PLEASE NOTE:
*
CCNet 9/2001 - 17 January 2001
------------------------------
"The project also aims to see if scientists can alter the
orbit of a
comet to protect the Earth from falling matter. The impact would
alter
the comet's orbit by a "just barely measurable" 62 to
620 miles (100 to
1,000 km), [Mike] A'Hearn said."
--The New York Times, 17 January 2001
"My research has been one disaster after another. [...] You
need to
have one interesting idea every day. Just like James Bond has a
license
to kill, I had a license to depart from the normal path of a
scientist."
--Richard A. Muller, 16 January 2001
(1) NASA AIMS TO BLAST COMET TO STUDY SOLAR SYSTEM
Oliver Morton <abq72@dial.pipex.com>
(2) ONE DISASTER AFTER ANOTHER
Scientific American, 17 January 2001
(3) LUSTING AFTER A LANDING ON EROS
Weired Magazine, 16 January 2001
(4) ICE CHANNELS ON MARS
Harvey Leifert<HLeifert@agu.org>
(5) SYNCHRONOUS PLANETARY ORBITS FOUND IN NEW SOLAR SYSTEM
UniSci, 16 January 2001
(6) DISASTER DIPLOMACY
Ilan Kelman <ilan_kelman@HOTMAIL.COM>
(7) WHERE DID SOLAR-SYSTEM LIFE BEGIN?
Oliver Morton <abq72@pop.dial.pipex.com>
(8) WHERE DID SOLAR-SYSTEM LIFE BEGIN?
Steve Drury <s.a.drury@open.ac.uk>
==============
(1) NASA AIMS TO BLAST COMET TO STUDY SOLAR SYSTEM
From Oliver Morton <abq72@dial.pipex.com>
Benny -- this is the first time I've seen Deep Impact talked of
-- albeit in
passing -- as having some implications for planetary defence.
Maybe I just
haven't been paying attention.
oliver morton
abq72@dial.pipex.com
NASA Aims to Blast Comet to Study Solar System
http://www.nytimes.com/2001/01/17/science/science-space-chile-d.html
January 17, 2001
By REUTERS
SANTIAGO, Chile - NASA scientists aim to blast a comet with a
copper
projectile to learn about the formation of the solar system as
part of a
$270 million project funded by NASA, the head of the project said
on
Tuesday.
The project, called Deep Impact and which will cause an explosion
capable of
destroying a small town, would be the first space mission to
probe inside a
comet, whose primitive core could reveal
clues about evolution of the solar system.
"All our studies of comets look only at the surface layer.
Our theoretical
models tell us the surface has changed, and only the interior has
the
original composition. So our main goal is to
compare the interior with the surface," the project's
director, Michael
A'Hearn, told reporters.
Scientists chose copper, Chile's No. 1 export, because it is less
likely to
interfere with the materials inside the crater.
In January 2004, a rocket would launch from Cape Canaveral,
Florida, a
spacecraft that would orbit the sun. In July 2005 the spacecraft
would
separate from a battery-powered, copper projectile that would
collide with
the comet 24 hours later at a velocity of 6 miles (10 km) per
second.
It would produce a crater the width of a football field and up to
100 feet
(30 meters) deep.
The spacecraft would observe the composition of the crater's
interior, while
telescopes on Earth would monitor the impact.
The project also aims to see if scientists can alter the orbit of
a comet to
protect the Earth from falling matter. The impact would alter the
comet's
orbit by a "just barely measurable" 62 to 620 miles
(100 to 1,000 km),
A'Hearn said.
The project would blast the Comet Tempel 1, which was discovered
in 1867 and
is a little less than Earth's distance from the sun, he said. It
was chosen
because its size, rotation and trajectory favor the project and
because the
collision would be observable from Earth.
In February, NASA will carry out a preliminary design review to
see if the
project can succeed.
Copyright 2000 The New York Times Company
==============
(2) ONE DISASTER AFTER ANOTHER
From Scientific American, 17 January 2001
http://www.sciam.com/2001/0201issue/0201profile.html
The father of the idea that a sibling of the sun periodically
wreaks havoc
on Earth finds inspiration in catastrophes
BERKELEY, CALIF.--I first meet Richard A. Muller during a
record-breaking
heat wave. The astrophysicist is on his way to get a refreshment.
