PLEASE NOTE:


*

CCNet, 6 October 1999
------------------------


(1) ANOTHER POTENTIALLY HAZARDOUS ASTEROID DISCOVERED
    SPACEVIEWS, 5 October 1999

(2) ASTRONOMERS ISSUE ASTEROID ALERT
    MSNBC SPACE NEWS, 5 October 1999

(3) COSMIC DUST AND CLIMATE CHANGE
    Doug Keenan <doug.keenan@virgin.net>

(4) THE 4000 BP EVENT
    Doug Keenan <doug.keenan@virgin.net>

(5) ESF WORKSHOP "METEORITE IMPACTS IN PRECAMBRIAN SHIELDS"
    Iain Gilmour <I.Gilmour@open.ac.uk>

(6) THE IMPACT HAZARD FROM SMALL ASTEROIDS
    Luigi Foschini <L.Foschini@isao.bo.cnr.it>

(7) COMPANION TO COMET GRIGG-SKJELLERUP
    Andrew Yee <ayee@nova.astro.utoronto.ca>

(8) SPACE DEBRIS MEETING
    Andrew Yee <ayee@nova.astro.utoronto.ca>

(9) SMOKE IN THE ATMOSPHERE INHIBITS RAINFALL
    NASANews@hq.nasa.gov



==================
(1) ANOTHER POTENTIALLY HAZARDOUS ASTEROID DISCOVERED

From SPACEVIEWS, 5 October 1999
http://www.spaceviews.com/1999/10/05b.html

Astronomers reported this week the discovery another near-Earth
asteroid that has an extremely small, but non-zero, chance of
colliding with the Earth in the mid-21st century.

The asteroid, 1999 RM45, has less than a 1-in-100 million chance of
colliding with the Earth in either 2042 or 2050, according to
preliminary orbit predictions made by scientists at the University of
Pisa, Italy, and announced Monday, October 4.

The asteroid, estimated to be between 340 and 770 meters (1,120 and
2,540 feet) in diameter, was discovered September 14 by the LINEAR
telescope in New Mexico. A total of 38 observations were made by
astronomers in the week following discovery, enough for a preliminary
orbit determination, although the asteroid has not been observed
since the 20th.

Based on the preliminary orbit, Steve Chesley of the University of
Pisa found two potential but very unlikely collisions between the
Earth and 1999 RM45 next century. In March of 2042, the asteroid
as about a 1-in-300 million chance of hitting the Earth, and eight
years later has a 1-in-250 million chance of a collision.

The asteroid is still a 0 on the Torino Scale, a 0-to-10 measurement
of the threat posed by an asteroid unveiled earlier this year. A 0 on
the Torino Scale corresponds to an object with a smaller probability
of impact than that for a random undiscovered object of similar size.

The announcement of the potential discovery was made to encourage
astronomers to observe the asteroid, currently at about magnitude 19
and dimming, before it is lost..

"Such a very low probability of impact means that the risk posed by
RM45 is not of serious concern to the public at large," said Chesley
in a posting to a minor planets mailing list, "however, I think it is
very important for the NEO [Near-Earth Object] community to take all
reasonable and practical steps to ensure that this PHA
[Potentially-Hazardous Asteroid] is not lost, or at least to improve
the orbit as much as possible before it does become lost."

Several asteroids have been discovered in the last two years that, at
least for a time, has a small possibility of a collision with the
Earth in the 21st century. In addition to the well-publicized 1997
XF11 affair in March 1998, asteroids 1999 AN10 and 1998 OX4 were
found earlier this year to have small impact probabilities. While
1998 OX4 has been lost, an impact by 1999 AN10 has been ruled out by
other observations.

These discoveries, however, have convinced at least one observer of
the need for dedicated telescopes to follow-up NEO discoveries.
"Given the faintness of RM45, it would appear that the most important
need for the NEO search community is to have at its disposal a large
telescope (specifically dedicated for NEO searches) which is powerful
enough to search faint objects such as RM45 (i.e. mag 22-23-24) when
such observations are really needed," noted Benny Peiser, moderator
of the Cambridge-Conference Network mailing list.

"With a record 9 new NEOs discovered in the last few days alone,"
Peiser adds, "it is clear that the need for adequate follow-up
instrumentation will become even more relevant in the near future."

Like so many other NEOs, 1999 RM45 was discovered by the LINEAR
telescope in New Mexico. Astronomers hope others will observe the
asteroid so they can better refine its orbit and determine what
collision probability, if any, it has.

Copyright 1999, SpaceViews

=======================
(2) ASTRONOMERS ISSUE ASTEROID ALERT

From MSNBC SPACE NEWS, 5 October 1999
http://www.msnbc.com/news/319598.asp?cp1=1#BODY

Astronomers issue asteroid alert
Further observations likely to eliminate chance of collision

By Alan Boyle
MSNBC

Oct. 5 — Asteroid-watchers are drawing attention to another potential
threat — although the risk of a collision with Earth is
astronomically small. There’s less than one chance in 100 million
that Asteroid 1999 RM45 could hit Earth in the year 2042 or 2050,
astronomers say. Further observations most likely will completely
eliminate even that small chance, but experts say they expect more
such alerts to crop up.

The extremely faint asteroid was first spotted by the Lincoln Near 
Earth Asteroid Research (LINEAR) project on Sept. 14, and its course
has been tracked over only six days’ worth of its orbit. In a message
to fellow asteroid-watchers, University of Pisa astronomer Steven
Chesley said Monday that there was a “critical need of follow-up.”

Based on the limited observations so far, Chesley and his colleagues 
calculated potential orbits that could put the asteroid, known as
1999 RM45, on an collision course with Earth in 2042 or 2050. But the
estimated risk of collision — less than one chance in 100 million —
is far lower than the probability of a previously undetected
half-mile-wide (1-kilometer-wide) comet or asteroid hitting the earth.
NASA has estimated that risk at between one in 100,000 to one in a
million.

Chesley, an American who works with Italian colleagues Andrea Milani 
and Giovanni Valsecchi at the Pisa program, said 1999 RM45 should not
be of serious concern to the public.

“However,” he said in his posting, “I think it is very important for 
the NEO (near-Earth object) community to take all reasonable and
practical steps to ensure that this PHA (potentially hazardous
asteroid) is not lost, or at least to improve the orbit by as much as
possible before it does become lost.”

The concern is that the asteroid, now in the constellation Cetus, may
fade from sight before enough observations are made to eliminate the
possibility of a collision in the foreseeable future.

