Simulations of Europa&#8217;s vapor plumes and ice-grain fallout
Authors: Boccelli Stefano , Tucker Orenthal J. 
Published: July 2024

Jupiter&#8217;s moon, Europa, is believed to host an ocean of liquid water under a km-thick shell of ice. Water inclusions within the ice or fractures of this solid shell, generated by Jupiter-induced tidal forces, have been proposed as possible mechanism of water-vapor plume generation [1]. Plume activity on Europa was observed in 2012 with the Hubble Space Telescope (HST) [2], from the magnetometer onboard the Galileo probe [3], and later from the Keck Observatory [4]. However these findings are challenged by a number of successive no-detections [5,6]. Europa Clipper, set to launch in 2024, hosts a suite of science&#160; instruments that will search for signs of plume activity and hopefully settle the debate. Plume measurements via the onboard mass spectrometers would probe, indirectly, Europa&#8217;s sub-surface ocean. Additionally, on-board imagers will study the composition of surface ice and search for cryovolcanic fallout from potential plumes.
In this work, we intend to perform numerical simulations of a plume and estimate the lateral extent of ice grain fallout. We will consider a vapor mass-flow-rate compatible with the HST observations, and a simplified vent geometry, selected compatibly with the 7-hour period of continued observed plume activity [7]. For such parameters, we use the Direct Simulation Monte Carlo (DSMC) method to obtain density, velocity and temperature maps within and near the vent aperture. These simulations include Europa&#8217;s gravity and will also indicate the amount of surface accretion due to molecular deposition. As a second step, the density, velocity and temperature fields are fed to a gas-drag model, to study the transport and deposition of ice grains. We compare our results with the findings of [8], that predicted grains to be localized within some tens of meters, vertically, from the vent. Our result will provide maps of lateral resurfacing that can be, as a future activity, converted into synthetic images, useful for a direct comparison with Clipper&#8217;s measurements.
References:
[1] Vorburger, A. &amp; Wurz, P., Modeling of possible plume mechanisms on Europa, Journal of Geophysical Research: Space Physics, 2021.
[2] Roth, L., Saur, J., Retherford, K. D., Strobel, D. F., Feldman, P. D., McGrath, M. A. &amp; Nimmo, F., Transient water vapor at Europa&#8217;s south pole, Science, 2014.
[3] Jia, X., Kivelson, M. G., Khurana, K. K. &amp; Kurth, W. S., Evidence of a plume on Europa from Galileo magnetic and plasma wave signatures, Nature Astronomy, 2018.
[4] Paganini, L., Villanueva, G. L., Roth, L., Mandell, A., Hurford, T., Retherford, K. D. &amp; Mumma, M. J., A measurement of water vapour amid a largely quiescent environment on Europa, Nature Astronomy, 2020.
[5] Villanueva, G., Hammel, H., Milam, S., Faggi, S., Kofman, V., Roth, L. and others, Endogenous CO2 ice mixture on the surface of Europa and no detection of plume activity, Science, 2023.
[6] Hansen, C.J., Ravine, M.A., Schenk, P.M., Collins, G.C., Leonard, E.J., Phillips, C.B., Caplinger, M.A., Tosi, F., Bolton, S.J. &amp; Jonsson, B., Juno&#8217;s JunoCam images of Europa, The Planetary Science Journal, 2024.
[7] Boccelli, S., Carberry Mogan, S.R., Johnson, R.E. &amp; Tucker, O.J., Can water-vapor deposition fill vents on Europa? An order-of-magnitude study. In preparation.
[8] Quick, L.C., Barnouin, O.S., Prockter, L.M. &amp; Patterson, G.W.,Constraints on the detection of cryovolcanic plumes on Europa, Planetary and Space Science, 2013.