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(meteorobs) Excerpts from "CCNet 80/2001 - 19 June 2001"
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From: Peiser Benny <B.J.Peiser@livjm.acdot uk>
To: cambridge-conference <cambridge-conference@livjm.acdot uk>
Subject: CCNet 80/2001 - 19 June 2001
Date: Tue, 19 Jun 2001 11:57:06 +0100
CCNet 80/2001 - 19 June 2001
---------------------------
"Using the relation given by Melosh one finds that an impact speed
in excess of 20 km/sec is necessary to achieve any substantial ejection
from Mars. Although numerically-speaking large body impacts on Mars
are dominated by asteroids, it seems very likely that an impact by a
comet is a rather better bet for liberating martian rocks onto heliocentric
orbits from which they may make their way to the Earth."
--Duncan Steel, Salford University, 18 June 2001
[...]
(3) USEFUL LEGACY OF NUCLEAR TREATY: GLOBAL EARPHONES
The New York Times, 19 June 2001
(4) COMETS NOT ASTEROIDS
Duncan Steel <D.I.Steel@salford.acdot uk>
[...]
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(3) USEFUL LEGACY OF NUCLEAR TREATY: GLOBAL EARPHONES
>From The New York Times, 19 June 2001
http://www.nytimes.com/2001/06/19/science/19NUKE.html
By WILLIAM J. BROAD
Though the Senate voted two years ago to reject a treaty that bans nuclear
testing, one of its provisions is alive and thriving: the global network of
sensors meant to listen for clandestine nuclear blasts.
Though still under construction, the International Monitoring System is
already yielding a wealth of science spinoffs, detecting violent winds,
volcanic eruptions and the crash of meteoroids from outer space.
"It's a vast new tool," said Hank Bass, director of the National Center for
Physical Acoustics, based at the University of Mississippi. "For the first
time, we'll have a global system of microphones listening to the atmosphere
of the planet."
The Comprehensive Test Ban Treaty calls for 90 countries to be host to a
network of 321 stations whose sensors monitor the land, sea and air for
faint vibrations and other telltale signs of nuclear blasts. More than 100
stations are now relaying data by satellite and cable to Vienna, where 220
people work at the system's headquarters.
Despite the Senate rebuff in 1999, the United States is a major backer of
the monitoring system. It pays about a quarter of the total costs, and
United States technical and scientific support is regarded as crucial to the
network's success.
Earlier this year, some treaty opponents tried to halt the financial aid,
saying the ban's goals were illusory or contrary to American interests. But
its backers fought back vigorously, led in part by Senator James M. Jeffords
of Vermont, whose defection from the Republican Party put Democrats in
control of the Senate earlier this month. Battles over the monitoring system
continue in Washington, and it is unclear if American support will continue.
Experts on both sides say the existence of an effective monitoring system,
which its proponents see as central to treaty policing, would increase the
chances that the accord might one day be revived.
In all, the surveillance system is to have 170 stations that detect
underground shock waves, 11 that track undersea explosions, 80 that sniff
the air for telltale radioactivity and 60 that listen for revealing sounds
in the atmosphere, including winds and shock waves.
Dr. Gerardo Suarez, a geophysicist from Mexico who directs the International
Monitoring System in Vienna, said the emerging network was starting to
excite experts far beyond the world of arms control. "The scientific
community is awakening to the enormous possibilities," he said in an
interview.
Interested groups, he said, include the World Meteorological Organization,
which wants wind data for global weather forecasting, and the World Health
Organization, which wants to track radioactivity in the atmosphere.
"It's a tremendous challenge," Dr. Suarez said of building the global
network. "There's never been anything like it. We have stations from the
Arctic to Antarctica."
New additions to the surveillance system include ground-based microphones
that listen to the air for low- frequency sounds far below the range of
human hearing. Dr. Douglas Christy, head of the acoustic group in Vienna,
said that by the end of the year some 20 of the 60 sound stations will be
operational.
"Things are moving along very rapidly," he said. "It's hectic. But we're
happy with it."
On April 23, the fledgling system detected a speeding meteoroid that crashed
into the atmosphere over the Pacific, where it produced a blast nearly as
powerful as the atomic bomb dropped on Hiroshima.
In the past, such explosions often escaped notice because they usually occur
over the sea or uninhabited lands. The new information will help scientists
calculate how often these strikes occur and the odds of "doomsday rocks"
hitting the planet.
Today, the International Monitoring System and its member states are keeping
the data private among themselves until global agreements can be made for
its wider release, Dr. Suarez said. A few nations, he said, fear that
improper analysis of the data might confuse small explosions in the mining
or construction industries with clandestine nuclear blasts.
Preliminary work on the monitoring system began in late 1996 after the
treaty was opened for signature and has been accelerating ever since. In the
United States, the Defense Department does much of the work.
Treaty opponents have argued that small blasts can elude the monitoring
system and that America might one day need to test its old nuclear arms or
design new ones.