Currently, Chesley told MSNBC in an e-mail message, “an observer
would have to be very lucky in order to detect it with a telescope 
much smaller than a half-meter (19 inches) in aperture. This puts it
out of reach of most, but not all amateurs, and there is only a small
handful of suitable professionally operated telescopes available to
do follow-up.”

On Tuesday, he reported that the Siding Spring Observatory in
Australia had made fresh observations of the asteroid. “It will be
some time before I know how these measurements affect the orbit,” he
told MSNBC.
                                
THE ASTEROID THREAT

Over the past couple of years, several near-Earth asteroids have
sparked urgent calls for closer monitoring, but in each case, more
detailed observations have reduced the collision risk to zero.
Nevertheless, those alerts — as well as Hollywood blockbusters such
as “Deep Impact” and “Armageddon” — have drawn increasing attention
to the potential threat posed by asteroids and comets.

Scientists say a collision with an object bigger than a kilometer
wide would cause a catastrophe of thermonuclear proportions. Past
impacts are thought to have caused mass extinctions, including the
demise of the dinosaurs 65 million years ago.

Last year, NASA said only 10 percent of such objects, estimated to
number more than 1,000, were being monitored. But since then, thanks
to LINEAR and other efforts, the detection rate has increased
dramatically.

Donald Yeomans, an astronomer at the Jet Propulsion Laboratory who
heads NASA’s Near-Earth Object Program Office, said he expected many
more cases like 1999 RM45 to arise.

“This is typical of a class of objects that we’re gong to get every
couple of months, now that we have the software to monitor them,” he
told MSNBC.

1999 RM45 was of “no real concern,” Yeomans said. He noted that the
asteroid would rate a “flat-out zero” on the recently announced
Torino scale now being used to evaluate impact hazards.

“But Chesley’s correct in pointing out that it would be nice if some
of the more sophisticated amateurs could get a few more observations
of it in an effort to pin its orbit down a little bit better,” he
added.

Chesley agreed that the threat posed by 1999 RM45 was “certainly only
of academic interest.” “The ones to be concerned about are the
undiscovered asteroids,” he said. “The so-called background risk
calls for an impact large enough to cause a global climatic disaster
every few hundred thousand years. This translates into about one
chance in 3,000 that such a catastrophe will occur in the typical
human life span.”

Copyright 1999, MSNBC

===================
(3) COSMIC DUST AND CLIMATE CHANGE

From Doug Keenan <doug.keenan@virgin.net>

Benny,

B. Napier [British Archaeological Reports 728 (editors--B.J. Peiser
et al.), 1998] suggests that the Little Ice Age might have been caused
by dust in the Taurid meteoroid stream.  S. V. M. Clube [BAR 728]
refers to a long-term climate rhythm--first indicated by G. Bond et al.
[Science, 1997] --and suggests that this rhythm might also be caused by
Taurid dust.

Bond et al. have just published some important follow-up work:

Bond, G. C. & seven others, "The North Atlantic's 1-2 kyr Climate
Rhythm", Mechanisms Of Global Climate Change At Millennial Time Scales
(editors-- P. U. Clark, R. S. Webb & L. D. Keigwin), Geophysical
Monograph Series 112 (American Geophysical Union, Washington DC, 1999).

They substantially strengthen their 1997 arguments for the climate
rhythm and give evidence that the rhythm has endured for at least 50k 
years.  The rhythm is also shown to be related to Heinrich Events
(massive discharges of icebergs into the N Atlantic),
Dansgaard/Oeschger Cycles (changes in Greenland ice cores that
indicate major changes in ocean circulation), and the Little Ice Age.
Bond et al. do not propose a mechanism for the rhythm.

The above is only suggestive.  But the suggestion seems to be that
cosmic dust might have a huge effect on climate.

Cheers,
Doug Keenan
http://freespace.virgin.net/doug.keenan

================
(4) THE 4000 BP EVENT

From Doug Keenan <doug.keenan@virgin.net>

Benny,

In his CCNet posting on 1999-09-24, Dr. Vaan makes some remarks that
merit comment.

> Proposing volcanic and impact theories is all very well, after all we
> do have evidence of an igneous event of sorts at around the same time.
> A couple of points though.
>
> 1. As far as the Akkad story goes, we have a tephra right before the
> dust event which correlates well from the Tell Leilan site to the
> Cullen and deMenocal Gulf of Oman core. One difficulty though - the
> Gulf of Oman tephra lies anything up to 140 years prior to the dust
> peak. There's a lag. Something that Courty (1998) is also aware of.

Cullen & de Menocal have not yet published their work.  Based on Kerr
[Science, 1998], the core was sampled at intervals that were ~140 years
apart. The tephra is in the sample preceding the earliest sample that
contains the dust peak.  For this reason, apparently, Kerr says "less than
about 140 years".  In other words, the tephra fell in the preceding sample:
the lag might be <<<140 years.

Additionally, it could take decades for the drought--which seems to 
have occurred only in winter--to force a desertification severe enough
to show up in places as isolated as the Gulf of Oman.

(Cullen & de Menocal have now submitted their paper.  I would prefer to
avoid more consideration of the lag's duration until that appears.)

> 2. At the moment it could have been either or neither.. I note also that
> Courty (1998) declines to make the distinction during the Syrian
> studies and also that the entire picture is shrouded somewhat by
> variations in the preservation of that tephra. We have absolutely no
> handle on the magnitude of the impact/eruption which is very important
> to implying it as an agent.

Courty [1998] reports the absence of the materials usually associated
with a cosmic impact: this is evidence against such an impact.  M.-A.
Courty [private comm.] has agreed that a possible explanation for her
data is an eruption whose ejecta contained oil/gas; no other credible
explanation has been suggested, as far as I know.

A variety of data has been cited to support the claim that the eruption
was colossal.  Dr. Vaan's remark appears to ignore this.

> 3. Importantly there is plenty of room for other mechanisms. Simple
> autofluctuation as a response to declining insolation over the
> Holocene, other oceanographic mechanisms, feedback involving vegetation
> cover and others. All are still firmly in the ring (a volcano elsewhere
> even...).

The cited studies show that the upheaval of 4k BP endured for at most a
few centuries, before climate largely recovered.  Changes in insolation
could not reasonably explain the timing or amplitude of the upheaval
(see, for example, section 4.1 of Gasse & Van Campo [EPSL, 1994]).

I don't know of other oceanographic mechanisms that could account for
the upheaval.  If Dr. Vaan does, he should describe them.

