PLEASE NOTE:
*
CCNet, 28 October 1999
------------------------
QUOTE OF THE DAY
"The biological puzzle of snowball
Earth is very interesting. Events
suggest that life was more robust than
we thought and that the Earth's
climate was much less stable than we
assumed."
-- James F. Kasting, professor of geosciences and meteorology
(1) THE NEO HAZARD AND THE POSITION OF THE JAPANESE
SPACEGUARD
ASSOCIATION
Syuzo Isobe <isobesz@cc.nao.ac.jp>
(2) LEONIDS IN THE CRYSTAL BALL
Ron Baalke <baalke@ssd.jpl.nasa.gov>
(3) NEW GRADUALIST ICE AGE THEORY
Andrew Yee <ayee@nova.astro.utoronto.ca>
(4) MYSTERY FOLLOWS METEORS
Andrew Yee <ayee@nova.astro.utoronto.ca>
(5) EARTH'S SECOND MOON IN A MENAGE A TROIS
Andrew Yee <ayee@nova.astro.utoronto.ca>
(6) CHARLES LYELL & THE UNIFORMITY PRINCIPLE
G. Camardi, UNIVERSITY OF CATANIA
(7) NEANDERTHALS & MODERN HUMAN COEXISTED & HAD GOOD FUN
UniSci, 26 October 1999
============
(1) THE NEO HAZARD AND THE POSITION OF THE JAPANESE
SPACEGUARD
ASSOCIATION
From Syuzo Isobe <isobesz@cc.nao.ac.jp>
Syuzo ISOBE, National Astronomical Observatory, Mitaka, Tokyo,
Japan
and Japan Spaceguard Association
Abstract
The Japanese Spaceguard Association, set up in October 1996, has
made
proposals to address the NEO hazard. In addition to
activities
including public lectures and the publication of our newsletter,
we try
to raise the support of the government and private organizations
to
build ground-based, and also space-based and lunar-based,
telescopes.
Two ground-based telescopes started to be built in January 1999,
and
will be in operation in 2000. Proposals for lunar-based and
space-based
NEO missions are under discussion within NASDA, Japan. In this
paper,
we discuss the ideas relevant to the various stages in our
proposed
scenario.
It is clear that a near-earth object (NEO) hit the Earth at a
point
presently appearing at Yucatan Peninsula, Mexico, 65 million
years ago
and that nearly all the dinosaurs were killed by this strike. The
degree of destruction is strongly dependent on the mass of an
impacting
object, or equivalently on its diameter. The 1992 Spaceguard
report
edited by Morrison showed that an object with a diameter larger
than
0.5 km is able to destroy nearly all human development and that
only a
small fraction of people in the world can survive. A collision of
an
NEO with a diameter smaller than 500 m produces only a local
catastrophe, but the probability of such an event is much higher
than
that of a globally catastrophic event.
Certainly, we have to work hard to prevent such a collision, but
it is
inevitably necessary to detect and track all NEOs in order to be
100%
certain of escaping a collision. However, the number and
brightness of
NEOs depend on the diameters, and it is very hard to detect all
the
small NEOs. Figure 1 shows the numbers of NEOs with large and
small
diameters as a function of aphelion distance. Since a
certain fraction
of NEOs have aphelion distances larger than 2.5 AU, we need to
observe
down to 21st magnitude for the NEOs with a diameter larger than
0.5 km.
From previous observations and research, the total number of
those NEOs
is estimated to be around 2,000 to 10,000.
Detection of objects with brightness of 21st magnitude can be
pursued
by ground-based telescopes, but needs 10 to 20 years given 10-20
NEO
detection telescopes of 1 m class. However, if one tries to
detect NEOs
with small diameter, one wants space-based and/or lunar-based
telescopes, and since the number of NEOs in this category is so
large,
it would take a very long time to detect all the NEOs even if
multiple
telescopes are launched.
There is a further consideration relating to NEO impacts. Before
the
desired level of completeness in NEO detection has been achieved,
there
is a significant possibility that the Earth will have been hit by
NEOs
approaching from around the solar direction (Isobe and Yoshikawa
1996,
Asher, Yoshikawa, and Isobe 1999). Isobe and Yoshikawa found that
the
percentage of this type of close approach to the Earth is much
higher
than would result from a uniform distribution of approach
directions.
This type of NEO impact has in principle no warning time.
Figure 1. Distribution of apocentric distances for near-earth
asteroids
with known orbits.
Considering the above discussion, three categories of
observations are
necessary as shown in table 1.
Table 1. Methods suitable for detecting various classes of
near-earth
asteroids.
