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From: Benny J Peiser B.J.PEISER@livjm.ac.uk
Subject: CC DIGEST, 13/03/98
To: cambridge-conference@livjm.ac.uk
Priority: NORMAL

CC DIGEST, 13 March 1998
------------------------
(1) ASTEROID WILL MISS EARTH BY "COMFORTABLE DISTANCE" IN 2028
Ron Baalke BAALKE@kelvin.jpl.nasa.gov

(2) ASTEROID 1997 XF11 FOUND ON 1990 FILM
Robert H. McNaught RMN@aaocbn2.aao.gov.au

(3) MORE EVIDENCE POINTS TO IMPACT AS DINOSAUR KILLER
NASANews@hq.nasa.gov

===================================
(1) ASTEROID WILL MISS EARTH BY "COMFORTABLE DISTANCE" IN 2028

From: Ron Baalke BAALKE@kelvin.jpl.nasa.gov
Thu, 12 Mar 1998 23:51:16 +0000 (GMT)

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov

FOR IMMEDIATE RELEASE March 12, 1998

ASTEROID WILL MISS EARTH BY "COMFORTABLE DISTANCE" IN 2028

Asteroid 1997 XF11 will pass well beyond the Moon's distance from Earth
in October 2028 with a zero probability of impacting the planet,
according to astronomers at NASA's Jet Propulsion Laboratory, Pasadena,
CA.

The asteroid "is predicted to pass at a rather comforable distance of
about 600,000 miles (about 960,000 kilometers) in 2028," reported Dr. Donald
K. Yeomans and Dr. Paul W. Chodas, JPL scientists who specialize in
computing the predicted orbits of comets, asteroids, planets and other
bodies in the solar system.

Data on the asteroid from March 1990 (well before its discovery in
December 1997) was integrated into the orbit calculations by Yeomans and
Chodas to arrive at the distance the asteroid will pass Earth. The 1990
observations of the object were found today in the Palomar Planet Crossing
Asteroid Survey conducted at Caltech's Palomar Observatory, by JPL's Eleanor
Helin and Ken Lawrence and by Brian Roman, formerly of JPL.

Even prior to the discovery of the earlier Palomar observations,
however, Yeomans and Chodas had determined that the impact probability would
be zero. The new calculations further underscore that conclusion, they said.

JPL is a division of the California Institute of Technology.

======================================
(2) ASTEROID 1997 XF11 FOUND ON 1990 FILM

From: Robert H. McNaught RMN@aaocbn2.aao.gov.au
Fri, 13 Mar 1998 11:49:43 +1100 (EST)

The asteroid had been found on 18" Palomar Schmidt films taken in 1990
by the PCAS group. Ken Lawrence of Helin's group identified the images
and from this new astrometry, covering an 8 year arc, both the
predicted position and its uncertainty in 2028 can now be stated with
some confidence. It won't hit the Earth, but it is a warning.

There were no plates at the UK Schmidt that had images of the asteroid.
Back to unemployment!

Cheers, Rob McNaught
(rmn@aaocbn.aao.gov.au)

==============================
(3) MORE EVIDENCE POINTS TO IMPACT AS DINOSAUR KILLER

From: NASANews@hq.nasa.gov

Douglas Isbell
Headquarters, Washington, DC March 12, 1998
(Phone: 202/358-1547)

Diane Ainsworth
Jet Propulsion Laboratory, Pasadena, CA
(Phone: 818/354-5011)

RELEASE: 98-42

MORE EVIDENCE POINTS TO IMPACT AS DINOSAUR KILLER

Two new impact crater sites in Belize and Mexico add further evidence
to the hypothesis that an asteroid or comet collided with Earth about
65 million years ago, subsequently killing off the dinosaurs and many
other species on the planet.

Researchers Adriana Ocampo of NASA's Jet Propulsion Laboratory (JPL),
Pasadena, CA, and Kevin Pope of Geo Eco Arc Research, La
Canada-Flintridge, CA, led an international team that discovered the
two new sites during a recent expedition sponsored by NASA's Exobiology
Program and The Planetary Society, Pasadena, CA.