The recent modelling work that I am aware of (most recently, M.
Claussen et al. [Geophys.Res.Lett., 1999]--discussed in CCNet July 9
[item 4]) is inconsistent with Dr. Vaan's indicated vegetation
response.

The hypothesis that the trigger for the upheaval was a very large
eruption has two characteristics in its favour.  First, there is a
plausible mechanism by which it (an eruption) could have triggered the
upheaval--at least for Europe, North Africa, and the Atlantic.  Second,
there is good evidence that it occurred immediately prior to the
upheaval.  No other hypothesis has been suggested that has either of
these characteristics.

> ....  The high NAO brings extra
> precipitation to northern Europe, what then of the widespread
> regressions in the majority of N. Europe's lakes? (Harrison et
> al.(1993)

Harrison et al. [Clim.Dynam., 1993] show (and model) lake levels in S
Sweden and Estonia. In S Sweden the regression began c. 5500 BP and
endured for well over a millennium.  As Harrison et al. note in their
follow-up work [Quatern.Res., 1996], real palaeodata shows that
"broad-scale patterns are interrupted by shorter term
fluctuations"--which they did not consider. They are interested in
millennial-scale changes; the upheaval lasted <300 years.

Harrison et al. [1993] show no real regression for Estonia.

> Other points include the fact that the event is not necessarily unique.
> The Early-Mid Holocene transition has a similar trace in the
> palaeo-record. Also there has been no clear separation made between
> this Mid-Holocene break and the general Mid-Holocene transition from
> the warmer Early/Mid Holocene (the end of the Atlantic period in the
> Blytt-Sernander classification). Some palaeo-records point to a
> distinct stepwise deterioration in climate across the 4-5KBP  period,
> of which this event could easily be a part of.

The Early-Mid Holocene transition does not have a similar trace. There
is a stepwise climatic change around 5k BP: the Mid-Late transition. 
That change lasted for millennia and occurred before the (non-step)
upheaval of 4k BP. Graphs of palaeodata readily show the difference
between (i) an enduring change c. 5k BP and (ii) a transient change c.
4k BP.

Cheers,
Doug Keenan
http://freespace.virgin.net/doug.keenan

================
(5) ESF WORKSHOP "METEORITE IMPACTS IN PRECAMBRIAN SHIELDS"

From Iain Gilmour <I.Gilmour@open.ac.uk>

ESF WORKSHOP "METEORITE IMPACTS IN PRECAMBRIAN SHIELDS"
Lappajarvi, Finland
May 24-28, 2000

with an excursion to Saaksjarvi and Karikkoselka impact structures

Conveners
Lauri J. Pesonen (Geological Survey of Finland (GTK))
Martti Lehtinen (Geological Museum)

co-conveners
Seppo Elo, Liisa Kivekas, Hannu Kujala, Marja-Liisa Leskinen, Pekka
Pihlaja, Markus Vaarma (all in GTK, Finland), Alex Deutsch (University
of Muenster, Germany) and Juri Plado (University of Tartu, Estonia)

The 4th workshop of the ESF-IMPACT programme will focus on
characterization of meteorite impact structures of all ages and
sizes occurring in Precambrian shields where the majority of the
recognized impact structures on the Earth have been found. The 
Fennoscandian Shield in northern Europe, for example, has at least
32 impact structures of which 9 are located in Finland. This
shield is important for impact cratering research because it is
well exposed, easily accessible and mapped in detail. Almost all
parts of Fennoscandia are now covered by high-resolution ground,
airborne and satellite geophysical maps and images providing an
excellent data base for identification and characterization of
impact structures in 3-dimensions and for dating impact events.

The workshop will cover the following themes:

* Impact records in time and space with a special focus on Precambrian
  shields
* Geophysical identification and modelling of impact structures on land
  and shallow seas
* Dating impact structures, impact events or impact generated layers
* The role of drilling through impact structures: case histories
* Shock effects in rocks from microstructures to mega features
* Economic significance of impact structures
* Special Session on the Popigai impact structure

The workshop will take place in the Kivitippu Spa Hotel ("Falling
Rock Hotel") within the Lappajarvi impact crater. A short
excursion to Lappajarvi impactite outcrops will be arranged during
the workshop. A post-workshop excursion will take place May 27-28,
2000, to the Karikkoselka and Saaksjarvi impact craters on the
return route from Lappajarvi to Helsinki. En route to Helsinki a
stop is planned to visit the Satakunta sandstone which hosts the
world's oldest micrometeorites. Abstracts of the workshop will be
published in a GTK-Special Paper. The presentations (oral or
poster) will be published in Lecture Notes in Earth Sciences
(Springer Verlag) after the workshop. No print-only contributions
are accepted. Partial financial assistance will be available from
ESF IMPACT programme funds to support participants from IMPACT
member countries. The annual meeting of the ESF IMPACT steering
committee will be held at the workshop.

Abstract deadline: March 15, 2000

For Further Information

Dr. Lauri J. Pesonen
Geological Survey of Finland
P.O. Box 96, FIN-02151 Espoo, Finland
Phone: +358-205 50 2269/+358-40-5015533
Fax: +358-205 50 12
Email: Lauri.Pesonen@gsf.fi

Dr. Martti Lehtinen
Geological Museum
P.O.Box 11, FIN 00014 University of Helsinki, Finland
Phone: +358-9-19123424
Fax: +358-9-19123466
Email: Martti.Lehtinen@helsinki.fi

or see the ESF-IMPACT website at http://psri.open.ac.uk/esf

============
(6) THE IMPACT HAZARD FROM SMALL ASTEROIDS

From Luigi Foschini <L.Foschini@isao.bo.cnr.it>

Dear Friends,

I would like to inform you that today I have submitted the paper:
"The impact hazard from small asteroids: current problems and open
questions" by Luigi Foschini,

for the special issue of Planetary and Space Science dedicated to the
IMPACT Workshop held in Torino on June 1-4, 1999.

In this paper I have exposed some questions about the impact hazard
from small asteroids, I hope in way better than during my short
intervention in Torino.

You can download the PS file of the preprint from my personal home page:

http://www.isao.bo.cnr.it/~dinamica/foschini/

I will greatly appreciate any comment or suggestion.

Greetings

Luigi

Dr. Luigi Foschini
ISAO - CNR
Via Gobetti 101, I-40129 Bologna (Italy)
Tel. +39 0516399620; Fax  +39 0516399654
Email: L.Foschini@isao.bo.cnr.it
Home Email: luifosc@tin.it <=== NEW !!
* PERSONAL HOME PAGE: <=== NEW !!
http://www.isao.bo.cnr.it/~dinamica/foschini/

=============
(7) COMPANION TO COMET GRIGG-SKJELLERUP?

