Diamond Rain

Diamond rain on giant icy planets could be more common than previously thought: Research

An experiment that simulated the conditions on ice giant planets like Neptune and Uranus has helped researchers discover that "diamond rains" may be more common on these planets than previously thought.

A new study has found that “diamond rain” may be more common on ice giant planets like Neptune and Uranus than previously thought. For the first time, scientists were able to observe diamond rain as it formed with their experiment designed to mimic the extreme temperatures and pressure found on those planets.

Diamond rain forms when hydrogen and carbon found in the interior of these planets are squeezed by the high pressure and form solid diamonds that sink slowly further into the interior. The research has been published in the journal Nature Astronomy.

The researchers simulated the kind of environment found inside these planets by creating shock waves in plastic using an intense laser at the Matter in Extreme Conditions (MEC) instrument at the Stanford National Accelerator Laboratory in Menlo Park, California.

In the experiment, researchers used PET plastic, often found in food packaging, plastic bottles and containers, to reproduce the composition of these planets. “PET has a good balance between carbon, hydrogen and oxygen to simulate the activity in ice planets,” said Dominik Kraus, a physicist and professor at the University of Rostock, in a press statement.

As they created shockwaves in the plastic using the laser, they observed the atoms of the material rearrange into small diamond regions. They used a method called “small-angle scattering” to measure how fast and large those regions grew. The researchers found that these diamond regions grew up to a size of a few nanometres. With the presence of oxygen in the material, the nanodiamonds were able to grow at lower pressures and temperatures than was observed in previous experiments.

The research team predicts that the diamonds on Neptune and Uranus would become much larger than the nanodiamonds produced in these experiments; maybe even weighing in millions of carats. Over thousands of years, these diamonds could have slowly sunk through the planets’ icy layers to assemble as a thick layer around the solid planetary core.

This research also opens up the potential to produce nanodiamonds using this laser-driven method. Such nanodiamonds are already included in abrasives and polishing agents and in the future, they can potentially be used for quantum sensors, medical contrast agents and reaction accelerators for renewable energy.

“The way nanodiamonds are currently made is by taking a bunch of carbon or diamond and blowing it up with explosives. This creates nanodiamonds of various sizes and shapes and is hard to control. What we’re seeing in this experiment is a different reactivity of the same species under high temperature and pressure. In some cases, the diamonds seem to be forming faster than others, which suggests that the presence of these other chemicals can speed up this process,” said SLAC scientist and collaborator Benjamin Ofori-Okai, in a press statement.

According to Ofori-Okai, this laser production method could offer a cleaner and more easily controlled method to produce nanodiamonds.

Next, the researchers envision conducting similar experiments using liquid samples containing ethanol, water and ammonia, which is what Uranus and Neptune are mostly made out of. This will help them get even closer to understanding how diamond rain forms on other planet.