PLEASE NOTE:
*
CCNet, 29 November 1999
------------------------------
QUOTE OF THE DAY
The approach towards a meteor strike
would depend on its size,
Lord Sainsbury said. Asked whether this
would involve nuclear
weapons, he responded: "In some
cases it might just be a question
of evacuating the area where it took
place. In others, if it was
a very large object, one might
seek to deflect it. Either way,
it's clearly very sensible to have as
much time as possible to
devise any plans and that's why, it
seems to me sensible that
there should be international effort to
monitor these objects.
[...] If you knew one was going to land
on London you might think
it was worth spending a lot of money to
do something about it."
-- British Science
Minister, Lord Sainsbury, 29 November 1999
(1) UK GOVERNMENT PREPARES FOR METEOR (sic!) STRIKE
BBC Online News, 29 November 1999
(2) LUNAR LEONID METEORS
IAU Circular 7320
(3) 5000+ METEORS PER HOUR: LEONIDS YIELD FORMIDABLE STORM
Daniel Fischer <dfischer@astro.uni-bonn.de>
(4) JAPAN SPACEGUARD ASSOCIATION REGISTERED AS
NON-PROFIT
ORGANISATION
Syuzo Isobe <isobesz@cc.nao.ac.jp>
(5) COSMIC IMPACTS & THE MYSTERY OF THE MISSING MARTIAN
ATMOSPHERE
Andrew Yee <ayee@nova.astro.utoronto.ca>
(6) PURPLE SALT & TINY DROPS OF WATER IN METEORITES
Ron Baalke <baalke@ssd.jpl.nasa.gov>
(7) LUNAR LINK TO VOLCANIC PAST
Michael Paine <mpaine@tpgi.com.au>
==============
(1) UK GOVERNMENT PREPARES FOR METEOR (sic!) STRIKE
From the BBC Online News, 29 November 1999
http://news.bbc.co.uk/hi/english/uk_politics/newsid_541000/541376.stm
The UK government is to establish a panel of experts to advise on
the
risk of the Earth being hit by a meteor (sic!). Reactions to such
a
potential disaster could involve using nuclear weapons to deflect
a
meteor (sic!), or evacuating whole areas where it could strike.
Professor Mark Bailey, Director of the Armagh Observatory, has
campaigned for the establishment of a national centre and told
the BBC:
"Asteroids and comets pose a unique hazard to civilisation -
it is
unbounded in the sense that the potential risk is destruction,
even
extinction of our species.
"However, it is predictable with high precision and years
ahead,
provided you discover the objects," he added.
Science Minister Lord Sainsbury wants to establish a position on
the
possibility of a meteor (sic!) hitting the UK in order to
co-ordinate
an international approach.
He said: "We need to have a position in terms of
international
discussions on this and I've put together a team of people to
advise me
on that.
"It would be absurd to have each country to have programmes
like this
on their own. If ever there is a case to have international
action,
this is it."
The approach towards a meteor strike would depend on its size,
Lord
Sainsbury said. Asked whether this would involve nuclear weapons,
he
responded: "In some cases it might just be a question of
evacuating the
area where it took place. "In others, if it was a very
large object, one
might seek to deflect it.
"Either way, it's clearly very sensible to have as much time
as
possible to devise any plans and that's why, it seems to me
sensible
that there should be international effort to monitor these
objects.
"There are already programmes in other countries, America
already has a
substantial programme and I think Japan is taking action."
Nations would take whatever action was appropriate, regardless of
the
cost, Lord Sainsbury continued. "If you knew one was going
to land on
London you might think it was worth spending a lot of money to do
something about it."
Copyright 1999, BBC
MODERATOR’S NOTE: In view of the rather flawed terminology
used in
today’s BBC report, may I politely suggest that the first
task of the
new Spaceguard UK task force should be to advise science
reporters and
science ministers on the use of accurate information when dealing
with
the impact hazard. It would reassure the public to know that the
people
reporting on this endeavour actually know the difference between
meteors, asteroids and comets.