From Andrew Yee <ayee@nova.astro.utoronto.ca>

ESA Science News
http://sci.esa.int

28 Sep 1999

Companion to comet Grigg-Skjellerup discovered using Giotto data?

On 13/14 March 1986, the European Space Agency's Giotto spacecraft
obtained the first close-up pictures of a comet nucleus during its
close flyby of Halley's Comet. An historic second comet encounter
followed on 10 July 1992 when Giotto flew within 200 km of Comet
Grigg-Skjellerup.

Seven years later, continuing analysis of data from Giotto's Energetic
Particle Detector (EPONA) has led to the conclusion that a second
comet, possibly a fragment of the main nucleus, may have been
accompanying Grigg-Skjellerup. The new results have been obtained by
Professor Susan McKenna-Lawlor, the Irish Principal Scientific
Investigator for the EPONA instrument, and Russian scientist Dr.
Valeri Afonin. Their discovery is based on fluctuations in the
energetic particle data recorded by EPONA.

One of the most important aspects of the Grigg-Skjellerup encounter
was that it enabled scientists to use the same instruments to compare
the fairly inactive Grigg-Skjellerup with Comet Halley, its much
larger, more active cousin. A number of experiments on board Giotto
were functioning during both encounters.

One of these was EPONA, which has the capability to record charged
particles -- protons and heavier ions -- with energies ranging from
several tens of keV to several tens of MeV. (One electron volt or eV
is the amount of energy gained by an electron when it is accelerated
through a potential difference of one volt.) Characteristic
fluctuations in the energetic particle records allowed EPONA to
detect the same cometary boundaries at Halley and Grigg-Skjellerup as
Giotto's other particles and fields experiments.

Recent, detailed analysis of EPONA data by McKenna-Lawlor and Afonin,
(described in the journal Planetary and Space Science Vol. 47, p.
557-576 and Circular No. 7243 Central Bureau for Astronomical
Telegrams IAU, 1999 August 25), has revealed a complex particle
enhancement in the energy range 60-100 keV. This increase was
recorded by EPONA some 90,000 km beyond Grigg-Skjellerup.

Several possible explanations for this flux enhancement were
considered, but the overall conclusion was that it constituted the
signature of a 'companion' comet, three to four times smaller than
Grigg-Skjellerup and with a correspondingly lower gas production
rate. It is unlikely that these two objects have existed side by side
from the beginning of their existence. A more probable explanation is
that the smaller object broke away from Grigg-Skjellerup shortly
before the Giotto encounter. Splitting of cometary nuclei is a well
known phenomenon that can occur even at large distances from the Sun.

This is the first time that the discovery of a comet using energetic
particle data has been claimed.

Contacts:
Prof. Susan McKenna-Lawlor
Space Technology Ireland
National University of Ireland
Maynooth, Co. Kildare, Ireland
Phone: +353-1-6286788
E-mail: stil@may.ie

Dr. Valeri Afonin
Institute of Space Research
Moscow
Phone: +7-0953331023
E-mail: vafonin@mx.iki.rssi.ru

Note for the editors:
Splitting of cometary nuclei is a well known phenomenon that can
occur even at large distances from the Sun. In the case of
Grigg-Skjellerup, evidence for small-scale fragmentation of the
nucleus was also identified from Giotto's Optical Probe Experiment
(OPE).

The Optical Probe detected a number of striking 'spike' features or
'events' during the Grigg-Skjellerup flyby. While scattering of
sunlight caused by dust impacts on the spacecraft body may account
for some of these, the complex data profiles can also be explained by
activity from dust jets in the comet's inner-most coma.

One particular event occurring at least 1000 km from the comet may
have been caused by the presence of a small nucleus fragment. The
evidence indicates that a chunk, 10-100 m in radius, had broken away
from the comet and passed around 50 km from the spacecraft. Despite
its small size, it seemed to be producing a small dust coma of its
own. Unfortunately, the particular event detected by EPONA was not
seen in the OPE data.

(ref. McBride, N., S.F. Green, A.C. Levasseur-Regourd, B.
Goidet-Devel and J.-B. Renard, The inner dust coma of comet
26P/Grigg-Skjllerup: multiple jets and nucleus fragments? MNRAS 289,
535--553, 1997.)

USEFUL LINKS FOR THIS STORY

* Space Technology Ireland
  http://www.may.ie/academic/physics/stil.shtml

* Giotto's encounter with Grigg-Skjellerup
  http://sci.esa.int/pr-doc/thirty-dis3.html

[IMAGE CAPTION:
http://sci.esa.int/image.cfm?TypeID=1&ContentID=6991&table=ContentTable&Storytype=9]
Energetic particle signature recorded by the EPONA instrument on
board Giotto in the energy range ~ 60-100 keV. The data are believed
to represent the signature of a companion to Comet Grigg-Skjellerup.
Particle count rate is shown on the vertical axis. Time and distance
from the comet are shown on the bottom scale. (Courtesy Susan
McKenna-Lawlor)

=================
(8) SPACE DEBRIS MEETING

From Andrew Yee <ayee@nova.astro.utoronto.ca>

European Space Agency
Press Release Nr. 41-99
Paris, France 4 October 1999

World experts on space debris meet in Europe on 11-13 October

Space debris experts from around the globe will gather from 11 until
13 October 1999, at the European Space Agency Operations Centre
(ESOC) Darmstadt/Germany for the 17-th meeting of the Inter-Agency
Space Debris Coordination Committee (IADC). IADC is concerned with
all technical issues of the space debris problem. The main objectives
of IADC are to exchange results of research in the field of space
debris, to cooperate in research activities and to identify debris
mitigation options.

The 17-th IADC will discuss ways and methods to control the growing
amount of orbiting debris. Radar and optical telescopes regularly
track over 10,000 artificial objects in space. The number of
untrackable objects in the size range from 1 cm to 10 cm, that could
seriously damage an operational spacecraft, is estimated at between
100,000 and 150,000. The International Space Station (ISS) will be
equipped with about 200 shields in order to defeat impacts of
particulates up to about 1 – 2 cm size.

Some recent and current topics of the IADC include

* guidelines for the disposal of spacecraft in the geostationary orbit;
* data exchange procedure and communications for reentry of risk
  objects;
* common database of space objects;
* risk assessment for the 1999 Leonids and countermeasures;
* measures to reduce the growth of the debris population in Low-Earth
  Orbit.