When the Senate in 1999 rejected the treaty, conservative Republicans tried,
but failed, to cut the monitoring funds as well.
Early this year, just after President Bush took office, they launched a new
drive. On March 12, Senator Jesse Helms, the North Carolina Republican who
then was chairman of the Foreign Relations Committee, wrote the State
Department to urge that the United States remove its signature from the
test-ban treaty and "terminate funding" for its organizations, including the
network of sensors.
On April 4, 10 Senate Republicans, including Mr. Helms and Trent Lott of
Mississippi, then majority leader, made the same argument to Donald H.
Rumsfeld, the defense secretary. "We urge you," they wrote, "to terminate
Defense Department efforts to implement the treaty."
Treaty opponents call support for the system - or any provision or
organization called for in the treaty - a surrogate for backing the treaty
itself, which is why they want the monitoring effort halted.
Frank J. Gaffney Jr., a former Pentagon official who opposes the pact, said
in an interview that the monitoring is "a backdoor way to get us" into the
treaty. Mr. Gaffney, who directs the Center for Security Policy, a private
group in Washington, said establishing the monitoring system "creates a
rubric in which a future administration might endorse the treaty."
Senator Jeffords, a longtime treaty supporter, fought back on April 6,
urging Secretary of State Colin L. Powell to persevere. "We must avoid any
weakening of our commitment to international nuclear test monitoring," he
wrote in a letter with Senator Lincoln Chafee, a moderate Republican from
Rhode Island.
A few weeks later, on May 10, Secretary Powell told Congress that the Bush
administration would seek $20 million for the test-ban work next year. That
figure is what the program office in Vienna had requested.
Secretary Powell is one of the few officials in the Bush administration to
have supported the Senate's approval of the treaty, which he did in January
1998 along with three other former chairmen of the Joint Chiefs of Staff.
Mr. Jeffords, in announcing his departure from Republican ranks on May 24,
made no mention of the test ban or its monitoring. But aides said the topic
was one of many where he foresaw growing disagreements with the Bush
administration and Senate leaders.
Daryl Kimball, executive director of the Coalition to Reduce Nuclear
Dangers, a private group in Washington, said the Senate's shift into
Democratic hands will aid the monitoring and "make life far more difficult
for the Dr. Strangelove caucus."
If the United States and the 159 other nations of the treaty organization
maintain their contributions, construction of the monitoring system could be
completed by late 2005, Dr. Suarez said. That is somewhat behind the
schedule envisioned a few years ago.
By late this year, he said, his team will have finished surveying 90 percent
of the proposed station sites around the world, many of which lie in remote
or inhospitable regions.
In the United States, despite the political clash over monitoring, 26 of 37
planned stations have already been built, a Bush administration official
said.
The White House might want to pull out of the monitoring program after it
finishes its reviews of nuclear policy, the official added. But the
president and his aides, though largely treaty opponents, will probably
choose to avoid that step and the likely uproar.
"The politics are really hairy," the official said. "They may want to let it
limp along because of its high political profile."
Copyright 2001, The New York Times
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* LETTERS TO THE MODERATOR *
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(4) COMETS NOT ASTEROIDS
>From Duncan Steel <D.I.Steel@salford.acdot uk>
Dear Benny,
In his nice essay concerning transpermia, Michael Paine begins by talking
about "the ejection of surface rocks from Mars during impacts by large
asteroids".
The feasability of target (planetary) material being thrown off Mars depends
critically upon the impact speed. Using a sample of over 600 observed
Mars-crossing asteroids I calculated a mean impact speed of 9.3 km/sec, with
less than five percent of the impacts at greater than 20 km/sec and rather
less than one percent occurring at greater than 30 km/sec. On the other
hand, with an assumed spherical distribution of near-parabolic comets with a
uniform distribution in perihelion distance (i.e., coming from the classical
Oort-Opik cloud) I find a mean impact speed of 45 km/sec, a mode of 55-56
km/sec, and a maximum impact speed just below 60 km/sec, with a very small
fraction having any impact speed *below* 30 km/sec. (Reference: Duncan
Steel, "Distributions and moments of asteroid and comet impact speeds upon
the Earth and Mars", Planetary and Space Science, volume 46, pp.473-478,
1998.)
Using the relation given by Melosh (H.J. Melosh, "The rocky road to
panspermia", Nature, volume 332, pp.687-688, 1988) one finds that an impact
speed in excess of 20 km/sec is necessary to achieve any substantial
ejection from Mars.
Although numerically-speaking large body impacts on Mars are dominated by
asteroids, it seems very likely that an impact by a comet is a rather better
bet for liberating martian rocks onto heliocentric orbits from which they
may make their way to the Earth. If I recall correctly, the known Mars
meteorites show groupings in space exposure ages that would indicate a small
number of impacts having ejected these objects within the last 10-100
million years or so. This would be consistent with the very occasional
high-speed comet impacts being responsible, rather than the greater number
of lower-speed asteroid impacts.
Duncan Steel
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