Tuesday, March 08, 2005

Sticky Ice

The origin of planets, their orbital irregularities, and their differences in chemical composition has confounded astronomers for hundreds of years. A new theory put forth in the Astrophysical Journal has a very interesting take on this classical problem.

Pre-planetary dust was covered, or composed mostly of, frozen water. When water freezes at normal temperatures and pressures on our planet, you get a hard inelastic substance. This is not the only form that solid H2O can take though (remember Ice-9?). The diagram on the left shows some of the different phases that solid H2O can take as a result of pressure and temperature.

This recent publication from scientists at the Pacific Northwest National Lab studies ice produced at temperatures between 5 and 100 Kelvin. The ice produced at these extremely low temperatures is rather different from the stuff used to chill martinis. This solid can become spontaneously polarized - an electric force that allows this sticky ice to clump together.

To demonstrate the elasticity (read: stickiness) of this form of ice, the authors measured the rebound of a ceramic ball bouncing off of a surface of normal ice-cube ice, and their extremely cold sticky ice. The ceramic ball rebounded to 80% of the drop height when bounced off of normal ice, while that height was diminished to only 8% when the sticky ice was used (image shown at right), demonstrating that ice particles (at pre-planetary temperatures) could have run into other ice particles to form clumps. This clumping of ice and dust eventually, apparently, leads to planet formation.

For background on classical theories of planet formation see this entry in the Columbia encyclopedia.

Via: EurakAlert!


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