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CCNet DIGEST, 8 July 1999
--------------------------

     QUOTE OF THE DAY

     "The transition to today's arid climate was not gradual, but
     occurred in two specific episodes. The first, which was less
     severe, occurred between 6,700 and 5,500 years ago. The second,
     which was brutal, lasted from 4,000 to 3,600 years ago. Summer
     temperatures increased sharply, and precipitation decreased,
     according to carbon-14 dating. This event devastated ancient
     civilizations and their socio-economic systems."
     (Martin Claussen, Claudia Kubatzki, Victor Brovkin, Andrey
     Ganapolski, Philipp Hoelzmann, Hans-Joachim Pachur, "Simulation of
     an abrupt change in Saharan vegetation in the mid-Holocene")


(1) NEWS ROUNDUP ON THE NEW ZEALAND METEOR SIGHTINGS
    Andrew Yee <ayee@nova.astro.utoronto.ca>

(2) SPACE COLLISION HELPED CREATE CHESAPEAKE BAY
    EXPLOREZONE, 7 July 1999

(3) WHERE ARE THE CRATERS?
    Michael Paine <mpaine@tpgi.com.au>

(4) SOFTWARE TO SAVE THE WORLD
    Michael Paine <mpaine@tpgi.com.au>

(5) NASA TAPS DAVID THOLEN FOR MUSES-C ASTEROID MISSION
    Andrew Yee <ayee@nova.astro.utoronto.ca>

(6) NASA SELECTS MISSIONS TO MERCURY AND A COMET'S INTERIOR AS NEXT
    DISCOVERY FLIGHTS
    NASA NEWS <NASANews@hq.nasa.gov>

(7) WHAT CAUSED THE DESERTIFICATION OF THE SAHARA
    Harvey Leifert <HLeifert@agu.org>


=============
(1) NEWS ROUNDUP ON THE NEW ZEALAND METEOR SIGHTINGS

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

Hi Benny,

Here's a news roundup on the New Zealand meteor sightings.  Note the
links to an amateur video in the AP story, and a still photo in the NZ
Herald story.

*****

[http://asia.yahoo.com/headlines/070799/technology/931327620-90707060728.technology.html]

Huge meteor sweeps across New Zealand

Wednesday, July 7, 1999, 2:07 AM EDT

AUCKLAND (AFP) -- A huge fireball or meteor swept across New Zealand
Wednesday afternoon, seen by thousands around large area of the
country, media reported. Television New Zealand said fragments had come
to ground in several parts of the country but there were no reports of
damage. TV3 Network said the fragments were briefly monitored by air
traffic control.

Copyright © 1999 Agence France-Presses. All rights reserved.

*****

[http://cnn.com/WORLD/asiapcf/9907/07/BC-NewZealand-Meteor.ap/]

Wednesday, July 7, 1999, 10:27 a.m. EDT

Meteor Explodes Above New Zealand
By RAY LILLEY, Associated Press Writer

WELLINGTON, New Zealand (AP) -- A meteor exploded in the sky above New
Zealand on Wednesday, casting an eerie blue light and showering the
earth with fragments from space.

The explosion at 4:15 p.m. (1:15 a.m. EDT) was followed by smoke and a
flood of phone calls from people who saw the meteor streaking across
the sky, the Carter Observatory in Wellington said. No injuries were
reported.

"It was picked up by aircraft and on radar, so we've had some air
traffic controllers calling too,'' said John Field, the observatory's
public programs officer. The meteor was likely to have been either
metal or rock and was probably as big as a car, Field said. A rock
meteor would have broken up into a shower of stones as it came through
the atmosphere. On average, one meteor falls to Earth each week, he
said.

Police said hundreds of people reported seeing the meteor over a remote
part of New Zealand's North Island -- between the cities of Napier on
the east coast and New Plymouth on the west coast.
 
After a loud explosion, the meteor apparently broke up in the
atmosphere, leaving a vapor trail and blue cloud hanging, police said.

