EXPLORATION OF SATURNALIA FOSSA AND ASSOCIATED STRUCTURES IN VESTA'S NORTHERN HEMISPHERE

Since its arrival at Vesta on July 16^th 2011, NASA’s Dawn spacecraft has collected spectacular imaging, compositional and geophysical data. Dawn is scheduled to depart Vesta on August 26^th and during this eventful year many unexpected discoveries have been made about this diverse asteroid. One such discovery is the Saturnalia Fossa trough in Vesta’s northern hemisphere. Saturnalia Fossa is the chief structure of at least 5 parallel troughs, many of which partly coalesce into one another at various locations. The sizeable Saturnalia Fossa dominates Vesta’s northern hemisphere and lends its name to the Saturnalia Ridge and Trough Terrain. Saturnalia Fossa has a maximum width of ~39 km, making it almost twice the width of the ~ 22 km wide Divalia Fossa equatorial trough. Currently Saturnalia Fossa (~366 km long) is shorter than Divalia Fossa (~465 km long) (Buczkowski et al., 2012, submitted to GRL). But, Saturnalia Fossa extends into the currently shadowed northern region and its length will increase as Dawn gains coverage in this enigmatic area. The northern troughs are covered in an obscuring layer of regolith, which makes identifying their specific form challenging. Comparative planetology, along with the analysis of Dawn data, helps to indicate whether the troughs are graben or another structure. The orientation of the troughs makes it likely that their formation is linked to that of the southern Veneneia basin (Buczkowski et al., 2011, AGU). There are many smaller structures, which include grooves, pit crater chains and small ridges that are preferentially oriented sub-parallel or sub-perpendicular to the troughs. This suggests that they have a related formation mechanism. An initial analysis of the distribution of the troughs and smaller structures indicates that they are oriented as if they were formed by large-scale shearing. This shear is possibly a result of the Veneneia-forming impact.