Lab tests hint at where xenon hides out

New experiments conducted at high temperatures and pressures may explain the puzzlingly low concentration of xenon gas in the atmosphere.

Under conditions normally found at Earth’s surface, atoms of xenon don’t bond with other atoms, a trait common to the other elements known as inert gases, including neon, argon, and krypton.

But atmospheric concentrations of the gas on Mars and Earth are one-twentieth of what would be the expected values from its abundance in the universe, says Chrystèle Sanloup, a geophysicist at Pierre and Marie Curie University in Paris. Now, she and her colleagues may know why.

The researchers heated capsules filled with xenon and powdered quartz to a temperature of 2,000°C and squeezed them at up to 50,000 times atmospheric pressure at sea level, mimicking conditions many kilometers below Earth’s surface. Passing high-energy X rays through the samples revealed that xenon had dissolved into the quartz, says Sanloup. Some of the xenon atoms had even bonded with oxygen in the quartz’s crystalline structure, she notes. The other inert gases don’t form such bonds and fully escape to the atmosphere when pressure is released.

If such xenon storage takes place in the abundant silicate minerals found in the crusts of Earth and Mars, it could explain the dearth of that gas in the planets’ atmospheres, the researchers say in the Nov. 18 Science.

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