Reports of objects falling to the ground were received across the
region, police said, but no pieces have been reported found.

Brendon Bradley, an instructor with the New Plymouth Aero Club, said he
was flying when he saw the meteor.

"It was just a bright light, exactly like a flare,'' he said.
"Afterwards there was smoke in the sky." Other witnesses described a
bright flash, followed by an explosion and a cloud of brown smoke.

"A big fiery ball came down. There was a terrific red glow and it sort
of went pop," said Eric Ray, a resident of the town of Te Aroha. One
man told police the explosion sounded like a natural gas tanker
igniting.

[Video: http://tvone.co.nz/news/movies/meteor_explodes.avi]
Amateur video seconds after the explosion.

Copyright 1999 Associated Press. All rights reserved.

*****

[http://www.nzherald.co.nz/nzherald99/story.cfm?theStoryID=10004]

Thursday, July 8, 1999

Shooting star goes pop, boom, bang
By Stacey Bodger and Philip English

The shooting star that raced over New Zealand skies from Nelson to
Napier yesterday might have been the size of a pea but could be more
valuable than gold.

Dr Joel Schiff, editor of the international Meteorite magazine, urged
people to look for the remains not only because of the scientific value
but also because the rarity of recovered meteorites made them highly
valuable.

The meteor was seen leaving a trail of smoke in the sky before it was
heard detonating in the atmosphere as a pop in Te Aroha, a boom in
Taranaki and an explosion in Napier. The explosion was so loud that
many people thought a plane had crashed in the suburb of Bay View.

However, Dr Schiff said it was probably a rock the size of a pea or
perhaps the size of an apple which had been blasted on course for New
Zealand following a collision in the asteroid belt between Mars and
Jupiter.

It was not known last night whether any part of it reached the ground
after the explosion but Dr Schiff, of the University of Auckland maths
department, said people should look for small black rocks with a crusty
outside as if they had been barbecued.

"Many of them are much more valuable than gold. "There are a few that
have come from Mars. Some have been blasted off the moon. "If you found
a piece of the moon in your backyard -- if this turned out to be
a piece of the moon and there's a very small chance it could be -- you could
retire for life no matter how small it was."

The meteorite was also probably older than rocks on Earth. It would be
4.5 billion years old, the same age as the solar system, while the
oldest rocks on Earth subjected to the planet's geological processes
are about 3.8 billion years old.

"People near where the detonation took place should definitely look
under every rose bush and leave no stone unturned. There is a chance
something could be found but people will have to scour the area."

The Carter Observatory in Wellington received reports of the meteorite
about 4:15 pm. It was picked up by aircraft and radar. Victoria Radley,
of Tukino, Mt Ruapehu, said she saw an extremely bright light shooting
across the sky at a tremendous speed and then dropping to the ground.

It was travelling beneath the sun and resembled a shooting star except
that its point of light was much bigger.

Pictured: Smoke from the meteor's explosion.

© Copyright 1999, NZ Herald

*****

[http://203.98.9.153/news/1999/07/07/00007157.htm]

Wednesday, July 07, 1999

Flood of calls over meteorite

Police say it appears a meteorite hit the ground near Napier.

The police have had hundreds of calls from throughout the central North
Island reporting a loud explosion and smoke in the sky.

They say it appears something travelling west to east hit a hill near the
suburb of Bay View near Napier.

The fire service and Civil Aviation also say they have received reports
of a meteorite over the upper to central North Island.

Civil Aviation says a number of pilots reported seeing bright lights and
explosions in the sky, particularly in Tarakani.

ONE News | Copyright © TVNZ: 1999. All rights reserved.

*****

[http://dailynews.yahoo.com/headlines/sc/story.html?s=v/nm/19990708/sc/space_newzealand_1.html]

Thursday, July 8, 1999, 12:46 AM EDT

Meteor's Sonic Boom Shakes NZ Seismographs

WELLINGTON (Reuters) -- A sonic boom created by a meteor passing low
over New Zealand's North Island was loud enough to set off seismographs
that monitor volcanic activity, a government science agency said
Thursday.

