'Diamond rain' on Uranus and Neptune seems likely

The ice giants Neptune and Uranus don't get a lot of attention, but their larger siblings Jupiter and Saturn do.
At first glance, the balls of uninteresting molecule are bland. There is a constant rain of diamonds hidden beneath the outer layers of those worlds.

Icy planets' diamond rain was created in a laser laboratory.

"ice giants" may conjure up images of a creature similar to J.R.L.'s "The Lord of the Rings", but it's the name that astronomy uses to categorize the planets of the solar system.

The name has nothing to do with ice in the way that ice cubes in your drink would. The planets are made of something. The gas giants of the system, Jupiter and Saturn, are made of hydrogen and helium. These huge planets were created through the rapid accretion of those elements.

Water, ammonia, and methane are the main ingredients of Neptune and Uranus. Astronomers call these elements "ices", but there is no good reason for it, except that when the planets first formed, those elements were likely in solid form.
Into the icy depths.

There's a lot of water, ammonia and methane beneath the green or blue cloud tops of Neptune and Uranus. These ice giants have rocky cores with elements that are compressed into exotic quantum states. At some point, the quantum weirdness transitions into a soup that thins out the closer you get to the surface.

We don't know a lot about the interiors of the ice giants. The last time we got close-up data of those two worlds was three decades ago.

Since then, Jupiter and Saturn have hosted multiple probes, yet our views of Uranus and Neptune have been limited to telescope observations.

Astronomers and planetary scientists have to combine meager data with laboratory experiments to try to understand what's inside those planets. They use a lot of old-fashioned math. Astronomers use mathematical modeling to understand what's happening in a given situation.

Through the combination of laboratory experiments and mathematical modeling, we realized that Neptune and Uranus might have diamond rain.

There are amazing photos of a monster storm.

It's raining diamonds.

The idea of diamond rain was first proposed in 1977. The reason was simple: we know what Uranus and Neptune are made of, and we know that stuff gets hotter and denser deeper into a planet. The innermost regions of the planets' mantles are likely to have temperatures around 7,000 kelvins and pressures around 6 million times that of Earth's atmosphere.

The models tell us that the outer layers of the mantles are less pressurized and cooler than the inner layers. It's natural to ask what happens to water, ammonia and methane at those kinds of temperatures and pressures.

The intense pressures can break the molecule apart, releasing the carbon. The carbon forms long chains after finding its brethren. The long chains form a pattern similar to diamonds.

The term "diamond rain" refers to the dense diamond formations that drop through the layers of the mantle until it gets too hot.

There are lab-grown diamonds.

The best way to verify this idea is to send a spaceship. That won't be an option in the near future, so we have to use laboratory experiments.

We can shoot powerful lasers at targets to recreate the temperatures and pressures found inside ice giants. One experiment with Styrofoam was able to make diamonds. The plastic was much easier to handle in the laboratory than it was in the field, and it behaves very similar to methane.

The diamonds could grow to be a lot larger than they are because the pressures can be kept up for a long time by Neptune and Uranus.

The end result? Diamond rain is a very real thing because of everything we know about the composition of the ice giants, their internal structures, results from laboratory experiments and our mathematical modeling.

"Ask a Spaceman" and "Space Radio" are hosted by Paul M. Sutter, who is also an astronomer at the Flatiron Institute and author of "How to Die in Space."

You can listen to the "Ask A Spaceman" podcast on the internet. You can ask your own question using the #AskASpaceman or following Paul on Facebook.