Uranus is Full of Diamonds (and so is Neptune)

Uranus and Neptune imaged by Voyager 2 in January 1986 and August 1989, respectively. Approximate true color and relative scale sizes. Both are about four times wider than Earth.

The conditions found deep inside the ice giants Uranus and Neptune are intense and exotic, to say the least. The incredibly frigid and windy environments found at the cloud tops, where hydrogen and helium are mixed with methane and ammonia, eventually give way to warmer interiors and crushing pressures with increasing depth. And as scientists gain the ability to recreate these kinds of temperatures and pressures in a lab and analyze the results, they’re confirming some long-standing hypotheses of what’s going on thousands of kilometers inside Uranus and Neptune: a steady rain of diamonds, created by crushed hydrocarbons.

The research was conducted by an international team at the SLAC National Accelerator Laboratory at Stanford University. Building on the results of earlier 2017 experiments, the team recently used a technique called X-ray Thomson scattering that precisely reproduces previous diffraction results while also allowing them to study how elements mix in non-crystal samples at extreme conditions.

As reported by Helmholtz-Zentrum Dresden-Rossendorf (HZDR) on June 24, 2020, “Recreating extreme conditions in the lab, like those in the interior of planets and stars, is very complex and can only be achieved for fractions of a second. An international research team led by the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) has now presented a new, very precise method of evaluating the behavior of mixtures of different elements under high pressure with the help of X-ray scattering. The results hone previous measurements and reinforce the premise that the matter in planets like Neptune and Uranus can alter dramatically: the hot hydrocarbon mixture in the interior of the ice giants can produce a kind of diamond rain.”

See the full news release from HZDR here.

Methane ice clouds on Neptune imaged by Voyager 2 in August 1989.

According to the team’s published paper in Nature Communications: “On icy giants like Uranus and Neptune, water, methane and other hydrocarbons are highly abundant. Experimental evidence shows the dissociation and polymerization of methane under pressure, leading to a heavy hydrocarbon fluid. Under certain conditions, diamond can form and will precipitate towards lower layers due to its high density.”

Read more: Surprising Structures Discovered at the Bottom of Uranus

Read the team’s published findings here. (Frydrych, S., Vorberger, J., Hartley, N.J. et al. Demonstration of X-ray Thomson scattering as diagnostics for miscibility in warm dense matter. Nat Commun 11, 2620 (2020).)

According to a 2017 article by Nathaniel Scharping for Discover, which covered the earlier X-ray laser experimentation, “What this likely means for the ice giants is that much larger diamonds, on the order of millions of carats, could exist deep within, born out of the intense pressures and temperatures. These massive jewels likely precipitate slowly through the liquid mantles of the planets like diamond showers, eventually settling into a layer nestled near the rocky core.”

The sinking motion of all those diamond crystals generates heat—a phenomenon that has long been known about at Neptune, which is curiously just as warm as Uranus despite having a similar atmospheric composition and being half again as far from the Sun.

What’s next for the research is to move on to a recreation of the environments found deep inside Jupiter and Saturn with pressurized hydrogen and helium—and where diamond rain has also been hypothesized.

“This technique will allow us to measure interesting processes that are otherwise difficult to recreate,” says Dominik Kraus, a scientist at Helmholtz-Zentrum Dresden-Rossendorf who led the study. “For example, we’ll be able to see how hydrogen and helium, elements found in the interior of gas giants like Jupiter and Saturn, mix and separate under these extreme conditions. It’s a new way to study the evolutionary history of planets and planetary systems, as well as supporting experiments towards potential future forms of energy from fusion.” (Source)

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