DIAMOND RAIN-NEPTUNE !

When we look out the window. The sky was tar-black and the large clouds were moving towards us. A tapping sound on the window and then it became a pitter-patter. People ran for cover outside and umbrellas were opened as the clouds spat out their beads of water. Puddles began plinking as the rainfall became heavier. But what if the tiny droplets are made of diamonds? Yeah you heard me right! it rains diamonds in Neptune. Now it’s time to start exploring and learning more about intriguing diamond worlds of the Solar system.

Harshil Gudka on Unsplash

Neptune is the eighth and farthest planet from the Sun in the Solar System (sorry Pluto). Neptune’s atmosphere is composed primarily of hydrogen and helium, along with traces of hydrocarbons and possibly nitrogen; however, it contains a higher proportion of “ices” such as water, ammonia and methane. Neptune and Uranus are called the ”ice giants” of our Solar system because their outer two layers consist of compounds that include hydrogen and helium . In astrology slang, ice refers to light elements containing hydrogen (the planet’s water H2O), ammonia(NH3) and methane(CH4) make them icy. As for the rain, it’s estimated that at a depth of 7000 km, the conditions may be such that methane decomposes into diamond crystals that rain downwards like hailstones. On Neptune, beneath the hydrogen-helium atmosphere has an ice layer that is 17,500kms thick. Neptune has pressure one million times higher than earth, high temperature (several thousand Kelvin) and the gravity compresses “ices” in this layer to high densities. Under such conditions of temperature and pressure methane and ammonia react chemically. In 1981, Marvin Ross wrote an article on Nature titled “The ice layer in Uranus and Neptune-Diamonds in the sky?”, he proposed that huge quantities of diamonds might be found in the interior of these planets. He suggested that the carbon and hydrogen of hydrocarbons such as methane separate at high temperatures and high pressures inside the ice giant planets. Under such conditions, clusters of isolated carbon would be squeezed into a diamond structure (the most stable form of carbon).

Photo by NASA on Unsplash

Theoretical modelling and others predicted that diamonds would form at pressures over 300GPas, but even at lower pressures methane would be disrupted and form chains of hydrocarbons. High pressure experiments at the University of California Berkeley using a diamond anvil cell found that only at 50GPa and a temperature of 2500k, equivalent to depths of 7000kms below Neptune cloud tops. Water and hydrogen mixed with the methane may alter the chemical reactions. A physicist at the Fritz Haber Institute in Berlin showed that the carbon on these planets is not concentrated enough to form diamonds from scratch. Diamond is denser than the methane, ammonia and water left in the ice layer, the carbon crystals would start to sink toward the planet’s core. It would accumulate into new layers as it falls when it touches other isolated carbon atoms or diamonds. This allows individual diamond blocks to reach a size of meters in diameter. As a result, a thick layer of carbon surrounds the rocky cores of Neptune. This layer consists of solid diamond blocks, or if temperature increases it either consists of liquid carbon or a mix of solid and liquid carbon. If it’s so, the solid carbon would be of lower density than liquid carbon, resulting in large “diamond bergs” floating on the top of liquid carbon.

Neptune is emitting more energy than it receives from the Sun. This is because diamond precipitation releases gravitational energy, which is converted into heat by friction between the diamonds and surrounding materials. This internal energy source accounts for the origin of violent storms on the planet's surface. Diamond formation also explains the exotic magnetic fields on Neptune. These ice giant fields originate in a thin variable layer of conducting materials such as metallic hydrogen (a by-product of making diamond), unlike Earth’s magnetic field that extends from pole to pole. Other exotic processes such as super-ionic structure of water and ammonia also contribute to the magnetic fields.

But planet earth's atmosphere is not of the type of Neptune. What will you do if the earth rains diamond? Make sure you mention in the comment section...

  - Divya