The results from the work of IADC will provide a technical basis for
deliberations on space debris at the United Nations Committee on the
Peaceful Uses of Outer Space (UNCOPUOS).

Media representatives will have the opportunity to be briefed on the
space debris problem and on the main results of the 17-th IADC on 13
October at 15:00, at ESOC, Building H, Robert-Bosch Strasse 5,
Darmstadt.

Those wishing to attend the briefing are kindly requested to fill out
the attached form and fax it to ESOC Public Relations, Darmstadt.
Fax: +49 6151 902 961. [NOTE: Form is not attached here. - A.Y.]

=================
(9) SMOKE IN THE ATMOSPHERE INHIBITS RAINFALL

From NASANews@hq.nasa.gov

David E. Steitz
Headquarters, Washington, DC                  Oct. 5, 1999
(Phone:  202/358-1730)

Allen Kenitzer
Goddard Space Flight Center, Greenbelt, MD
(Phone:  301/286-2806)

Harvey Leifert
American Geophysical Union, Washington, DC
(Phone:  202/777-7507)

RELEASE:  99-110

SPACECRAFT PROVIDES FIRST DIRECT EVIDENCE: 
SMOKE IN THE ATMOSPHERE INHIBITS RAINFALL

     For the first time, researchers have proven that smoke from
forest fires inhibits rainfall. The findings, to be published in
the Oct. 15 issue of Geophysical Research Letters, are based on an
extensive analysis of data taken from NASA's Tropical Rainfall
Measuring Mission (TRMM) spacecraft.

     The study shows that the "warm rain" processes that often
create rain in tropical clouds are practically shut off when the
clouds are polluted with heavy smoke from forest fires.  In these
clouds, scientists found, the cloud tops must grow considerably
above the freezing level (16,000 feet) in order for them to start
producing rain by an alternative mechanism.

     "We've seen evidence of decreased precipitation in clouds
contaminated by smoke, but it wasn't until now that we had direct
evidence showing that smoke actually suppresses precipitation
completely from certain clouds," said Dr. Daniel Rosenfeld, the
paper's author and a TRMM scientist at the Institute of Earth
Sciences, Hebrew University of Jerusalem.

     Scientists have a keen interest in how changes in global
precipitation affect human activities, such as crop production,
and the global rainfall weather pattern.  More precise information
about rainfall and its variability is crucial to understanding the
global climate and predicting climate change.

     In his paper, Rosenfeld highlights one specific area:
Kalimantan, Indonesia.  During the satellite's overpass on March
1, 1998, the southeastern portion of the island was engulfed in
smoke, while the northwestern portion was relatively smoke free. 
The spacecraft's radar detected precipitation in smoke-free
clouds, but almost none in the smoke-plagued clouds, showing the
impact of smoke from fires on precipitation over the rainforest.

     "It's important to note that this is not a unique case," said
Rosenfeld.  "We observed and documented several other cases that
showed similar behavior.  In some instances even less severe smoke
concentration was found to have comparable impacts on clouds."

     This research further validates earlier studies on urban air
pollution showing that pollution in Manila, the Philippines, has
an effect similar to forest fires, according to Rosenfeld.

     "Findings such as these are making the first inroads into the
difficult problem of understanding humanity's impacts on global
precipitation," said Dr. Christian Kummerow, TRMM project
scientist at NASA's Goddard Space Flight Center, Greenbelt, MD.

     Raindrops in the atmosphere grow by two means.  In the first,
called the "warm rain" process, a few cloud drops get large enough
to start falling.  As they fall, they pick up other cloud drops
until they become big enough to fall to Earth as raindrops.

     The second process requires ice particles and water colder
than 32 degrees Fahrenheit.  Ice particles surrounded by this
"supercooled" water may grow extremely rapidly as water freezes
onto the ice core.  As these large ice particles fall, they
eventually melt and become raindrops.

     Scientists have known for some time that smoke from burning
vegetation suppresses rainfall, but did not know to what extent
until now.  Thanks to TRMM observations, scientists are able to
see both precipitation and cloud droplets over large areas,
including clouds in and out of smoke plumes.

     TRMM has produced continuous data since December 1997. 
Tropical rainfall, which falls between 35 degrees north latitude
and 35 degrees south latitude, comprises more than two-thirds of
the rainfall on Earth.

     TRMM is a U.S.-Japanese mission and part of NASA's Earth
Science Enterprise, a long-term research program designed to study
the Earth's land, oceans, air, ice and life as a total system.  
Information and images from the TRMM mission are available on the
Internet at URL:    http://trmm.gsfc.nasa.gov/


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*

THE BIG ORIGIN OF LIFE DEBATE CONTINUES
----------------------------------------

From Larry Klaes <lklaes@bbn.com>

From Science-Week <prismx@scienceweek.com>

ON INTERPLANETARY BIOTIC TRANSFER

The techniques and data available to any generation in science differ
more or less from the techniques and data available to the generation
that preceded it. And so it makes sense for each generation to
reexamine important still-unanswered questions in terms of
possibilities. One such question concerns the origin of life on
Earth: Did life originate here on Earth, or did "living" entities
arrive here from elsewhere as the result of one or more natural
cosmic processes? What are the possibilities to be reasonably
considered, now that several decades of modern astronomy,
astrophysics, and space exploration have occurred? In general, the
term "panspermia" is the name given to the idea that life was
introduced on Earth from elsewhere in the Universe. This is a
classical notion, fostered by the chemist Svante A. Arrhenius
(1859-1927) in the early part of the 20th century [*Note #1].

... ... Paul Davies (Imperial College London, UK) presents a review
of current ideas concerning the seeding from elsewhere of life on
Earth, the author making the following points:

     1) In recent years, several experiments have been performed to
test the viability of bacteria and viruses under space conditions. In
one of these experiments, the bacterial species Bacillus subtilis was
maintained nearly 6 years in space aboard the NASA Long Duration
Exposure Facility, and a series of filters were used to determine
separately the effects of vacuum, solar radiation, and cosmic rays.
Another experiment simulated the effect of 250 years of space
exposure in the laboratory. The results of these experiments indicate
that microbes cope relatively easily with the cold and the vacuum, in
effect becoming freeze-dried and this acting as a preservative. Some
bacteria form *spores under these conditions. In general, under harsh
conditions such as these, microbes apparently go into suspended
animation, their metabolism ceases, and they merely remain inert
until circumstances improve.

