The use of extra-terrestrial oceans to test ocean acoustics students
(Color online) Predictions of the variation of sound speed with depth for a model Europa-type ocean, under the assumption that, at all depths, the ocean has a constant temperature of 4 °C and an ionic content which translates into Eq. (1) as though S = 35 g kg−1. (a) The prediction of the UNESCO equation (solid line) is compared to those of Eq. (1) for example values of of (dashed line) and (dotted line). (b) The error function between the sound speed predicted by the UNESCO equation () and that predicted by Eq. (1), , as varies, showing that the best fit is for .
(Color online) Schematic (not to scale) showing the supposed locations of water on three of Jupiter’s moons: Ganymede (diameter ∼ 5268 km), Callisto (diameter ∼ 4800 km) and Europa (diameter ∼ 3138 km); and Saturn’s largest moon, Titan (diameter ∼ 5150 km). Images created by A. D. Fortes, University College London.
Predicted ray paths within the curved model ocean of Europa, calculated for the conditions indicated in the text. The deepest of the selection of rays calculated in this way had a launch angle of 35° below the horizontal, and is plotted with a thick solid line, and labeled “35° ray.” If the trajectory of the ray with a 35° launch angle were instead recalculated with the variation in gravity neglected, and the hydrostatic pressure calculated using rectilinear (as opposed to conic) sections, its trajectory would change to the one shown with the thick dashed line. The rays propagate within the upwardly-refracting water column, reflecting specularly off the sea/ice interface. To illustrate the error in geometry that a “flat world” assumption produces on Europa (quite apart from the error introduced in the calculation of hydrostatic pressure) the location of the ocean boundaries if curvature is ignored are also shown, using dash-dot lines. From Ref. 5.
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