(Henry Spencer) wrote in message ...
In article ,
Pat Flannery wrote:
You know NASA keeps claiming that Galileo was responsible for the
subsurface ocean on Europa idea; this is not the case...the first time
that good images of Europa were received from the Voyager probes, its
relatively crater free surface was noticed and speculation started on it
having a subsurface ocean.

Believe it or not, speculation about a subsurface ocean in Europa started
*before* the Voyager images. If (dim) memory serves, the same guys who
predicted volcanic activity on Io had a paper in press at the time of the
Voyager encounter, suggesting that tidal heating might produce an internal
ocean in Europa.

The waters within the Galileans even predates Pearle, Yoder and
Cassen's predictions on tidal heating. In the mid seventies an
undergraduate project/masters thesis by Guy Consolmagno demonstrated
that radioactivity was enough to cause interior melting.

Interesting, Cassen et al was forced to do a partial recall of the
Europa work soon after Voyager- there appears to be a very strong
positive feedback between shell thickness and tidal heating, so if
Europa's ocean ever started to freeze over, in theory you would never
get the ocean back.

Whether the ocean penetrates the shell is very controversial - the
Europa session at the Lunar and Planetary Science Conference is always
good for a fight these days. There is a strongly polarized division
into "thin-icers" who think the fractures go all the way to the
ice-liquid interface and the we a seeing a surface in geological
equilibrium; and "thick-icers" who say you can get most of the geology
through solid state convection of an unbreached ice crust over an
ocean, and that we are seeing a progression in geological style over
time. The astrobiologists prefer the first, the traditional geological
mapping crowd prefer the second; I think they are talking past each
other.

At the end of one particularly testy session a couple of years back, a
third party stood up and asked the main "thin-icer" and the main
"thick-icer" how thick they thought the shell actually was; both said
about 20 kilometers.

Which goes to show how important semantics are in a data limited
environment.

Bring on JIMO! (Jupiter Icy Moons Orbiter; not Oberg...)
Cheers,
Duncan