An artist’s impression of Uranus and its five largest moons (innermost to outermost) Miranda, Ariel, Umbriel, Titania and Oberon.
Image credit: NASA/Johns Hopkins APL/Mike Yakovlev


Researchers have reanalyzed nearly 40-year-old data accumulated by NASA’s Voyager 2 and now speculate that two moons of Uranus may have oceans beneath their icy surfaces.

The moons – Ariel and Miranda — may be releasing energetic particles into space, according to a new study led by specialists at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland.

Even better is that Uranus is a newly recommended target for a NASA flagship mission over the coming decade.

Unknown, mysterious mechanism

Accepted for publication in the journal Geophysical Research Letters, and detailed last week at the annual Lunar and Planetary Science Conference, the research suggests that one or two of Uranus’ 27 moons — Ariel and/or Miranda — are adding plasma into the space environment through an unknown and mysterious mechanism.

Miranda, a moon of Uranus.
Image credit: Voyager 2/NASA/JPL

Scientists took another look into particle data collected by the APL-built Low-Energy Charged Particle (LECP) instrument carried by Voyager 2, uncovering something peculiar: a trapped population of energetic particles the spacecraft had observed while departing Uranus.

During its approximately three-day flyby of Uranus in 1986, Voyager 2 captured the only on-the-spot observations of the planet and its system.

Tantalizing explanation

One tantalizing explanation for the particles is that one or both moons have oceans beneath their icy surfaces and are actively spewing material, possibly through plumes.

The team suspects the particles arise from Ariel and/or Miranda through either a vapor plume or through sputtering — a process where high-energy particles hit a surface, ejecting other particles into space.

As for what’s taking place on Ariel and/or Miranda, “right now, it’s about 50-50 whether it’s just one or the other,” reports Ian Cohen, a space scientist at APL and the lead author of the new study.

“What was interesting was that these particles were so extremely confined near Uranus’ magnetic equator,” Cohen said in an APL statement. Magnetic waves within the system would normally cause them to spread out in latitude, he explained, but these particles were all cramped near the equator between the moons Ariel and Miranda.

The complex terrain of Ariel is viewed in this image, the best Voyager 2 color picture of the Uranian moon.
Image credit: Voyager 2/NASA/JPL

Eruptions of water?

Originally, scientists attributed these features to Voyager 2 flying through a chance stream of plasma being “injected” from the distant tail of the planet’s magnetosphere. But that explanation doesn’t hold, Cohen said. “An injection would normally have a much broader spread of particles than what was observed.”

Scientists had previously suspected Uranus’ five largest moons — Ariel and Miranda included — may have subsurface oceans. Voyager 2 images of both moons show physical signs of geologic resurfacing, including possible eruptions of water that froze on the surface.

The rehashed Voyager 2 data and determining the source of the particles has given rise to the potential of there being an active ocean moon there, Cohen said. “We can always do more comprehensive modeling, but until we have new data, the conclusion will always be limited.”

This new research potentially hints that the Uranian magnetosphere may harbor an ocean world like those known or believed to exist at the other Giant Planets.

For more information, go to – “A localized and surprising source of energetic ions in the Uranian magnetosphere 1 between Miranda and Ariel” – at:

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