     2) The most lethal form of radiation in interplanetary space is
the ultraviolet radiation of the Sun. This radiation, however, can be
screened by a thin layer of material, and it has been pointed out
that cool *red giant stars spew out large quantities of carbon, and
that space-faring bacteria in such a star system might therefore
become coated in soot and be shielded from the worst of the
ultraviolet radiation.

     3) Another harmful radiation in space is galactic *cosmic
radiation, the collection of high-energy subatomic particles that
arises from the deeps of space. It is expected that over time the
cumulative effects of such radiation would prove deadly to living
systems. However it is possible to imagine scenarios in which
microbes are at least partially shielded even from this ubiquitous
hazard. In general, the long-term survival of bacteria or other
microbes in space might occur because of rock-shielding from cosmic
rays. A thin film of carbon affords protection from ultraviolet
light, but a thick mantle of rock is needed to shield organisms from
high-energy cosmic rays. Since this form of radiation creates a
cascade of secondary particles upon impact, microbes embedded in
small rocks would actually suffer higher radiation doses than those
exposed directly to space. It has been estimated that for adequate
shielding from cosmic radiation, the enclosing rock must be
approximately 1 meter across.
-----------
Paul Davies: Interplanetary infestations.
(Sky & Telescope September 1999)
QY: Paul Davies, Imperial College London, UK.
-----------
Text Notes:
... ... *Note #1: As the author points out, the physicist William
Kelvin (1824-1907), in a lecture at a meeting of the British
Association in Edinburgh in 1871, speculated that from time to time
an astronomical body might strike a planet with enough force to blast
debris into space, and that as a result "many great and small
fragments carrying seed and living plants and animals would
undoubtedly be scattered through space... If at the present instant
no life existed upon this Earth, one such stone falling on it
might... lead to its becoming covered with vegetation."
... ... *spores: Only certain bacterial species form spores, which
are specialized cell structures that may allow survival in
extreme environments. In general, under conditions of nutritional
depletion, each bacterium forms a single internal spore that is
liberated when the mother cell undergoes destruction (autolysis).
The spore is a resting system, highly resistant to desiccation,
heat, and chemical agents; when returned to favorable nutritional
conditions and activated, the spore germinates to produce a
single bacterium.
... ... *red giant stars: A "red giant star" is a star in a late
stage of evolution, having exhausted the hydrogen fuel in its core.
It has a surface temperature of less than 4700 degrees Kelvin and a
diameter 10 to 100 times that of the Sun.
... ... *cosmic radiation: Cosmic rays are highly energetic
particles moving at close to the speed of light and continuously
bombarding the Earth's atmosphere from all directions. The energies
of the particles are enormous and range from 10^(8) to over 10^(19)
electronvolts. The term "highest energy cosmic rays" refers to cosmic
rays with energies of the order of 10^(20) electronvolts or greater,
apparently from extra-galactic sources, but the origins are not
clear.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 8Oct99


5. A CONTINUING FEUD CONCERNING NANOBACTERIA

     Ultimately, the labeling of a system as "living" or "nonliving"
is an anthropocentric question and perhaps not of paramount
importance in the effort to unravel the workings of nature. But
labels and the categories they name do have utility: in particular,
labels and categories do help us conceptually organize the enormous
variety that nature presents to us. During the past few years, there
has been a strong debate in progress concerning the use of the label
"nanobacteria" to characterize certain inclusions found in samples of
Martian rock, and also recently in kidney stones. (For details, see
the related background material appended below.)

     These nanobacterial entities are extremely small, an order of
magnitude smaller than the systems biologists classify as "bacteria",
but not smaller than a number of small viruses.. Are these entities
bacteria? Biologists do not use the term "bacteria" loosely, and the
defining parameter of bacteria is not size. For example, there are
protozoa, which as a group consists of organisms considerably more
complex structurally and dynamically than bacteria, that are smaller
than certain bacteria. There are also fungi that are smaller than
certain bacteria. In biology, structure and dynamics are the criteria
for differentiating bacteria, protozoa, fungi, and viruses -- not
size. Biologists, for example, never use the term "microbacteria"
to characterize living systems which are not bacteria but which are
smaller than bacteria. Again, the term "bacteria" puts no constraint
on the size of a system, except that the system must be at least
large enough to contain those molecular entities and structures that
differentiate bacteria from other known living
forms.

     So when several years ago a group of NASA space researchers
announced to the world in a press conference that they had discovered
"nannobacteria" (their first spelling of the term) in a Martian rock,
and that these inclusions were of the order of 20 to 50 nanometers in
diameter, a host of biologists rose up to complain (and even
effectively shout) that these inclusions could not be "bacteria"
because they were simply too small as systems to include the
molecular and structural repertoires known to exist in bacteria,
which repertoires differentiate bacteria from viruses, protozoa,
fungi, etc. To provide an analogy that might be helpful in
understanding the uproar among biologists, if a team of sociologists
would call a press conference to announce to the world that a group
of six people holding hands in a closed loop would thenceforth be
called by them a "benzene ring", and they would further announce
their intent to seek the financial support of various funding
agencies for research in chemistry -- given such a scenario, one
might understand a few thousand chemists rising to their feet to
shout that a benzene ring is much more than six entities joined in a
closed loop. "Never mind," the sociologists reply: "We know chemistry
when we see it."

     Considering the use of labels, one wonders whether to label
this affair as out of Harold Pinter or Groucho Marx. Certainly, at
the outset, it would have been advisable to have called the Martian
rock inclusions something other than "nannobacteria".

     Apparently, rather than dissipate, the debate has now become
more structured. A Finnish scientist has now formally requested the
University of Kuopio to investigate the work of one of its senior
researchers, Olavi Kajander, the accuser charging that Kajander is
making misleading but widely publicized claims that he has discovered
a new form of life, known as "nanobacteria". This has some
international ramifications, since Kajander is now formally
associated with the NASA Institute of Astrobiology, a "virtual
institute" involving 11 research centers in the US, and collaborating
with David McKay of the Johnson Space Center in Texas on Mars rock
research (details of the work of both Kajander and McKay is included
in the related background material below).

     In brief, Kajander claims that he has identified DNA in
nanobacteria. Jouni Issakainen (Turku University, FI), the Finnish
scientist (mycologist) who is requesting investigation, says this
cannot be substantiated because controls were not shown, and because
Kajander increased the normal concentration of a DNA stain by an
order of magnitude, as well as increasing the reaction time. Under
these conditions, says Issakainen, the stain can become nonspecific.

     Kajander, in turn, states: "In fact, I don't care whether
nanobacteria have genetic material or not -- we have shown that they
are automatically replicating particles that produce apatite, and
that they are involved in disease. And I want to cure disease."

