Energetic neutral atoms may help map Uranus's odd magnetic environment

Uranus appears beyond the horizon of its moon Miranda in this illustration. If detectable, high-energy neutral particles produced near Uranus could help scientists decipher the structure and dynamics of the icy planet’s magnetosphere. Credit: NASA’s Goddard Space Flight Center Conceptual Image Lab

Sending a spacecraft to the underexplored planet Uranus is at the top of many planetary scientists' wish lists . But which spacecraft-mounted instruments would be most useful for answering questions about the mysterious ice giant?

Several missions to other parts of the solar system have included an instrument that detects energetic neutral atoms (ENAs) zipping through space. An ENA is created when a fast-moving, positively charged ion collides with a neutral particle and "steals" an electron. The now-neutral atom maintains its high energy, and because it is no longer charged, it escapes the influence of a magnetic field and flies onward in a straight line—perhaps right into a spacecraft-mounted ENA detector.

By measuring the numbers, directions and energies of ENAs produced in a magnetic system, scientists can create three-dimensional images that illuminate that system's structure and dynamics. ENA imaging previously deepened understanding of the space environments surrounding Earth, Mars, Saturn and the sun and highlighted interaction mechanisms occurring at the edge of our solar system.

However, whether ENA imaging would be useful in future exploration of Uranus has been unclear. New simulations by Santos-Costa and Andre suggest that ENAs are, indeed, likely detectable at Uranus and that studying the ice giant with ENA imaging could yield valuable insights into its complex magnetosphere.

On the left, Uranus is seen by Voyager 2's analog cameras during the 1986 flyby, when the spacecraft was a few dozen planetary radii from Uranus. The composite image on the right illustrates the hypothetical observation of Uranus's magnetosphere from an energetic neutral atom perspective based on one of the case scenarios of charged and neutral particle distributions around Uranus discussed by the authors. The Z and M axes indicate the orientation of the planetary and magnetospheric systems, respectively. Credit: Left: NASA/University of Arizona/Erich Karkoschka; right: SwRI/Daniel Santos-Costa

The simulations incorporate realistic parameters drawn from what scientists already know about Uranus, such as its strangely offset magnetic field, clouds of neutral particles surrounding its icy moons and the planet itself, and the presence of protons trapped in the planet's magnetic field. The researchers used the simulations to explore what scientists might have seen if an ENA detector similar to the one mounted on the Saturn probe Cassini had been aboard Voyager 2 during its brief flyby of Uranus in 1986.

The results point to a strong probability that a "Voyager 2 ENA detector" would have observed ENAs created by collisions between protons and neutral particles that escape the atmosphere and populate a vast region of space—aiding understanding of Uranus' magnetospheric system. Because the distribution of protons within Uranus' magnetosphere is poorly understood, the researchers ran the simulations with a few different distribution scenarios. Even in their worst-case scenario, ENAs remained detectable. The study is published in the Journal of Geophysical Research: Space Physics .

ENAs could also result from collisions between protons and neutral particles surrounding Uranus' moons, rather than from the neutral environment originating from the planet itself, but the simulations did not conclusively show whether a Cassini-like detector might capture them.

The researchers conclude that their simulations make a compelling case for including ENA imaging in future exploration of Uranus.

More information

D. Santos‐Costa et al, What Observations Would an Energetic Neutral Atom Imager Have Made During the Voyager 2 Flyby of Uranus?, Journal of Geophysical Research: Space Physics (2026). DOI: 10.1029/2026ja035080

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