Returning to the Voyager 2 data, scientists discovered another secret about Uranus

Hello reader! My name is Irina, I’m conducting a telegram channel about astrophysics and quantum mechanics “Quant” . Today I have prepared for you a translation of an article about the planet Uranus, or rather, about its secret, which was discovered recently.

Enjoy reading!



Voyager 2 took this picture on January 14, 1986, as it approached the planet Uranus. The foggy bluish color of the planet is due to the presence of methane in its atmosphere, which absorbs red waves of light.

After eight and a half years of his grand journey through the solar system, NASA's Voyager 2 spacecraft was ready for a new meeting. This happened on January 24, 1986, and soon he will meet with the mysterious seventh planet, icy Uranus.
Over the next few hours, Voyager 2 flew within 50,600 miles (81,433 kilometers) from the cloudy peaks of Uranus, collecting data that revealed two new rings, 11 new moons and temperatures below minus 353 degrees Fahrenheit (minus 214 degrees Celsius). The dataset is still the only close dimension we have ever done on the planet.

Three decades later, scientists, having re-examined these data, discovered another secret.
Unbeknownst to the entire space physics community, 34 years ago, Voyager 2 flew through a plasmoid, a giant magnetic bubble that could have carried Uranus into space. This discovery raises new questions about the unique magnetic medium of the planet.

The atmosphere of planets throughout the solar system seeps into space. Hydrogen rises from Venus to join the solar wind, a continuous stream of particles leaving the Sun. Jupiter and Saturn throw out balls of their electrically charged air. Even the earthly atmosphere is leaking. (Don’t worry, she will stay here for another billion years or so).

These effects are negligible on the scale of human time, but with a sufficiently long time, an atmospheric leak can radically change the fate of the planet. As an example, consider Mars.

“Mars used to be a wet planet with a dense atmosphere,” said Gina Dibraccio, a space physicist at NASA's Goddard Space Flight Center and a research fellow at the Mars Atmosphere and Volatile Evolution project, or the MAVEN mission. “It has evolved over time” - 4 billion years of leakage into space - “to become the dry planet we see today.”



The magnetic field of Uranus. The yellow arrow indicates the Sun, light blue indicates the magnetic axis of Uranus, and dark blue indicates the axis of rotation of Uranus.

The atmospheric escape is controlled by the magnetic field of the planet, which can both help and hinder this process. Scientists believe that magnetic fields can protect the planet by reflecting the explosions of the solar wind that destroy the atmosphere. But they can also create flight opportunities, like giant balls that break away from Saturn and Jupiter when the lines of the magnetic field get tangled. In any case, to understand how the atmosphere is changing, scientists pay close attention to magnetism.

This is another reason Uranus is such a mystery. The flight of Voyager 2 in 1986 showed how magnetically strange this planet is.

“The structure, the way it moves ...” says Dibraccio, “Uranus really exists by itself.”

Unlike any other planet in our solar system, Uranus spins almost perfectly on its side, making a complete revolution in 17 hours. The axis of its magnetic field is 60 degrees from the axis of rotation, so when the planet rotates, its magnetosphere, the space cut out by its magnetic field, oscillates like a badly thrown soccer ball. Scientists still do not know how to model it.

This oddity attracted Dibraccio and her co-author Dan Gershman, a colleague in space physics, to the project. Both were part of a team developing plans for a new mission to the ice giants Uranus and Neptune, and they were looking for riddles that could be solved. The strange magnetic field of Uranus, last measured over 30 years ago, seemed like a good starting point.

Therefore, they uploaded the readings of the Voyager 2 magnetometer, which tracked the strength and direction of magnetic fields near Uranus as the spacecraft flew past. With no idea what they would find, they came closer than previous studies, drawing a new data point every 1.92 seconds. Smooth lines gave way to serrated spikes and dips. And then they saw him: a tiny zigzag with a big story.

"What do you think, it could be ... a plasmoid?" Gershman asked Dibraccio, noting this squiggle.

Plasmoids, little known during the Voyager 2 flight, have since become recognized as an important way to lose mass by planets. These giant bubbles of plasma, or electrified gas, are plucked from the end of the planet’s magnetic tail - the part of its magnetic field that the Sun blows back like a wind shock. With sufficient time, elusive plasmoids can merge ions from the planet’s atmosphere, fundamentally changing its composition. They have been observed on Earth and other planets, but no one has discovered plasmoids on Uranus - yet.

“I think it really is,” said Dibraccio.



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The plasmoid discovered by Dibraccio and Gershman took only 60 seconds of the 45-hour flight of Voyager 2 on Uranus. It was like a quick up and down burst in magnetometer data. “But, if you depict it in a three-dimensional image, it will look like a cylinder,” said Gershman.

Comparing their results with the plasmoids observed on Jupiter, Saturn and Mercury, they estimated the cylindrical shape to be at least 127,000 miles (204,000 kilometers) in length and up to about 250,000 miles (400,000 kilometers) across. Like all planetary plasmoids, it was full of charged particles - mostly ionized hydrogen.
Instrument readings inside the plasmoid - when Voyager 2 flew through it - alluded to its origin. While some plasmoids have a twisted internal magnetic field, Dibraccio and Gershman observed smooth closed magnetic loops. Such loop-shaped plasmoids usually form when a spinning planet throws pieces of its atmosphere into space.

“Centrifugal forces take over, and the plasmoid comes off,” Gershman said. According to their estimates, plasmoids like this can account for 15 to 55% of the mass loss of the atmosphere on Uranus, which is more than on Jupiter or Saturn. It is possible that it is in this way that Uranus dumps its atmosphere into space.

How did a plasmoid escape change Uranus over time? Having only one set of observations is hard to say.

“Imagine that one spaceship just flew through this room and tried to characterize the whole Earth,” says Dibraccio. “Obviously, he will not tell you anything about what the Sahara or Antarctica is.”

But the results help formulate new questions about the planet.
“That's why I love planetary science,” said Dibraccio. “You always go where you really don't know.”