William B. McKinnon proposed that Io may be a bizarre analog of Europa -- with a deep subsurface ocean not of liquid water or soft ice but of magma (underground lava), in which blocks of hardened surface material can crack apart and then, while floating on the magma sea, tilt and tumble into new attitudes like the "icebergs" that Galileo photographed jutting out of Europa's patches of "chaotic terrain".

"The ultimate result at Io is similar: tilted, thermally eroded rockbergs, only now the presumably heavily disrupted crust (the Io 'matrix') is covered with fresh silicate and sulfur" lava flows -- which have covered all but a few small patches of Io's own great areas of "chaotic terrain".

Finally, the erosion of Io's tall mountains is as puzzling as their formation -- Galileo's close up photos confirmed that they are flanked by debris from great landslides down their slopes, and the edges of some of them show a puzzling "scalloped" pattern that has been referred to as "amphitheaters". These formations are quite clearly visible at the edges of the mesas in Galileo's famous photo of the Tvashtar eruption. James M. Moore and E.P. Turtle suggested that it is due to the fact that the mountains' rock is riddled with deposits of sulfur dioxide and hydrogen sulfide, which gradually vent into space and leave the loosened rocks to crumble and slide down the slopes -- but there is still debate over the details.

Everyone at the Conference is eagerly awaiting the new photos and other data from the February flyby, which may resolve many of the remaining Ionian mysteries.

Hydrogen deposits detected at the Moon's poles by Lunar Prospector are nothing more than hydrogen from the solar wind

Back To The Moon
There was also intriguing news from the Moon, with debate still raging over whether ice as been proven beyond doubt to exist in permanently shadowed craters at the lunar poles.

D.H. Crider and L.V. Starukhina still hold out for the idea that the hydrogen deposits detected at the Moon's poles by Lunar Prospector are nothing more than hydrogen from the solar wind, chemically deposited in the cold rocks of the shadowed areas over billions of years -- and that the radar-bright areas detected at the poles of the Moon and Mercury may be nothing more dramatic than cold, and thus radar-reflective, rock.

And R.A. Simpson repeated his skepticism that the indirect and rather insensitive radar experiment on the "Clementine" spacecraft detected any radar-bright patches at the Moon's poles at all.

Harrison Schmitt agrees with this, at least where the Moon (though not necessarily Mercury) is concerned.

Despite his status as the only scientist ever to actually visit the Moon, he describes himself as a "contrarian" both on the subject of lunar water and on the now strongly-favored theory that the Moon was formed out of debris from the collision of an ancient planet with the Earth: he still believes that the Moon itself is that ancient planet, which drifted close enough to Earth to be gravitationally captured by it.

Lunar Farside: This projection is centered at 0 degree latitude and 180 degrees longitude. Mare Moscoviense (dark albedo feature upper left of image center) and South Pole-Aitken Basin (dark feature at bottom) represent maria regions largely absent on the lunar farside. The Clementine altimeter showed Aitken Basin to consist of a topographic rim about 2500 km in diameter, an inner shelf ranging from 400 to 600 km in width, and an irregular depressed floor about 12 km in depth.

Another remaining major puzzle about the Moon is the obvious question: why are there almost no dark lava "maria" on its far side?

The natural assumption would seem to be that something about the Earth's tidal tuggings made the crust thinner on that side, so that the gigantic meteorite impacts that hit the Moon during the Solar System's early days could more easily punch through the crust on that side and release floods of darker underlying lava.

But this idea has fallen into disfavor, to be replaced by the idea that the pattern is actually the result of chance events (like the similar difference between the northern and southern hemispheres of Mars).