It’s Raining Diamonds in Neptune and Uranus, but How Is This Possible?

The atmospheres of Neptune and Uranus are primarily made up of hydrogen, helium, and a small amount of methane. Beneath these atmospheric layers is a superhot, superdense fluid of 'icy' materials like water, methane, and ammonia that also wraps around the planet's core.

These two planets could also be raining diamonds and scientists have now produced new experimental evidence showing how this could be possible.

They hypothesize that the intense heat and pressure of thousands of kilometers below the surface of Neptune and Uranus should split apart hydrocarbon compounds, with the carbon compressing into a diamond which sinks towards the planetary cores.

Knowing How Neptune Rains With Diamonds

The researchers conducted a new experiment using the SLAC National Accelerator Laboratory's Linac Coherent Light Source (LCLS) X-ray laser. This is to get the most precise measurement yet of how Neptune came to have a diamond rain and find out carbon transitions directly into a crystalline diamond.

Plasma physicist Mike Dunne, the director of the LCLS, who is not part of the paper, explained that this new experiment provides information on a phenomenon that is very difficult to model computationally, which is the miscibility of the two elements.

Neptune and Uranus are the most poorly understood planets in the Solar System since they are located very far with only a single space probe, Voyager 2, has even been close to them.

But according to NASA, ice giants are fairly common in the Milky Way, with Neptune-like exoplanets are ten times more widespread than Jupiter-like exoplanets.

Calculations and experiments done decades ago to understand what happens in the atmospheres of Uranus and Neptune have shown that sufficient pressure and temperature, methane can be broken down into diamonds.

Physicist Dominik Kraus at the Helmholtz-Zentrum Dresden-Rossendorf in Germany led an experiment before which used X-ray diffraction to demonstrate this process. Presently, he and his team are taking it a step further, hopeful that their new approach based on X-ray scattering will become more relevant the more exoplanets are discovered.

It is difficult to replicate the atmospheric conditions of the giant planets here on Earth because it will need intense equipment. Through LCLS and a material that replicates the things inside the giant planet-which they used the hydrocarbon polystyrene (C8H8) in place of methane (CH4) - the researchers were able to create a model that somehow replicates the giant planets.

Replicating Neptune's Diamond Rain

The researchers first heated and pressurized the material to replicate the conditions inside Neptune at a depth of 6,214 miles (10,000 kilometers). Pulses of optical laser produce shockwaves in the polystyrene that heats the material to 8,540 degrees Fahrenheit (4,727 degrees Celsius).

This also created intense pressure, at about 1.5 million bars. This is equivalent to the pressure exerted by the weight of 250 Africa elephants on the surface of a thumbnail, Kraus said.

In his previous experiment, X-ray diffraction was used to probe the material, especially those with crystalline structures. But in the new experiment, the researchers used a different method. They measured how X-rays scattered off electrons in the polystyrene.

Through this, they were able to observe carbon turning into a diamond and see the rest of the sample split off into hydrogen that left no carbon after.

This experiment showed that there is no alternative explanation as of yet, and it also showed a method to 'probe' interiors of other planets in the Solar System. They published their study in Nature Communications.