Europa – a far away (480 million miles, give or take), a frozen world – covered with ice that is 19-40 feet thick, has a radiation level on its surface equivalent to a fatal dose (~5400 mSv/540 rem) per day – is of major interest to scientists, to NASA, and to me. (Although that last part may not interest you!)
When last I gave my presentation ‘NASA Takes on the Universe’ a question was presented regarding the convection process on Europa, the ice, the underlying ocean…After talking about all the planets in NASA’s expanding berth of places to visit, I discussed how we ‘know’ Europa has an ocean of water below the ice. First remember that Europa’s orbit around Jupiter is more elliptical than circular. AND so Europa feels the gravitational pull and like a beach ball under the same stress, flattens a bit as it gets to its furthest point from Jupiter and then springs back to a spherical shape when at its closest point. This constant stretch and snap results in the ice & water beneath sloshing about and then when the ice slams inward, a water plume extends into space, the Hubble is watching and so we see Hydrogen and Oxygen atoms all over the place – Houston? We have water!
Is convection involved in this? Still before going over the convectively driven ocean circulations, first what is convention?
Convection: is the efficient redistribution of heat in planetary bodies (such as Europa) through
fluid motions. The Coriolis force figured into this as rotating convection experiments have shown the patterns formed in the heat transfer. The equator realizes peak flux and the poles, minimal.
This leads me to; Coriolis Force: the deflection of objects moving relative to a rotating frame. Deflection occurs in a left motion, in one counter-clockwise rotation and to the right when in a clockwise rotation. [When in the presence of Newton’s laws, the law of motion comes to mind. When the laws are transformed to a uniformly rotating frame of reference, Coriolis and Centrifugal forces appear. [Want an example of the Coriolis Effect? When water is flushed in one hemisphere it turns clockwise, the other hemisphere, counter clockwise.]
Tidal dissipation and radiogenic heating are said to enough to keep the ocean in a liquid
phase and to drive fluid motions. It has been hypothesized that chaos terrain tends to occur in the equatorial region because convectively-driven ocean circulations preferentially emit heat near the equator. Such ocean-driven heat exchange from the interior of the moon to the base of the ice shell is important because it will increase the equatorial ocean temperature and influence the pattern of ice melt and accretion at the base of the shell. These factors may not only reduce the ice shell thickness at low latitudes through melting, but also enhance the likelihood that an ice diapir will be generated at the base of the ice shell depending on the stability and heterogeneity of the heat flux.
Okay so if the ice thickness can be affected then is it possible that the plumes go up into space due to convection and not gravitational pull (indirectly)? Actually it is.
These plumes appear to be transient, appearing in seven hour sequences. While a day on Europa is 3.551( that is about 85 Earth hours) there doesn’t seem to be a correlation there, but the plumes do peak when Europa is at its furthest from Jupiter and calm the most when it comes its closest to Jupiter. In fact this would seem to indicate tidal acceleration is the culprit. Though personally I think both may be to blame ultimately. As the drops and shifts in the plates on the floors to the great oceans might combined with the heat that softens the ice to allow for the bursts of which some do occur at the equator though many occur at Europa’s pole (’they’ say at the South Pole).
Truth be told – maybe we actually need to hear from the Europa Clipper due to be in the neighborhood in 2030’s.
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