Voyager 2: "Cosmic coincidence" caused misleading measurements on Uranus
Almost 40 years ago, Voyager 2 passed Uranus. Since then, people have been puzzling over the measurement data collected there. Now there is an answer.
On the left the normal state of the magnetosphere, on the right the state found by Voyager 2.
(Image: NASA/JPL-Caltech)
Immediately before the only flyby of a space probe to date, Uranus was hit by an unusually strong solar wind, which distorted important measurements of the magnetosphere. This is the result of new analyses of almost 40 years of data, solving an old mystery, NASA's Jet Propulsion Laboratory now reports. If Voyager 2 had flown past Uranus just a few days earlier in the late fall of 1986, the probe would have observed a "completely different" magnetosphere, says research leader Jamie Jasinski from JPL. Instead, it had been puzzled for decades why almost no charged plasma was found above the atmosphere of Uranus. However, due to the solar wind and a "cosmic coincidence", the magnetosphere was temporarily compressed enormously and the plasma was pushed away, it is now said.
Changed image of Uranus and its moons
As Jasinski's research team now recalls, Voyager 2 was the first and so far only space probe to fly past Uranus on November 4, 1986. It discovered ten previously unknown moons there and was also able to photograph the rings discovered years earlier. However, it was inexplicable that almost no plasma was found in the vicinity of the planet, despite the intense radiation belts. It was therefore unclear where the charged particles that feed the active radiation belts came from. During the flyby, Voyager 2 found conditions on Uranus that only occur four percent of the time, the team writes. Otherwise, it behaved more as expected. The explanation now found also means that some of the five largest moons of Uranus could be geologically active after all. This had been considered impossible based on the original measurements.
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The study on Uranus now published in the journal Nature Astronomy shows once again that data collected decades ago can still provide new insights. It was only at the beginning of the year that a research group pointed out that Uranus and Neptune look much more similar than was previously perceived, especially by the public. This was proven by newly processed images taken by Voyager 2 during its visits in 1986 and 1989. After more than three decades, the main aim of the work was to correct the image that mankind had of the two distant planets. A few weeks later, three more moons were discovered on Uranus.
Voyager 2 and its sister probe Voyager 1 are NASA's oldest active space probes. Launched in 1977, they were able to take advantage of a rare constellation for their journey in which the four largest planets in the solar system came particularly close to each other. Both visited Jupiter and used it to gain momentum towards Saturn, where their paths diverged: Voyager 1 catapulted out of the plane of the solar system there, Voyager 2 set course for Uranus and Neptune. Originally only a four-year mission was planned; they have now been traveling for 47 years and are still active. The twins finally reached interstellar space.
(mho)