Bottles of
his favorite cold dairy drink--mocha milk--are stacked in a
nearby vending
machine. Through the clear front, the scientist notices something
out of
place: a juice can trapped obliquely against the glass.
"I'll get either two
drinks or none," he predicts playfully, inserting his change
and selecting
the beverage he thinks is most likely to knock the can free.
Muller is
unconcerned (or perhaps oblivious) that this selection is
vanilla, not the
flavor he came for. His purchase grazes the target but fails to
knock the
bottle down. Gambles like this one typify the life of Richard
Muller--although usually the stakes are higher. The restless
researcher
loves to prowl for new scientific territory to conquer. "You
need to have
one interesting idea every day," he says. His graduate
research concerned
particle physics, but his accomplishments range from inventing an
improved
technique for carbon dating to designing an experiment for
measuring the
cosmic background radiation left over from the big bang about 15
billion
years ago.
These and other accomplishments won Muller a MacArthur Fellowship
in 1982, a
year after these so-called genius awards began. It was a turning
point.
After that, Muller felt liberated to do "crazy things,"
as he puts it. "Just
like James Bond has a license to kill, I had a license to depart
from the
normal path of a scientist." On the surface at least, he
fits the stereotype
of a scientist. He will head to the lab in the middle of the
night when an
idea strikes him. His cluttered office, which overlooks the
Berkeley campus
of the University of California, where he has been since he
received his
Ph.D. in particle physics here 32 years ago, could be a set from
an
absentminded-professor comedy. There's hardly enough floor space
for a
visitor amid filing cabinets and desks and cartons overflowing
with journals
and papers. His in-box groans under a two-foot-high stack.
"My research has
been one disaster after another," Muller puckishly offers.
This
well-rehearsed line is quite literally true. He did work on the
big bang. He
studied the violent supernova explosion preceding the creation of
the sun.
And then there's his Nemesis.
"Nemesis" refers to a seemingly bizarre hypothesis
concerning the evolution
of life on Earth. Muller hatched it one day in 1983 when his
mentor, Nobel
laureate Louis Alvarez, enlisted the young physicist to debunk a
research
paper showing that Earth has sustained significant plant and
animal
extinctions at regular intervals--every 26 million years. Alvarez
and his
son, Walter, had recently advanced the theory that dinosaurs were
the
casualty of a Mount Everest-size comet that hit the planet 65
million years
ago. At the time, the hypothesis was scoffed at; now it is
generally
accepted. Playing devil's advocate for Alvarez, Muller conjured
up a
scenario. Suppose, he suggested, the sun has a sibling around
which it
do-si-dos every 26 million years. And suppose that once each
revolution the
star swings through the Oort cloud, a calving ground for comets
between four
trillion and 10 trillion miles from us. Perhaps some of those icy
balls, of
which there are billions, would be knocked off-kilter and sent
hurtling into
Earth.
At first the idea seemed preposterous, even to Muller himself.
But neither
Muller nor Alvarez could think of any reason why the theory
couldn't be
true. With a touch of whimsy, Muller dubbed the star Nemesis,
after the
Greek goddess who fends off human folly. "We worry that if
the companion is
not found," he stated in the scientific article introducing
the theory,
"this paper will be our nemesis."
It seems counterintuitive that the solar system could be looping
around an
unknown star, but in fact most stars have partners: some 85
percent have
some kind of companion. The only way to identify which, if any,
of the
catalogued stars is the sun's sibling requires measuring the
distances to
them. Muller says the elliptical orbit of Nemesis would get no
farther than
about 18 trillion miles from Earth, about three light-years away
and three
quarters the distance to the closest known star, Alpha Centauri.
It could be
a red dwarf star, which might be bright enough to be seen with a
small
telescope, or, less likely, a brown dwarf, which might not be
visible at
all. When he dreamed up the theory nearly two decades ago, Muller
thought he
would locate Nemesis in just a few years. Given its putative
distance and
brightness, it should be easy to find such a star through
parallax
measurements--seeing how it shifts against the more distant
stellar
background as Earth moves along in its orbit. But the search,
short on funds
for telescope time, languished and stalled. Muller says most
astronomers
think his theory was disproved, when in fact it is simply in
limbo.
