[meteorite-list] Superglue of Planet Formation: Sticky Ice

From: Gerald Flaherty <grf2_at_meteoritecentral.com>
Date: Mon Mar 21 13:24:55 2005
Message-ID: <00c701c52524$5b712800$6401a8c0_at_Dell>

COOL!
----- Original Message -----
From: "Ron Baalke" <baalke_at_zagami.jpl.nasa.gov>
To: "Meteorite Mailing List" <meteorite-list_at_meteoritecentral.com>
Sent: Wednesday, March 09, 2005 1:45 PM
Subject: [meteorite-list] Superglue of Planet Formation: Sticky Ice


>
> http://www.eurekalert.org/pub_releases/2005-03/dnnl-sop030805.php
>
> Public release date: 8-Mar-2005
>
> Contact: Bill Cannon
> cannon_at_pnl.gov
> 509-375-3732
> DOE/Pacific Northwest National Laboratory
>
>
> Superglue of planet formation: Sticky ice
>
>
> Pacific Northwest National Lab experiments point to clingy grains of
> ice to solve age-old mystery of how primordial dust pulled together
> to form planets
>
> ------------------------------------------------------------------------
>
> SOFT-LANDING-Pacific Northwest National Laboratory researchers armed
> with a high-speed camera observed that ceramic bb's consistently
> rebounded about 8 percent of their dropped height from so-called fluffy
> ice grown at 40 Kelvin; the rebound on the much-higher-temperature ice
> people encounter on Earth, which is also much more compact, is 80
> percent. This cushioning feature of extreme low-temperature ice is a key
> attribute in planet formation.
> ------------------------------------------------------------------------
>
> RICHLAND, Wash.--How dust specks in the early solar systems came
> together to become planets has vexed astronomers for years. Gravity,
> always an attractive candidate to explain how celestial matter pulls
> together, was no match for stellar winds. The dust needed help coming
> together fast, in kilometer-wide protoplanets, in the first few million
> years after a star was born, or the stellar wind would blow it all away.
>
> Scientists at the Department of Energy's Pacific Northwest National
> Laboratory, reporting in the current issue of Astrophysical Journal,
> offer a cool answer to the planet- formation riddle: Micron-wide dust
> particles encrusted with molecularly gluey ice enabled planets to bulk
> up like dirty snowballs quickly enough to overcome the scattering force
> of solar winds.
>
> "People who had calculated the stickiness of dust grains found that the
> grains didn't stick," said James Cowin, PNNL lab fellow who led the
> research. "They bounce, like two billiard balls smacked together. The
> attraction just wasn't strong enough."
>
> Cowin's team has spent years studying, among other things, the chemical
> and physical properties atmospheric dust and water ice, using an array
> of instruments suited to the task at the PNNL-based W.R. Wiley
> Environmental Molecular Sciences Laboratory.
>
> Much of the pre-planetary dust grains were either covered by or largely
> composed of water ice, having condensed at temperatures close to
> absolute zero, at 5 to 100 Kelvin. Evidence of this icy solar system can
> be seen in comets, and planets and moons a Jupiter's distance from its
> star and beyond are icy.
>
> "This ice is very different from the stuff we chip off our windows in
> winter," Cowin said. "For example, we saw that at extreme cold
> temperatures vapor-deposited ice spontaneously becomes electrically
> polarized. This makes electric forces that could stick icy grains
> together like little bar magnets."
>
> PNNL staff scientist Martin Iedema, a member of Cowin's group with an
> astronomy undergraduate degree, surveyed the astrophysics literature and
> found that the planet growth mystery resided in the same cold
> temperatures of the lab ices.
>
> Iedema found that the high background radiation in the early solar
> system would have neutralized a polarized, micron-sized ice grain in
> days to weeks--or hundreds of thousands of years before it could accrete
> a critical mass of material and grow to the size of a medicine ball,
> enabling it to get over the critical size hurdle in planet formation.
>
> But, Iedema said, ice grains colliding into each other would have
> chipped and broken in two to upset electrical equilibrium and, in
> essence, recharging the ice grains and restoring their clinginess. Then
> he discovered an additional feature that gave the sticky ice theory a
> new bounce.
>
> "More of an anti-bounce," Cowin emended, "from the cushioning, or
> fluffiness, of this ice. The more technical phrase is 'mechanical
> inelasticity.' We knew that ice, when grown so cold, isn't able to
> arrange its molecules in a well-ordered fashion; it becomes fluffy on a
> molecular scale."
>
> Cowin conjured an image of "billiard balls made of Rice Krispies." Such
> balls would barely bounce. "Colliding fluffy ice grains would have
> enough residual electrical forces to make them stick, and survive
> subsequent collisions to grow into large lumps."
>
> To test this, PNNL postdocs Rich Bell and Hanfu Wang grew ice from the
> vapor in a chamber that reproduced primordial temperatures and vacuum.
> They measured bounce by dropping hard, 1/16th- inch hard ceramic balls
> on it. With a high-speed camera, they observed the balls consistently
> rebound about 8 percent of their dropped height from fluffy ice grown at
> 40 Kelvin, whereas on the hard, warmer and much more compact ice that
> forms naturally on Earth, the ice rebound was as high as 80 percent.
>
> "This huge inelasticity provides an ideal way for fluffy icy grains to
> stick and grow eventually to protoplanets," Cowin said. Cowin and
> colleagues further speculate that similar electrical forces, minus the
> fluffy cushioning, were at work during the infancy of hotter inner
> planets like Earth, involving silicate dust grains instead of ice.
>
> ###
>
> PNNL ( www.pnl.gov <http://www.pnl.gov> ) is a DOE Office of Science
> laboratory that solves complex problems in energy, national security,
> the environment and life sciences by advancing the understanding of
> physics, chemistry, biology and computation. PNNL employs 3,900, has a
> $650 million annual budget, and has been managed by Ohio-based Battelle
> since the lab's inception in 1965.
>
>
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Received on Wed 09 Mar 2005 10:50:52 PM PST