QUOTE (karolp @ Dec 23 2006, 07:42 AM)
From what I see Baumgardner's composite images show the "unknown" hemisphere to be even more Moon-like with a rayed crater and a large "mare"-like structure. Is it possible that Solar tides have induced lava outflows which formed Mercurian "maria" just like those on the "near" side of the Moon? Did Mariner 10 photograph the "near" (facing Sun) or "far" side of Mercury?
Mercury isn't locked to the Sun in the same way that the Moon is to the Earth, so it would be surprising if the difference between hemispheres is as striking; the mass imbalance between lunar hemispheres probably helped the Moon achieve its tidal lock.
Mercury has a 3:2 ratio between its day & year, which means that the planet completes three sidereal rotations for every two orbits. Might this argue for relatively uniform mass distribution, and/or could this be a side effect of the planet's liquid core?