Benny J Peiser
============
(2) LUNAR LEONID METEORS
From the IAU Circular 7320
http://cfa-www.harvard.edu/iauc/07300/07320.html#Item1
On Nov. 19 D. W. Dunham, Applied Physics Laboratory, Johns
Hopkins
University, reported the visual observation by B. Cudnik
(Houston, TX,
0.36-m telescope) on Nov. 18 of a brief flash near the center of
the
moon's dark limb, at least as bright as psi1 Aqr nearby.
This event,
1'.7 from the moon's edge, was apparently confirmed by Dunham
(Mount
Airy, MD, 0.13-m telescope) on two half-frames of a videotape
that
showed fading by about 5 mag during the intervening 1/60
second. On
Nov. 23 and 24 Dunham reported his confirmation of two lunar
flashes
videorecorded by P. V. Sada (Monterrey, Mexico, 0.13-m telescope)
half
an hour after Cudnik's observation, as well as of two lunar
flashes
videorecorded by D. Palmer (Greenbelt, MD) up to an hour or so
earlier;
there was also a probable untimed additional visual confirmation
of the
Cudnik event by S. Hendrix (Cameron, MO, 0.11-m telescope).
Dunham has
summarized his own measurements of the five Nov. 18 events as
follows:
Disc.
UT
m1 m2 lambda beta Lunar location
h
m s
s
deg deg
Palmer 3 49 40.5 +/- 0.4
3 7 48 W 1
N 175 km SW of Kepler
Palmer 4 08 04.1 +/- 0.6
5 8 70 W 15 S 175
km S of Grimaldi
Cudnik 4 46 15.2 +/- 0.1
3 8 71 W 14
N 50 km ENE of Cardanus
Sada 5 14 12.93 +/- 0.05
7 8 58 W 15 N 200
km WNW of Marius
Sada 5 15 20.23 +/- 0.05
4 7 59 W 21
N 75 km S of Schiaparelli
The magnitude m1 is that on the first frame showing the event, m2
that
on the following half-frame; the first event listed also seems to
be
present on a third half-frame at mag 9. The selenographic
coordinates
(longitude lambda and latitude beta) and lunar location for the
first
two events are uncertain by 5 deg or more, but the others should
be
accurate to within about 2 deg (50 km). Following Dunham's
suggestion
that the flashes resulted from Leonid impacts on the moon, D. J.
Asher,
Armagh Observatory, computed that the center of the 1899 dust
trail
that evidently produced the 1999 Nov. 18 Leonid activity (cf.
IAUC
7311) by nominally passing 0.0007 AU from the geocenter would
have
passed 0.0002 AU from the selenocenter around 4h49m UT.
DD CIRCINI
A. C. Gilmore provides further photometry of DD Cir = Nova Cir
1999,
obtained as before (see IAUC 7249): Sept. 3.415 UT, V = 10.42,
U-B =
-0.43, B-V = +0.38, V-R = +2.01, V-I = +1.65, airmass = 1.50;
4.389,
10.38, -0.43, +0.35, +2.00, +1.57, 1.42; 13.368, 10.98, -0.46,
+0.14,
+1.82, +1.05, 1.43. Standard deviations are 0.01 mag or less.
(C) Copyright 1999 CBAT
1999 November
26
(7320)
Brian G. Marsden
Reproduced by permission.
===============
(3) 5000+ METEORS PER HOUR: LEONIDS YIELD FORMIDABLE STORM
From Daniel Fischer <dfischer@astro.uni-bonn.de>
Dear Benny,
You might be interested in this review about the Leonids'99 I
just put
at
http://www.astro.uni-bonn.de/~dfischer/mirror/158.html
Regards,
Daniel
===========
(4) JAPAN SPACEGUARD ASSOCIATION REGISTERED AS
NON-PROFIT
ORGANISATION
From Syuzo Isobe <isobesz@cc.nao.ac.jp>
Dear Dr. Peiser:
The Japan Spceguard Association (JSGA) was set up in October 1996
as a
working team with private members. Its activities were therefore
somewhat limited. Since the Japanese Congress introduced a new
law to
support the creation of non-profit organizations, the JSGA
applied to
become a NPO. On November 26, the JSGA was registered as an
official
NPO. We now have the right to set up contracts with our
governmental
agencies and organizations. It is requested by our funding
organization
for JSGA to operate our Bisei Spaceguard Center with two NEO and
Space
Debris telescopes.