     Apparently despite the controversy, the medical and scientific
sections of the Academy of Finland have continued to support
Kajander's work. Reviewers of a US$120,000 (FM706,000) 3-year grant
application for work on nanobacteria "combining microbiology,
geology, and astrobiology" recommended rejection, but the grant was
approved after the publication of Kajander's paper in the
_Proceedings of the National Academy of Sciences US_, and evidently
funded with money from the Academy's "risk fund". An academy
spokesman states: "Although we recognize that there are no solid
elements of a scientific basis, the academy decided to take a risk
with the work."
-----------
Alison Abbott: Battle lines drawn between "nanobacteria"
researchers.
(Nature 9 Sep 99 401:105)
QY: Alison Abbott [nature@nature.com]
-------------------
Summary by SCIENCE-WEEK [http://scienceweek.com] 8Oct99
-------------------

Related Background:

THE MARTIAN METEORITE MICROBES CONTROVERSY: AN UPDATE

In 1984, a 1.9 kilogram meteorite the size of a potato (designated
ALH84001) was found in Antarctica, and because of its chemical
composition the consensus is that this meteorite (and a dozen similar
meteorites) originated from the planet Mars. The basis for the
consensus is the detailed quantitative correspondence of the trapped
gases in the meteorites to Martian atmospheric gases, and the
specific distributions of oxygen isotopes. In 1996 a group of
researchers, D. McKay et al (National Aeronautics and Space
Administration Johnson Space Center, US; Stanford University, US)
reported they had concluded that unusual characteristics of the
meteorite ALH84001 can be most reasonably interpreted as vestiges of
ancient Martian bacterial life. In particular, the authors noted the
presence of tubules 20 to 40 nanometers in diameter (called by some
"nannobacteria"), and they proposed these structures were fossilized
bacteria or parts of microorganisms. The report was first delivered
at a press conference in August 1996 (published as a paper 9 days
later) and provoked considerable media attention and controversy when
it appeared. The controversy has continued, with many biologists
objecting to the interpretation of the rock data, and in particular
objecting to the idea of "bacteria" 20 to 40 nanometers in diameter.
... ... Allan Treiman (National Aeronautics and Space Administration,
US) presents a review and update of the ALH84001 meteorite
controversy, the author making the following points:
1) Early hopes for a fast resolution of the controversy concerning
meteorite ALH84001 have evaporated: no agreement has emerged on
whether or not the meteorite ever contained Martian life.

2) There is no disagreement that ALH84001 formed on Mars 
approximately 4.5 billion years ago, that the meteorite was probably
ejected into space approximately 16 million years ago by an asteroid
impact, that the meteorite fell in Antarctica 13,000 years ago, and
that the meteorite remained in Antarctica until found on the ice in
1984.

3) ALH84001 is an igneous rock (i.e., a rock congealed from a molten
mass) that apparently crystallized slowly from molten lava and which
contains globules of carbonate minerals scattered along fractures.
All the evidence for life is in the carbonate globules or their rims.

4) The 4 lines of evidence originally proposed by the McKay group
were a) the presence in the meteorite of carbon compounds (polycyclic
aromatic hydrocarbons) suggestive of decayed organic matter; b) the
presence in the meteorite of unusual small crystals of magnetite (an
iron oxide) matching identical crystals believed to be produced only
by Earth bacteria; c) the presence in the meteorite of apparently
incompatible minerals (e.g., iron-sulfide and iron-oxide) close
together whose proximity would suggest organic action if the rock
were from Earth; and d) the presence in the meteorite of
bacteria-shaped formations.

5) The author [Treiman] suggests that a) The polycyclic aromatic
hydrocarbons may or may not be Martian, and if they are, they may or
may not be related to life. b) The magnetite crystals are indeed
Martian, but there is evidence that some of these crystals formed
without life and the origin of the others remains unclear. c) The
mineral associations in the carbonate globules do not prove life, but
also do not exclude it. d) The bacteria-shaped objects in
ALH84001 are not fossil bacteria but could be fossils of bacteria
fragments. (McKay's group now agrees that the objects are too
small to be fossil microbes.)

6) The author concludes: "McKay's original hypothesis (as expressed
in the 1996 paper) depended on all four lines of evidence working
together... The evidence has not been verified, so the hypothesis has
not succeeded... Despite world attention, significant spending, and
the work of the best laboratories on Earth, the question [of life on
Mars] is unresolved."
-----------
Allan Treiman: Microbes in a Martian meteorite?
(Sky & Telescope April 1999)
QY: Allan Treiman [treiman@lpi.jsc.nasa.gov]
-------------------

Related Background:

NANOBACTERIA AND PATHOGENIC EXTRACELLULAR CALCIFICATION

The formation of discrete and organized inorganic crystalline
structures within macromolecular extracellular matrices is a
widespread biological phenomenon generally referred to as
biomineralization. Mammalian bone and dental enamel are examples
of biomineralization involving *apatite minerals, but the molecular
basis of such mineralization remains largely unknown. Recently,
bacteria have been implicated as factors in biogeochemical cycles for
mineral formation in aqueous sediments. The principle constituent of
modern *authigenic phosphate minerals in marine sediments is
carbonate apatite. Microorganisms are capable of depositing apatite
in sea water, and they can segregate Ca from Mg and actively nucleate
carbonate apatite by means of specific *oligopeptides under
conditions of pH < 8.5 and an Mg/Ca concentration ratio of greater
than 0.1. Such conditions are also present in the human body.
... ... Kajander and Ciftcioglu (University of Kuopio, FI) report a
study of biogenic apatite production by "nanobacteria", identified by
the authors as "the *smallest cell-walled bacteria, only recently
discovered in human and cow blood and commercial cell culture serum."
The authors report that nanobacteria can act as crystallization
centers for the formation of biogenic apatite structures, and that
nanobacteria can produce apatite in media mimicking tissue fluids and
*glomerular filtrate, and provide a unique model for in vitro studies
of calcification. The authors suggest that nanobacteria may play a
key role in the formation of all kidney stones, and they report they
have found nanobacteria in all 30 human kidney stones that they have
screened. The authors suggest their findings are of concern in
medicine because nanobacterial *bacteremia occurs in humans, and
nanobacterial crystallization centers might initiate pathological
calcification.
QY: E. Olavi Kajander <Olavi.Kajander@uku.fi>
(Proc. Natl. Acad. Sci. US 7 Jul 98 95:8274)
(Science-Week 7 Aug 98)
-------------------

