A recent analysis of energetic particle and magnetic field data taken by NASA's Voyager 2 spacecraft suggests that Uranus' moons Ariel and/or Miranda may be actively spewing material into space, possibly through plumes from oceans beneath their icy surfaces. The findings, presented at the annual Lunar and Planetary Science Conference by researchers at Johns Hopkins Applied Physics Laboratory, highlight the potential for finding extraterrestrial life and the critical role that energetic particle measurements play in understanding our solar system's composition.
Recent findings suggest that Uranus may join the ranks of other planets, including Jupiter, Saturn, and Neptune, as a host to at least one icy moon that’s emitting particles into its planetary system.
The Study
Scientists at the Johns Hopkins Applied Physics Laboratory (APL) in Maryland have conducted a new study that revisits data from NASA’s Voyager 2 spacecraft, which remains the only spacecraft to have explored Uranus so far. The study, recently accepted for publication in Geophysical Research Letters, indicates that one or two of Uranus’ 27 moons, Ariel and/or Miranda, may be contributing to plasma in the space environment through an unknown and mysterious mechanism. According to the researchers, one possible explanation is that the two moons possess oceans beneath their icy surfaces and are actively emitting material, possibly through plumes. This finding provides intriguing new evidence that Uranus may host an “ocean world,” a term used to describe celestial bodies with subsurface oceans that may harbor life.
The Presentation
The research team shared their latest findings during the annual Lunar and Planetary Science Conference on March 16. According to Ian Cohen, who is the lead author of the study and a space scientist at APL, energetic particle measurements have often provided vital clues about the existence of ocean worlds. As an example, particle and magnetic field data have previously helped to provide evidence of the existence of two unequivocal ocean moons in our solar system: Jupiter’s Europa and Saturn’s Enceladus. Ian Cohen’s comments emphasize the vital role that energetic particle measurements play in our understanding of the composition of the solar system and in our search for extraterrestrial life.
A Return Mission to Uranus and Neptune
The increasing interest in a return mission to Uranus and Neptune has prompted numerous research teams to revisit old flyby data, often resulting in new and exciting discoveries. These findings have influenced a panel of planetary scientists, who recommended a $4.2 billion flagship mission to Uranus as NASA’s next major planetary endeavor over the coming decade. The potential for new insights into the mysteries of the outer solar system has fueled growing momentum for such a mission, and the recent findings on Uranus’ moons Ariel and Miranda provide further evidence of the scientific potential of a return mission to the planet.
The Findings
Cohen and his team’s recent discoveries prompted them to further investigate the particle data gathered by Voyager 2’s Low-Energy Charged Particle instrument. Through their analysis, they found a trapped population of energetic particles observed by the spacecraft as it departed from Uranus. Cohen noted that the particles were confined near the planet’s magnetic equator, an unusual occurrence. Initially, scientists thought Voyager 2 had flown through a stream of plasma injected from the distant tail of Uranus’ magnetosphere, but Cohen argued that this explanation doesn’t fully account for the observed phenomena.
“An injection would normally have a much broader spread of particles than what was observed,” he said.
The Explanation
By utilizing simple physical models and building upon nearly four decades of knowledge since the Voyager 2 mission, the research team sought to recreate the observed energetic particle population. They determined that the explanation required a consistent and robust source of particles and a specific mechanism to energize them. After exploring several potential scenarios, the team arrived at the conclusion that the particles most likely originated from a nearby moon. The scientists propose that Ariel and/or Miranda could be releasing the particles via either a vapor plume, similar to what has been observed on Enceladus, or through a process known as sputtering. Sputtering involves high-energy particles striking a surface and ejecting other particles into space.
The Uncertainties
The team’s conclusion is limited by the lack of available data on the composition of the plasma and measurements of the full range of electromagnetic waves within the region. As such, it’s impossible to definitively determine the source of the particles. Despite these uncertainties, the study’s findings support the idea of the presence of an active ocean moon on Uranus. Cohen acknowledged that there is room for more comprehensive modeling, but until further data is available, any conclusions must remain provisional.
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