It is scheduled that the 0.5 m telescope will be set at the BSGC
at the
beginning of January, 2000, and the 1.0 m telescope around May,
2000.
Yours sincererly,
Syuzo Isobe
President of Japan Spaceguard Association
National Astronomical Observatory
2-21-1, Osawa, Mitaka, Tokyo 181, Japan
Tel: 81-422-34-3645, Fax: 81-422-34-3641
E-mail: isobesz@cc.nao.ac.jp
==================
(5) COSMIC IMPACTS & THE MYSTERY OF THE MISSING MARTIAN
ATMOSPHERE
From Andrew Yee <ayee@nova.astro.utoronto.ca>
New Scientist
http://www.newscientist.com
UK Contact:
Claire Bowles, claire.bowles@rbi.co.uk,
44-20-7331-2751
US Contact:
New Scientist Washington office, newscidc@idt.net, 202-452-1178
Mystery of the missing atmosphere
As atmospheres go, it has mostly gone. Admittedly, if you plough
into
the Martian atmosphere at the speed of a meteorite, as the
misguided
Mars Climate Observer did in September, there is still enough
there to
tear you apart. But under most other circumstances, it is a poor
excuse
for an atmosphere. At the planet's surface, the pressure is a
paltry 1
per cent of that on Earth.
Why should Mars have so little atmosphere when Venus and Earth
have so
much? Though it might simply have been born that way, there are
plenty
of hints that the atmosphere was once much thicker -- the
evidence of
water, for example. Today the Martian surface is cold and
exceedingly
arid. But the surface bears unmistakable signs that liquid water
once
raged through flood channels and valleys, left shorelines in
craters
and may even have formed oceans in the Great Northern Basin. It's
hard
to be wet with an average temperature of about -53 C, so liquid
water
implies warmth. And warmth implies a thick insulating atmosphere,
replete with warming greenhouse gases such as carbon dioxide.
If the Martian atmosphere was once much thicker, where did all
the gas
go? Despite diligent searching, no one knows. But in the past
year,
NASA's Mars Global Surveyor -- which itself used the atmosphere
to
brake and change orbit -- has been collecting information that
could
answer that question. And its findings are not at all what its
designers expected.
In the 1980s, researchers developed a theory for why Mars was
once warm
and wet. First they calculated how much CO2 it would take to melt
the
Martian ice and allow water to flow, and came up with a figure of
between 5 and 10 bars (one bar is the pressure of about one Earth
atmosphere). That's rather a lot for a planet with only a few
millibars
left today, so they had to explain where the CO2 might have
disappeared
to since. According to their picture, the atmosphere sowed the
seeds of
its own destruction.
When liquid water is around, a CO2 atmosphere becomes unstable --
the
gas dissolves, chemically weathers the silicate rocks on the
planet's
surface and is ultimately locked up in the form of carbonates.
The
proof is beneath your feet. There was a time when CO2 dominated
the
Earth's atmosphere, which was probably a good deal thicker than
it is
today. Now, despite humanity's eager attempts to redress the
matter,
CO2 has dwindled to a trace of its former glory, making up less
than a
thousandth of the air we breathe.
The reason is that over billions of years, chemical weathering
has
stored a great deal of CO2 as carbonates. According to Jim
Kasting of
Pennsylvania State University in University Park, who was one of
the
researchers who put together the warm, wet, early Mars theory --
and
one of the first to point out some of its flaws -- if you
released all
the CO2 that is now locked up in the Earth's carbonate sediments
you'd
get about 60 atmospheres worth of the stuff.
If chemical weathering can destroy greenhouses so easily, why did
the
Earth not freeze as Mars did? The answer, the researchers
decided, was
recycling. On Earth, some of the CO2 from carbonates is recycled
through plate tectonics. When carbonate-rich sediments start
their
journey down into the mantle at a subduction zone, where one
plate
slides under another, they are heated up and release CO2 back
into the
atmosphere, where it can warm the planet.
On cold little Mars, though, the recycling seems not to have been
so
good. Unlike Earth, Mars doesn't have enough internal heat to
keep
pushing lumps of its crust around, or to resurface itself with
great
big burps, as Venus may have done. There is little evidence that
Mars's
inner fires ever drove a system of plate tectonics, and while the
planet may well have had some other ways of using its internal
heat to
recycle carbonates, they would have run out of oomph fairly early
on as
the planet's innards cooled down. CO2 recycling would have
started to
lag behind the production of new carbonates, and the atmosphere
would
have begun to shrink in earnest.
