부산대학교 도서관

The Cassini spacecraft revealed that Saturn's magnetic field displayed oscillations at a period originally thought to match the planetary rotation rate but later found not to. One of many proposed theories predicts that a polar twin‐cell neutral weather system drives this variation, producing observable differences in flows within Saturn's ionosphere. Here, using spectral observations of auroral H3+ ${\mathrm{H}}_{3}^{+}$ emission lines taken by the Keck Observatory's Near Infrared Echelle Spectrograph (Keck‐NIRSPEC) in 2017, we derive ion line‐of‐sight velocity maps after grouping spectra into rotational quadrants matching phases of the planetary magnetic field. We measure 0.5 km s−1 wind systems in the ionosphere consistent with predicted neutral twin‐vortex flow patterns. These findings demonstrate that neutral winds in Saturn's polar regions cause the rotational period, as determined via the magnetic field, to exhibit differences and time variabilities relative to the planet's true period of rotation in a process never before seen within planetary atmospheres. Plain Language Summary: We observed Saturn's northern aurorae in the infrared using the Keck Observatory in Mauna Kea, Hawaii over the course of June, July and August of 2017. Using this data we investigate the motion of an ion, H3+ ${\mathrm{H}}_{3}^{+}$, in the planet's upper atmosphere. This is done after first placing the data into four groups corresponding to the rotational phase of the planet's magnetic field. By doing so we are able to detect twin‐vortex flows in the upper atmosphere of Saturn, consistent with theories that predict the presence of such a polar feature, thus providing direct evidence that Saturn's measured variable rotation rate is driven by these flows. These twin‐vortex flows are ultimately responsible for the time differences relative to the planet's true rotation period observed throughout Saturn's planetary environment. Key Points: Keck‐NIRSPEC observations of Saturn's northern H3+ infrared auroral emission from 2017 are analyzedFirst clear picture of how the ionosphere moves in relation to planetary period currents is providedSaturn's measured variable rotation rate is driven by twin‐vortex flows in the upper atmosphere [ABSTRACT FROM AUTHOR]