It is no coincidence that so much of his career has been spent
studying such
tumultuous events. For centuries, scientists have predicated
theories about
Earth's evolution on the principles of uniformitarianism and
gradualism,
which posit that by and large the planet evolved slowly, relying
on the same
forces we see at work today, such as erosion and continental
drift. Muller,
however, believes infrequent, violent events are just as
important--a
doctrine some call catastrophism. Muller says neglect of
catastrophic
explanations gives him a strategic opportunity: "That's
where the
discoveries are."
Most recently, Muller has begun delving into the ice ages.
Geologists still
have a hard time explaining why they come and go. Muller insists
the answer
is of much more than academic interest. Springing from his office
chair, he
heads to a blackboard in an adjoining room--he couldn't locate
any chalk in
his office--and sketches a graph of global temperature since the
industrial
revolution. Overall, global temperature has gone up about 1.5
degrees
Fahrenheit in the past 120 years--and 15 to 20 degrees since
glaciers
receded 12,000 years ago. "Anything that can have an impact
of 15 degrees is
probably having an impact on the present climate," he
reasons. Ice ages come
and go at approximately 100,000-year intervals. The conventional
explanation, refined and popularized by Serbian mathematician
Milutin
Milankovitch in the decades before World War II, involves subtle
irregularities in Earth's motion. The theory mainly posits that
the
eccentricity, or out-of-roundness, of Earth's orbit varies the
amount of
sunlight bathing our planet.
Painstaking reconstructions of Earth's past movements show that
the planet's
orbit around the sun goes from almost perfectly round to slightly
oval and
back in 100,000 years, matching the interval between ice ages.
But there are
problems. For instance, the modest change in orbital eccentricity
does not
make nearly enough difference in sunlight reaching Earth to
produce ice
ages. Another problem is that some ice ages appear to have begun
before the
orbital changes that supposedly caused them.
Although adherents think that more research will explain such
conflicts,
Muller believes the textbook Milankovitch theory is hopelessly
flawed. His
own answer rests on a different aspect of Earth's orbit: Imagine
the solar
system is a vinyl record. Earth travels precisely on the record,
called the
ecliptic, only some of the time. At other times, the orbit is
inclined a few
degrees to the disk. Over a 100,000-year cycle, Earth's orbit
begins in the
ecliptic, rises out of it, then returns to where it started. This
slow
rocking, Muller proposes, is responsible for Earth's ice ages. He
says the
regions above and below the ecliptic are laden with cosmic dust,
which cools
the planet.
Muller's inclination theory got a shot in the arm in 1995, when
Kenneth
Farley, a geochemist at the California Institute of Technology,
published a
paper on cosmic dust found in sea sediments. He began the
research expecting
to give Muller's theory a knockout punch but discovered that
cosmic dust
levels do indeed wax and wane in sync with the ice ages.
But most researchers seem to echo the sentiment of Wallace
Broecker, a
geochemist at Columbia University, who thinks Muller is fooling
himself. In
1996 Broecker brought a group of top-flight climate researchers
together to
hear Muller's theory. He says they found the presentation
"riveting," but
"they didn't buy it."
"There's no mechanism attached to the idea," states
Nicholas J. Shackleton,
a marine geologist at the University of Cambridge and a leading
proponent of
the Milankovitch theory. He questions how small changes in
interplanetary
dust could result in effects as dramatic as the coming and going
of ice
ages. Muller responds that dust from space influences cloud cover
on Earth
and could have profound climatic implications. He says his
theory, if viewed
objectively, does just as well at explaining the facts as
Milankovitch's.
Referring to football, Muller calls himself a free safety of
science, a
generalist who scores intellectual touchdowns because he is
unrestrained by
questionable preconceived ideas. "Every once in a while
there's a fumble"
that no one notices, Muller says, "and I can grab that ball
and run into the
end zone."
--DANIEL GROSSMAN
DANIEL GROSSMAN is a freelance writer based in Watertown, Mass.
Copyright 2001, Scientific American
===========
(3) LUSTING AFTER A LANDING ON EROS
From Weired Magazine, 16 January 2001
http://www.wired.com/news/technology/0,1282,41119,00.html
by Lisa Nadile
Take these ingredients: A spinning rock about 21 miles in length
and covered
with small boulders and craters. An automobile-sized craft that
weighs 1,775
pounds. No fuel. A blindfold. Johns Hopkins space jockeys. A dash
of
adventure. What do you have? Not the script to another bad space
disaster
movie, but an actual scientific endeavor that aims to land a
vehicle on a
asteroid.
