Hidden in data that NASA’s iconic Voyager 2 spacecraft gathered on Uranus more than 30 years ago and that represents the only close-up we’ve ever made of the planet, NASA scientists have found the signature of a massive bubble that it could have stolen. part of the gaseous atmosphere of the planet.
Every planet with an atmosphere in the solar system filters some of it into space and the magnetic field of the solar system plays an important role in this process: on Venus , hydrogen sprouts to join the solar wind, on Jupiter, the continuous stream of plasma particles is escape into space; Saturn expels bubbles of electrically charged air … even our own planet leaks not worryingly 90 tons of atmospheric material a day (at least for about a billion years we won’t have to worry). It seems that the same thing happens to the icy Uranus (it is the coldest of all our planets).
The researchers were working on a new mission proposal for the ice giants Uranus and Neptune, but their analysis looked at Voyager 2’s magnetometer readings, plotting the data with greater precision than before. In doing so, they observed 60 seconds – out of the 45 hours of the space probe flyby – of a peculiar magnetic signal. The team believes they have detected a plasmoid – a structure or bag of plasma packed with charged particles – that is funneled away from Uranus by its magnetic field.
It would be the first time that a plasmoid or magnetic bubble has been seen in connection with an ice giant , demonstrating not only that the atmosphere of Uranus is also escaping, but also the peculiar dynamics of the magnetic field of this cold planet.
The planet’s off-center magnetic field, tilted relative to Uranus’ axis of rotation, produces a wobbly and unpredictable magnetosphere . In general, magnetic fields are believed to protect a planet’s atmosphere from the escape of its gases, largely by providing protection against the solar wind coming from the Sun, but they can also do the opposite. We have already seen that leaky atmospheres are not that uncommon.
But if the magnetic bubble pulls charged particles out of the atmosphere and throws them into space, it also changes the planet’s atmosphere, and thus the planet itself. And the situation of Uranus is particularly complicated because it rotates on its side and its magnetic field is skewed both from that axis and from the plane in which all the planets are located.
It is difficult to determine how important this process is to Uranus for its global atmosphere, as it is based on a single Voyager data set. The team estimates that plasmoid ejections could represent between 15 and 55% of the planet’s atmosphere that escapes into space . However, without further observations, many questions remain in the air. For when a return to Uranus?
“The nature of the magnetospheric circulation and the processes of mass loss remain salient and essential topics on both Uranus and Neptune. In order to definitively determine the relative contributions of planetary rotation and the force of the solar wind in the conduction of global dynamics of plasma, further measurements will be necessary in situ . Until then, the enigmatic ice giant magnetospheres await further exploration, “the authors state.
Referencia. Gina A. DiBraccio et al. Voyager 2 constraints on plasmoid‐based transport at Uranus, Geophysical Research Letters (2019). DOI: 10.1029/2019GL083909
