09/22/2025
By Lynne Schaufenbil

Please join the Lowell Center for Space Science and Technology on Thursday, Oct. 2 at 11 a.m. for the talk "Ionospheric Plasma Outflow at Saturn" by Marianna Felici.

Abstract
At Earth, the ionosphere is known to supply substantial plasma to the magnetosphere, especially during geomagnetic storms. This outflow plays a critical role in shaping magnetospheric dynamics. In contrast, the ionosphere’s contribution to Saturn’s magnetosphere has been comparatively underexplored.

Felici et al. (2016) provided evidence of ionospheric plasma escaping into Saturn’s magnetotail—the elongated, nightside extension of the magnetosphere shaped by the solar wind. Specifically, Cassini observed this outflow in the northern lobe of the magnetotail, a region characterized by low plasma density and strong magnetic fields. At the time, Cassini was located at approximately 2200 Saturn local time and 36 Saturn radii (RS) from the planet. During repeated crossings into the magnetotail lobe, the spacecraft detected a cold, tailward-flowing beam of light ions, primarily hydrogen (H⁺). These ions exhibited energy dispersion. Simultaneous ultraviolet observations revealed a brightening of Saturn’s aurora near the dawn sector, indicating enhanced magnetospheric activity. Solar wind propagation models suggested that Saturn’s magnetosphere was being compressed by a region of elevated solar wind ram pressure, potentially triggering or amplifying the ionospheric outflow.

Building on this case study, we conducted a broader survey of similar ionospheric outflow events using data from the Cassini Plasma Spectrometer Singles (CAPS). By analyzing the spacecraft’s position relative to the plasma sheet, the direction of ion flow, and ion composition—using data from Cassini instruments—we identified and mapped multiple events consistent with the criteria established by Felici et al. (2016).

To place these events in context, we examined auroral activity using Cassini’s Ultraviolet Imaging Spectrograph (UVIS), investigated possible internal magnetospheric drivers, and modeled solar wind conditions using the ENLIL propagation model. From this analysis, we derived ion number fluxes at an altitude of 10,000 km, providing quantitative insight into the scale and variability of Saturn’s ionospheric contribution to its magnetosphere.

To RSVP or for the Zoom link, please email Lynne_Schaufenbil@uml.edu