"You got the picture. We're winging it," said Dr.
Robert Farquar, NEAR
Shoemaker mission director at Johns Hopkins University Applied
Physics
Laboratory in Laurel, Maryland.
NEAR stands for Near Earth Asteroid Rendezvous. Shoemaker is for
the late
Eugene "Super Gene" Shoemaker, a world-renowned
geologist at the U.S.
Geological Survey in Flagstaff, Arizona, and a close friend of
Farquar.
The asteroid is named Asteroid 433 Eros, and the
"rendezvous" originally
meant to fly around the rock, take some pictures and then crash.
The mission
was to last a year, then on Feb. 12 come to a rather abrupt end.
That mission has changed somewhat. Now they're actually trying to
land the
darn thing -- a challenge Farquar says has about a 1 percent
chance of
success.
"It'll end up on the surface one way or another,"
Farquar said. "I like the
description of landing on a moving aircraft carrier, if it's
spinning and
the deck is coming up at you."
Admittedly the landing is a piloting exercise for the John
Hopkins
University based team.
"This exercise in landing on small bodies like Eros is
applicable. I can see
asteroids used as temporary quarters for traveling larger
distances," he
said. "We'll slow the NEAR Shoemaker down and try the
landing at about
jogging speed."
However, there is more to the landing than just derring-do.
"This is the first time we've taken pictures this close of
anything since
the moon and a few small areas of Mars," said Dr. Clark
Chapman, a NEAR
imaging team member and a geologist for the Southwest Research
Institute in
San Antonio, Texas.
The photos taken during the landing are expected to be 10 times
better than
those taken from orbit. "We want to find out what it's made
of," he said.
NEAR Shoemaker totes a range of scientific tools. A magnetometer
to check
for magnetic materials like those found in meteorites. An
X-ray/Gamma-ray
spectrometer for measuring silicon, magnesium, iron, uranium,
thorium and
potassium. A near-infrared spectrometer to map the mineral
composition of
the surface by measuring the spectrum of sunlight reflected by
the asteroid.
A multispectral camera and a laser rangefinder to measure the
clog
shoe-shaped EROS landforms and colors. And the craft has
performed
experiments to evaluate the density of Eros.
"When we looked at the moon's lunar surface we saw a few
scattered boulders
but mostly the moon was covered with small craters, but EROS is
covered with
small boulders and hills, he said.
"Asteroids are strange places from what little we know.
Eventually we will
mine and take samples and deal with what they can tell us,"
Dr. Chapman
said. "With this kind of imaging, it's no different from
taking a camera and
going hiking, expect we're hiking into Wonderland. We didn't know
what to
expect."
The NEAR Shoemaker doesn't have to land, but the activities of
the space
jockeys like Farquar is all gravy, Chapman said. The plans for
landing were
a surprise to many. "I thought about doing this early on,
but I didn't have
the nerve to say anything," Farquar said.
"He is mischievous and intriguing. NASA is extremely
risk-adverse ... and a
bit straitlaced. Farquar is a breath of fresh air," Chapman
said. Launched
from Cape Canveral Air Station in 1996, NEAR's arrival at Eros on
Valentine's Day of last year was no accident.
Eros is 1.3 astronomical units from the Sun, where Earth is 1
astronomical
unit. It is classified as a near-Earth asteroid, which means it
travels
within 121 million miles of the Sun. Scientists theorize that
these types of
asteroids are from the main belt between Mars and Jupiter.
The NEAR Shoemaker adventure is not only about the adventurers
who man our
space programs, but about trying the impossible. Farquar, Chapman
and the
rest of the NEAR Shoemaker team engage in friendly competition
with their
NASA counterpart, the Jet Propulsion Laboratory. But they all
want the same
thing. Repeat after me: To boldly go ...
Copyright © 2001 Wired Digital Inc., a Lycos Network site. All
rights
reserved.
===========
(4) ICE CHANNELS ON MARS
From Harvey Leifert<HLeifert@agu.org>
American Geophysical Union
January 16, 2001
AGU RELEASE NO. 01-2
For Immediate Release
Contact: Harvey Leifert
(202) 777-7507
hleifert@agu.org
Martian ice streams, not floods, may have shaped
channels
WASHINGTON - Some channels visible on the surface of Mars may
have been
gouged by ice, rather than by catastrophic flooding, as is
generally
believed. That is the view of Dr. Baerbel K.
