icy planets – Lightsources.org

‘Diamond rain’ on icy planets offers clues into magnetic field mysteries

2024/01/082024/01/18

A new experiment suggests that this exotic precipitation forms at even lower pressures and temperatures than previously thought and could influence the unusual magnetic fields of Neptune and Uranus.

An international team of researchers led by researchers from the Department of Energy’s SLAC National Accelerator Laboratory gained new insights into the formation of diamonds on icy planets such as Neptune and Uranus. Scientists believe that, following their formation, these diamonds would slowly sink deeper into the planetary interior in response to gravitational forces, resulting in a ‘rain’ of precious stones from higher layers.

The results, published today in Nature Astronomy, suggest that this “diamond rain” forms at even lower pressures and temperatures than previously thought and provide clues into the origin of the complex magnetic fields of Neptune and Uranus.

“‘Diamond rain’ on icy planets presents us with an intriguing puzzle to solve,” said SLAC scientist Mungo Frost, who led the research. “It provides an internal source of heating and transports carbon deeper into the planet, which could have a significant impact on their properties and composition. It might kick off movements within the conductive ices found on these planets, influencing the generation of their magnetic fields.”

Longer timescales

In earlier work conducted at SLAC’s Linac Coherent Light Source (LCLS) X-ray free-electron laser (XFEL), scientists were able to observe “diamond rain” as it formed in high-pressure conditions, confirming the possibility of diamond formation on icy planets, which are primarily composed of water, ammonia, and hydrocarbons. They later discovered that the presence of oxygen makes diamond formation more likely, allowing diamonds to form and grow at a wider range of conditions and throughout more planets.

Previously, the high pressures and temperatures were generated by shock compressing the hydrocarbons with high power lasers, which only allows the conditions to be maintained for a few nanoseconds. In this new experiment, conducted at the European X-ray free-electron laser in Germany, the team studied the reaction over much longer timescales than other experiments using a different approach.

Read more on the SLAC website

Possible detection of hydrazine on Saturn’s moon Rhea

2021/06/012021/07/07

We present the first analysis of far-ultraviolet reflectance spectra of regions on Rhea’s leading and trailing hemispheres collected by the Cassini Ultraviolet Imaging Spectrograph during targeted flybys. In particular, we aim to explain the unidentified broad absorption feature centred near 184 nm. We have used laboratory measurements of the UV spectroscopy of a set of candidate molecules and found a good fit to Rhea’s spectra with both hydrazine monohydrate and several chlorine-containing molecules. Given the radiation-dominated chemistry on the surface of icy satellites embedded within their planets’ magnetospheres, hydrazine monohydrate is argued to be the most plausible candidate for explaining the absorption feature at 184 nm. Hydrazine was also used as a propellant in Cassini’s thrusters, but the thrusters were not used during icy satellite flybys and thus the signal is believed to not arise from spacecraft fuel. We discuss how hydrazine monohydrate may be chemically produced on icy surfaces.

High-pressure experiments provide insight into icy planets

2021/03/122021/03/16

Research team determines compression behaviour of water ice in unprecedented detail

An international team of scientists has been using X-rays to take a look inside distant ice planets. At the PETRA III Extreme Conditions Beamline, they investigated how water ice behaves at high pressure, under conditions corresponding to those inside the planet Neptune, for example. At pressures up to almost two million times atmospheric pressure at sea level on Earth, the researchers were able to observe in unparalleled detail how water ice behaves under compression. The team, led by Hauke Marquardt from the University of Oxford, is presenting its findings in the scientific journal Physical Review B.

Planetary ices – such as water ice (H₂O), methane ice (CH₄) and ammonia ice (NH₃) – make up large parts of the ice giants in our solar system and are very likely to occur inside many exoplanets, which are planets outside our solar system. “However, the physical properties and phase diagrams of these compounds are not sufficiently known at the pressures and temperatures that prevail inside planets,” explains Marquardt. “Previous experimental studies using X-ray diffraction in a static diamond anvil cell have contributed a great deal to our understanding of ices at high pressure, but they have been unable to adequately answer numerous questions.”