Our knowledge of the NEO problem was much smaller when a working
group
on NEOs was set up within the IAU in 1991. This was just around
the
time when the significance of the Chicxulub crater was
recognized. It
has a diameter of 180 km and was produced 65 million years ago,
clearly
being associated with the extinction of the dinosaurs. We
set up an
NEO study-group in Japan, in 1993, and held an international
conference
on the Hirayama Families of asteroids. Following the start
of the
Spaceguard Foundation in March, 1996, we set up the Japan
Spaceguard
Association in October, 1996.
We visited different funding organizations to make them aware of
the
proposals shown in table 1. Fortunately, we succeeded in getting
a
budget for 1998 to 2001 from the Science and Technology Agency to
build
a 1.0 m detection telescope and a 0.5 m follow-up telescope
(Figure 2).
As Yoshikawa (1999) showed, if we are able to determine exact
orbital
elements, we can determine when an object approaches the
Earth.
Fortunately, no NEO on a collision course has been detected,
although
such NEOs as 1997 XF11 and 1999 AN10 show close approaches to the
Earth
within 30 to 50 years. After completing our telescopes, we shall
have a
capability to detect NEOs matching the LINEAR telescope of the US
Air
Force in New Mexico. However, the number of telescopes to detect
NEOs
is not enough and we need more than 100 years may be needed to
detect
all the NEOs with diameter larger than 500 m. More than 10 high
quality
telescopes are necessary to make this time duration short.
Figure 2. Spaceguard observation facilities under
construction(September 29,
1999).
Until we detect all the NEOs there is always a possibility for an
asteroid coming from the blind (near-solar) direction to collide
with
the Earth. This gives no warning time. Therefore, to give a
certain
length of warning time, we are proposing a lunar-based or
space-based
small telescope which searches continuously areas surrounding the
solar
direction.
For NEOs with a diameter between 50-500 m we need to observe down
to
27th magnitude, for which either 8 m class ground-based
telescopes or
1-2 m class space-based or lunar-based telescopes are
necessary.
Considering all the NEOs we are proposing the strategy shown in
table 2
to avoid not only the extinction of humans but also the total
destruction of a country. We would like to detect all the NEOs
before a
collision occurs.
Table 2. A strategy to detect the near-earth asteroids.
There is much debate as to how to publicize a calculated
collision
probability of a given asteroid at its discovery. At this stage
there
is a background collision probability of 10^-6 event/year for an
asteroid producing global damage. In the case of 1999 AN10 the
collision probability varied between 10^-4 - 10^-6 event/year as
new
observational data were progressively added. However, the Japan
Spaceguard Association claims that since the collision
probability is
so small, since a much more accurate collision probability will
be
available after follow-up observations within a few years, and
since we
have a fairly long warning time, we should not publicize the
information. If this kind of information is publicized
repeatedly, it
would result in accusations of crying wolf and the public would
not
believe astronomers working on the NEO problem.
Table 3. Necessary mass of colliding satellite to change an
asteroid
orbit to its collision course.
There are some proposals to prevent an NEO collision with short
warning
time. One should be careful on this point. If the warning time is
short, we need much energy to mitigate the NEO. As an indication
table
3 shows the necessary mass of a space satellite to deflect an NEO
from
a colliding orbit, for different warning times. Since this mass
is very
large for the case of an asteroid with a diameter larger than 500
m,
there is practically no way to mitigate an asteroid collision
except
using many space nuclear weapons. The Japan Spaceguard
Association does
not take this option, because we need much money to maintain such
nuclear shield systems and we may not use this system since the
collision probability is once in a hundred thousand years. There
remains a danger in keeping nuclear weapons which may also used
for
war.
A perfect Spaceguard system can be set up with a cost less than
that to maintain a nuclear space shield system for one
year. When we
detect all the NEOs and determine those orbits, we can estimate
the
time of an asteroid collision well in advance. If we find an NEO
colliding with the Earth within 10 years, we should suffer a
global
catastrophe, since that probability is far below that for your
car
accident (which is said once one hundredth per person per his
hundred
year lifetime). Following the above discussion, the Japan
Spaceguard
Association is proposing the strategy to detect NEOs as shown in
table
4.
References
Asher, D. J., Yoshikawa, M. and Isobe, S. 1999, Asteroid
Collision
Frequencies and Directions for the Terrestrial
Planets, ICARUS, submitted.
Isobe, S. and Yoshikawa, M. 1996, Asteroids Approaching the Earth
from
Directions around the Sun, Earth, Moon, and Planets,
Volume 72, pp263-266.
Yoshikawa, M. 1999, private communication.
For further informations icluding its figures and tables can be
seen in
Isobe's web page http://neowg.mtk.nao.ac.jp/~isobe/
which will be open
on December 1, 1999.
=================
(2) LEONIDS IN THE CRYSTAL BALL
From Ron Baalke <baalke@ssd.jpl.nasa.gov>
Leonids In The Crystal Ball
Marshall Space Flight Center
http://science.nasa.gov/newhome/headlines/ast27oct99_1.htm
Most experts agree that 1999 is a likely year for a Leonids
meteor storm.
