How Thick is Europa’s Ice Shell Crust?. David Galvan ESS 298 The Outer Solar System. Outline. Our interest in Europa’s ice shell crust Evidence for Ice/Water crust Methods of estimating thickness Gravity measurements Induced magnetization Impact Craters
The Outer Solar System
Image from Greenberg, American Scientist, Vol 90, No. 1, Pg. 48
Where λ = longitude from Jupiter-Europa line, and φ=latitude.
One model that explains this is a conducting spherical shell (probably liquid salt water) at a depth of at least ~8 km below the ice crust.
Magnetometer measurements show that Europa’s dipole moment changed due to a change in the relative orientation of Jupiter’s magnetic field, as Europa was in a different location in its orbit.
Solid=no central peak
Open with solid center = central peak
Nested ring = multiring basins
9 km ice
5 km ice
Hence, ice crust must be > 3 km!
Scalebars are 30 km for G/C
and 10 km for Europa
Thicknesses not to scale
They attempt to balance the heat budget of Europa’s H20 layer by plotting tidal dissipation (heat production rate) and heat flux through the ice layer (convecting and conducting cases) for different melting-point viscosities as a function of ice thickness.
Ice Crust thickness range: ~30 km, and surface heat flow = 20mW/m^2
Cilix crater with topographic profiles.
Derived from Galileo stereographic images
Combined topographic profile for ice crust with rigidity D loaded against by a trapesoidal mass, with a best fit model of Te = 6 km
Lowest value of the combined root mean square “misfit” again shows best fit at Te = 6 km
Conductive ice crust:
Tb = melting temp, tc is crust thickness.
Convective ice crust:
Tb = temp of convecting ice, tc is conducting lid thickness.
Leads to crust thickness of 15 - 35 km!
JIMO: would launch no earlier than 2015