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21 September 2016

How Does Ice Withstand 500°C Temperatures in Space?

On our rocky little planet, the qualities of water and ice are fairly consistent. The Celsius scale is of course based upon this fact; water freezes at 0°C and boils at 100°C, with some minor variation. So, when scientists encountered a planet called Gliese 436b orbiting very close to its parent star and reaching surface temperatures over 520°C, they were surprised to find that the planet is likely comprised largely of ice.

An artist's impression of Gliese 436b
The surface temperatures of Gliese 436b are so high that liquid water cannot exist, so surely the presence of ice makes no logical sense?

As it turns out, ice is not as simple as you might think. There are in fact over 17 phases of water ice known to scientists, each one with its own unique structure and properties, and many of them don’t even require low temperatures. They key lies in how water molecules connect and bond.

Ice X Lattice Diagram - Source: Martin Chaplin
When water molecules bond, they use a hydrogen molecule to make the connection, which gives water a boiling point much higher than that of its component parts alone. These bonds can stretch, reducing the distance between the oxygen and hydrogen molecules when the temperature rises, and increasing the distance under high pressures.

The ice that makes up the bulk of Gliese 436b is under extremely high pressure, compressing its molecules and altering its crystalline structure. The ice phase present is likely ice X, which has a wire-fence shaped structure that is formed under significantly higher pressures than those found on the Earth’s surface. This has the effect of raising its melting point substantially, which is how the icy mass manages to endure to sweltering heat of its nearby parent star.

The effect of pressure on the properties of water and ice can actually be observed to a smaller extent on Earth. At high altitude, water boils at a much lower temperature, with the exact boiling point decreasing as you increase your elevation.

Sam Bonson

Sam is an aspiring novelist with a passion for fantasy and crime thrillers. He is currently working as a content writer, journalist & editor in an attempt to expand his horizons.