October 27, 1999: Imagine tuning in to the local TV weather
report and
hearing this from the weatherman:
"Good evening space weather lovers! Last night Earth was hit
by a
high-pressure solar wind stream. It's expected to persist for 3
or 4 more
days producing a 50% chance of mid-latitude aurora. But the big
news today
is the 1999 Leonid meteor shower. Experts are predicting a big
storm on
November 18th with up to 100,000 shooting stars per hour. Of
course, we
could be off by a couple of years. The storm might hit in 2001
instead. Or
maybe not at all! Hey, if predicting these things were easy we
wouldn't need
experts!"
One day, space weather forecasts like this could be commonplace.
As our
society comes to rely on satellites, cell phones, and other
space-age
gadgets, forecasting solar storms and meteor showers can be just
as
important as knowing the chances of rain tomorrow. Three weeks
from now we
may be treated to a very visible reminder of space weather when
the Leonid
meteor shower strikes on November 18, 1999.
What's the probability of significant meteoroid precipitation?
That's what
stargazers and satellite operators everywhere would love to know.
Most experts would agree that predicting the Leonids can be
tricky. To
understand why it's helpful to know the difference between a
"meteor shower"
and a "meteor storm." Simply put, meteor showers are
small and meteor storms
are big. Meteor showers produce a few to a few hundred shooting
stars per
hour. Meteor storms produce a few thousand to a few hundred
thousand meteors
per hour. A meteor storm, like a total solar eclipse, ranks as
one of
Nature's rarest and most beautiful wonders.
A Leonid meteor shower happens every year around November 17 when
Earth
passes close to the orbit of comet Tempel-Tuttle. Usually not
much happens.
The Earth plows through a diffuse cloud of old comet dust that
shares
Tempel-Tuttle's orbit, and the debris burns up harmlessly in
Earth's
atmosphere. A typical Leonid meteor shower consists of a meager
10 to 20
shooting stars per hour.
Every 33 years something special happens. Comet Tempel-Tuttle
swings through
the inner solar system and brings a dense cloud of debris with
it. For 3 or
4 years after its passage the Leonids can be very active. In 1966
for
instance, over 100,000 meteors per hour were seen from parts of
North
America. Curiously, there isn't a full-fledged storm every time
Tempel-Tuttle passes by. Sometimes there's simply a
stronger-than-average
shower. Sometimes nothing happens at all!
Will there be a storm in 1999? (Probably, yes.)
Tempel-Tuttle visited the inner solar system most recently in
late 1997 and
early 1998. The subsequent Leonids display, in Nov. 1998, was
marvelous as
observers all over the world were treated to a dazzling display
of fireballs
(shooting stars with magnitudes brighter than -3). Nevertheless,
the 1998
Leonids were a shower, not a storm. The maximum rate of meteors
last year
was about 250 per hour. Scientists have learned that if Earth
crosses the
orbit of Tempel-Tuttle too soon after the comets passage, then
there is no
storm, just a strong shower. Apparently that's what happened in
1998. In
recent history no Leonid storm has ever occurred less than 300
days after
Tempel-Tuttle passed by Earth's orbit. In 1998, Earth followed
the comet to
the orbit-crossing point by only 257 days.
The period of maximum activity during the 1998 Leonid shower took
place
about 12 hours before the earth crossed Tempel-Tuttle's orbital
plane. The
early activity caught many observers by surprise, but it was
business as
usual for the unpredictable Leonids. Rainer Arlt of the
International Meteor
Organization noted that while the maximum activity came early,
there was a
secondary maximum when the Earth passed the comet's orbit. This
pattern is similar to that observed in 1965, the year that
preceded the
great Leonids storm of 1966. In his report, Bulletin 13 of the
International
Leonid Watch: The 1998 Leonid Meteor Shower, Arlt wrote:
[T]he radar, visual, and photographic
records of the 1965 Leonids
indicate an activity profile which
resembles that of the 1998
Leonids. Even the low population index
seems comparable. Judging
from these phenomenological facts, we
may expect 1999 to show a
similar shape of activity as in 1966.
The actual maximum meteor
numbers are hardly predictable.
If the 1999 Leonids are anything like the 1966 storm, stargazers
are
definitely in for a treat. The 1966 event was, predictably,
somewhat
unexpected. The comet had passed by Earth's orbit in 1965, so
astronomers
were aware that something might happen. But, judging by the
paucity of the
1899 and 1932 showers, it was widely thought that the orbit of
the debris
stream had been deflected so much by gravitational encounters
with other
planets (mainly Jupiter) that a close encounter with Earth's
orbit was no
longer possible. The best predictions suggested a strong shower
over Western
Europe with 100 or so meteors per hour.