The meteor, seen from various locations throughout the country late
Wednesday, was probably a fragment or remnant of a comet, Terry Webb, a
seismologist at the Institute of Geological and Nuclear Sciences, said.

The meteor was likely to have entered the earth's atmosphere at a
relatively low trajectory and at about 72,000 km per hour (44,000 mph)
before exploding into multiple fragments.

Meteors typically break up at between 60 and 80 km (36 and 48 miles)
above the earth's surface and only rarely do any fragments reach the
ground, Webb said.

Copyright © 1999 Reuters Limited. All rights reserved.

*****

[http://203.98.9.153/news/1999/07/08/00007168.htm]

Thursday, July 08, 1999

Meteor may have been a big one

An astronomer believes a meteor that blazed across the North Island
yesterday was probably about the size of a small boulder, but may have
been as big as a car.

Reports of the large bright object streaking across the sky came from
Auckland, Hawke's Bay, Taranaki, Wellington and Canterbury.

The only damage reported was a small scrub fire in Napier after some of
the debris exploded in the atmosphere and sparks dropped into a bush
area.

An astronomer at the Carter Observatory in Wellington, Richard Hall,
says the meteor appears to have been a stoney-type and he estimates it
was about two feet in diameter.

David Skinner, a geologist who has studied meteorites in the Antarctic
says it is unlikely the meteor hit land, and it probably headed out to
sea.

On Tv One's Breakfast this morning, Ian Griffin from the Auckland
Observatory appealed for the public to help them discover more about the
meteor.

He asked for information about sightings to confirm the meteor's size
and location, and said that any fragments recovered could be quite
valuable.

ONE News | Copyright © TVNZ: 1999. All rights reserved.

===============
(2) SPACE COLLISION HELPED CREATE CHESAPEAKE BAY

From EXPLOREZONE, 7 July 1999
http://explorezone.com/archives/99_07/07_chesapeake_impact.htm

Space collision helped create Chesapeake Bay, leaves drinking water
salty

By Robert Roy Britt, explorezone.com . 07.07.99

A huge object from space slammed into Earth 35 million years ago,
carving the largest crater ever found in the United States, researchers
said today. The 56-mile-wide crater was gutted from what is now the
mouth of Chesapeake Bay in a cataclysmic collision that kicked a cloud
of debris high into the atmosphere and spawned devastating tsunami waves
up to 2,000 feet high.
   
The white lines on this satellite image show the inner and outer rims of
the buried crater. The area inside the inner rim suffered the full brunt
of impact, compressing and vaporizing rock and leaving the deepest hole.
IMAGE: USGS

The impact left a now-buried, unstable crater rim that still generates
earthquakes and that holds clues to salty groundwater woes experience by
some 2 million people living in the region.

The incoming comet or asteroid -- researchers aren't sure which it was
-- was about two or three miles wide. It created a two-tiered
depression, like an inverted sombrero, in what was then a shallow part
of the ocean, said David Powars, a hydrologist with the U.S. Geological
Survey.

"All of a sudden you had this giant hole," Powars told explorezone.com.
"Through the 35 million years since it happened the hole has been
filling in."

Over time, rivers in the region turned to flow into the crater before
going out to sea, which along with glacial advances and retreats carved
out Chesapeake Bay, Powars said. The bay, he said, is no more than a
"drowned river system."

The impact

"It's an incredible collision that we're talking about," Powers said. He
likened it to putting all the world's nuclear weapons in one spot and
detonating them simultaneously. "The force of the impact ejected huge
amounts of debris into the atmosphere and spawned a train of gigantic
tsunamis that probably reached as far as the Blue Ridge Mountains."

The crater is now buried under 400 to 1,200 feet of sand, silt, and
clay, Powars said. Its existence was originally suspected in 1993 after
Powers and colleagues studied oil company seismic data. The new research
confirms that the crater was in fact caused by an impact.

