Molecular Monday: Hot as Ice VII

Welcome to Molecular Mondays! Every other Monday, we examine the atoms and molecules that serve as the building blocks of our universe, both in reality and in science fiction. Today we continue our investigation of:


Water is basically everywhere in our universe. On Uranus and Neptune, most of the water is in the form of ice.

Nv06 Ice Ice Baby

But this ice isn’t cold. It’s hot. Like thousands of degrees Celsius hot.

The ice you and I are most familiar with is called ice Ih (pronounced ice one-h). The I is a Roman numeral one, and the h stands for hexagonal, because the water molecules form hexagon-shaped crystals.

Another form of ice is called ice Ic (ice one-c). In this case, the c stands for cubic.  The water molecules crystalize into cube shapes.

Nv06 Ice Cube

Ice Ic requires extremely cold temperatures (-50 to -140ºC) and is believed to form in the uppermost reaches of Earth’s atmosphere.

There are at least fifteen more crystalline forms of ice, ranging from ice II to ice XVI. Some have been created in the laboratory. Others remain purely hypothetical. Water molecules will line up to form ice crystals of wildly different shapes, sizes, and complexities depending on various combinations of pressure and temperature.

Nv06 Snowflake

Somewhere deep inside the planets Uranus and Neptune, water molecules probably “freeze” as ice VII and ice VIII. I’m not sure how to describe the geometry of these types of ice; just click the links to see some diagrams.

Pressures on Uranus and Neptune may even be great enough for ice X to form. In ice X, water molecules are so tightly packed that they lose their identities. It would be better to think of oxygen and hydrogen atoms squeezed together, not separate water molecules. For this reason, ice X is sometimes called non-molecular ice.

Of course, all of this seems very strange and exotic to us Earthlings. And yes, things like ice VII or ice X aren’t exactly common in our universe. But that doesn’t mean ice Ih is normal either.

In the next edition of Molecular Mondays (two weeks from today), we’ll meet yet another kind of ice. A kind of ice that doesn’t play by the rules and doesn’t need no Roman numerals.


Is Salt the Key to Unlocking the Interiors of Neptune and Uranus? from Science Daily.

Phase Diagram of Water from Wikipedia.


4 Responses to Molecular Monday: Hot as Ice VII

  1. Spacer Guy says:

    Oddly enough uranus is the coldest planet in the solar system even though it isn’t the farthest from the sun. The planet is an amazing puzzle in itself tilted at 98 degrees – I wouldn’t like to be a tourist visiting the planet when my Voyager3 rocket ship runs out of fuel. Its poles are flooded in darkness and light for 42 years a pop owing to the odd rotation of the planet and then theres the 900 kph weather patterns, Scotty beam me out of here – on the double!


  2. […] earlier this year in Nature Communications, might help explain what’s going on. Remember those exotic forms of water ice, like ice VII, ice VIII, and ice X? Those weird “hot” ices believed to exist in the […]


  3. […] my previous Molecular Monday post, I told you about some of the exotic forms of water ice believed to exist on other planets, where […]


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