Related Background:
... ... *apatite minerals: A group of phosphate-containing
minerals.
... ... *authigenic phosphate minerals: Authigenic minerals
(authigenes) are minerals that came into existence with or after
the formation of the rock of which they constitute a part. The
principal constituent of modern authigenic phosphate minerals in
marine sediments is carbonate (hydroxy)fluorapatite:
Ca(sub10)(PO(sub4))(sub6-x)(CO(sub3))(subx)(F,OH)(sub2+x).
... ... *oligopeptides: A peptide composed of no more than 10
amino acids.
... ... *smallest cell-walled bacteria: The electron micrographs
in this report show various forms with diameters 0.2 to 0.5
microns. See related reports below concerning the reported size
of nanobacteria.
... ... *glomerular filtrate: A glomerulus is a tuft-like
structure composed of blood vessel capillaries or nerve fibers,
and in this context, a glomerulus is a blood vessel capillary
structure and part of the nephron, the fundamental filtration
unit of the kidney. The filtrate from kidney glomeruli consists
of small solute molecules filtered under pressure from blood.
... ... *bacteremia: This is a general term referring to the
presence of bacteria in blood.
-------------------

Related Background:

EVIDENCE THAT MARTIAN METEORITE AMINO ACIDS ARE CONTAMINANTS

As the subunits that compose protein polymers in living systems, the
detection of certain amino acids in a material is often interpreted
as indicating a possible biological origin. The meteorite ALH84001,
along with a number of other discovered meteorites, has a composition
that suggests it was apparently ejected from the surface of Mars, and
during the past year it has been proposed that microanalysis of this
meteorite indicates the possible presence of bio-organics and
biogenic fossils. This proposal, however, has met with considerable
controversy, and the controversy is still in full force. ... .... Bada
et al (4 authors at 3 installations, US) now report that the amino
acids present in a sample of the ALH84001 meteorite appear to be
terrestrial in origin and similar to those found in the ice where the
meteorite was discovered, although the possibility remains that
minute amounts of endogenous amino acids are preserved in the
meteorite. The authors suggest that radiocarbon studies (cf.
contiguous report: Jull et al, Science 279:366 1998), coupled with
their own amino acid results, indicate that major and minor organic
constituents in the Martian meteorites are contaminants.
QY: Jeffrey L. Bada  <jbada@ucsd.edu>
(Science 16 Jan 98) (Science-Week 30 Jan 98)
-------------------

Related Background:

AN ARGUMENT FOR RELIC LIFE ON MARS

... ... Gibson et al (National Aeronautics and Space Administration
Houston, US; University of Georgia, US), the group including some of
the authors of the 1996 McKay report, in a review of the evidence for
relic life on Mars, consider the ALH84001 meteorite not only the
strongest evidence for Martian relic life, but also for the
possibility of present Martian microbial life. The authors are
hopeful that in 2005 a "sample return" mission will be launched to
robotically collect Martian rocks and soil and return them to Earth.
QY: Everett K. Gibson <egibson@ems.jsc.nasa.gov>
(Scientific American December 1997) (Science-Week 28 Nov 97)

-------------------

Related Background:

EVIDENCE AGAINST NANOFOSSILS IN MARTIAN METEORITE

The term "nanofossils" (originally spelled "nannofossils" by the
group that introduced the term) refers to elongated microscopic forms
found in the Martian meteorite ALH84001. Several groups in the space
and geology communities have proposed these forms are fossilized
bacteria, but most biologists have rejected the idea on the basis
that the forms are too small to be bacteria and should not be
classified as such. Bradley et al (3 installations, US) now report
that new analysis of material from the ALH84001 meteorite indicates
the majority of the elongated microscopic forms can be resolved as
either emergent substrate layers or magnetite whiskers, rather than
biogenic nanofossils. Their report is followed by a response from
McKay et al (3 installations, US CA), some of the original proponents
of the nanofossil idea, and in their response McKay et al say the
artifact possibilities mentioned by Bradley et al are already
known to them, but are not related to their own observations.
They add that living bacteria as small as 70 nanometers in diameter
have been observed in mammalian blood, and that soil bacteria as
small as 80 nanometers have also been observed. The references for
these bacterial forms are one unpublished paper and two recently
published papers in Proc. Soc. Photo-Opt. Instrum. Eng. 3111:420,429
(1997). It is evident that the nanofossil controversy has not yet
been resolved.
QY: J.P. Bradley, Georgia Inst. Technol. 404-894-2000;
David S. McKay <david.s.mckay@jsc.nasa.gov>
(Nature 4 Dec 97) (Science-Week 26 Dec 97)
-------------------

Related Background:

A CONTROVERSY CONCERNING MINIMUM POSSIBLE DIMENSIONS OF BACTERIA
Apart from their heuristic significance, scientific controversies
can be either amusing or irritating. In recent months, a controversy
between some geologists and many biologists has developed, and it is
apparently irritating the biologists. The issue concerns the minimum
possible dimensions of bacteria. The geologists are led by Robert L.
Folk (University of Texas, Austin TX US), and they have proposed that
certain microscopic entities found in the Martian meteorite ALH84001
are fossils of what they term "nannobacteria" (their own unique
spelling of the prefix nano-), which they say are similar to those
found in Earth travertine and limestone rocks, and which have
dimensions of 30 to 50 nanometers. This has caused a furor among
biologists, whose understanding of bacteria and life forms in general
is that the smallest dimensions possible for a life form with a
bounding plasma membrane is about 200 nanometers. In fact no
membrane-bound bacterium with dimensions less than 340 nanometers has
ever been identified, and one can make simple calculations that a 50
nanometer bacterium would not have enough internal volume to sustain
its chemistry. Folk published papers on the subject in several
geological journals in 1996, starting the debate, and in the Letters
section of the 20 June 1997 issue of *Science* the debate continues,
and this week it is being reported in the popular media as a "debate
about life on earth". What evidently irritates biologists is the
apparent misunderstanding by these geologists of experimental methods
in biology. Characterizations of "living" vs. "non-living" by
biologists are made on the basis of experimental laboratory
replicability of an organism, and not on the basis of the visible
structure of an entity. Which means the geologists involved need to
attempt to culture their Earth-rock entities, and which means
decisions that the Martian meteorite's so-called "nannobacteria
fossils" are actually such will require demonstration of cultured
entities with those dimensions. Biologists are not unwilling to admit
the existence of new species of life forms, of which they have
already recognized several million entities, but they argue that one
does not classify pieces of rock as a life form on the basis of
structure alone.

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