Jupiter's icy moon Europa has captivated and perplexed the scientific community since the discovery of its global liquid water ocean. Over the course of several missions to the Jovian system, high-resolution observations of Europa have determined that there are spreading zones where new crust is created, similar to the mid-ocean spreading tectonic process we observe on Earth. These features, known as bands, have symmetric hills and valleys, indicating brief events of activity where material from the interior is exuded through a central crack, and solidifies on both sides, creating two positive topography. Recently, Europan scientists have been questioning how these features affect the total ice volume of the moon. After all, if ice is being created at these features, then the total volume of ice on Europa would be increasing, unless there was some mechanism in place to balance this net positive change in volume.
In this thesis, I begin with a hypothesis: maybe the volume of ice being created through band extension can be compensated by compressional features. To test this hypothesis, we map, measure, and calculate surface area and volume estimates for bands and ridges in four regions across a global mosaic of Europa using moderate resolution images from the Galileo spacecraft. From our results, we may be able to draw important constraints on the thickness of the outer ice shell, which has been highly debated among scientists for decades.
Initial results of this study show that the surface area of ridges can compensate for 35-70% of band surface area, with percentages varying greatly by region. Volume ratios of ridges to bands were calculated for several plausible values of shell thickness, ranging from 100 m - 50 km. It appears that in order to compensate for band spreading, the bands would need to propagate to depths of 200 m – 1 km. While these calculations are only indicative of a small percentage (4.62%) of the total surface area of Europa and therefore are not yet conclusive for understanding the surface expression of tectonic activity, they prompt further investigation on a more global scale.
"Band Extension and Possible Ridge Compression on Europa,"
Macalester Journal of Physics and Astronomy: Vol. 8
, Article 5.
Available at: https://digitalcommons.macalester.edu/mjpa/vol8/iss1/5