One of the strangest things about Uranus and Neptune is their magnetic fields. Each of these planets has a hot mess of a magnetosphere, displaced and tilted wildly from its spin axis in a way not seen on any other planet.
It’s not entirely clear why, but thanks to a team of researchers from China and Russia, we may have a new piece of the puzzle: a really strange, ionized form of water called aquadium that may exist deep within the extremely high-pressure interiors of these strange, ice worlds.
Aquodiium consists of a normal water molecule with two extra protons, giving it a net positive charge that – in sufficient quantities – can produce a planetary magnetic field like that of Uranus and Neptune.
Planetary magnetic fields extend far into space around the planets that produce them. However, they are generated deep within the planet by moving charges, although the exact mechanism may vary.
On Earth, it’s an iron-nickel alloy that sloshes around the core, spinning, convecting, and electrically conducting, converting all that kinetic energy into streams of electrons in what is called a dynamo. For Jupiter and Saturn, scientists believe it is metallic hydrogen that provides a conductor for flowing electrons.
Earth, Jupiter, and Saturn have relatively ordered magnetic fields that resemble those of a giant bar magnet moving along the planet’s spin axis, whose field lines look like a cell neatly connecting the north and south poles.
The magnetic poles of Uranus and Neptune, on the other hand, are tilted by 59 and 47 degrees, respectively, to the axes of rotation, and the magnetic field lines are constantly changing and shifting. And they are not actually centered in the cores of the planets.
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One possible explanation is that the magnetic fields could be generated by an ionically conducting liquid in which the ions are the charge carriers, rather than the liquid acting as a conductor for electrons.
“The hydrogen around Jupiter’s rocky core at these [high-pressure] conditions is a liquid metal: It can flow like molten iron flows inside the Earth, and its electrical conductivity is due to the free electrons shared by all the hydrogen atoms pressed together,” explains theoretical chemist, mineralogist and physicist Artem Oganov from the Skolkovo Institute of Science and Technology in Russia.
“In Uranus, we think that the hydrogen ions themselves—i.e. protons – are the free charge carriers.”
The question then is which ions? Some, like ammonia, are obvious possibilities. But could the planets’ water molecules play a more significant role in the process as well?
Led by physicist Jingyu Hou of Nankai University in China, a team of researchers went back to first principles combined with models of how molecules might evolve, delving into a concept called chemical hybridization.
This is when the orbital elements of an atom are mixed or combined to create an atom that can bond in new ways. There are different types of hybridization, but the one that is relevant here is sp3 hybridization in which four orbitals form a tetrahedral arrangement around the central nucleus.
Each of the four points of the tetrahedron has either a lone electron capable of bonding with another atom, or an electron pair that cannot form bonds with other atoms.
Oxygen has two lone electrons and two electron pairs in its outer shell. If you attach a hydrogen atom to each of the available valence electrons, you get H2Oh – water.
Sometimes hydrogen without its electron—also known as a plain old proton—will attach itself to one of the electron pairs to form a molecule called a hydronium ion.
“The question was: Can you add another proton to the hydronium ion to fill in the missing piece? Such a configuration under normal conditions is energetically very unfavorable, but our calculations show that there are two things that can make it happen,” says physicist Xiao Dong of Nankai University.
“First, very high pressure forces matter to shrink in volume, and sharing a previously unused electron pair of oxygen with a hydrogen ion (a proton) is a neat way to do this: like a covalent bond with hydrogen, except the two electrons in the pair come from oxygen, you need a lot of protons available, and that means an acidic environment, because that’s what acids do—they donate protons.”
The researchers ran computational modeling, and under conditions similar to those believed to exist on Uranus and Neptune, this happened. At temperatures of about 3,000 degrees Celsius (5,430 Fahrenheit) and pressures of 1.5 million atmospheres, protons combine with hydronium to form H4O2 – aquadium.
It’s still theoretical, of course. More detailed observations of the two outermost planets will be needed to explore the possibility further; but the findings give us a new way to understand the blue freaks that are Uranus and Neptune.
And they also have implications for chemistry in general, representing, the researchers wrote, “an important addition to traditional physical and chemical theories such as the valence shell electron pair repulsion model, proton transfer, and acid-base theory.”
The study was published in Physical examination C.
