Two new superionic ice phases found for Neptune and Uranus — SkimNews
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- Neptune and Uranus are the ice giant planets whose bizarre magnetic fields the new ice phases could explain, since their fields are tilted and off-centre compared to Earth's dynamo-driven field.
- Gunnar Weck at the French Alternative Energies and Atomic Energy Commission used a diamond anvil combined with a laser to compress water to millions of atmospheres of pressure and thousands of degrees, producing a new phase called hexagonal close-packed (hcp) ice.
- In hcp ice, oxygen atoms stay locked in a solid lattice while hydrogen moves freely like a liquid, giving the phase far higher electrical conductivity than ordinary ice.
- That conductivity could generate the ice giants' magnetic fields if charge flows through superionic ices closer to the planets' surfaces rather than through some central dynamo mechanism.
- Israel Osmond at the University of Edinburgh and his team independently found another new phase called ice XXII, which is stable at pressures nearly double those required for hcp ice.
- Next step, per Weck: researchers need to precisely map the transition lines between these phases and determine the depths at which each superionic phase is stable inside the planets.
- Ordinary water ice is just one of more than 20 known phases, each with a different crystal structure, mechanical behaviour, and electrical properties under varying temperature and pressure.
Why it matters: Spacecraft have directly observed that Neptune and Uranus have tilted, off-centre magnetic fields unlike any other planet, but until now no laboratory-confirmed phase of matter could explain how they form. If superionic ices closer to the planets' surfaces generate those fields through flowing charge, planetary scientists get a testable mechanism — and a clearer picture of what's physically happening deep inside worlds we cannot otherwise see.
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