Instead, there was an stunning display of shooting stars over
western North
America. This recollection by James Young at JPL's Table Mountain
Observatory in California gives a sense of what the storm was
like:
"This very noteworthy [1966] meteor
shower was nearly missed
altogether... There were 2-5 meteors
seen every second as we
scrambled to set up the only two cameras
we had, as no real
preparations had been made for any
observations or photography.
The shower was expected to occur over
the European continent.
The shower peaked around 4 a.m., with
some 50 meteors falling per
second. We all felt like we needed to
put on 'hard hats'! The sky
was absolutely full of meteors...a sight
never imagined ... and
never seen since! To further understand
the sheer intensity of
this event, we blinked our eyes open for
the same time we normally
blink them closed, and saw the entire
sky full of streaks ...
everywhere!"
The 1966 return of the Leonids was one of the greatest displays
in history,
with a maximum rate of 2400 meteors per minute or 144,000 per
hour.
Joe Rao, a Leonids expert who lectures at New York's Hayden
Planetarium,
also advocates 1999 as possibly the best year for a storm during
this 33
year cycle. Writing for Sky &Telescope he says:
Based on what happened last November, I
will venture a prediction.
If a meteor storm is to take place at
all, 1999 would appear to be
the most likely year for it to happen.
But even if this year's
Leonids are richer in number, observers
should not expect the same
high proportion of fireballs that were
seen in 1998. Instead, a
more even mix of bright and faint
meteors is likely. [ref]
Rao bases his argument on historical precedent and the
Earth-comet geometry.
During the seven most recent Leonid storms when Earth crossed
Tempel-Tuttle's orbit soon after the comet, the average distance
between the
comet and Earth was 0.0068 astronomical unit. The average number
of days
between the comet's passage and the Earth's arrival at the plane
of the
comet's orbit was 602.8 days. With the 1999 values of 0.0080 AU
and 622.5
days, Rao says we ought to be in a prime position to see
significant, if not
storm-level, activity.
Rao is also a meteorologist for News 12 Westchester, which seems
a suitable
occupation for predicting meteor showers.
In 1999, the Earth will pass nearly three times as far from the
comet's
orbital path as it did in 1966 and more than six times farther
than it did
during the great storm of 1833. If the peak of the Leonids
arrives exactly
when the Earth passes through the comet's orbital plane, Donald
Yeomans of
JPL gives 01:48 UT on November 18, 1999 as the most likely time
for the 1999
maximum [ref]. That would make Europe and West Africa the best
places to
watch the show. However, Leonid meteor showers frequently arrive
much
earlier or later than predicted, so any place on the globe could
be favored.
If the peak of the Leonids occurs over Europe or the Atlantic
Ocean, then
observers in the USA could be in for an unusual treat. The Leonid
radiant
would just be rising over North America at the time. In the
eastern US sky
watchers would see a large number of earth-grazing meteors
skimming
horizontally through the upper atmosphere. "Earth
grazers" are typically
long and dramatic, streaking far across the sky.
To look or not to look, that is the question
All sorts of conjectures were made by
all sorts of people ... We
may learn of this that, when men are in
a high state of
excitement, their testimony must be
taken with many grains of
allowance.
From a first-hand account of the 1833 Leonid Meteor
Shower. by Elder Samuel Rogers
Most experts agree that 1999 is the most likely year for a
Leonids meteor
storm during the current 33 year cycle. However, if 1999 turns
out to be a
disappointment, don't despair! There are other studies that
suggest 2000,
2001 or even 2002 could be better years. The Leonids are simply
hard to
forecast.
If 1999 is the year, when should you look? Most experts predict
that the
Leonids peak will occur between 0100 and 0400 Universal Time on
November
18th. However, it is important to remember that such predictions
are always
uncertain. The 1998 Leonid fireball display occurred nearly 16
hours before
the predicted maximum! No matter where on Earth you live, the
morning of
November 18 will probably be the best time to look for Leonids in
1999. This
is true even if morning where you live occurs much earlier or
later than
0100-0400 UT.
Conventional wisdom says that meteor observing is always best
between
midnight and dawn local time on the date of the shower (November
18 in this
case). For a shower or storm like the Leonids that might be
relatively
brief, it is best to start watching no later than midnight. In
fact, when
the author of this story went outside last year at midnight to
view the 1998
Leonids, the shower was already well underway! With this in mind
you may
decide it's a good idea to begin observing even earlier, say, 10
p.m. on
November 17.
In the coming weeks Science@NASA will post more stories about the
Leonids
with observing tips for meteor watching with the naked eye, video
cameras
and other types of recording devices. One thing seems sure, no
matter where
you live: The Leonids are coming and, on Nov 18, 1999 the place
to be is
outside, looking up!
