A decade after arriving at Jupiter, NASA’s Juno mission continues to reveal details about the solar system’s largest planet and the complex processes shaping planetary atmospheres. In a new study, Jian-Zhao Wang, a research scientist at the University of Colorado Boulder’s Laboratory for Atmospheric and Space Physics (LASP), and colleagues have made the first direct detection of trihydrogen ions (H₃⁺) escaping into space from Jupiter’s polar atmosphere. The findings, published last week in Nature Astronomy, confirm a previously unknown pathway for the transfer of mass and energy between the giant planet’s atmosphere and its powerful magnetic field.
“This study confirms a new coupling mechanism between Jupiter’s atmosphere and magnetosphere,” Wang said. “It also suggests there may be new processes contributing to the energy balance in Jupiter’s upper atmosphere.”
The study provides an important new piece of the puzzle of Jupiter’s long-standing “energy crisis”—the observation that the planet’s upper atmosphere is far hotter than current models predict the gas giant should be at its distance from the Sun. Previous studies have suggested that Jupiter’s Great Red Spot and auroras could be contributing the excess heat to the atmosphere.
Until now, trihydrogen ions could only be observed indirectly through remote sensing techniques, such as infrared emissions measured by telescopes and spacecraft instruments. Those remote observations provided valuable information but could not directly measure the ion or track its behavior at higher altitudes.
NASA’s Juno spacecraft, which launched on Aug. 5, 2011, has been probing beneath the gas giant’s dense clouds for a decade now, seeking to answer questions about the origin and evolution of Jupiter, our solar system, and giant planets across the cosmos.
Wang and his colleagues, including LASP research scientists Fran Bagenal and Rob Wilson, used observations collected by Juno’s Jovian Auroral Distributions Experiment (JADE), which was built by the Southwest Research Institute (SwRI), to directly detect H₃⁺ particles as Juno passed through Jupiter’s polar regions.
The team also identified a three-step process driving the outflow: First, plasma waves in Jupiter’s auroral regions energize and heat the trihydrogen ions. Second, magnetic mirroring lifts the ions upward and funnels them along the magnetic field. Third, electric acceleration further boosts the ions to higher speeds as they escape Jupiter. The team estimated that 0.57 kilograms of H₃⁺ escape from Jupiter every second. While that may seem like a relatively small amount, it accounts for about 20 percent of the material escaping from the planet’s atmosphere.
“This is the first time that we have direct in-situ detection of H₃⁺ and confirmation that it is escaping,” Wang said. “Before this, it was predicted, but we never had the evidence. We’ve now detected very strong signals of H₃⁺.”
The discovery establishes H₃⁺ as a direct channel for transferring mass and energy between Jupiter’s atmosphere, ionosphere, and magnetosphere. Although the newly observed escape process does not by itself explain Jupiter’s unexpectedly hot upper atmosphere, the study may provide important clues.
“From this study, we’ve found the temperature of H₃⁺ is much hotter than previously detected by remote sensing,” Wang said, “so there may be some new mechanisms at work.”
The study’s results could also have implications beyond Jupiter. Similar H₃⁺ auroral emissions have been observed at Saturn, Uranus, and Neptune, raising the possibility that similar atmospheric escape processes occur throughout the outer solar system. The new measurements also provide valuable data for improving models of how the atmospheres of gas giants interact with their magnetic fields.
“This study is just the first dip into the Juno-JADE data over the poles,” said Bagenal, a LASP senior research scientist and professor emerita at CU Boulder and co-investigator and co-chair of the Juno mission’s Magnetospheres Working Group and the Science Planning Working Group. “Next, we hope to map out the ionospheric escape fluxes and explore what processes are driving the outflow.”
By Sara Pratt, LASP Sr. Communications Specialist
Founded a decade before NASA, the Laboratory for Atmospheric and Space Physics at the University of Colorado Boulder (LASP) is revolutionizing human understanding of the cosmos. LASP is deeply committed to inspiring and educating the next generation of space explorers. From the first exploratory rocket measurements of Earth’s upper atmosphere to trailblazing observations of every planet in the solar system, LASP continues to build on its remarkable history with a nearly $1 billion portfolio of new research and engineering programs.