Tremendous tsunami

Powars said the incoming projectile lifted the ocean floor as much as
200 feet. Like a giant paddle, this would have sent huge waves traveling
outward in all directions and back and forth, carving a crater that is
much different than the more evenly sculpted variety caused by impacts
on land.

"Because of the giant hole ... you could have had water from the ocean
slosh in and slosh out," Powars said, explaining that the waves created
a jagged and irregular outer rim that jumps in and out a mile or so in
various spot.

"You have a real mess in there," Powars said.

And, interestingly, ancient marine fossils and other debris sloshed in
and are now buried deep inside the former hole. What isn't in there is a
whole lot of debris from the object that caused the whole mess. Most of
it seems to have vaporized.

Drinking water still affected

The irregular, unstable outer crater rim -- which extends ten to twenty
miles inland in Virginia -- appears to answer several questions about
unusual phenomena in the region, including salty ground water and
earthquakes around the crater's perimeter.

Powars said the rim's instability, caused when the underlying Earth's
crust was "banged up" during the impact, may explain the high seismic
activity in the region. The rim is constantly shuffling and settling,
triggering seismic waves.

The rim is also a boundary between salty ground water within the
crater's confines and fresh ground water on the outside. Powars said
about 2 million people count on the region's ground water, and experts
have long worried that frequent intrusions of saltwater into the
drinking water were caused by overpumping. Powers said the new
explanation has helped utility companies dig wells outside the crater
rim to more successfully search for potable water.

High impact activity

Researchers say similarly large impacts caused by asteroids or comets
occur every 6,000 to 10,000 years or so (estimates vary widely). More
frequently impacts occur in the oceans, which cover more of the planet's
surface.

Powars said a crater off the coast of New Jersey and others around the
world have been dated to the same time period as the Chesapeake impact,
indicating that 35,000 years ago might not have been a very safe time on
Earth. He said researchers are beginning to understand there may be
cycles of high impact activity related to Earth's position in the
cosmos.

A larger, older crater off the coast of the Yucatan Peninsula in Mexico
is thought by many scientists to have killed off most of the larger
dinosaurs. The crater is difficult to study, however, because it is in
relatively deep water.

Powars said the Chesapeake crater is in shallower water and will be
easier to study. "Ongoing analysis of this impact crater will yield a
wealth of information," he said. ez

Copyright 1999, Explorezone

===========
(3) WHERE ARE THE CRATERS?

From Michael Paine <mpaine@tpgi.com.au>

The article METEOR CRATER ASTEROID WAS SHOCK MELTED (CCNet 2 July
1999) estimates that a Canyon-Diablo-sized meteor
[meteoroid/asteroid] slams into a land mass every 6,000 years. My
rough calculations confirm this (50m impactor once per century, 5%
are "irons", one third of Earth surface is land  100 x 20 x 3 =
6,000!). We could therefore expect another 8 such events on land
since the Meteor Crater impact 50,000 years ago. The database of
terrestrial craters maintained by Natural Resources Canada

http://gdcinfo.agg.emr.ca/crater/paper/cratering_e.html

only has craters a few metres in diameter that are younger than
50,000 years. Even allowing for the random nature of these events and
the possibility that some have been eroded or covered over by
vegetation it seems surprising that one or two other 1km diameter
craters have not been found. Maybe we haven't looked hard enough.

Michael Paine

===============
(4) SOFTWARE TO SAVE THE WORLD

From Michael Paine <mpaine@tpgi.com.au>

Dear Benny,

I came across the following shareware while surfing: "Close Approach,
is named after the Close Approach tables kept by NASA on asteroids
whose orbits bring them in close proximity with the Earth. Set in the
year 2100, the aim is to pilot your ship and two probes in 3D space
and blast the asteroids out of existence before they collide with the
Earth"

http://www.winsite.com/info/pc/win95/games/cappfull.zip/


Michael Paine

=================
(5) NASA TAPS DAVID THOLEN FOR MUSES-C ASTEROID MISSION

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

University of Hawai'i
University Relations                                     
Media & Publications                                 
Honolulu, HI 96822                                   
Telephone: (808) 956-8856
Facsimile: (808) 956-3441=20
E-Mail: ur@hawaii.edu