=================
(3) NEW GRADUALIST ICE AGE THEORY
From Andrew Yee <ayee@nova.astro.utoronto.ca>
Pennsylvania State University
Contacts:
A'ndrea Elyse Messer, (814) 865-9481 (o), aem1@psu.edu
Vicki Fong, (814) 865-9481 (o), vyf1@psu.edu
Embargoed For Release: October 27, 1999 p.m.
Oxygen May Be Cause of First Snowball Earth
Denver, Colo. -- Increasing amounts of oxygen in the atmosphere
could
have triggered the first of three past episodes when the Earth
became
a giant snowball, covered from pole to pole by ice and frozen
oceans,
according to a Penn State researcher.
"We have convincing evidence that at least six of the seven
continents were once glaciated, and we also have evidence that
some
of these continents were near the equator when they were covered
with
ice," says Dr. James F. Kasting, professor of geosciences
and
meteorology. "Two of these global glaciations occurred at
600 and 750
million years ago, but the earliest occurred at 2.3 billion years
ago."
According to Kasting, if it is assumed that the magnetic evidence
for
glaciation at the equator is correct, then only two possible
explanations for equatorial glaciation exist.
One is that the Earth's tilt, which is now at 23.5 degrees from
vertical, was higher than about 54 degrees from vertical. This
would
have positioned Earth so that the poles received the most solar
energy and the equator would receive the least, creating a
glacier
around the middle but still leaving the poles unfrozen.
The other possibility, which is the one that Kasting leans toward
now, is that the greenhouse gases in the atmosphere fell low
enough
so that over millions of years, glaciers gradually encroached
from
the poles to 30 degrees from the equator. Then, in about 1,000
years,
the remainder of the Earth rapidly froze due to the great
reflectivity of the already ice-covered areas and their inability
to
capture heat from the sun. The entire Earth became a snowball
with
oceans frozen to more than a half mile deep.
"For the latest two glaciations, carbon dioxide levels fell
low
enough to begin the glaciation process. However, for the earliest
glaciation, the key may have been methane," Kasting told
attendees at
the annual meeting of the Geological Society of America today
(Oct.
27) in Denver.
"The earliest known snowball Earth occurred around the time
that
oxygen levels in the atmosphere began to rise," says
Kasting, who is
a member of the Penn State Astrobiology Center. "Before
then, methane
was a major greenhouse gas in the atmosphere in addition to
carbon
dioxide and water vapor."
As oxygen levels increased, methane levels decreased dramatically
and
carbon dioxide levels had not built up enough to compensate,
allowing
the Earth to cool. Oxygen levels need only reach a hundredth of a
percent of present-day oxygen levels to convert the methane
atmosphere completely. Once the Earth is snow covered, it takes 5
to
10 million years for the natural activity of volcanoes to
increase
carbon dioxide enough to melt the glaciers.
Regardless of the greenhouse gas involved, the pattern of
freezing
and defrosting would be the same. Because the sun has been
constantly
increasing in brightness, it would take more greenhouse gas in
the
past to compensate for the fainter sun. For the glaciations at
600
and 750 million years ago, estimates are that carbon dioxide
levels
equal to recent pre-industrial levels or up to three times
pre-industrial levels would have been sufficient for snowball
Earth
to occur.
Because many continents existed in the warm equatorial areas
during
the most recent glaciations, Kasting believes that rapid
weathering
of calcium and magnesium silicate rocks, which consumes carbon
dioxide, lowered levels sufficient to cool things.
"It would have taken nearly 300 times present levels of
carbon
dioxide to bring the Earth out of its ice cover," says
Kasting.
"Then, once the high reflectivity ice was gone, the carbon
dioxide
would have overcompensated and the Earth would become very warm
until
rapid weathering would remove carbon dioxide from the
atmosphere."
One reason that many scientists initially rejected the snowball
Earth
theory was that biological evidence does not suggest that the
various
forms of life on Earth branched out from the latest total
glaciation.
A variety of life forms had to survive from before the
glaciation,
which is difficult to imagine on an ice-covered world. Perhaps
the
ancestors of life today survived in refuges like hot springs or
near
undersea thermal vents.
"The biological puzzle of snowball Earth is very
interesting," says
Kasting. "Events suggest that life was more robust than we
thought
and that the Earth's climate was much less stable than we
assumed."
EDITORS: Dr. Kasting is at (814) 865 - 3207 or at
kasting@essc.psu.edu by
email.
====================
(4) MYSTERY FOLLOWS METEORS
From Andrew Yee <ayee@nova.astro.utoronto.ca>
[http://www.abqjournal.com/scitech/1sci10-26-99.htm]
Tuesday, October 26, 1999
Mystery Follows Meteors
By John Fleck, Albuquerque Journal Staff Writer
Astronomers chasing rare and mysterious "glowworms in the
sky" that
swarm every 33 years or so will converge on Albuquerque next
month.
The occasion is the annual Leonid meteor shower, an
every-November
light show in the night sky that once every 33 years turns into
an
extravaganza of shooting stars.
