyright © 2001 Institute for Scientific Information
===========
(13) SIMULATED DEGRADADTION OF LUNAR IMPACT CRATERS
Craddock RA, Howard AD: Simulated degradation of lunar impact
craters and a
new method for age dating farside mare deposits
JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS 105: (E8) 20387-20401 AUG
25 2000
With the advent of Clementine data it is now possible to
determine the
lithology and extent of geologic materials on the Moon,
particularly the
farside mare deposits. However, traditional crater counting
techniques do
not provide reliable age estimates of these materials owing to
their small
surface areas, To support such studies, we present a model for
estimating
their age by analyzing the morphometry of degraded craters 1-3 km
in
diameter. A photoclinometric model was adapted for use with
monoscopic
0.750-mu m ultraviolet-visible and high-resolution images where
we extracted
the topography of fresh craters. A two-dimensional computer model
simulating
linear diffusional creep was applied to fresh craters at a
variety of
diameters. The resulting profiles were then compared to
photoclinometric
profiles of degraded craters of known ages for calibration.
Application of
the resulting model to degraded craters in the mare deposit of
the central
Apollo basin (-36.5 degrees latitude, 208.0 degrees longitude)
indicates
that this material was emplaced during the early Imbrian period
(similar to
3.85 Ga). By calculating the amount of material eroded from each
of the
degraded craters observed in this unit, the average erosion rate
is
estimated to be 2.0+/-0.1 x 10(-7) mm/yr on the Moon since the
Imbrian. The
estimated amount of material eroded during any given period
suggests that
the erosion rate has decreased with time, implying that the flux
of larger
impactors has as well.
Addresses:
Craddock RA, Smithsonian Inst, Natl Air & Space Museum, Ctr
Earth &
Planetary Studies, Room 3776, MRC-315, Washington, DC 20560 USA.
Smithsonian Inst, Natl Air & Space Museum, Ctr Earth &
Planetary Studies,
Washington, DC 20560 USA.
Univ Virginia, Dept Environm Sci, Charlottesville, VA 22903 USA.
Copyright © 2001 Institute for Scientific Information
================
(14) TOPOGRAPHY OF VENUSIAN IMPACT CRATERS
Herrick RR, Sharpton VL: Implications from stereo-derived
topography of
Venusian impact craters
JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS 105: (E8) 20245-20262 AUG
25 2000
Using radargrammetry we have created high-resolution topographic
maps of 74
Venusian craters, including all blight-floured craters over 12 km
in
diameter covered by Magellan stereo imagery, Our trend for
rim-floor depths
RF as a function of diameter D for bright-floored craters in the
volcanic
plains is RF = (0.3450.05) D0.2350.05, and for dark-floored
craters in the
plains, RF = (0.50.1) D0.0350.07. Rim heights RH for
bright-floored craters
in the plains are RH = (0.060.03) D0.40.2 (D > 15 km), and for
dark-floored
craters in the plains, RH = (0.0270.015) D0.40.2. These trends
indicate that
bright-floored craters 30 km in diameter are, on average, deeper
than
dark-floored craters by 180 m from rim to floor and have a 140 m
higher rim,
and at 90 km in diameter they are 380 m deeper from rim to floor
and have a
220 m higher rim. The bright- and dark-floored populations ale
different at
a 99% confidence level for both rim-flour depths and rim heights.
The
interpretation most consistent with our data and previous work by
others is
that Venusian craters with radar-dark floors have been partially
filled and
had their ejecta blankets embayed by regional-scale lava
flooding. When the
topography is examined in conjunction with the imagery, it is
clear that
many dark-floored craters have been surrounded by lavas that rose
neatly to
the crater rim even though a substantial portion of the crater's
ejecta
blanket was retained. Most previous analyses of the resurfacing
history of
Venus have relied on past interpretations that only a small
percentage of
Venusian craters are embayed by exterior volcanism. Because most
craters on
Venus have dark floors, our data indicate that the majority of
Venusian
craters have been surrounded and partially filled by postimpact
lavas, and
consequently, those previous analyses may have significantly
underestimated
the amount of volcanism on the Venusian surface over the past few
hundred
million years. Rim-floor depths for Venusian craters are
consistent with the
inverse gravity trend observed for the terrestrial planets, and
they are
similar to 50% deeper than current estimates for complex craters
on the
Earth. Unlike the other terrestrial planets, neither
terrain-floor depths
nor central structure heights increase with increasing crater
diameter. An
interesting trend fur which we have no explanation is that on
Venus, the
Moon, Mars, and Ganymede, central peaks generally rise to within
a constant
elevation relative to the surrounding ten ain, but that elevation
is lower
on the Moon and Mars than on Venus and Ganymede.
