[▲ Figure 1: An experiment was conducted to reproduce the interior of Uranus and Neptune using PET resin, which is also used in PET bottles, and a laser. (Image Credit: Blaurock / HZDR)]
The solar system has four giant planets: Jupiter, Saturn, Uranus, and Neptune.In the past, these were collectively called “gas planets”, but nowJupiter and Saturn「gas giant (Jupiter – Gas Giant)”,Uranus and Neptune「giant ice planet (Uranus-type planet/Ice Giant)”.
In planetary science, only hydrogen and helium, gases that rarely form liquids or solids in space, are referred to as “gases.” On the other hand, “iceIce giant planets are more like “ice” than gas giant planets, that is,water, methane, ammoniaIt is classified as a separate category because it contains a lot of
The presence of “ice” is said to affect the properties of ice giant planets. A prime example would be Uranus and Neptune appearing blue. This is due to the absorption of light other than blue by methane. However, the interiors of Uranus and Neptune are more dramatic. Ice giant planets have high temperatures and high pressures inside, and the “ice” forms a liquid “sea”. It is believed that methane is decomposed in this sea to form diamond crystals.
Because the diamond sinks as it grows, the appearance is “rain of diamonds” is called. It is very romantic, but not only that, but it is also pointed out that the potential energy is converted into thermal energy by the diamond sinking, affecting the heat generation and heat circulation inside the ice giant planet. . Uranus and Neptune are known to radiate much more heat than they receive from the Sun, so the phenomena inside the ice giant planets are interesting to study.
Around 1981, when diamond rain was theoretically demonstrated, it was difficult to reproduce the internal environment of an ice giant planet in a laboratory. I was. By irradiating a target substance from all directions with a powerful laser, a state of high temperature and high pressure is created instantaneously. Although the time is extremely short, it is technically possible to investigate the properties of substances under high-temperature and high-pressure conditions by examining the X-rays that hit the materials.
However, until now, mainly polystyrene ([C8H8]n) and other hydrocarbons (substances made up of only carbon and hydrogen). Since there are substances such as water containing oxygen inside the giant ice planet, it is difficult to say that experiments using polystyrene that does not contain oxygen completely reproduce the environment inside the actual planet. To investigate the properties of ice giant planets, we need to know whether the presence of oxygen affects diamond formation.
An international research team led by Zhiyu He of the Dresden-Rossendorf InstituteSLAC National Accelerator Instituteand RIKENSPring-8Using powerful X-ray free electron laser devices located at two locations in , we conducted experiments to reproduce the internal environment of an ice giant planet.
The major difference between this experiment and previous experiments is the “PET resin (Polyethylene terephthalate)” was used as a target to replace polystyrene. Since PET resin can be completely decomposed into carbon and water chemically
it can be considered to closely resemble the internal environment of a giant ice planet where water and methane are mixed.[C10H8O4]*…When polyethylene terephthalate is considered only in terms of its chemical composition,n⇆n(10C+4H2
[▲Figure2:SchematicdiagramofthisexperimentAlaserwasappliedmomentarilytothetargetPETresinfilmforonly8nanoseconds(1/125millionthofasecond)toseeifnanodiamondsweregenerated(ImageCredit:Heetal)】
[▲Figure2:SchematicdiagramofthisexperimentAlaserwasappliedmomentarilytothetargetPETresinfilmforonly8nanoseconds(1/125millionthofasecond)toseeifnanodiamondsweregenerated(ImageCredit:Heetal)】
A target containing a thin PET resin film with a thickness of 0.1 mm is instantly heated to high temperature and high pressure by laser irradiation. By applying X-rays here, it is possible to investigate what substances have been produced in the target.