This year's show is expected to be a doozy.
That's a problem for satellite operators, a treat for stargazers
and
a potential scientific bonanza for Air Force astronomer Jack
Drummond
and his colleagues.
They're trying to understand how little grains of dust and sand
slamming into Earth's atmosphere can leave twisting, billowing,
glowing trails that sometimes last for hours.
The trails, which Drummond calls "glowworms in the
sky," were first
noticed in 1833, but they've never been explained, Drummond said.
Last year, the scientists used a modest Leonid show to study a
handful of glowworms, armed with a telescope and lasers at an Air
Force observatory on a hilltop south of Albuquerque.
This year they'll be back in force, using a suite of special
instruments to try to pin down the cause of the strange glowing
trains.
The Leonids occur when Earth, on its orbit around the sun, passes
through the trail of dust left by a comet called Tempel-Tuttle,
which
orbits the sun every 33 years.
The trail is always there, which is why we get Leonids every
November.
But in 1998, Tempel-Tuttle passed near us, leaving a load of
fresh
dust, which is why scientists expect a light show this year.
"Ninety-nine's the big year. I'm willing to make small bets
-- not
big bets, but small bets," said Kevin McKeown, an
Albuquerque amateur
astronomer and veteran meteor-watcher.
The storm of shooting stars is caused when grains of dust and
sand
collide with Earth's atmosphere, explained Sandia National
Laboratories physicist Dave Crawford.
They might not be big, but their speed as they slam into Earth's
atmosphere is prodigious -- about 40 miles per second.
That pumps enough energy into the atmosphere to heat it so much
that
electrons are stripped off of its molecules, creating the brief
flash
of a meteor.
"That's really what you're seeing is glowing air,"
Crawford said.
But in some cases, there's more.
Some of the brightest meteors leave a more lasting luminous
trail,
and therein lies the mystery Drummond and his colleagues are
trying
to solve.
Drummond's "glowworms in the sky" were first recorded
during a Leonid
shower in 1833, the scientist told reporters during a briefing
Monday.
According to McKeown, they are visible in other meteor showers
but
most common during the especially bright and spectacular Leonids.
At their best, he said, they are "very easy naked-eye
objects,"
requiring no telescope or binoculars to see.
Drummond and his colleagues used the Air Force's Starfire Optical
Range telescope on a Kirtland Air Force Base hilltop to study
them
during last November's Leonid shower.
They shone a laser at it hoping to see the light reflected back.
When
it wasn't, they knew the glowworm wasn't a smoky trail.
Instead, something in the trail itself, 50 miles high in the
thinnest
part of the atmosphere, is generating its own light. But what?
This year, they aim to find out.
Three instruments called spectrographs, which split light into
its
various colors, will be used.
Because different chemicals emit different colors of light, a
spectrograph can be used to determine the glowworms' chemical
composition.
The scientists will be training their instruments on the sky
shortly
after midnight on the mornings of Nov. 17 through 19, hunting
glowworms.
And for members of the general public, it's also worth staying up
late, said McKeown. A dark spot out of town is best, but the
Leonids
are likely to be bright enough that even in the glare of city
lights
they should put on a show.
"You've got to go out and look," he said. "If you
miss it, you'll
never be able to live with yourself."
Copyright © 1999 Albuquerque Journal
[NOTE: Images from the Starfire Optical Range experiment are
available at http://www.sor.plk.af.mil/Leonids.htm
- A.Y.]
===================
(5) EARTH'S SECOND MOON IN A MENAGE A TROIS
From Andrew Yee <ayee@nova.astro.utoronto.ca>
ESA Science News
http://sci.esa.int
26 Oct 1999
Earth's 'Second Moon' in a 'ménage à trois'
We will never see it but the Earth has at least one other natural
satellite. In discovering several new types of orbital motion, a
team
of British scientists has shown that the gravitational forces of
our
planet and of the Sun allow our planet to capture passing
asteroids.
One of them is named 'Cruithne', and can be considered -- at
least
for the next 5000 years -- as 'Earth's second Moon'.
The work of coorbital dynamics by a team from Queen Mary and
Westfield College in London was published 27 September in the US
publication 'Physical Review Letters'. Fathi Namouni, Apostolos
Christou and Carl Murray have taken even further the discoveries
of
Joseph-Louis Lagrange.
The 18th century French mathematician gave his name to the five
special points of equilibrium between the gravitational forces of
a
planet like our Earth and those of the Sun. The 'Lagrangian
points'
-- also known as libration points -- demonstrate the so-called
'three-body problem' when a planet and its Sun can catch a third
companion (see diagram).
The first point L1 is situated on a line between the planet and
its
Sun. SOHO, the ESA-NASA Solar and Heliospheric Observatory is the
first spacecraft to exploit such a position. It is currently
orbiting
the inner L1 position 1.5 million km from Earth using this
vantage
point to study the Sun. L2 is on the same line but on the outer
side
from Earth.