So far so good. Now all the researchers needed to do was find
some
carbonates on the planet's surface to confirm their story. The
best
technology for doing the job from space is infrared spectroscopy,
which
picks up features in the infrared spectrum unique to specific
minerals.
This year, Mars Global Surveyor's spectrometer, the Thermal
Emission
Spectrometer (TES), completed its first thorough study of the
planet,
covering almost three-quarters of the surface. According to the
scientist in charge of the instrument, Phil Christensen of
Arizona
State University, Tempe, it has found that carbonates make up
less than
15 per cent of the surface. Probably a lot less. "We're
trying to be
conservative with the 10 or 15 per cent -- there's basically no
discernible carbonate signature," says Christensen. "My
guess is that
the most profound discovery that TES will make and the most
interesting
paper we'll write is that there aren't carbonates on Mars, at the
surface at least."
If Christensen's suspicions are correct, then Mars researchers
face
some intriguing choices. They must either find another way to get
rid
of the atmosphere or make do with less atmosphere in the first
place --
or possibly do a bit of both.
Take the other hiding places first. There is probably some CO2
frozen
into the planet's soil, or hidden in dry-ice deposits underneath
the
water-ice exteriors of the polar caps (though other observations
from
Mars Global Surveyor are throwing some doubt on that second
possibility). Reservoirs like these could account for ten times
as much
CO2 as is currently seen in the atmosphere. But since the current
atmosphere is less than a hundredth of a bar, that isn't enough
to
explain the difference between past and present.
Then there could be carbonates hidden below the surface. The 13
Martian
meteorites found on Earth all contain faint traces of carbonate,
and
the oldest of them, ALH 84001, has veins of carbonate running
through
it. It's conceivable that you could lose a fair amount of CO2 in
the
Martian underground. Again, though, it doesn't seem likely that
you
could get rid of a few bars of atmosphere without leaving any
discernible carbonate sediments on the surface.
So perhaps the atmosphere quit the planet altogether. There are
two
ways this could have happened: very big impacts and very small
impacts. Asteroids and comets hitting a planet's surface can
throw
swathes of the atmosphere off at such high speeds that they
escape the
planet's gravity for good. In the very early days of the Solar
System,
when the planets had only just been assembled, there was plenty
of
rubble left over. During this period, known as the late heavy
bombardment, Mars was hit by dozens of large chunks and hundreds
of
smaller ones, all of which could mark the passing of parts of the
atmosphere.
After asteroid impacts eroded the early Martian atmosphere from
the
bottom up, a subtler process could have nibbled at it from the
top
down. The upper atmosphere of the planet is constantly being
buffeted
by the solar wind. In itself this wind is fairly harmless, since
it is
thin and made of very light particles, but it also carries a
magnetic
field. This can pick up ions from the upper atmosphere,
accelerate them
and then slam them back into their fellows. "You can have
ions slammed
into the upper atmosphere at more than 400 kilometres per
second," says
Bruce Jakosky of the University of Colorado at Boulder.
"It's like
shooting pool. On the break shot you knock everything all to
hell. You
can knock stuff out of the atmosphere entirely." This
process, called
sputtering, is still thought to be eroding Mars's atmosphere
today,
though no one knows how quickly.
How do these different processes fit together? The biggest factor
was
probably impacts. According to Kevin Zahnle of NASA's Ames
Research
Center in California, the evidence suggests that they stripped
off a
huge amount of the original atmosphere -- more than 99 per cent
of it,
in fact. That figure, he says, comes from looking at the ratios
of
different isotopes of xenon in the atmosphere.
The mixture of xenon isotopes in the Martian atmosphere today
contains
a far higher proportion of xenon-129 than is found in the Earth's
atmosphere, or in the Sun. Xenon-129 is produced by the decay of
iodine-129. For xenon-129 to be so predominant, the original
atmosphere
-- in which the mixture of xenon isotopes was presumably similar
to
that in the rest of the Solar System -- must have been more or
less
stripped off the planet before most of the radioactive iodine
inside
the planet had decayed. With hardly any other xenon around, the
newly
released gas would have quickly come to dominate the isotopic
distribution, as it does today.
