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(meteorobs) Excerpts from "CCNet 54/2001 - 6 April 2001"




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From: Peiser Benny <B.J.Peiser@livjm.acdot uk>
To: cambridge-conference <cambridge-conference@livjm.acdot uk>
Subject: CCNet, 6 April 2001
Date: Fri, 6 Apr 2001 10:38:44 +0100 


CCNet 54/2001 - 6 April 2001
----------------------------

	Wishing all CCNet readers a happy Passover & restful Easter break.
		--Benny J Peiser, CCNet Moderator

[...]

(2) WAS JOHNNY APPLESEED A COMET? [Full Story]
    NASA Science News for April 5, 2001

[...]

(5) BIG-ORBIT OBJECT CONFOUNDS DYNAMICISTS
    Sky & Telescope, 5 April

[...]

===========================================================================

(2) WAS JOHNNY APPLESEED A COMET?

>From NASA Science News for April 5, 2001
http://science.nasadot gov/headlines/y2001/ast05apr_1.htm?list20392

A new experiment suggests that comet impacts could have sowed the seeds of
life on Earth billions of years ago. 
 
April 5, 2001 -- Four billion years ago Earth was bombarded by a hail of
comets and asteroids. The shattering collisions rendered our planet
uninhabitable during a period scientists call the Late Heavy Bombardment
(LHB).

It surely sounds like the LHB was an awful time for the beleaguered young
planet -- but perhaps the pelting was a good thing after all, say
researchers. Kamikaze comets could have delivered important organic
molecules to Earth -- sowing the seeds for life.

Genesis by comets is a controversial idea, but it's just received an
important boost. A NASA-supported experiment reveals that complex molecules
hitchhiking aboard a comet could have survived an impact with Earth.

"Our results suggest that the notion of organic compounds coming from outer
space can't be ruled out because of the severity of the impact event," says
Jennifer Blank, a geochemist at the University of California, Berkeley.
Blank and colleagues simulated a comet collision by shooting a soda-can
sized bullet into a metal target containing a teardrop of water mixed with
amino acids - the building blocks of proteins.

Not only did a good fraction of the amino acids survive, but many
polymerized into chains of two, three and four amino acids, so-called
peptides. Peptides with longer chains are called polypeptides, while even
longer ones are called proteins.

"The neat thing is that we got every possible combination of dipeptide, many
tripeptides and some tetrapeptides," said Blank. "We saw variations in the
ratios of peptides produced depending on the conditions of temperature,
pressure and duration of the impact. This is the beginning of a new field of
science."

Freezing the target to mimic an icy comet increased the survival rate of
amino acids, she added.

Blank's ballistic test was designed to simulate the sort of impact that
would have been frequent in Earth's earliest history when rocky, icy debris
in our solar system combined to form the planets. Much of the debris would
have resembled comets - dirty snowballs thought to be mostly slushy water
surrounding a rocky core - slamming into Earth at velocities greater than 16
miles per second (25 km/sec).

The severity of the laboratory impact was akin to that of an oblique
collision between the rocky surface of Earth and a comet coming in at an
angle of less than 25 degrees from the horizon.

Benton Clark, chief scientist of Flight Systems at Lockheed Martin
Astronautics, proposed in 1988 that if comets are slowed sufficiently -- by,
e.g., drag from Earth's atmosphere, which would be greatest at low impact
angles -- some water and organic compounds might survive the collision.

"At very low angles, we think that some water ice from the comet would
remain intact as a liquid puddle concentrated with organic molecules," ideal
for the development of life, Blank said. "This impact scenario provides the
three ingredients believed necessary for life: liquid water, organic
material and energy."

Though comet hunter Eugene Shoemaker estimated that in Earth's early history
only a few percent of comets or asteroids arrived at low enough angles, the
bombardment would have been heavy enough to deliver a significant amount of
intact organic material and water, according to Blank's estimates.

One well-known model for the beginnings of life on Earth posits that
terrestrial life sprang from complex molecules such as amino acids and
sugars produced by electrical discharges in a primeval atmosphere replete
with gases such as methane, hydrogen, ammonia and water. The famous
Miller-Urey experiment in 1953, conducted by Stanley Miller and Harold Urey
of the University of Chicago, demonstrated that a lightening-like discharge
in a test tube filled with these molecules could produce amino acids.

