Europa Geology and Astrobiology
by Cynthia Phillips, Christopher Chyba
Jupiter's satellite Europa could harbor a biosphere beneath its icy surface. Co-Investigator Cynthia Phillips will study possible environments for life on Europa. Her work will have two main components. First, she will use the dataset of images taken by the Galileo spacecraft to search for any changes on Europa's surface, which could be due to current geological activity. This will be a follow-up to previous work, which searched for changes by comparing Voyager and Galileo images of Europa. The second component of her work will involve studying various models of geological activity on Europa to determine their implications for creation and/or transport of biogenic material from the surface to a subsurface ocean and vice versa. One such model, of sputtering and impact gardening, studies the interaction between processes, which create, destroy, and preserve interesting chemical compounds at Europa's surface.
|Comparison of two images, taken on Galileo orbits C3 (11/1996) and E15 (5/1998). Overlapping images were tied together, reprojected, masked, and coregistered. The ratio image (g) highlights changes between the images. Phase angles and filters were well-matched, but differences in illumination are apparent in g: ridges and troughs approximately parallel to the terminator show the most changes in lighting and thus appear most prominent in the ratio image.
No changes unambiguously attributable to geological activity are present in this image pair.
Project Progress: The project has two components. The first, an overview of the astrobiological potential of various geological features on Europa, is proceeding well – we are continuing the study of various proposed formation mechanisms for different feature types such as ridges, bands, and chaotic terrain. The second, a search for current geological activity by comparing Galileo images taken on different orbits, is also in progress. We have completed a first-stage search of the Galileo Europa images to find overlapping images, and are continuing to work on improving our automated search method to make sure that we find all possible comparison images. We have processed a number of comparison pairs, and are currently working on automated techniques for speeding up the comparison process.(2006 NAI Annual Report)
Europa Surface and Subsurface Chemistry
by Kevin Hand, Christopher Chyba
|Salinity of the europan ocean . Amplitude, A, as a function of conductivity, ocean thickness, and ice shell thickness. At low conductivities the ocean thickness dominates the amplitude response, however, as the conductivity of the solution increases, ocean thickness becomes less important and the thickness of the non-conducting ice shell dominates the inductive amplitude response. (a) Three-layer spherical model with non-conducting ice shell and mantle. The only solutions consistent with the magnetometer data [Schilling et al. (2004) require A = 0.97±0.02] and the gravity data (Anderson et al., 1998) are those in which the ice shell is thin (between 0 and 15 km thick).The optimal fit for an ocean dominated by NaCl is 4 km thickness. The maximum allowable ice shell thickness for anMgSO4 dominated ocean is 7 km. (b) Five-layer half-space model. Results are very similar to the three-layer spherical model. Values for the conductivity of individual layers are: σIonosphere = 2 °— 10−4 Sm−1;σIce = 1 °— 10−10 Sm−1; σMantle = 0.01 Sm−1; σCore = 3.3 °— 105 Sm−1. Again the optimal fit to the magnetometer data is achieved with a 4 km thick ice shell. The maximum thickness allowed by the error bars is 16 km