The L3 point is precisely on the other side of the Sun. L4 and L5
are
at the summit of two equilateral triangles with a common base
being
the line between the Earth and the Sun. Joseph-Louis Lagrange had
already shown that objects turning around L4 and L5 could easily
stay
there. This configuration applies to other planets of the solar
system. Indeed Jupiter has hundreds of Trojan asteroids and Mars
has
at least two. Although Saturn itself has none, its own moons
Tethys
and Dione maintain Trojan asteroid satellites at Lagrangian
points.
The orbits of these third bodies are exotic. The Trojan asteroids
describe a 'tadpole-shaped' pattern around the L4 and L5 points.
Even
more peculiar is the 'horseshoe orbit' in which the third body
turns
around the three points of equilibrium, L3, L4 and L5.
Cruithne is such an object. Discovered in 1997, it is a 5-km
diameter
asteroid that takes 770 years to complete its horseshoe orbit.
Thus
every 385 years it comes to its closest point to Earth, some 15
million kilometres. Last time was in 1900, next -- if you can
wait --
will be in 2285.
The British team integrated Cruithne's parameters into their
mathematical models, deducing that it can remain in its present
state
for 5,000 years before leaving. They have even calculated that
'Earth's second moon' is likely to be a second-comer having been
trapped in a similar orbit some time in the past 100,000 years.
"Cruithne is a case example, proof that our work is not just
abstract
calculations," says Carl Murray. "The mathematical
model that we have
developed has been able, not only to predict several new types of
previously unsuspected motion, but has it has subsequently been
confirmed by investigating numerically the orbits of real solar
system objects. Nature has already provided examples of every
kind
of orbit that the theory can provide."
Examining existing catalogues of near-Earth objects to see
whether
there were any other similar cases, the Queen Mary and Westfield
College team have discovered four: three concerning Earth and one
for
Venus.
The main significance of the work is that it provides a complete
classification of coorbital motions. It could lead to a greater
understanding of other asteroids, including their likelihood of
hitting Earth and of how the planets were formed. Space mission
planners could devise new gravitational tricks for their space
probes. Murray himself is one of the European members of the
Imaging
Science Subsystem team on the Cassini orbiter part of the
Cassini-Huygens mission.
The team also shows that the forces of attraction in the
three-body
problem are also present in other domains of science -- such as
chemistry where, for instance, two electrons of an atom of helium
display a similar 'ménage à trois' around their nucleus.
USEFUL LINKS FOR THIS STORY
* Physical Review Letters abstract
http://ojps.aip.org/journal_cgi/getabs?KEY=PRLTAO&cvips=PRLTAO000083000013002506000001&gifs=Yes
* More about SOHO
http://sci.esa.int/soho
* More about Huygens
http://sci.esa.int/huygens
* The Lagrange points (NASA webpage)
http://map.gsfc.nasa.gov/html/lagrange.html
[NOTE: Illustrations supporting this release are available at
http://sci.esa.int/categories/newsitem.cfm?TypeID=5&ContentID=7331
]
============
(6) CHARLES LYELL & THE UNIFORMITY PRINCIPLE
G. Camardi: Charles Lyell and the uniformity principle. BIOLOGY
&
PHILOSOPHY, 1999, Vol.14, No.4, pp.537-560
UNIVERSITY OF CATANIA,DIPARTIMENTO SCI UMANE,PIAZZA DANTE
32,I-95124
CATANIA,ITALY
The theoretical system Lyell presented in 1830 was composed of
three
requirements or principles: 1) the Uniformity Principle which
states
that past geological events must be explained by the same causes
now in
operation; 2) the Uniformity of Rate Principle which states that
geological laws operate with the same force as at present; 3) the
Steady-state Principle which states that the earth does not
undergo any
directional change. The three principles form a single thesis
called
'uniformitarianism' which has been repeatedly questioned and
which has
been reputed to be unable to face the competing 'directional
synthesis'
based on the theory of the earth's cooling down. As a result, the
significance of Lyell's system has been reduced to a simple
'actualism'
which admits the validity of the only Uniformity Principle. I
believe
that the only way to understand Lyell's role in the history of
science
is to maintain the unity of his synthesis. To show the Newtonian
roots
of this synthesis I will compare Lyell's principles and Newton's
Rules
of Reasoning. I will conclude with an analysis of the
methodological
function of principles in Lyell's scientific endeavour. Copyright
1999,
Institute for Scientific Information Inc.
==================
(7) NEANDERTHALS & MODERN HUMAN COEXISTED & HAD GOOD FUN
From UniSci, 26 October 1999
http://unisci.com/stories/19994/1026991.htm
It appears that Neanderthals coexisted with early modern humans
in
central Europe for thousands of years -- and very likely mated
with
them -- according to new radiocarbon dating by an international
team of
scientists. They documented the fact that Neanderthals roamed
central
Europe as recently as 28,000 years ago, the latest date ever
recorded
for Neanderthal fossils worldwide.
