A strange molecule could be hiding inside Uranus and Neptune, affecting their magnetic fields

Skoltech scientists and their Chinese colleagues have determined the conditions that allow the existence of a very particular ion. Nicknamed aquodiium, it can be conceptualized as an ordinary neutral water molecule with two extra protons stuck to it, resulting in a net double positive charge.

The team suggests that the ion could be stable inside the ice giants Uranus and Neptune and that, if so, it should play a role in the mechanism that gives rise to these planets’ unusual magnetic fields. . The study is published in Physical examination B

A strange magnetism

The magnetic fields of Uranus and Neptune are not as well understood as those of Jupiter and Saturn, or even our own planet.

Inside the Earth, the circulation of the electronically conductive liquid iron-nickel alloy produces magnetism. It is believed that deep within Jupiter and Saturn, hydrogen is pushed into a metallic state and gives rise to magnetic fields in the same way.

In contrast, the magnetic fields of Uranus and Neptune are hypothesized to arise from the circulation of ion-conducting media, in which the constituent ions are themselves charge carriers, rather than simply a supporting structure enabling the flow of electrons.

If planetary scientists knew exactly which ions are involved and in what proportions, they might be able to understand why the magnetospheres of ice giants are so bizarre: misaligned with the direction of rotation of the planets and offset from their physical centers.

Professor Artem R. Oganov of Skoltech, co-author of the paper, explains how ionic and electronic conductivities are different and where the newly predicted ion fits in: “Hydrogen surrounding Jupiter’s rocky core under these conditions is a liquid metal: it can flow, the way molten iron circulates inside the Earth, and its electrical conductivity is due to the free electrons shared by all the hydrogen atoms pressed together.

“On Uranus, we think that the hydrogen ions themselves, i.e. the protons, are the free charge carriers. Not necessarily as a stand-alone H.⁺ ions, but perhaps in the form of hydronium H₃Oh⁺ammoniumNH₄⁺, and a series of other ions. Our study adds an additional possibility, the H₄Oh²⁺ ion, which is extremely interesting from a chemical point of view.

Missing link

In chemistry, there is the notion of sp³ hybridization, which refers to the way electronic orbitals combine with each other and amounts to something like a natural template for creating plausible molecules and ions. Under sp³ During hybridization, the nucleus of an atom, for example carbon, nitrogen or oxygen, occupies the central point of an imaginary tetrahedron.

Each of the four vertices hosts either a valence electron or two paired electrons that are not available to make bonds with other atoms. The simplest example would be a carbon atom with four unpaired electrons at the four vertices: add four hydrogen atoms and you get a methane molecule: CH₄.

For an oxygen atom, which has two pairs of electrons in its outermost shell, as well as two valence electrons, sp³ hybridization would mean that only two of the vertices could host a covalent bond with hydrogen, with the other two occupied by electron pairs, giving H₂Oh, water.

If you attach a hydrogen ion (a proton) to one of the electron pairs, you get a hydronium H ion.₃Oh⁺and this is actually what you get in an acidic solution, because acids donate H protons⁺ into the solution and isolated protons are immediately attracted to pairs of electrons.

Pressure and acid

“But the question was: Can you add yet 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 get there,” explains Professor Xiao Dong of China’s Nankai University, whose original idea is the basis of this research.

“First, very high pressure forces matter to reduce its volume, and sharing a previously unused pair of oxygen electrons with a hydrogen ion (proton) is an interesting way to do this: as a covalent bond with l hydrogen, except the two electrons in the pair come from oxygen Second, you need lots of protons available, which means an acidic environment, because that’s what acids do: they donate protons.

The team used advanced computational tools to predict what happens to hydrofluoric acid and water under extreme conditions. The result: given a pressure of about 1.5 million atmospheres and a temperature of about 3,000 degrees Celsius, well-separated aquodiium H₄Oh²⁺ ions appear in the simulation.

The scientists believe their newly discovered ion is expected to play an important role in the behavior and properties of water-based media, particularly those under pressure and containing acid.

This roughly corresponds to conditions on Uranus and Neptune, where an extremely deep ocean of liquid water produces extremely high pressures and some amount of acid can also be expected. If so, aquodiium ions will form and, by participating in ocean circulation, contribute to the magnetic fields and other properties of these planets in a manner distinct from other ions.

Perhaps aquodiium could even form previously unknown minerals under these extreme conditions.