Lucchitta of the U.S. Geological Survey in Flagstaff, Arizona,
who compared
the Martian features with strikingly similar ones on the
Antarctic sea
floor. Her findings are reported in the February 1 issue of
Geophysical
Research Letters, a publication of the American Geophysical
Union.
Outflow channels on Mars may be tens of kilometers [miles] wide
and hundreds
of kilometers [miles] long, as are some that Lucchitta studied in
Antarctica. Ice flows in streams within Antarctica's ice sheets
before
merging with ice shelves in the surrounding ocean;
the ones she studied flow from West Antarctica into the Ross and
Ronne Ice
Shelves. The martian channels arise suddenly from chaotic
terrains or
fractures and terminate in the northern plains, where there may
once have
been an ocean.
Both the Antarctic ice streams and some martian channels are
based below sea
level, which on Mars is defined as the average surface elevation
of the
hypothetical ancient northern plains ocean. The Antarctic
channels were
mapped using recently available sonar imagery.
Lucchitta demonstrates that martian channels, especially one
known as Kasei
Valles, display similar characteristics to those of Antarctic
channels known
to have been carved by ice streams. She compares the Rutford Ice
Stream at
its confluence with the Ronne Ice Shelf, where it diverges around
an ice
rise, formed of more stable ice than the adjacent flow, with Ares
Vallis.
The latter diverges around an island and displays similar curved
flow lines
where it enters the hypothetical ocean. The configuration of
these two
streams is identical, she writes.
Lucchitta infers that Ares Vallis was filled by material that had
the
characteristics of flowing ice that entered an ice covered body
of water.
She believes that dust covered ice may persist in Ares Vallis or
that rocky
material left an expression of the flow forms after the ice
evaporated. "The
observations strongly support the notion that an ocean once
existed in the
northern plains of Mars," she says.
Another similarity between Antarctica and Mars noted in the study
is that
some streams and channels rise in altitude in the downstream
direction. On
Earth, uphill flow at the base of ice is common, because the
surface
gradient drives the ice, whereas water does not flow uphill for
extended
distances.
There are differences between Antarctica and Mars regarding the
origin of
ice in ice streams. On Earth, the streams flow from ice sheets,
while on
Mars, it derived from fluids erupting from below the surface.
Also, on
Earth, the ice flows between ice walls, while on Mars it flowed
between rock
walls, but the width to depth ratio on Mars is more like that of
ice streams
than of mountain glaciers on Earth, Lucchitta notes.
The study was funded by NASA's Planetary Geology and Geophysics
Program.
**********
Notes for journalists only:
1. A copy of the paper, Baerbel K. Lucchitta, "Antarctic Ice
Streams and
Outflow Channels on Mars," (four pages) may be obtained by
fax or mail. Send
your request to Harvey Leifert:
<hleifert@agu.org>.
The paper will be published in Geophysical Research
Letters (GRL), Vol. 28, no. 3 (February 1, 2001), pages 403-406.
2. Pronunciation of author's name: BEAR-bel Lu-KEE-ta
3. Images: Three figures accompany this paper. They may be
obtained from the
AGU web site at the following URL:
http://www.agu.org/grl/images/vol28/ant_chan.html
[Figure 3 will appear on the cover of GRL.]
4. This press release and the Lucchitta paper are not embargoed.
5. Dr. Lucchitta may be contacted at her office.
Phone: +1 (520) 556-7176;
email <blucchitta@usgs.gov>.
=============
(5) SYNCHRONOUS PLANETARY ORBITS FOUND IN NEW SOLAR SYSTEM
From UniSci, 16 January 2001
http://unisci.com/stories/20011/0116011.htm
Johannes Kepler succeeded in establishing a formula for relating
a planet's
orbital period to its mean distance from the sun, but he failed
in his
ardent attempt to discern a pattern in the spacings or periods
among the
planets. Such a pattern, enforced by resonant gravity effects,
was
subsequently observed in the commensurate periods of some of
Jupiter's
moons.
Now the reality of synchronous planetary orbits has turned up in
a solar
system unknown to Kepler -- or to anyone else -- until recently.
Geoffrey Marcy (UC Berkeley) and his associates, discoverers of
tens of
extrasolar planets, now report that the star Gliese 876, 15 light
years from
Earth, is orbited by one planet every 60 days and by a second
every 30 days.
