Revisiting Decades-Old Voyager 2 Data, Scientists Find One More Secret

by | Mar 26, 2020 | planets, Science, Uranus | 0 comments

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Voyager 2 took this image as it approached the planet Uranus on Jan. 14, 1986. The planet’s hazy bluish color is due to the methane in its atmosphere, which absorbs red wavelengths of light.
CREDIT: NASA/JPL-Caltech

Right now, all around the world, we’re seeing museums, libraries, and other centers of knowledge set their content free. The Smithsonian museum has dropped millions of images onto the internet, and libraries are making online books even easier to access. This is awesome – it does raise the question of “If you had all this content already, why were you not sharing?” but… I’m hoping this data sharing is our new normal. In space science we have a long tradition of sharing our data, with major telescopes like the Very Large Array and Hubble Space Telescope putting their observations in vast databases that people can continue to explore for generations to come. Over the years, as technology and our understanding of science changes, we’re seeing new science come from old data. This week, NASA shared that planetary scientists revisiting Voyager 2’s data on Uranus had discovered that Voyager 2 flew through a plasmoid of atmosphere that Uranus had lost to space.

Voyager 2’s 1986 flyby of Uranus revealed an oddly tilted magnetic field that can’t be explained in a nice neat way. Something bad happened to this outer world at some point in the past, and now it is permanently tilted on its side, with its pole pointed at the sun twice a year as it goes through it’s weird summer and winter solstices. The magnetic field, however, isn’t aligned with the planet’s rotation. It’s actually tilted about 60 degrees off. It’s not unusual for a magnetic field to not be completely aligned with a world’s rotation, but Uranus goes to an extreme. If the Earth’s magnetic pole behaved like this, the North magnetic pole might be pointing out through New Orleans or Houston, instead of somewhere in the arctic sea. 

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Animated GIF showing Uranus’ magnetic field. The yellow arrow points to the Sun, the light blue arrow marks Uranus’ magnetic axis, and the dark blue arrow marks Uranus’ rotation axis.
CREDITS: NASA/Scientific Visualization Studio/Tom Bridgman

While planning for a hoped-for future mission to Uranus and Neptune,  Gina DiBraccio and Dan Gershman reviewed Voyager 2’s data on Uranus’s weird magnetic field, and noticed a weird blip in the data. This odd shape in a graph of magnetic data is consistent with a blob of Uranus’s atmosphere getting pulled off where Uranus’s magnetic field and the Sun’s Magnetic field and the solar wind interact and tangle. These kinds of blobs are called plasmoids, and we didn’t know about them yet in 1986, and it was in the context of our modern understanding – brought to us from satellites orbiting Earth, Mars, Jupiter, and Saturn, that they could understand this data blip for Uranus. 

Plasmoids like this carry away a world’s atmosphere a small bit at a time. While this has been devastating for world’s like Mars, Uranus is large enough that we won’t see it noticeably diminish over human timescales. 

There isn’t a lot of new science to this story. Plasmoids happen, and there was no reason to think Uranus would be any different. This is a cool story, however, because the ability to say Uranus has plasmoids has been there for more than 30 years, but because no one looked at the right data since plasmoids were discovered, this discovery has just been sitting on magnetic tape, waiting to be spun up. 

Right now, a lot of observatories have ceased scientific observations as people go home to socially distance. This doesn’t mean that new research can’t be done with data we already have. This new discovery, highlighted in a paper in the Geophysical Research Letters, shows old data still has a lot to offer. Now, I know a lot of people are struggling against the increased entropy of having a house full of children and often a partner. Most people are going to have their productivity destroyed by a lack of childcare and the loss of their support network. For those that don’t have chaos, however, science can go on. Let’s dig into the archive and make 1980’s data all the rage again.

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