[▲Figure3:ThestatesofhydrocarbonsthatappearundervariousconditionsoftemperatureandpressureTheareapaintedinpurpleinthemiddleistherangeoftemperatureandpressureinwhichdiamondsareproducedtheoreticallywhichagreeswiththeexperimentalresultsofthistime(ImageCredit:Heetal)】
[▲Figure3:ThestatesofhydrocarbonsthatappearundervariousconditionsoftemperatureandpressureTheareapaintedinpurpleinthemiddleistherangeoftemperatureandpressureinwhichdiamondsareproducedtheoreticallywhichagreeswiththeexperimentalresultsofthistime(ImageCredit:Heetal)】Not a hydrocarbon as a result of the experimentEven with PET resin, extremely small nanodiamonds of 1/100 millionth of a meter are generated
However, we also discovered many other new things.
First, below 74 gigapascals and above 125 gigapascals (1 gigapascal = 10,000 times atmospheric pressure) did not produce diamonds. In the former, the pressure was insufficient to generate diamond, and in the latter, the diamond melted due to the high temperature of regarding 6000K (regarding 5700℃).On the other hand, in the range of 74 to 125 gigapascals, it was found that the larger the pressure, the larger the diamond grains. once more,PET resin is easier to form diamonds than polystyrene
It also turned out that This point has already been demonstrated theoretically, but this is the first time it has been confirmed experimentally.from these things,Presence of Oxygen Atoms Helps Diamond Formation
It turns out. It is also possible that more diamonds are being formed inside ice giant planets than previously estimated. In addition, the experimental results were consistent with the theoretical boundary where water generated from decomposed PET resin changes from an insulator to a conductor under high temperature and high pressure conditions.Ice giant planets, which are located between gas giants and rocky planets, were once thought to be rare.Ice giants are the majority of planets
has been found to occupy Since the results of this experiment are closer to the physical properties of ice giant planets, they provide clues to the formation and evolution of the majority planets in this universe.In addition, in this experiment, we found that nanodiamonds can be generated by applying a single laser beam. In experiments that apply high pressure with lasers, it has been necessary to irradiate powerful lasers from all directions, and extremely advanced control has been required.However, in this experiment, not so muchNanodiamonds can be generated without advanced laser control
I understand.
In addition, the size of the diamond can be adjusted by adjusting the laser energy and irradiation time. Since nanodiamonds are also attracting attention in the medical, catalytic chemistry, and electronics industries, this experimental method may cause a stir in the nanodiamond industry.
- Source Zhiyu He, et.al.
- “Diamond formation kinetics in shock-compressed C─H─O samples recorded by small-angle x-ray scattering and x-ray diffraction”. (Science Advances) Dominik Kraus.
- (Sep 2, 2022) “Nanodiamonds from plastic bottles”. (Helmholtz Center Dresden-Rossendorf) Marvin Ross.
- “The ice layer in Uranus and Neptune—diamonds in the sky?”. (Nature) M. A. Barrios, et.al.
- “High-precision measurements of the equation of state of hydrocarbons at 1–10 Mbar using laser-driven shock waves”. (American Institute of Physics, Physics of Plasmas) Tristan Guillot & Daniel Gautier.
- “Giant Planets”. (arXiv) R. Stewart McWilliams, et.al.
- “Optical Properties of Fluid Hydrogen at the Transition to a Conducting State”. (Physical Review Letters) D. Kraus, et al.
- “Formation of diamonds in laser-compressed hydrocarbons at planetary interior conditions”. (Nature Astronomy) M. Bethkenhagen, et.al.
- “Planetary Ices and the Linear Mixing Approximation”. (The Astrophysical Journal) D. Kraus, et al.
- “High-pressure chemistry of hydrocarbons relevant to planetary interiors and inertial confinement fusion”. (American Institute of Physics, Physics of Plasmas) Ludwig Scheibe, Nadine Nettelmann & Ronald Redmer.
- “Thermal evolution of Uranus and Neptune”. (Astronomy & Astrophysics) A. K. Schuster, et.al.
- “Measurement of diamond nucleation rates from hydrocarbons at conditions comparable to the interiors of icy giant planets”. (Physical Review B) J. Lütgert, et.al.
- “Measuring the structure and equation of state of polyethylene terephthalate at megabar pressures”. (Scientific Reports) N. Nettelmann, et.al.
“Theory of Figures to the 7th order and the interiors of Jupiter and Saturn”. (arXiv)
Text: Riri Ayae
