Scientists have revealed new insights into the structure and composition of Uranus, challenging long standing assumptions about the seventh planet from the Sun. Although the third largest planet in our solar system, this ice giant has remained one of the least understood planets since its discovery in 1781.
In 1986, Voyager 2 became the first, and only, spacecraft to explore Uranus. This flyby lasted five hours and came within 50,000 miles of Uranus’s cloudtops. In addition to its unusual 98-degree tilt and having the lowest temperature recorded of all the planets, Uranus seemed to have characteristics that differed from all other planets worth exploring. Firstly, it lacked plasma, ionized gases, in its magnetosphere, a region surrounding planets, despite the existence of five moons that should have been producing ionized gases. This led scientists to conclude that these moons were all inactive and therefore did not have water ions or hidden oceans. Secondly, there were electron radiation belts only second in intensity to Jupiter, but the lack of plasma meant there was no source of energetic particles to drive these intense belts. These abnormalities challenged scientists’ understanding of magnetospheres and how they capture energetic particles. Uranus has remained a mysterious planet since Voyager 2’s initial findings were published.
However, a recent analysis on Voyager 2’s flyby of Uranus showed that, “We just caught it at this freak moment in time,” said Jamie Jasinski, a space plasma physicist at NASA. Turns out, there was a burst of solar wind that hit the planet just before the space probe flew by. Had Voyager 2 arrived a few days earlier, the solar wind present would have been 20 times less strong, and an entirely different magnetospheric configuration would have been observed. As a result of this phenomenon, Uranus’ magnetosphere was dramatically compressed, providing a possible explanation for the energetic electron fluxes and lack of plasma present. The radiation belts were filled with electrons from the Sun, while plasma would have been trapped closer to the planet than could be detected by Voyager 2. “The spacecraft saw Uranus in conditions that only occur about 4% of the time,” Jasinski said. As such, findings from Voyager 2’s flyby of Uranus should not be regarded with typicality.
It is likely that the normal composition of Uranus’s magnetosphere would be similar to ones observed from the other gas giants in our solar system. It is also possible that the moons observed by Voyager 2 are actually geographically active, as the ions they produced could have been swept away by the solar wind. Since everything we know about Uranus is from an unconventional snapshot in time, this perspective could guide future missions, making it easier to study the planet and uncover its mysteries.