Contact:
David Tholen
808-956-6930, tholen@galileo.ifa.hawaii.edu

Karen Rehbock, Institute for Astronomy
808-956-6829, rehbock@ifa.hawaii.edu

DonnEB Florence, UH Media Relations
808-956-7522, donne@hawaii.edu

Mary Beth Murrill, JPL Media Relations
818-354-6478, mary.b.murrill@jpl.nasa.gov

Beta SP video is available from JPL; high-res images at JPL website,
   http://www.jpl.nasa.gov/pictures/solar/musspccrft.html

For Immediate Release: July 1, 1999

NASA taps UH astronomer David Tholen for asteroid mission

David Tholen, an astronomer at the University of Hawai'i Institute
for Astronomy, is one of a half-dozen U.S. scientists selected by the
National Aeronautics and Space Administration (NASA) for the world's
first expedition to place a robotic lander on an asteroid and return
pieces of the space rock to Earth for in-depth study. The U.S.
scientists selected will collaborate with Japanese colleagues on the
MUSES-C project, the world's first asteroid sample return mission.

"MUSES-C" stands for Mu Space Engineering Spacecraft, with the "C"
signifying it is the third in a series. The mission is a cooperative
venture of Japan's Institute of Space and Astronautical Science
(ISAS) and NASA.

Asteroid Nereus, a one kilometer-diameter (about one-half mile)
object, is the preferred target of the mission. (An alternative
target is the asteroid 1989 ML.) "Nereus is one of Earth's closest
neighbors, easily accessible for a spacecraft rendezvous and an
object of key scientific interest," according to Donald K. Yeomans,
NASA's MUSES-C mission project scientist.

David Tholen is an internationally recognized authority on the
categorization of asteroids. He will use data from the spacecraft
camera to determine the asteroid's rotational state, to estimate the
age of the asteroid and its shape and size, as well as other
properties such as density.

Nereus is thought to be a relatively unaltered asteroid, having
changed little since Earth and the other planets of the inner solar
system formed some 4.6 billion years ago. Detailed studies of Nereus
and other asteroids are expected to provide scientists with crucial
information about Earth's initial chemical composition and the
conditions under which it and the other inner planets originally
formed.

The MUSES-C spacecraft, provided by the Japanese, will be launched on
a Japanese M-5 launch vehicle in January 2002 from Kagoshima Space
Center, Japan, toward a touchdown on the asteroid Nereus in April
2003. The Japanese spacecraft will deliver a NASA-provided miniature
robotic rover to the surface of Nereus to study the asteroid up
close. The MUSES-C spacecraft will gather samples of the asteroid and
depart for Earth, leaving the rover behind. The asteroid samples will
be returned to Earth in January 2006.

Nereus has a gravity field estimated to be about 100,000 times weaker
than Earth's. This presents an unusual challenge for engineers at
NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, where
the miniaturized rover is being developed. The cigar box-size rover
is being designed to take advantage of the low gravity field and will
be able to hop tens of meters above the surface by drawing its wheel
struts together, then springing them outward. This would give the
cameras and other instruments onboard a bird's-eye view of the
asteroid terrain, and would allow the rover to cover much more ground
overall. The weak gravity would pull the rover back to land gently on
the surface. Solar panels on the rover's back and belly allow it an
uninterrupted flow of electricity, no matter which way it lands. Like
an agile cat, the rover is also equipped to right itself if
necessary.

The MUSES-C spacecraft will carry a camera, an infrared spectrometer
and a lidar instrument (a laser-based altimeter) that will be used by
Japanese scientists and their NASA colleagues to study the asteroid
from a distance of about 20 kilometers. An X-ray spectrometer will
also be onboard to study the asteroid's bulk chemical composition.
The NASA rover will carry a camera, an infrared spectrometer and an
alpha X-ray spectrometer for analyzing the composition of the
asteroid surface.