(The presence of the planets around the star and their orbital
properties
are deduced from the subtle wobble of the star's position as it
is tugged by
its satellites.)
The almost exact 2:1 (octave) ratio in the orbital periods should
help
theorists model the formation of planetary systems.
Marcy, speaking at last week's meeting of the American
Astronomical Society
(AAS) in San Diego, also reported a second two-planet extrasolar
system no
less novel.
The star HD168443, 123 light years from Earth, is circled every
58 days by
one heavy planet (7.7 Jupiter masses) at a distance of only 0.3
astronomical
units (1 AU is the distance from Earth to sun) and by another
every 4.8
years.
The second planet's mass, estimated to be at least 17 Jupiter
masses, is the
most massive exoplanet ever found, and calls into question the
notion that
planets could not reach much above 13 Jupiter masses without
igniting as
stars.
(Editor's Note: This story reprints, with only minor editing, an
item from
PHYSICS NEWS UPDATE, the American Institute of Physics Bulletin
of Physics
News Number 520 January 12, 2001 by Phillip F. Schewe, James
Riordon, and
Ben Stein.)
Copyright © 1995-2001 UniSci. All rights reserved
=============
(6) DISASTER DIPLOMACY
From Ilan Kelman <ilan_kelman@HOTMAIL.COM>
Disaster Diplomacy
(edited by Ilan Kelman and Theo Koukis)
in the Cambridge Review of International Affairs
vol. XIV, no. 1, Autumn-Winter 2000
"Greek-Turkish Rapprochement: The Impact of 'Disaster
Diplomacy'?", by James
Ker-Lindsay:
"To claim that the earthquakes brought about rapprochement
is both factually
wrong, and indeed weakens the basis for the process."
"Climate-Related Disaster Diplomacy: A US-Cuban Case
Study," by Michael H.
Glantz
"A broad-ranging rapprochement is not likely to result from
a specific
response to a climate-related problem."
"Drought Emergency, Yes...Drought Disaster, No:
Southern Africa 1991-93,"
by Ailsa Holloway
"While diplomatic dividends can indeed flow from disaster
relief efforts, in
this instance, joint cooperation was only possible once potential
military,
economic, and other forms of regional confrontation had been
controlled."
"Disaster: Agent of Diplomacy or Change in International
Affairs?" by Louise
K. Comfort
"Disaster--or threat of disaster--provides opportunities for
enhancing
collaboration among states, but the properties and mechanisms for
adaptation
must either exist or be developed for effective results."
Plus, from Vincent T. Gawronski and Richard S. Olson:
"'Normal' Versus
'Special' Time Corruption: An Exploration of Mexican
Attitudes."
Copies of this issue are available for GBP10 plus postage from:
Cambridge Review of International Affairs
Centre of International Studies
Fitzwilliam House
32 Trumpington Street
Cambridge CB2 1QY
UNITED KINGDOM
Telephone: + 44 (0) 1223 741311
Fax: + 44 (0) 1223 741313
E-mail: intstudies-cria@lists.cam.ac.uk
============================
* LETTERS TO THE MODERATOR *
============================
(7) WHERE DID SOLAR-SYSTEM LIFE BEGIN?
From Oliver Morton <abq72@pop.dial.pipex.com>
Re: EARTH IS THE MOST LIKELY PLACE FOR LIFE'S ORIGIN IN OUR SOLAR
SYSTEM
From Steve Drury <s.a.drury@open.ac.uk>
In their paper "Refugia from asteroid impacts on early Mars
and the early
Earth" JGR v103, E12, pp28, 529-28,544 Norm Sleep and Kevin
Zahnle offer two
reasons to prefer Mars as a solar-system origin of life, both
intriguing but
not compelling. If you think life is very likely whenever there
are organics
on a planet and the temperature allows liquid water, then Mars
meets the
criteria in a continuous way earlier than the earth because the
moon-causing
impact effectively resets the earth's clock. Sleep and Zahnle
also point out that ocean sized
bodies of water might count against the earth, since large
impacts can boil
the earth's oceans, causing a steam atmosphere that persists for
thousands
of years. This steam atmosphere allows the 100 deg C isotherm to
penetrate
reasonably deep into the subsurface all around the planet. On
drier Mars --
if Mars was drier -- the global effects of these really large
impacts are
less dramatic. This raises the intriguing logical possibility
that the
conditions for the origin of life need not be the same as the
conditions for
its persistence.