Addresses:
Herrick RR, Univ Alaska Fairbanks, Inst Geophys, POB 75732,
Fairbanks, AK
99775 USA.
Univ Alaska Fairbanks, Inst Geophys, Fairbanks, AK 99775 USA.
Copyright © 2001 Institute for Scientific Information
============
(15) DEGRADATION OF IMPACT CRATERS ON CALLSITO
Basilevsky AT, Ivanov MA, Kryuchkov VP: On the degradation of
impact craters
on Callisto
SOLAR SYSTEM RESEARCH 34: (4) 277-284 JUL-AUG 2000
The impact-crater population on Jupiter's satellite Callisto was
studied
with the use of two Galileo images. It is found that craters with
diameters
below similar to 1 km are bowl-shaped, like similar-sized impact
craters on
the Moon, and the morphological degradation of these craters
proceeds in the
way typical of small lunar craters: their contours become less
prominent.
Larger craters on Callisto vary from bowl-shaped to flat-floor
and, further,
to central-peak, like their lunar counterparts. However, these
craters on
Callisto differ radically from the lunar ones in that their
degradation
proceeds by fragmentation of their rims. An average cumulative
density of
raters 1 to 32 km across in the two examined regions of Callisto
is
described by the equation N->D = 0.03D(-1.6), and the
densities of craters
from 5.7 to 32 km in diameter on Callisto and on the farside of
the Moon are
nearly the same. Our studies give grounds to believe that most of
the impact
craters above similar to 1 km in diameter were formed late in the
period of
heavy meteoritic bombardment. On Callisto, not only was the
formation of
craters intensive at that time, but also an approximate balance
had been
reached between formation and degradation. Sublimation of the icy
component
of the Callistan "crust" probably made a major
contribution to the crater
degradation. The conditions on Callisto during this period were
possibly
different from the present-day ones. Frequent falls of meteoroids
on
Callisto might have led to the formation of a temporary
atmosphere. Under
such conditions, the landform degradation could proceed not only
by
sublimation of CO2 ice (as suppose Moore ct al., 1999) but also
by
sublimation and even melting of water ice and possibly other icy
components.
New meteorite impacts and down-slope movement of the surface
material were
of secondary importance in the crater degradation during this
period. When
the period of heavy meteorite bombardment ended, the development
of
large-scale relief on Callisto virtually ceased. Only the
formation of small
impact craters and their slow evolution following the lunar
pattern
continued for the most part.
Addresses:
Basilevsky AT, VI Vernadskii Inst Geochem & Analyt Chem, Ul
Kosygina 19,
Moscow 117975, Russia.
VI Vernadskii Inst Geochem & Analyt Chem, Moscow 117975,
Russia.
Copyright © 2001 Institute for Scientific Information
============
(16) LONG-TERM RETENTION OF IMPACT CRATERS ON GANYMEDE
Dombard AJ, McKinnon WB: Long-term retention of impact crater
topography on
Ganymede
GEOPHYSICAL RESEARCH LETTERS 27: (22) 3663-3666 NOV 15 2000
Previous analyses into viscous relaxation of impact craters on
Ganymede have
predicted short characteristic relaxation times (of the order of
100 Myr or
less for larger craters), in disagreement with the apparent great
ages of
Ganymede's terrains. By applying improved understanding of
theologic
parameters and initial crater shapes to a viscoelastic model, we
calculate
upper limit (zero heat flow) relaxation times in excess of the
age of the
solar system, eliminating this discrepancy. These very long
relaxation times
are not due to elastic effects, but are simply due to the
effective
viscosity of water ice at the appropriate temperatures and
stresses.
Addresses:
Dombard AJ, Carnegie Inst Washington, Dept Terr Magnetism, 5241
Broad Branch
Rd NW, Washington, DC 20015 USA.
Washington Univ, Dept Earth & Planetary Sci, St Louis, MO
63130 USA.
Washington Univ, McDonnell Ctr Space Sci, St Louis, MO 63130 USA.
Copyright © 2001 Institute for Scientific Information
===============
(17) SEARCHING FOR SMALL SPACE DEBRIS
Flury W, Massart A, Schildknecht T, Hugentobler U, Kuusela J,
Sodnik Z:
Searching for small debris in the geostationary ring -
Discoveries with the
Zeiss 1-metre telescope
ESA BULLETIN-EUROPEAN SPACE AGENCY (104) 92-100 NOV 2000
More than 800 satellites and rocket upper stages have been
inserted into the
geostationary ring or its vicinity over the years, but only about
250 to 270
of these satellites are currently being used operationally.