But though Zahnle's calculations suggest that impact erosion was
a
scourge of biblical proportions, it did not succeed in flaying
away all
the atmosphere. It's hard to say how thick that remnant
atmosphere
was, but it could have been a good bit thicker than it is today.
Zahnle thinks some of the atmosphere may have sat out the
bombardment
trapped in the crust, emerging only when it was safe to do so. In
a
paper presented at the Fifth International Mars Conference in
Pasadena,
California, this summer -- the first really big meeting to be
saturated
with the heady new findings of the Mars Global Surveyor --
Kattathu
Mathew and Kurt Marti from the University of California, San
Diego,
described a new analysis of the gases trapped in the meteorite
ALH 84001.
These ancient Martian gases apparently correspond to the time
when the
rock first formed. They bear a xenon ratio quite like that seen
today,
and so presumably postdate the first great flaying. But the
meteorite's
nitrogen isotopes set it apart from the modern Martian
atmosphere.
Today's atmosphere is highly enriched with the heavy isotope of
nitrogen. But Mathew's samples of ALH 84001 show no such
enrichment.
As it happens, sputtering is particularly good at removing light
nitrogen. In the upper reaches of the atmosphere there is very
little
turbulence, and so a delicate isotopic layering takes place, with
the
lighter isotopes of each gas rising to the top. Since sputtering
works
from the top down, it is more likely to knock lighter isotopes
out than
the heavier ones. So the sample in ALH 84001 looks as though it
comes
from a time when sputtering had not yet begun -- from a time when
the
upper atmosphere of Mars was protected against the depredations
of the
solar wind. And this is where another intriguing discovery from
Mars
Global Surveyor comes in.
While the spacecraft was using the upper atmosphere of Mars to
change
its orbit, it flew quite low over the planet's southern highlands
--
low enough for its magnetometer to pick up unexpected signals
from the
crust. Since then it has become clear that, although Mars has no
global
magnetic field today, in its youth it had a very strong one,
traces of
which were imprinted on its crust. Again, Mars was too small to
keep
up such exertions for long. The internal energy that drove its
magnetic
dynamo must have run out fairly quickly, since it is only in the
oldest
crust that the magnetic field's signature has been seen.
As long as the magnetic field was around, it would have shielded
the
planet from the depredations of the solar wind. So the post-
bombardment atmosphere might have been able to stay reasonably
thick --
or at least thicker than it is today -- for as long as the
magnetic
field held up.
But was there enough to explain the water? It's hard to say.
Nobody
knows how fast the sputtering is happening today, or how strong
the
solar wind was in the early Solar System. While most estimates
have put
sputtering loss at a tenth of a bar or so over the planet's
lifetime,
Jakosky -- who made some of those predictions -- thinks it could
conceivably have been ten times more.
That still wouldn't add up to the pressure of between 5 and 10
bars
that researchers originally thought they needed to explain a
sustained,
relatively wet period early on. But they may have overestimated
the
planet's requirements. The models that called for many bars of
CO2 to
explain the presence of liquid water did not take into account
the
formation of clouds. It turns out that, in principle, clouds of
solid
CO2 might have warmed Mars up quite nicely, even with an
atmospheric
pressure of only half a bar.
In November 1997, Francois Forget of Pierre and Marie Curie
University
in Paris and Raymond Pierrehumbert of the University of Chicago
calculated that large dry-ice crystals in such an atmosphere
could be
very good at scattering thermal radiation back towards the ground
while
letting incoming visible and ultraviolet light through (Science,
vol
273, p 1273). A thin but cloudy atmosphere could have warmed Mars
during the earliest phases of its history and then been sputtered
away
when the cooling core shut down the magnetic field. As the
atmosphere
thinned, the soil would have been able to absorb most of the
relatively
small amount of CO2, and carbonate production could have been
minimal.
The problem is that just because cooling clouds can be found in a
model, doesn't mean they were ever there in real life. And
Kasting
points out that while some sorts of cloud may have warmed the
surface,
others might have cooled it -- just as different clouds affect
the
temperature in different ways on Earth.
