The Search for Europa’s Plumes: No Surface Patterns or Changes 1979–2007?

With the apparent detections of eruptive plumes of water vapor at Europa, we use low-resolution global imaging maps of the surface obtained in 1979, 1996–1998, and 2007 by Voyager, Galileo (GLL), and New Horizons to search for plume-related deposits on the surface or changes to them. These imaging data were acquired using different imaging filters, and at different observation geometries. Though not ideal, these maps reveal no obvious albedo or color patterns or surface changes related to plume activity that can be identified with confidence on the surface of Europa over this 28 yr time period. Either plume activity was relatively continuous over these time periods and produced neither distinctive color nor photometric patterns or observable changes, plume activity produces vapor-only "stealth" deposits that are not apparent in currently available data sets, or these are not plumes in the expected sense. We also examine the proposed E12 GLL plume site at 5°S, 115°E, which was observed by GLL at pixel scales of 0.23–1.6 km pixel−1 before and as little as 4 months after the E12 magnetometer observations. We observe no unusual or anomalous photometric features or changes at this or any other sites, including the Hubble Space Telescope site at 17°S, 72–96°E. Prominent dark double ridges flanked by diffuse dark reddish deposits, and sporadic chaos formation events, are among the best-candidate eruptive sites on Europa, but none are linked with the proposed plume detection sites. Novel approaches to plume deposit detection may be required during the Europa Clipper mission.