Up to three asteroid samples will be collected after small pellets
are fired into the asteroid's surface. Ejecta from the pellets'
impact will be collected through an inverted funnel and stored in a
sample-return capsule onboard the orbiter. The capsule will parachute
to Earth's surface when the orbiter re-approaches the planet in
January 2006.

In addition to David Tholen, the scientists selected for the
mission's U.S. team are:

Beth Clark of Cornell University, a UH alumna (PhD '93) who will use
the rover camera and infrared spectrometer to study the physical and
light- scattering properties of the surface of Nereus. This will aid
in differentiating between data that characterizes the asteroid's
chemical composition and data that shows optical effects of the
surface.

Faith Vilas of the NASA Johnson Space Center, who will use the
spacecraft infrared spectrometer to determine the nature of the
minerals on the surface of Nereus through the comparison of spectral
features with laboratory spectra of meteorites and terrestrial rocks.

Peter Smith of the University of Arizona, who will use the rover
camera to study the surface characteristics of Nereus to understand
how the surface and its structures evolved over time. Smith has
worked with the cameras on numerous NASA missions including the Mars
Pathfinder mission and the Cassini-Huygens mission to Saturn and
Titan.

Andrew Cheng of the Johns Hopkins University Applied Physics
Laboratory, who will use the spacecraft lidar (a laser-based
altimeter) instrument to determine the size, shape, mass and rotation
of Nereus. Cheng is the project scientist for NASA's Near-Earth
Asteroid Rendezvous mission, which will encounter the asteroid Eros
in February 2000.

Michael Zolensky of the NASA Johnson Space Center, who will
participate in the preliminary petrologic, mineralogic, and
compositional analysis of the asteroid samples returned to Earth by
the MUSES-C spacecraft. Zolensky is a leader in the development and
application of sample analysis techniques to extra-terrestrial
samples and is a co-investigator on NASA's Stardust mission to
collect a comet sample and return it to Earth.

The alpha X-ray spectrometer for the rover, which will be used to
determine the chemical composition of many surface rocks, is being
supplied by Thanasis Economou of the University of Chicago. Economou
supplied a similar instrument for the Sojourner rover on the Mars
Pathfinder mission and for many other NASA missions.

JPL is managing the U.S. contribution to the MUSES-C mission for
NASA's Office of Space Science. For the NASA portions of the MUSES-C
mission, Ross M. Jones of JPL is the NASA project manager, and Brian
Wilcox of JPL is the lead engineer for the asteroid roving vehicle.
The Institute of Space and Astronautical Science (ISAS) manages the
MUSES-C project for Japan's Ministry of Education, Science, Sports
and Culture, where Jun'ichiro Kawaguchi is the MUSES-C project
manager and Akira Fujiwara the project scientist.

=================
(6) NASA SELECTS MISSIONS TO MERCURY AND A COMET'S INTERIOR AS NEXT
    DISCOVERY FLIGHTS

From NASA NEWS <NASANews@hq.nasa.gov>

Douglas Isbell
Headquarters, Washington, DC              July 7, 1999
(Phone:  202/358-1753)

RELEASE:  99-77

NASA SELECTS MISSIONS TO MERCURY AND
A COMET'S INTERIOR AS NEXT DISCOVERY FLIGHTS

     The first comprehensive mission to map pockmarked Mercury and a
radical mission to excavate the interior of a comet have been selected
as the next flights in NASA's Discovery Program.

     The Mercury Surface, Space Environment, Geochemistry and Ranging
mission, or Messenger, will carry seven instruments into orbit around
the closest planet to the Sun. It will send back the first global
images of Mercury and study its shape, interior and magnetic field. 
Dr. Sean Solomon of the Carnegie Institution, Washington, DC, will lead
Messenger.