Then there's the possibility that it was never really all that
warm in
the first place. Water can contrive to be liquid in some pretty
cold
places, at least fleetingly, and some think that a great many of
the
watermarks on Mars's surface may have formed in a few short, wet
catastrophes. As Zahnle puts it, "I have seen evidence of
liquid
silicate lavas on the surface of the Earth: do I need to conclude
that
the global temperature was 1500 K? All I can fairly conclude is
that
the liquid was there, and that the liquid was hot." The
river valleys
might have formed through the action of groundwater heated by
local
volcanism or impacts. Or they might have formed under transient
ice
sheets that later sublimed away.
Maybe warmth came in very brief spurts.. That would explain why,
despite
the presence of valleys, there is little evidence of sustained
erosion
in many of the old craters, and some of them maintain an almost
Moon-like sharpness.
Victor Baker of the University of Tucson in Arizona believes that
Mars
has sometimes been very wet indeed thanks to gases from inside
the
planet forcing warm water from the depths of the crust out onto
the
surface. But these floods would have lasted only ten thousands
years or
so. Even a dozen such wet spells would add up to only a tiny
fraction
of Martian history, and leave the southern highlands untouched by
erosion.
It shouldn't really come as a surprise that you can't make sense
of a
whole planet with a few space missions. But the complexities and
seeming contradictions of Mars's past are forcing the lesson
home. The
history of Mars may be more complex than the
"warm-and-wet-then,
cold-and-dry-now" model allowed. Mars's first billion years
may have
thrown up all sorts of perplexing puzzles, and to solve them
researchers will propose theories that stretch, like Jakosky's
ideas,
from the planet's molten heart to the very edge of space. The
thin
Martian atmosphere may make a poor planetary blanket, but as a
springboard for speculation it's second to none
###
Oliver Morton is a science writer based in London
New Scientist issue: 20th November 99
Source: Geo-Marine Letters (vol 18, p 285)
PLEASE MENTION NEW SCIENTIST AS THE SOURCE OF THIS STORY AND, IF
PUBLISHING ONLINE, PLEASE CARRY A HYPERLINK TO:
http://www.newscientist.com
===============
(6) PURPLE SALT & TINY DROPS OF WATER IN METEORITES
From Ron Baalke <baalke@ssd.jpl.nasa.gov>
Written by G. Jeffrey Taylor
Hawaii Institute of Geophysics and Planetology
November 24, 1999
Some meteorites, especially those called carbonaceous chondrites,
have
been greatly affected by reaction with water on the asteroids in
which
they formed. These reactions, which took place during the first
10
million years of the Solar System's history, formed assorted
water-bearing minerals, but nobody has found any of the water
that
caused the alteration. Nobody, that is, until now. Michael
Zolensky and
team of scientists from the Johnson Space Center in Houston and
Virginia Tech (Blacksburg, Virginia) discovered strikingly purple
sodium chloride (table salt) crystals in two meteorites. The salt
contains tiny droplets of salt water (with some other elements
dissolved in it). The salt is as old as the Solar System, so the
water
trapped inside the salt is also ancient. It might give us clues
to the
nature of the water that so pervasively altered carbonaceous
chondrites
and formed oceans on Europa and perhaps other icy satellites.
However,
how the salt got into the two meteorites and how it trapped the
water
remains a mystery - at least for now.
Full story here:
http://www.soest.hawaii.edu/PSRdiscoveries/Nov99/PurpleSalt.html
=================
(7) LUNAR LINK TO VOLCANIC PAST
From Michael Paine <mpaine@tpgi.com.au>
Dear Benny,
See the BBC item: Lunar link to volcanic past
http://news.bbc.co.uk/hi/english/sci/tech/newsid_536000/536814.stm
This reports on a new theory that tidal effects within the
Earth's
crust may have caused some major lava eruptions. I question,
however,
whether theory would survive Occam's razor. A large comet or
asteroid
impact seems much more plausible. For example, with the latest
research
suggesting that it has a diameter of 70km (CCNet 23 Nov 99),
Comet
Hale-Bopp would have done very nicely (overkill, in fact).
Michael Paine
The Planetary Society Australian Volunteers
----------------------------------------
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