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Physical Sciences
Research Highlights

May 2005

Sticky ice may explain plant formation

A ceramic ball dropped on fluffy ice bounces to about 10% of the height from which it was dropped; if dropped on an unyielding surface, it would bounce to about 80% of the original height.

Planetary systems form as dust particles in a nebula accrete to form proto planets. As the protoplanets grow, their increasing gravitational strength attracts even more particles. This model has a couple of flaws. First, when the proto sun at the center of the nebula becomes massive enough to initiate fusion reactions, the generated solar wind will quickly (a few million years is quick in astronomical terms) blow the dust particles away, preventing planet formation. Second, when dust particles, which are expected to be coated with ice, collide, they would recoil and not stick together.

PNNL researchers have demonstrated a mechanism that would encourage planetary formation. Water ice formed at cryogenic temperatures creates particles that have an electrostatic dipole. These charged particles are more inclined to stick together than neutrally charged particles. The solar wind would rapidly neutralize the charges, but collisions break the particles into asymmetric pieces that have net charges, re-establishing the attractive force.

As ice is formed in the near-vacuum at cryogenic temperatures, it takes on a fluffy form. This cushions collisions and reduces recoil. When formed under terrestrial conditions, ice particles will recoil with about 80 percent of their original energy. The fluffy ice only recoils with about 10 percent of the original energy.

The combination of electrostatic attraction and cushioning results in a sticky form of ice that would encourage the growth of dirty snowballs to a size where gravitation would take over for further growth. PNNL researchers speculate that the asymmetric shattering producing charged grains, but without cushioning effect, may account for the accretion of the inner planets, composed primarily of heavy elements.

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