     The Deep Impact mission will send a 1,100-pound (500-kilogram)
copper projectile into comet P/Tempel 1, creating a crater as big as a
football field and as deep as a seven-story building.  A camera and
infrared spectrometer on the spacecraft, along with ground-based
observatories, will study the resulting icy debris and pristine
interior material. Dr. Michael A'Hearn will lead Deep Impact from the
University of Maryland in College Park.

     "These low-cost missions are both fantastic examples of the
creativity of the space science community," said Dr. Edward Weiler,
associate administrator for space science at NASA Headquarters in
Washington, DC.  "Messenger is a flagship-quality effort that, in
tandem with a separate Pluto mission, enables us to seize the
opportunity to complete our historic initial reconnaissance of the
Solar System.  Deep Impact presents a special chance to do some truly
unique science, and it is a direct complement to the other two comet
missions already in the Discovery Program."

     Messenger, to be launched in spring 2004, will be NASA's first
mission to Mercury since the Mariner 10 flybys in 1974 and 1975, which
provided information on only half the planet. Its challenging flight
plan begins with two Venus flybys, then two Mercury flybys in January
and October 2008 and a subsequent orbital tour of Mercury beginning in
September 2009.

     Among Messenger's goals will be to discover whether Mercury has
water ice in its polar craters.  The cost of Messenger to NASA is $286
million.  It will be built and managed by the Johns Hopkins
University's Applied Physics Laboratory, Laurel, MD. Further
information about the mission is available on the Internet
at:
             http://sd-www.jhuapl.edu/MESSENGER

     Deep Impact will be launched in January 2004 toward an explosive
July 4, 2005, encounter with P/Tempel 1. It will use a copper
projectile because that material can be identified easily within the
spectral observations of the material blasted off the comet by the
impact, which will occur at an approximate speed of 22,300 mph (10
kilometers per second.)   The total cost of Deep Impact to NASA is $240
million.  Deep Impact will be managed by NASA's Jet Propulsion
Laboratory in Pasadena, CA, and built by Ball Aerospace in Boulder, CO.

     NASA selected these missions from 26 proposals made in early 1998.
The missions must be ready for launch no later than Sept. 30, 2004,
within the Discovery Program's development cost cap of $190 million in
Fiscal 1999 dollars over 36 months and a total mission cost of $299
million.

     The Discovery Program emphasizes lower-cost, highly focused
scientific mission. NASA has developed six other Discovery Program
missions.  Two have completed their primary missions, two are
operational and two more are under development:

     -- The Lunar Prospector orbiter has mapped the Moon's composition
and gravity field for the past 18 months.  It will complete its highly
successful mission on July 31, when it is sent on a controlled impact
into a crater near the south lunar pole. Scientists hope to observe a
resulting plume of water vapor that would help confirm the presence of
water ice in some of the Moon's permanently shadowed craters. In 1997,
the Mars Pathfinder lander, carrying a small robotic rover named
Sojourner, landed successfully on Mars and returned hundreds of images
and thousands of measurements of the Martian environment.

     -- The Near Earth Asteroid Rendezvous (NEAR) spacecraft is
scheduled to enter orbit around the asteroid Eros in February 2000,
after a problem with its initial attempt to do so early this year.  The
Stardust mission to gather samples of comet dust and return them to
Earth was launched in February 1999.

     -- The Genesis mission to gather samples of the solar wind and
return them to Earth and the Comet Nucleus Tour (CONTOUR) mission to
fly closely by three comets are being prepared for launch in January
2001 and June 2002, respectively.