Geostationary
satellites are therefore increasingly at risk of colliding with
uncontrolled
objects. Contrary to the situation with satellites at very low
altitude,
there are no effective natural removal mechanisms for objects in
Geostationary Earth Orbit (GEO). Ground-based radars and optical
telescopes
belonging to the United States' Space Surveillance Network (SSN)
are able
routinely to detect objects larger than 1 m across in GEO. ESA
has recently
upgraded a telescope at the Teide Observatory in Tenerife (E)
with an
optimised debris-detection system. Its early observations show a
hitherto
unknown but significant population of uncatalogued objects with
diameters as
small as 10 cm in the geostationary ring. Objects smaller than 10
cm are
also expected to exist, but these are unobservable even with the
1 m Teide
telescope. Further observations are urgently needed to determine
the extent
and origin of this debris population, and the resulting hazard to
operational spacecraft.
Addresses:
Flury W, ESOC, ESA Directorate Tech & Operat Support, Mission
Anal Sect,
Darmstadt, Germany.
ESOC, ESA Directorate Tech & Operat Support, Mission Anal
Sect, Darmstadt,
Germany.
Astron Inst, Bern, Switzerland.
ASRO, Turku, Finland.
European Space Agcy, Estec, Div Mech Syst, Directorate Tech &
Operat
Support, NL-2200 AG Noordwijk, Netherlands.
Copyright © 2001 Institute for Scientific Information
=================
(18) AND FINALLY: THE DUBIOUS DATA 2000 AWARDS
From the Statistical Assessment Service, 1 January 2001
http://www.stats.org/awards/dubious00.htm
The Top Ten Silliest, Most Misleading Stories of the New
Millennium
(at least, we think it's ten, and we're pretty sure that the
Millennium has
already started)
Yes, science fans, it's that time of year again, when STATS --
the
Statistical Assessment Service -- looks back with amusement at
the glitches
and goofs served up by the media over the last twelve months. It
was a
banner year for dubiousity, ranging from failed presidential pop
quizzes
(Vajpayee, Lee, and um, that general from Pakistan -- we knew
that) to the
amazing electoral counting catastrophe (we thought those were
boxes of
Florida grapefruit; turns out that's just what happens to a
pregnant chad).
So, return with us now to those thrilling stories from
yesteryear...
1). "Well, OK, maybe it's the SECOND time in 50 million
years..."
The August 19 New York Times front page was a real scorcher -
complete with
color photograph. "The North Pole is melting" read the
first sentence. It
seems tourists on a Russian ice-breaker saw open water in the
middle of the
polar ice, clicked the shutter, and rushed right to The Times
with "evidence
that global warming may be real and already affecting
climate." It was a
sight "presumably never before seen by humans... the last
time the pole was
awash in water was more than 50 million years ago." National
Public Radio
also heralded the news (Aug. 22), but their science reporter,
Richard
Harris, started to notice the story's own thin ice, and got a
skeptical
response from other Arctic experts. It turns out during a typical
summer,
about 90 percent of the high Arctic is covered with ice, but
about 10
percent of the time there's open water over the pole. The Times
started
backtracking, and on August 29 revisited the entire matter with a
Science
Times article altering the claim and its link to global warming.
2). Perhaps you should stick to the swimsuit competition?
Could nuclear power plants be a cause of infant mortality? This
charge was
leveled in Washington, DC (Reuters Apr. 27) by activist groups
coupled with
the star power of supermodel Christie Brinkley. Though infant
mortality
rates have been in sharp decline at the same time that nuclear
power spread
around the country, the activists had an angle -- improvements in
infant
health were linked to the closing of nuclear plants. But a quick
call to the
National Cancer Institute (NCI) by Newsday reporter Earl Lane
pulled the
plug. An NCI study that examined 900,000 cancer deaths in
counties near
nuclear facilities showed that childhood deaths from diseases
such as
leukemia were actually higher before, not after, their
construction. If
anything, the facilities were associated with better infant
health.
3). Migrating Monarchs Take Wrong Turn?
What was the notorious Butterfly Ballot doing in wintry Canada,
so far from
its Palm Beach electoral home? The December 7 issue of Nature
presented
research from a Canadian psychologist who offered ballot choices
to shoppers
at the Bonnie Doon Mall in Edmonton, Alberta. It seems that 3 out
of 53
Canadian shoppers made the alleged "Buchanan error"on
the ballot form; that
is, they got confused and voted for the wrong candidate. The San
Francisco
Chronicle (Dec. 1) and other papers were quick to net the story,
reporting
evidence of "systematic confusion" and arguing the data
"call into question
the validity of the presidential election results." A story
with, er, wings,
or just a lepidopteran let down?
