Something has already tilted the planet on its side, so its orbit is perpendicular to the orbits of other planets in the solar system. And now scientists have discovered that Uranus's atmosphere is seeping into space.
In the data of the historical approach of Voyager 2 with the ice planet, in 1986, the presence of a plasmoid, a pocket of atmospheric material directed from Uranus by the planet's magnetic field, has not yet been discovered.
This is the first time a plasmoid has been discovered near an ice giant, and it doesn't just show us that Uranus's atmosphere is leaking away. It also shows some dynamics in this planet's unusual twisted magnetic field.
In fact, leaking atmospheres are not so rare. This is called an atmospheric blowout, and this is how Mars, for example, turned from a rather humid planet to a dusty, barren wasteland. Venus is running out of hydrogen. Jupiter's moon Io and Saturn's moon Titan also lose their atmospheres. Even the Earth loses about 90 tons of atmospheric material per day (don't worry, we have about 5140 trillion tons, it will take a long time to completely disappear).
(David Stern, Reviews of Geophysics, 1996).
There are several mechanisms through which this can happen, and one of them is through plasmoids. These are large cylindrical bubbles of plasma-ionized gas bound by magnetic field lines emanating from the Sun, an area known as a magnetotail. The image above shows what this looks like for Earth.
Ions from the atmosphere are directed along the magnetic field to this region. When the solar wind forces the magnetic field to burst on the side facing the Sun – at the point where the impact bends – they twine and reunite in the tail, pinching off the spinning plasmoids. Some of the ions bounce back towards the planet (producing auroras on Earth), and the plasmoid bounces back in the opposite direction, carrying atmospheric ions with it.
For the Earth, this is quite simple and understandable. And there is evidence that the solar wind pulls plasmoids away from Mars in a slightly different way on a daily basis, since Mars does not have a global magnetic field.
But Uranus is a tricky planet, and let's be honest, its magnetic field is a mess.
Where the Earth's magnetic field is more or less consistent with the orientation of the planet, Uranus is all bent, the magnetic poles are located at an angle of 59 degrees to the geographic poles. Not even centered. If you were to draw a line between these two poles, it would be offset from the center of Uranus by a fairly large distance.
It was this disorder of the magnetic field that caught the attention of astronomers Gina DiBraccio and Dana Gershman of NASA's Goddard Space Flight Center, who planned potential probe flights and believed this oddity would be a good starting point.
They looked at the data collected by the Voyager 2 magnetometer in January 1986 at a higher resolution than any previous study and noticed fluctuations in the data, a flash in the magnetic field.
They processed the data and came to the conclusion that yes. Despite the fact that Uranus has a strange, distorted, wobbly magnetic field, this burst was indeed a plasmoid, roughly 204,000 kilometers long and 400,000 kilometers across, full of ionized hydrogen receding from the planet.
According to the researchers' analysis, this shows that Uranus's magnetic field is reuniting in the tail, just like Earth's. It also suggests that internal forces play a role in the planet's magnetic dynamics.
And, of course, he discovers a mechanism by which Uranus can lose a significant portion of the atmosphere carried away by plasmoids.
The Voyager data used for this analysis is more than two decades old, so the researchers suggest that the best way to confirm the theory is to send another probe to test it.
The study was published in Geophysical Research Letters.
Sources: Photo: (Voyager 2 / NASA / Erich Karkoschka)
