Auroral displays continue to intrigue scientists, whether the bright lights shine over Earth or over another planet. The lights hold clues to the makeup of a planet's magnetic field and how that field operates.

New research about Jupiter proves that point -- and adds to the intrigue.

Peter Delamere, a professor of space physics at the University of Alaska Fairbanks Geophysical Institute, is among an international team of 13 researchers who have made a key discovery related to the aurora of our solar system's largest planet.

The team's work was published April 9, 2021, in the academic journal Science Advances. The research paper, titled "How Jupiter's unusual magnetospheric topology structures its aurora," was written by Binzheng Zhang of the Department of Earth Sciences at the University of Hong Kong; Delamere is the primary co-author.

Research done with a newly developed global magnetohydrodynamic model of Jupiter's magnetosphere provides evidence in support of a previously controversial and criticized idea that Delamere and researcher Fran Bagenal of the University of Colorado at Boulder put forward in a 2010 paper -- that Jupiter's polar cap is threaded in part with closed magnetic field lines rather than entirely with open magnetic field lines, as is the case with most other planets in our solar system.

"We as a community tend to polarize -- either open or closed -- and couldn't imagine a solution where it was a little of both," said Delamere, who has been studying Jupiter since 2000. "Yet in hindsight, that is exactly what the aurora was revealing to us." 

Open lines are those that emanate from a planet but trail off into space away from the sun instead of reconnecting with a corresponding location in the opposite hemisphere.

On Earth, for example, the aurora appears on closed field lines around an area referred to as the auroral oval. It's the high latitude ring near -- but not at -- each end of Earth's magnetic axis.

Within that ring on Earth, however, and as with some other planets in our solar system, is an empty spot referred to as the polar cap. It's a place where magnetic field lines stream out unconnected -- and where the aurorae rarely appear because of it. Think of it as an incomplete electrical circuit in your home: No complete circuit, no lights.

Jupiter, however, has a polar cap in which the aurora dazzles. That puzzled scientists.

The problem, Delamere said, is that researchers were so Earth-centric in their thinking about Jupiter because of what they had learned about Earth's own magnetic fields.

The arrival at Jupiter of NASA's Juno spacecraft in July 2016 provided images of the polar cap and aurora. But those images, along with some captured by the Hubble Space Telescope, couldn't resolve the disagreement among scientists about open lines versus closed lines.

So Delamere and the rest of the research team used supercomputer modeling for help. Their research revealed a largely closed polar region with a small crescent-shaped area of open flux, accounting for only about 9 percent of the polar cap region. The rest was active with aurora, signifying closed magnetic field lines.

Jupiter, it turns out, possesses a mix of open and closed lines in its polar caps.

"There was no model or no understanding to explain how you could have a crescent of open flux like this simulation is producing," he said. "It just never even entered my mind. I don't think anybody in the community could have imagined this solution. Yet this simulation has produced it."

"To me, this is a major paradigm shift for the way that we understand magnetospheres."

What else does this reveal? More work for researchers.

"It raises many questions about how the solar wind interacts with Jupiter's magnetosphere and influences the dynamics," Delamere said.

Jupiter's aurorally active polar cap could, for example, be due to the rapidity of the planet's rotation -- once every 10 hours compared to Earth's once every 24 hours -- and the enormity of its magnetosphere. Both reduce the impact of the solar wind, meaning the polar cap magnetic field lines are less likely to be torn apart to become open lines.

And to what extent does Jupiter's moon Io affect the magnetic lines within Jupiter's polar cap? Io is electrodynamically linked to Jupiter, something unique in our solar system, and as such is constantly stripped of heavy ions by its parent planet.

As the paper notes, "The jury is still out on the magnetic structure of Jupiter's magnetosphere and what exactly its aurora is telling us about its topology."

It may be possible in the future to use information technology where electron spin is used to store, process, and transfer information in quantum supercomputers. It has long been the goal of scientists to be able to use spin-based quantum information technology at room temperature. A team of researchers from Sweden, Finland, and Japan has now constructed a semiconductor component in which information can be efficiently exchanged between electron spin and light at room temperature and above.

It is well known that electrons have a negative charge, and they also have another property, namely spin. The latter may prove instrumental in the advance of information technology. To put it simply, we can imagine the electron rotating around its own axis, similar to how the Earth rotates around its own axis. Spintronics - a promising candidate for future information technology - uses this quantum property of electrons to store, process, and transfer information. This brings important benefits, such as higher speed and lowers energy consumption than traditional electronics. 

Developments in spintronics in recent decades have been based on the use of metals, and these have been highly significant for the possibility of storing large amounts of data. There would, however, be several advantages in using spintronics based on semiconductors, in the same way, that semiconductors form the backbone of today's electronics and photonics.

"One important advantage of spintronics based on semiconductors is the possibility to convert the information that is represented by the spin state and transfer it to light, and vice versa. The technology is known as opto-spintronics. It would make it possible to integrate information processing and storage based on the spin with information transfer through light", says Weimin Chen, professor at Linköping University, Sweden, who led the project.

As electronics used today operate at room temperature and above, a serious problem in spintronics development has been that electrons tend to switch and randomize their direction of spin when the temperature rises. This means that the information coded by the electron spin states is lost or becomes ambiguous. Thus, it is necessary to develop semiconductor-based spintronics that we can orient essentially all electrons to the same spin state and maintain it, in other words, that they are spin polarised, at room temperature and higher temperatures. Previous research has achieved the highest electron spin polarisation of around 60% at room temperature, untenable for large-scale practical applications.

Researchers at Linköping University, Tampere University, and Hokkaido University have now achieved an electron spin polarisation at room temperature greater than 90%. The spin polarisation remains at a high level even up to 110 °C. This technological advance, which is described in an academic journal, is based on an Opto-spintronic nanostructure that the researchers have constructed from layers of different semiconductor materials. It contains nanoscale regions called quantum dots. Each quantum dot is around 10,000 times smaller than the thickness of a human hair. When a spin polarised electron impinges on a quantum dot, it emits light - to be more precise, it emits a single photon with a state (angular momentum) determined by the electron spin. Thus, quantum dots are considered to have great potential as an interface to transfer information between electron spin and light, as will be necessary for spintronics, photonics, and quantum supercomputing. In the newly published study, the scientists show that it is possible to use an adjacent spin filter to control the quantum dots' electron spin remotely and at room temperature.

The quantum dots are made from indium arsenide (InAs), and a layer of gallium nitrogen arsenide (GaNAs) functions as a filter of spin. A layer of gallium arsenide (GaAs) is sandwiched between them. Similar structures are already being used in optoelectronic technology based on gallium arsenide, and the researchers believe that this can make it easier to integrate spintronics with existing electronic and photonic components. 

"We are very happy that our long-term efforts to increase the expertise required to fabricate highly-controlled N-containing semiconductors are defining a new frontier in spintronics. So far, we have had a good level of success when using such materials for optoelectronics devices, most recently in high-efficiency solar cells and laser diodes. Now we are looking forward to continuing this work and to unite photonics and spintronics, using a common platform for light-based and spin-based quantum technology", says Professor Mircea Guina, head of the research team at Tampere University in Finland.