"We discovered an important new site in Alvaro Obregon, Mexico, about
140 miles (230 kilometers) from the rim of the Chicxulub crater. This
crater was formed when a 6-to-8-mile diameter (10-to-14-kilometer
diameter) asteroid or comet collided with Earth," Ocampo said.

"The site contains two layers of material, or ejecta, thrown out by the
impact that flowed across the surface like a thick fluid, known as
fluidized ejecta lobes," added Pope. "This is the closest surface
exposure of ejecta to the Chicxulub crater that has yet been found and
the best example known on Earth from a really big impact crater."

Centered on the coast of Yucatan, Mexico, the Chicxulub crater is
estimated to be about 120 miles (200 kilometers) in diameter. The
impact 65 million years ago kicked up a global cloud of dust and sulfur
gases that blocked sunlight from penetrating through the atmosphere and
sent Earth into a decade of near-freezing temperatures. The drop in
temperature and related environmental effects are thought to have
brought about the demise of the dinosaurs and about 75 percent of the
other species on Earth.

The Earth orbits the Sun in a swarm of so-called near-Earth objects,
whether they are comets or asteroids, yet the science of detecting and
tracking them is still relatively young. Only a handful of astronomers
around the world search for these objects, and they estimate that
currently only about one-tenth of the population of near-Earth objects
has been detected. Chicxulub is the only impact event that has been
correlated with mass extinctions to date. The site has been dated
geologically to the boundary between the Cretaceous and Tertiary
periods, also known as the K/T boundary.

Local geologist Brian Holland of Punta Gorda, Belize, guided the
expedition to another new ejecta site about 290 miles (480 kilometers)
from the crater rim. This Belize site contains tiny spheres of altered
green glass, called tektites. Tektites are rocks that have been melted
to glass by the severe heat of an impact. Expedition member Jan Smit of
Free University, Amsterdam, noted that the Belize tektites were similar
to those found in Haiti and northern Mexico. This finding links the
stratigraphy of the Belize sites to the more distant Caribbean and
Mexican ejecta sites.

Alfred Fischer of the University of Southern California, Michael Gibson
of the University of Tennessee at Martin, and Jaime Urrutia and
Francisco Vega of the National Autonomous University of Mexico helped
the team collect 900 pounds (400 kilograms) of samples, including drill
cores, for paleomagnetic studies. They also collected fossils from the
site to help date the deposits and add new pieces to the puzzle of what
happened at Chicxulub 65 million years ago.

Impact ejecta is very rare on Earth, but covers much of the surface of
Mars because Mars' surface has remained stable and unchanged for
billions of years, thus preserving debris from these rare impact
events. Also, such fluidized ejecta lobes have never been observed
directly on Earth before and can serve as an excellent laboratory for
studying the ejecta lobes surrounding many Martian craters.

"The discovery of these new ejecta sites is very exciting," said team
co-leader Ocampo. "It is like seeing a bit of Mars on Earth."

The exact nature of these ejecta lobes on Mars remains a mystery,
Ocampo noted. Some scientists think they were created by an abundance
of water in the Martian crust, which turned the ejecta into a muddy,
molasses-like material. Others suggest the fluidized ejecta lobes were
enabled by a much thicker atmosphere in Mars' early history. As flying
ejecta from an impact event flew through the Martian atmosphere, it was
reduced by friction to a very dense, turbulent cloud of debris, which
also flowed like water. Study of the Chicxulub fluidized ejecta may
help settle this debate and shed new light on theories that the Martian
surface may once have been more hospitable for life.

Volunteers who assisted The Planetary Society and the scientists in the
field have posted their photographs of the expedition on The Planetary
Society web site at the following URL:

http://planetary.org

Information about and images of newly discovered near-Earth objects
found by JPL's ongoing Near-Earth Asteroid Tracking (NEAT) program are
available at:

http://huey.jpl.nasa.gov/~spravdo/neat.html

Ocampo and Pope's research was funded in part by the Exobiology Program
of NASA's Office of Space Science, Washington, DC. NASA's Jet
Propulsion Laboratory is a division of the California Institute of
Technology, Pasadena, CA.

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