First discovery of life-preserving magnetosphere outside the Solar System

When we think about the habitability of exoplanets, the role of magnetic fields in maintaining a stable environment is something to consider alongside things like atmosphere and climate.

Radiation belts are ring-shaped magnetic structures surrounding a planet filled with extremely high-energy electrons and charged particles.

First discovered around Earth in 1958 by the Explorer 1 and 3 satellites, radiation belts are ubiquitous in the Solar System: All planets with large-scale magnetic fields – including Earth, Jupiter, Saturn, Uranus and Neptune – have them. But until now, no radiation belts had been clearly observed outside our Solar System.

The magnetosphere helps preserve the life of a planet - (Photo: Internet).

Today, a small team of astronomers, led by Melodie Kao, formerly of Arizona State University and now a Research Fellow at the University of California Santa Cruz, with the collaboration of Professor Evgenya Shkolnik of the US Institute for Earth and Space Exploration, has discovered the first outer radiation belts of our Solar System . The results were published in the journal Nature on May 15.

The discovery was made around the 'brown dwarf' LSR J1835+3259, which is about the size of Jupiter but much denser. Located just 20 light-years away in the constellation Lyra, it is not massive enough to be a star, but it is massive enough to be a planet. Because radiation belts have never been clearly seen outside our Solar System before, we don't know if they could exist around other objects such as exoplanets.

Professor Evgenya Shkolnik, who has been studying the magnetic fields and habitability of exoplanets for many years, said: 'This is an important first step in finding more such objects and honing our skills to search for increasingly smaller magnetospheres, eventually allowing us to study Earth-sized, potentially habitable planets.'

Although invisible to the human eye, the radiation belt discovered by this team is a massive structure . Its outer diameter extends at least 18 Jupiter diameters, and the brightest regions within it are nine Jupiter diameters in size (remember, the Sun is only 10 Jupiter diameters). Made up of particles traveling near the speed of light and glowing brightest at radio wavelengths, this newly discovered outer radiation belt is nearly 10 million times more intense than Jupiter. It is also millions of times brighter than Earth and contains the most energetic particles of any planet in the Solar System.

The team captured three high-resolution images of radio-emitting electrons trapped in the magnetosphere of the brown dwarf LSR J1835+3259 over the course of a year using a renowned observational technique that we also used to image the black hole at the center of the Milky Way.

By combining 39 radio dishes stretching from Hawaii to Germany to create an Earth-sized telescope, the team resolved the brown dwarf's dynamic magnetic environment, known as the 'magnetosphere' , to observe the magnetosphere for the first time on an object outside the Solar System. They were even able to see the shape of this magnetic field clearly enough to deduce that it is likely a dipole like those of Earth and Jupiter.

Professor Jackie Villadsen of Bucknell University, who was part of the research team, said: 'By combining radio dishes from around the world, we can create extremely high-resolution images to see things no one has ever seen before. The power of our vision system is comparable to glasses that allow a person standing in Washington DC to clearly read the top row of an eye chart in California.'

In fact, Kao's team had a clue that they would find a radiation belt around the brown dwarf. By the time the team made these observations in 2021, radio astronomers had observed the brown dwarf LSR J1835+3259 emitting two types of detectable radio emissions. Kao himself had confirmed six years earlier, while on another team, that its periodically flashing radio emissions, similar to a lighthouse, were radio-frequency auroras.

But the brown dwarf LSR J1835+3259 also has a more consistent and fainter radio emission. The data suggest that these fainter emissions cannot come from stellar flares and are in fact very similar to Jupiter's radiation belts.

The team's discovery suggests that such a phenomenon may be more common than originally thought — occurring not only on planets but also on brown dwarfs, low-mass stars, and possibly even very high-mass stars.

The region surrounding a planet's magnetic field, or magnetosphere - including Earth's magnetic field - can protect the planet's atmosphere and surfaces from being damaged by solar and cosmic microwaves.

'When we think about the habitability of exoplanets, the role of magnetic fields in maintaining a stable environment is something to consider alongside things like atmosphere and climate,' says Kao .

In addition to the observed radiation belts, Kao's team's research shows differences in the 'shape' and spatial location of the aurora (similar to Earth's aurora) compared to a radiation belt from an object outside our Solar System.

'Auroras can be used to measure magnetic field strength, but not shape,' says Kao . 'We designed this experiment to demonstrate a method for assessing the shape of magnetic fields on brown dwarfs and eventually exoplanets.

The specific properties of each radiation belt tell us something about that planet's energy, magnetism and particle sources: how fast it spins, how strong its magnetic field is, how close it is to its parent star, whether it has moons that could deliver more particles, or whether there are Saturn-like rings that would absorb them, etc. I'm excited about the day when we can learn about exoplanets with magnetospheres, which could mean the possibility of preserving life'.