On December 17, 1986, A Solar Storm Buffeted Uranus -- Just As Voyager2 Was Zooming Past, And Taking Magnetosphere Readings... Blind Luck!

Now, nearly 40 years later, the mystery of why Uranus' plasma layer was missing -- from a giant body, like that. . . has been solved.

It turns out that Voyager happened to be whizzing by just as a much earlier solar flare/storm washed over the giant. That pressure collapsed the plasma field -- which in turn (as it does here on Earth) bounced back into a nearly spherical shape just a few days later. But by then Voyager, at ~58,000 miles an hour, had flown well out of range to make any readings.

In fact, it was facing outward, toward a rendezvous with Neptune and Pluto, by then. But now we know -- purely by chance -- it captured a solar storm, at the icy giant. Here's that story out of NASA yesterday:

. . .Magnetospheres serve as protective bubbles around planets (including Earth) with magnetic cores and magnetic fields, shielding them from jets of ionized gas — or plasma — that stream out from the Sun in the solar wind. Learning more about how magnetospheres work is important for understanding our own planet, as well as those in seldom-visited corners of our solar system and beyond.

That’s why scientists were eager to study Uranus’ magnetosphere, and what they saw in the Voyager 2 data in 1986 flummoxed them. Inside the planet’s magnetosphere were electron radiation belts with an intensity second only to Jupiter’s notoriously brutal radiation belts. But there was apparently no source of energized particles to feed those active belts; in fact, the rest of Uranus’ magnetosphere was almost devoid of plasma.

The missing plasma also puzzled scientists because they knew that the five major Uranian moons in the magnetic bubble should have produced water ions, as icy moons around other outer planets do. They concluded that the moons must be inert with no ongoing activity. . . .

It turned out that surmise was incorrect -- there are water ions around those moons, but it took a few weeks for them to "regen", after the solar flare event. So it is, that even in the distant, icy regions of our local system, barely warmed by the Sun's rays. . . activity has persisted for billions of years. And solar storms affect even these cold giants.

Grin. . . onward, despite Judge Merchan's slightly delaying his decision, this morning. Onward.

नमस्ते