September 12, 2013
Methane’s Secrets Hold Key To Understanding Planetary Interiors
Lee Rannals for redOrbit.com - Your Universe Online
Hydrocarbon methane (CH4) is one of the most abundant molecules in the universe, but its behavior under the conditions found in planetary interiors is poorly understand due to contradictory information from various modeling studies. Studying various phases of molecules formed from carbon and hydrogen under high pressures and temperatures helps scientists better understand what takes place beneath the surface of a planet.
"Our knowledge of physics and chemistry of volatiles inside planets is based mainly on observations of the fluxes at their surfaces. High-pressure, high-temperature experiments, which simulate conditions deep inside planets and provide detailed information about the physical state, chemical reactivity, and properties of the planetary materials, remain a big challenge for us," lead author Sergey Lobanov, of the Carnegie Institution for Science, said in a statement.
Lobanov and colleagues were able to examine methane's phases and reactivity under a range of temperatures and pressures mimicking environments found beneath Earth's surface.
They said that methane's melting temperature is below 1,900 degrees Fahrenheit even at pressures reaching 790,000 times normal atmospheric pressure. This suggests that methane is not a solid under any conditions deep within most planets. They also found that methane's melting point is even lower than melting temperatures of water and ammonia.
As methane's temperature increases above 1,700 degrees Farhenheit, it becomes more chemically reactive, partly disassociating into elemental carbon and hydrogen. After this, light hydrocarbon molecules start to form, and heavy hydrocarbons become apparent at pressures above 250,000 times atmospheric pressure, which indicates that even under deep mantle conditions the environment is likely methane poor.
The team's findings have implications for Earth's deep chemistry as well as the geochemistry of icy gas giant planets like Uranus and Neptune. They said this reactivity could play a role in the formation of ultra-deep diamonds deep within the mantle. Their findings should be taken into account in future models when looking into the interiors of Neptune and Uranus, which scientists believe have mantles consisting of a mixture of methane, water, and ammonia.
The scientists' findings will not only help scientists understand the chemistry of these icy planets, but also hydrocarbon energy resources and diamond formation here on Earth.