Planetology: when diamonds fall from the sky
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The atmosphere of Neptune and Uranus contains a lot of methane, a simple hydrocarbon which could dissociate under the effect of the pressures and the enormous temperatures which reign in the heart of these planets.
Uranus
Would it rain diamonds in the atmosphere of Neptune and Uranus? The question dates back forty years, after the Voyager probes flew over these planets. It comes from the observation that the atmosphere of the two icy giants contains a lot of methane (CH4), a simple hydrocarbon that could dissociate under the effect of the pressures and enormous temperatures that reign at the heart of these planets: on one side hydrogen, on the other carbon which, when subjected to high pressures, forms diamonds.
A vast setting
It remained to reproduce these conditions in the laboratory. This is what Dominik Klaus, professor at the German University of Rostock, and his colleagues did in 2017, by subjecting a hydrocarbon (polystyrene [C8h8]n) to a powerful laser beam. They created a pressure of 50 billion pascals and a temperature of 5,000 kelvins, the conditions that probably prevail 10,000 kilometers below the cloud surface of Neptune and Uranus.
They then saw the hydrogen and carbon atoms dissociate, and observed by X-ray diffraction... diamonds of a few nanometers. "The laser creates two shock waves which, by catching up, induce a pressure peak, during which the diamonds are formed", explains Dominik Klaus. In real conditions, falling in rain in the lower layers of the atmosphere of Uranus and Neptune, the diamonds would sink towards the center and would clump together in a vast case around the heart of these icy planets.
A high rate of pure and very dense carbon...
A phenomenon that can exist within exoplanets, such as 55 Cancri B, in the constellation of Cancer. The analysis of the light it emits shows that it contains a lot of carbon. The simulations that have tried to reproduce the signal emitted only explain it by a high rate of pure carbon and very dense ... Diamond.