SEARCHING FOR EVIDENCE OF PLUMES WITH THE EUROPA IMAGING SYSTEM (EIS)

The Europa Imaging System (EIS) for NASA's Europa Clipper Mission combines a narrow-angle camera (NAC) and a wide-angle camera (WAC) to address high-priority science objectives, including whether there is recent or ongoing geologic activity. The NAC is designed to be able to take advantage of favorable geometry even when distant from Europa to search directly for potential erupting cryovolcanic plumes via forward scattering above the limb at high phase angles or illuminated beyond the terminator. With a 10-μrad instantaneous field of view, the NAC achieves 10-km pixel scale from an altitude of 10⁶ km. Thus, EIS plume-search observation opportunities during Europa Clipper's tour in orbit at Jupiter provide good coverage of longitudes and orbital true anomalies.

In addition to searching for plumes, EIS observations can reveal signs of recent deposits or surface changes. Color observations using six broadband filters covering wavelengths between 355 and 1050 nm will map surface units that can be correlated with geologic landforms, topography, subsurface structures, and compositional information. The NAC will perform full-disk color scans at pixel scales of ~200-400 meters during approach or as the spacecraft recedes from Europa, and we will target regions of unusual color or photometric brightness to search for recent deposition or disturbance. Color imaging will identify areas that show fewer effects of exogenic modification (e.g., radiation, sputtering, Iogenic plasma implantation, impact gardening) and thus are younger. 1-μm:IR1 color ratios could indicate coarse-grained ice potentially related to thermal anomalies. Surface reflectivity variations with solar phase angle such as excess emission at high phase or very low phase (<1°) can also reveal possible modification. These data will complement other imaging constraints on relative surface ages from crater statistics and cross-cutting relationships. And we will compare EIS imaging over the duration of the ~3.5-year mission to look for short-term surface changes, as well as comparing EIS images to Voyager and Galileo data to detect changes over the intervening decades.

We will describe the EIS observational strategy to provide insight into the fundamental question of cryovolcanism at Europa.