The announcement was made jointly today by Washington University
in St.
Louis and Northern Illinois University.
The team's findings -- published in today's issue of the
Proceedings of
the National Academy of Sciences -- may force other scientists to
rethink theories of Neanderthal extinction, intelligence -- and
contributions to the human gene pool.
The research on Neanderthal fossils from the Vindija cave site in
Croatia also casts doubt on the theory that the Iberian Peninsula
was
the Neanderthals' last stand.
"Most scientists would have expected to find the latest
Neanderthal in
southwest Europe rather than in central Europe," said
paleontologist
Fred H. Smith, a research team member and chairman of the
Anthropology
Department at Northern Illinois University. "The new
radiocarbon dates
suggest Neanderthals would have coexisted with early modern
humans in
central Europe for several millennia."
"The extinction of the Neanderthals by early modern humans,
whether by
displacement or population absorption, was a slow and
geographically
mosaic process," said team member Erik Trinkaus, an
anthropologist at
Washington University in St. Louis. "The differences between
the two
groups in basic behavior and abilities must have been small and
rather
subtle."
Using direct accelerator mass spectrometry radiocarbon dating,
team
member Paul Pettitt and colleagues at Oxford University in
England
determined that two pieces of Neanderthal skulls from the Vindija
cave
site are between 28,000 and 29,000 years old. These new Croatian
dates
refute previous evidence indicating central European Neanderthals
had
disappeared as early as 34,000 years ago.
Neanderthals are commonly portrayed as prehistoric humans of
limited
capabilities who were rapidly replaced and driven to extinction
by
superior early modern humans, once the modern humans appeared in
Europe.
Scientists surmised that modern humans from the Near East moved
first
into central Europe and then into western Europe, pushing
Neanderthals
into the Iberian Peninsula, at the extreme southwest portion of
the
continent, where the Neanderthals died off about 30,000 years
ago.
Coupled with his earlier work at Vindija, Smith said the new
radiocarbon dates call into question this pattern of Neanderthal
migration and extinction. In his earlier work, Smith also argued
that
late Neanderthal fossils from the cave site had some modern human
anatomical characteristics.
The Croatian dates indicating thousands of years of coexistence
between
Neanderthals and early modern humans in central Europe forces a
new
interpretation of a study in which scientists compared the DNA of
a
Neanderthal with the DNA of contemporary humans. Published two
years
ago, the study concluded that, while Neanderthals and early
modern
humans may have coexisted in Europe, they probably didn't mate.
"The new dates, in my opinion, add some support to the idea
that there
was probably a good deal of genetic exchange between Neanderthals
and
modern humans," Smith said. "When you look at the
anatomy of early
modern Europeans, you also find a number of features that are
hard to
explain unless you allow the Neanderthals some ancestral status.
And
actually, the Neanderthal mitochondrial DNA is not completely out
of the
modern human range, just on its extreme periphery."
The finding in Portugal last year of a 24,500-year-old early
modern
human child with distinctive Neanderthal characteristics,
published by
Trinkaus and European colleagues in June 1999, strongly supports
the
conclusion that Neanderthals and early modern humans both could
and did
share mates when they came into contact.
"Not only do we have the skeleton of a child in Portugal
showing
characteristics of common descent, but now we have evidence of
the two
groups coinciding in central Europe for several millennia,
allowing
plenty of time for the populations to mix," said Trinkaus, a
Washington
University professor of anthropology in Arts and Sciences.
The new Croatian findings also raise the question of who created
the
ancient tools unearthed at the Vindija cave site, located about
34 miles
north of the Croatian capital of Zagreb. Neanderthals are
commonly
associated with relatively crude stone tools, while early modern
humans
made more sophisticated stone and bone tools.
The Vindija site produced both kinds of tools, including a
beveled bone
probably used as the tip of a spear. "The big question is:
'Why do we
have a combination of tools?'" Smith said.
"It's possible Neanderthals developed all these tools or got
the bone
tools through trade with moderns," he added. Both of these
possibilities run counter to the generally accepted idea that
Neanderthals could not produce bone or use more sophisticated
stone and
bone tools.
Smith and Trinkaus conceived of the research project, secured
permission for dating of fossils and assembled the research team.
Other
team members are Ivor Karavanic at the University of Zagreb and
Maja
Paunovic of the Croatian Academy of Sciences.
Copyright 1999, UniSci
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*
CATASTROPHES:
THE DILUVIAL EVIDENCE
By Trevor Palmer, Nottingham Trent University, UK (10/28/99)
Paper presented at the SIS Silver Jubilee conference at
Easthamstead Park, 19 September 1999