Astronomers have discovered new faint aurora features, which are distinguished by ring-like emissions that expand rapidly over time. These auroral emissions were caused by charged particles emitted from the edge of Jupiter’s massive magnetosphere, according to scientists.
The SwRI-led Ultraviolet Spectrograph (UVS) on NASA’s Juno spacecraft orbiting Jupiter has detected new faint aurora features, which are characterized by ring-like emissions that expand rapidly over time. SwRI scientists discovered that charged particles emitted from the edge of Jupiter’s massive magnetosphere were responsible for the auroral emissions.
The Juno spacecraft’s Ultraviolet Spectrograph (UVS) captured this glowing phenomenon, which is characterized by faint ring-shaped emissions that expand rapidly over time at speeds ranging from 2 to 4.8 miles per second (3.3 and 7.7 kilometers per second). According to a statement from the Southwest Research Institute (SwRI), where Juno’s UVS instrument was built, these auroral emissions are triggered by charged particles coming from the edge of Jupiter’s massive magnetosphere.
NASA’s Juno mission has detected new auroral emissions on Jupiter which appear to ripple over the planet’s poles.
“We believe these newly discovered faint ultraviolet features originate millions of miles away from Jupiter, near the boundary of the Jovian magnetosphere with the solar wind,” said Dr. Vincent Hue, lead author of a paper accepted for publication in the Journal of Geophysical Research: Space Physics. “The solar wind is a supersonic stream of charged particles that the Sun emits. When they reach Jupiter, they interact with its magnetosphere in ways that are still unknown.”
Jupiter and Earth both have magnetic fields that shield them from the solar wind. The magnetosphere expands with the strength of the magnetic field. Jupiter’s magnetic field is 20,000 times stronger than Earth’s, resulting in a magnetosphere so massive that it begins to deflect solar wind 2-4 million miles before it reaches Jupiter.
“Despite decades of observations from Earth and numerous in-situ spacecraft measurements, scientists still do not fully understand the role of the solar wind in moderating Jupiter’s auroral emissions,” said SwRI co-author Dr. Thomas Greathouse. “Jupiter’s magnetospheric dynamics, or the movement of charged particles within its magnetosphere, are largely governed by the planet’s 10-hour rotation, the fastest in the solar system. The role of the solar wind is still being debated.”
One of the goals of the Juno mission, which was recently extended by NASA until 2025, is to investigate Jupiter’s magnetosphere by measuring its auroras with the UVS instrument. Previous observations with the Hubble Space Telescope and Juno have revealed that the majority of Jupiter’s powerful auroras are caused by internal processes, specifically the motion of charged particles within the magnetosphere. However, UVS has detected a faint type of aurora on numerous occasions, characterized by rings of emissions that expand rapidly with time.
The charged particles detected by Juno’s UVS instrument appear to be coming from the magnetosphere’s outer reaches, where plasma from the solar wind interacts with Jovian plasma. As a result of this interaction, ring-like features known as Kelvin-Helmholtz instabilities may form and travel along Jupiter’s magnetic field lines. According to the statement, the newly detected auroral feature could also be the result of dayside magnetic reconnection events, in which interplanetary magnetic fields converge, rearrange, and reconnect.
“The high-latitude location of the rings suggests that the particles causing the emissions are coming from the distant Jovian magnetosphere, near its boundary with the solar wind,” said Bertrand Bonfond, a co-author on this study from Liège University in Belgium. Plasma from the solar wind frequently interacts with Jovian plasma in this region, resulting in “Kelvin-Helmholtz” instabilities. These phenomena occur when shear velocities exist, such as at the interface of two fluids moving at different rates. Dayside magnetic reconnection events, in which opposingly directed Jovian and interplanetary magnetic fields converge, rearrange, and reconnect, are another possible source of the rings.
Both of these processes are thought to produce particle beams that could travel along the Jovian magnetic field lines, eventually precipitating and triggering Jupiter’s ring auroras. “While this study does not conclude what processes produce these features,” Hue said, “the Juno extended mission will allow us to capture and study more of these faint transient events.”