================
(7) WHAT CAUSED THE DESERTIFICATION OF THE SAHARA

From Harvey Leifert <HLeifert@agu.org>

July 7, 1999
AGU RELEASE NO. 99-20
FOR IMMEDIATE RELEASE
Contact: Harvey Leifert
(202) 777-7507
hleifert@agu.org

Sahara's abrupt desertification started by changes in Earth's orbit,
accelerated by atmospheric and vegetation feedbacks

WASHINGTON -- One of the most striking climate changes of the past
11,000 years caused the abrupt desertification of the Saharan and
Arabia regions midway through that period. The resulting loss of the
Sahara to agricultural pursuits may be an important reason that
civilizations were founded along the valleys of the Nile, the Tigris,
and the Euphrates. German scientists, employing a new climate system
model, have concluded that this desertification was initiated by
subtle changes in the Earth's orbit and strongly amplified by
resulting atmospheric and vegetation feedbacks in the subtropics. The
timing of this transition was, they report, mainly governed by a
global interplay among atmosphere, ocean, sea ice, and vegetation.
Their research is published in the July 15 issue of Geophysical
Research Letters.

The researchers, headed by Martin Claussen of the Potsdam-Institut
fuer Klimafolgenforschung (Potsdam Institute for Climate Impact
Research) employed a model of intermediate complexity to analyze
climate feedbacks during the past several thousand years of the
current, or Holocene, era. Called CLIMBER-2 (for CLIMate and
BiosphERe, version 2.1), the model led to the conclusion that the
desertification of North Africa began abruptly 5,440 years ago (+/-
30 years). Before that time, the Sahara was covered by annual grasses
and low shrubs, as evidenced by fossilized pollen.

The transition to today's arid climate was not gradual, but occurred
in two specific episodes. The first, which was less severe, occurred
between 6,700 and 5,500 years ago. The second, which was brutal,
lasted from 4,000 to 3,600 years ago. Summer temperatures increased
sharply, and precipitation decreased, according to carbon-14 dating.
This event devastated ancient civilizations and their socio-economic
systems.

The change from the mid-Holocene climate to that of today was
initiated by changes in the Earth's orbit and the tilt of Earth's
axis. Some 9,000 years ago, Earth's tilt was 24.14 degrees, as
compared with the current 23.45 degrees, and perihelion, the point in
the Earth's orbit that is closest to the Sun, occurred at the end of
July, as compared with early January now. At that time, the Northern
Hemisphere received more summer sunlight, which amplified the African
and Indian summer monsoon.

The changes in Earth's orbit occurred gradually, however, whereas the
evolution of North Africa's climate and vegetation were abrupt.
Claussen and his colleagues believe that various feedback mechanisms
within Earth's climate system amplified and modified the effects
touched off by the orbital changes. By modeling the impact of
climate, oceans, and vegetation both separately and in various
combinations, the researchers concluded that oceans played only a
minor role in the Sahara's desertification.

The CLIMBER-2 models showed that feedbacks within the climate and
vegetation systems were the major cause of Saharan desertification,
building rapidly upon the effects of the initial orbital changes. The
model suggests that land use practices of humans who lived in and
cultivated the Sahara, were not significant causes of the
desertification. Further investigation is necessary, the researchers
say, to determine more precisely the specific effects of latitude and
oceanic feedback, as compared with biospheric feedback, on the timing
of the event.
*****

Notes for science writers and science public information officers:

1. You may receive a copy of this paper, Martin Claussen, Claudia
Kubatzki, Victor Brovkin, Andrey Ganapolski, Philipp Hoelzmann,
Hans-Joachim Pachur, "Simulation of an abrupt change in Saharan
vegetation in the mid-Holocene," by sending an email to Harvey
Leifert < hleifert@agu.org >. If you did not receive this press release
directly from AGU, please include your name, name of your publication
or organization, and your phone and fax numbers.

2. For further information on the science in this paper, you may
contact Prof. Dr. Martin Claussen, < claussen@pik-potsdam.de >, phone
+49 (0) 331 288 2522, or one of the co-authors, whose postal and
email addresses will be found at the end of the paper.

3. This press release and the paper to which it refers are not
under embargo..
----------------

MODERATOR'S NOTE: Please contact the CCNet moderator for further
information on the *global* aspect of this abrupt climatic downturn;
you may receive a copy of my paper "Comparative Analysis of Late
Holocene Environmental and Social Upheaval: Evidence for a global
Disaster around 4000 BP."


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