As to the amount of transfer between planets, isn't this a red
herring? The
important thing is that there is significant transfer, not
whether the net
flux is in the opposite direction. While it is true that if there
had been
life on earth and mars at the same time, more earthlife might be
expected to
have made the journey out than Marslife make the journey in. But
if there
was life on mars and not on earth at a given time, surely the
fact that Mars
to earth transfer was rarer than earth to Mars transfer is
irrelevant.
As far as I can see, if life originated on a planet in the solar
system and
transfer from planet to planet is indeed possible, then the
origin could
have been Venus, earth, Mars or the unnamed
Mars-sized earth-impactor that contributed to the moon. It's not
clear to me
that we can say anything more than that with certainty, and we
have to
realise that two of the four possible sources are now
unrecoverable.
Incidentally, could I make another plea for my neologism
"transpermia" to
describe this sort of transfer between neighbouring planets, as
opposed to
the more cosmic "panspermia". In cases where one is
being precise about the
origin and the method, transpermia seems preferable.
best, oliver
===============
(8) WHERE DID SOLAR-SYSTEM LIFE BEGIN?
From Steve Drury <s.a.drury@open.ac.uk>
Dear Oliver/Benny
Like I said, I don't wish to make a meal of this, because it is
all special
pleading in the absence of evidence. When we are dealing with the
period
from 4500-4000 Ma on Earth, all we have to go on are a couple of
dozen 30
micrometre zircon grains - see last issue of Nature, which is an
excellent
example of milking data to the limit! For Mars, a great deal
hangs on the
analyses of the Martian atmosphere from Viking - very imprecise,
but clung
to in claiming some rare meteorites are Martian in origin, with
no clear
justification of why such deeply excavated objects should carry
any
atmosphere at all. All we know for sure is that these objects are
geochemically quite evolved - i.e. from a body able to
fractionate
internally. That could be Venus, Earth, Mars, Io and any other
body known to
resurface itself periodically or continually
You mention the notion that Mars is more likely than Earth to
have developed
life early, because it was not involved in the Moon-forming
event. We
simply do not know whether or not it was involved in such
energetic
processes early on, for its surface is young, due to its cover of
wind- and
to a lesser extent water-transported sediments. All we have
to go on is
that the inclination of its rotational axis is similar to that of
the Earth
- possibly due to large-impact perturbation.
Large impacts can boil oceans, but converting all liquid water to
vapour
means distribution of impact energy from a point to the whole
planet - not
so easy as most is lost either to seismicity of radiated away
above site of
impact. The issue of sterilizing the subsurface is probably not
on, simply
because of the very low thermal conductivity of rocks - you can
stand on the
crust of a still-active lava flow with magma at 1200 C only 10 or
so metres
beneath the surface. Hyperthermophiles are today found to
depths of 2 km or
more. Besides that, Mars has a greater gravitational cross
section than the
Moon or the cratered moons of the giant planets, and is almost as
likely as
Earth to have been hit by bodies able to vaporize surface water
in the
Hadean.
My last word on the panspermia notion is the old saw that it
merely shifts
origins conveniently somewhere else. It is simply not
useful to say that
wherever there are CHON compounds and liquid water life will
spring up. The
pace of assembly of universal building blocks to hypercomplex,
self-replicating chemical systems is simply unknown, even though
a number of
possible pathways are beginning to emerge from simple
experimental systems.
What we do know is that the transition from naked genetic
material in
prokaryotes to its encapsulation in eukaryote nuclei and
organelles,
probably by some kind of endosymbiosis and genetic exchange
mechanisms, took
around 2 billion years under highly favourable conditions.
Personally, I
would be surprised if assembly of simple prokaryotic cells from
universally
available amino acids etc. (chemically and thermodynamically a
whole lot
more difficult) could be shown to have taken less than a few
hundred Ma.
But I can be smug in the certainty that no-one will find out in
my lifetime!
Incidentally, Hoyle's idea of flu viruses being delivered by
interplanetary
dust particles needs to be viewed in the context of two recent
revivals of
Triassic bacteria from fluid inclusions in rock salt. Every
time I go out
on a frosty night I worry now about what is being released by
salt on the
roads!
Steve Drury
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