Other scientists believe that the building blocks of life on Earth arrived
from space. Astronomers have detected many kinds of organic molecules in
space, floating in clouds of gas or bound up in dust particles. They range
from the simplest - water, ammonia, methane, hydrogen cyanide and alcohols,
including ethyl alcohol - to more complex molecules.

Interestingly, of the more than 70 amino acids found in meteorites, only
eight of them overlap with the group of 20 which occur commonly as
structural components of proteins found in humans and all other life on
Earth.

To test whether water and organic compounds could survive the high pressures
and high temperatures of a collision, Blank and her colleagues worked for
three years to design a steel capsule that would not rupture when hit with a
mile-per-second (1.6 kilometer-per-second) bullet fired from an 80-mm bore
cannon at the University of Chicago and later at Los Alamos National
Laboratory. The target she and her team developed - a two-centimeter
diameter stainless steel disk about a half-centimeter thick - was able to
withstand about 200,000 times atmospheric pressure without bursting.

They filled the small cavity with water saturated with five amino acids:
three from the list of 20 that comprise all proteins in humans
(phenylalanine, proline and lysine) and two varieties detected in the
Murchison meteorite (aminobutyric acid and nor-valine). That meteorite
plummeted to the ground in 1969 in Australia and is thought to be from the
core of a comet.

The survival of a large fraction of the amino acids and their polymerization
during the collision makes the idea of an extraterrestrial origin of organic
compounds a strong contender against Miller-Urey style theories, Blank said.

"About one comet per year arriving in a low-angle impact would bring in the
equivalent of all the organics produced in a year in an oxidizing atmosphere
by the Miller-Urey electric discharge mechanism," Blank estimated. "An
advantage is you get all of it together in a puddle of water rather than
diluted in the oceans."

The next hitchhikers she plans to subject to a shock test are bacterial
spores, which some have proposed arrived on Earth via comets to jump-start
evolution.

Ivan Semeniuk is a science writer and broadcaster based in Toronto 

===========================================================================

(5) BIG-ORBIT OBJECT CONFOUNDS DYNAMICISTS

>From Sky & Telescope, 5 April
http://www.skypub.com/news/news.shtml#bigorbit

To Marc W. Buie (Lowell Observatory), 2000 CR105 was at first just another
distant discovery among dozens found during his team's ongoing search for
trans-Neptunian objects using 4-meter telescopes in Arizona and Chile. But
its uniqueness became apparent when dynamicist Brian G. Marsden started
cranking out possible orbits for this 24th-magnitude find. "It was obviously
far away, 53 to 55 astronomical units," Marsden recalls, well beyond most
objects known to inhabit the Kuiper Belt.

In the months that followed, an international team led by Brett Gladman
(Nice Observatory) quietly tracked the dim interloper. Thanks to their
year-long pursuit, it's now clear that 2000 CR105 has a highly eccentric
orbit that stretches out to roughly 400 a.u. - more than 10 times Pluto's
mean distance from the Sun and far larger than that of any known Kuiper Belt
object. But more puzzling to dynamicists is the orbit's perihelion distance.
At 44.5 a.u. (6.7 billion km), it is well beyond the perturbing influence of
Neptune, whose gravity has flung countless other bodies out to the solar
system's most distant fringes. So how did 2000 CR105 end up stranded out
there?

Gladman and six colleagues offer several possibilities in an article
submitted to the journal Icarus and summarized here. According to coauthor
Matthew Holman (Harvard-Smithsonian Center for Astrophysics), the orbit of
2000 CR105 is dynamically chaotic and may simply be the consequence of eons
of erratic drift. But that's a statistical long shot, so the team has
explored other ideas. Perhaps the Kuiper Belt formed with numerous
planet-size bodies in its midst, which wreaked orbital havoc before
themselves being heaved out of the region. Or Neptune itself may have
ventured farther out before settling into its present orbit. And though the
notion is highly speculative, a massive perturber may yet await discovery
beyond the Kuiper Belt's known boundary. Holman notes that a body the size
of Mars 200 a.u. away could easily have escaped detection to date. 

Resolving this mystery will take time, but one implication is already clear.
Objects like 2000 CR105 should be exceedingly rare, so if others are found
then the Kuiper Belt is likely much more massive than currently envisioned.

- - J. Kelly Beatty

) 2001 Sky Publishing Corp. All rights reserved.

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