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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