Uranus' radiation belts exhibit a surprising characteristic: their intensity far exceeds scientific predictions. This observation, made nearly forty years ago, has long left researchers without a clear answer, forming a persistent question in the study of planets.
In 1986, the Voyager 2 probe made its single flyby near Uranus. Its instruments detected an exceptionally high level of electron radiation, which did not match the established models for other worlds in the Solar System. This unexpected discovery raised questions about the mechanisms at work around this distant planet.
Comparison of Uranus with Earth.
Image Wikimedia
To clarify this situation, a team from the Southwest Research Institute adopted an innovative comparative approach. By analyzing historical data from Voyager 2 and comparing it with recent observations of Earth, they identified similarities with space weather events. This method allows revisiting old measurements with updated knowledge.
The researchers propose that a specific structure of the solar wind, called a corotating interaction region, was passing through the Uranian system at the time of the flyby. Subsequently, this phenomenon would have generated high-frequency electromagnetic waves, similar to those observed during intense solar storms on Earth. These waves, known as 'chorus', could have accelerated the electrons, thereby increasing the detected radiation.
Robert Allen, lead author of the study published in
Geophysical Research Letters, indicates that scientific advances since the 1980s have transformed the understanding of these waves. While they were once considered to scatter electrons, they can also provide them with energy under certain conditions, as observed during recent events on our planet.
SwRI researchers compared the impacts of space weather on Earth in 2019 with conditions at Uranus in 1986 to elucidate a 39-year-old question about radiation belts. The 'chorus' wave could accelerate electrons.
Credit: Southwest Research Institute
For her part, co-author Sarah Vines adds that a similar episode on Earth in 2019 led to a marked acceleration of electrons in the radiation belts. Applying this mechanism to Uranus would explain the abnormal energy levels recorded by Voyager 2, offering a coherent clue for interpreting the data.
Planetary radiation belts
Radiation belts, like the Van Allen belts around Earth, are zones where charged particles, mainly electrons and protons, are trapped by a planet's magnetic field. Their formation occurs when the solar wind, a stream of particles emitted by the Sun, interacts with this field, creating regions of high energy that can influence satellites and space missions.
These structures exhibit different intensities and sizes depending on the planet, based on factors such as the strength of the magnetic field and the distance from the Sun. Jupiter, for example, has very powerful belts due to its intense magnetic field, while Mars, with a weak field, has less defined ones. Studying these differences helps anticipate risks for exploration.
Radiation belts play a central role in space weather, affecting communications and astronaut safety. Their analysis allows for the development of protections for space technologies and improves solar storm forecast models, which are essential for human activities outside the atmosphere.