It turns out the methodology was meandering. The shoppers were
only a
"convenience sample" not even representative of
Canadians, much less
Floridians. Second, the study acknowledged that "there was
no relation
between the amount of confusion and errors" made (so much
for "systematic").
Besides, the Associated Press (Nov. 10) had already reported
butterfly
ballot "research" from Bossier City, Louisiana. Down
there two fourth grade
teachers had tested 22 kids on the same confusing format, with
zero errors.
4). "So, have you stopped beating your wife yet?"
Reuters reported a poll (Feb. 4) which illustrated that
"although most
smokers in the US know that cigarettes can cause heart and lung
disease, few
have been able to kick the habit." In fact, out of the 70
percent of the
sampled respondents who had ever tried to quit, none had
succeeded.
Unfortunately, this should have come as little surprise, since
the poll
specifically sampled "more than 1,000 adult smokers."
No quitters allowed.
5). The View From... Lake Rudolf?
It''s not exactly "Eurocentric," but there's definitely
something wrong
here. According to the BBC (Oct. 30), research into the last
universal
common ancestor of human males living today "gives an
intriguing insight
into the journey of our ancestors across the planet, from eastern
Africa
into the Middle East, then to southeast and southern Asia, then
New Guinea
and Australia, and finally to Europe and Central Asia"
(emphasis added)
It seems that modern man hasn't yet reached North or South
America. Perhaps
the controversy over Kennewick Man goes deeper than we think.
6). Kindergarten Cop-out
An Associated Press story, "Federal study shows kindergarten
improves all
young minds" (Dec. 4), seemed to suggest that kindergarten
was a very good
thing. From a sample of 22,000 children who attended
kindergarten, the study
found that five times as many of them could do simple sums as in
the
previous year.
But the fifth paragraph of the story reveals how the study
doesn't really
prove anything about children's education in general: "The
Education
Department-funded study offers no comparison with children who do
not attend
kindergarten." In other words, we don't know whether
kindergarten-educated
children are better off than other children. All the study showed
was that
kindergarten helps educate children who are in kindergarten. But
"all young
minds?" - we just don't know.
7). Fuzzy Math
Nobody at the AP raised an eyebrow when its Oct. 28 story,
"Clinton signs
law to combat violence against women," repeated the
President's claim,
"'Every 12 seconds, another woman is beaten,' he said.
'That's nearly
900,000 victims every year.'"
Errr, no. One incident every twelve seconds translates to over
two and one
half million incidents a year. Or, looked at the other way,
900,000
incidents a year is one every 35 seconds. Either way, those two
figures
don't add up.
8). Cashew, Cashew, We All Fall Down
New York Times columnist Paul Krugman found another way to
criticize
anti-globalization protestors in his April 19 column, "A
Real Nut Case." He
claimed that the World Bank's intervention in Mozambique's cashew
industry
benefitted the country's poor farmers, who had suffered compared
with the
nation's 10,000 nut processing workers.
Unfortunately for Mr. Krugman, and for Mozambique as well,
investigations
later in the year by the Washington Post ("A Less Than
Helpful Hand; World
Bank, IMF Blamed for Fall of Mozambican Cashew Industry,"
Oct. 18) and
Knight Ridder ("World Bank Policies Had Mixed Results in
Mozambique," Sep.
17) found that the World Bank's policies had not only put over
7,500 factory
workers out of a job in one of the world's poorest countries, but
that the
farmers who were supposed to have benefitted had lost out to nut
speculators, many of them foreign.
(Thanks to TomPaine.com for initially drawing our attention to
this one).
9). Ancestral Vices
A sense of perspective is important when you deal with
statistics. A
spokesman for the White House Office of Drug Control Policy
clearly lost his
when he responded to a study on the number of drug offenders in
prison by
saying, "Over the same period of time, drug use has gone
down and crime is
at an all-time low." ("Drug Offenders Jailed at High
Rate, AP, Jul. 27)
While crime has gone down recently, it still has not reached the
low levels
it began to leave behind in the late Sixties. Murder rates are
lower than in
the gangster-ridden 1920's and 1930's, but far above the levels
of the
1950's and the first two decades of the century.
Of course, we don't have the data to talk about crime levels
before that,
but perhaps the spokesman had something else in mind. When Cain
murdered
Abel, after all, the homicide rate peaked at 25,000 per 100,000
individuals.
And the Garden of Eden suffered a 50 percent larceny rate, which
was,
naturally, motivated by a desire for illegal substances.
10). And Finally...
"Hyper-hyperbole. It's massive!"-- article title in the
UK newspaper The
Observer, Feb. 27, criticizing news media which make exaggerated
claims to
bolster their arguments.
"It's apocalypse now as world boils over."-- headline
in the same newspaper,
same day.
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