Changes

Io is more dense even than Earth's Moon and in fact is more dense than any other satellite of Jupiter (or any other planet).<ref name=ssdphys/> For that reason, and taking into account mass-concentration and other findings from flybys of all the Galilean satellites, Io is ''not'' suspected of having an underground saltwater ocean. Instead, it likely has a metal core of [[iron]] and/or [[iron sulfide]]. According to the best model available so far, the radius of this core likely extends to half the total radius of Io itself. Surrounding this would be a partially molten silicate-rich mantle with a thin rocky surface crust.<ref name=solarviews/><ref name=Anderson>Anderson, J. D.; ''et al''. "Galileo Gravity Results and the Internal Structure of Io". ''Science'' 272:709–712, 1996.</ref>

Io is more dense even than Earth's Moon and in fact is more dense than any other satellite of Jupiter (or any other planet).<ref name=ssdphys/> For that reason, and taking into account mass-concentration and other findings from flybys of all the Galilean satellites, Io is ''not'' suspected of having an underground saltwater ocean. Instead, it likely has a metal core of [[iron]] and/or [[iron sulfide]]. According to the best model available so far, the radius of this core likely extends to half the total radius of Io itself. Surrounding this would be a partially molten silicate-rich mantle with a thin rocky surface crust.<ref name=solarviews/><ref name=Anderson>Anderson, J. D.; ''et al''. "Galileo Gravity Results and the Internal Structure of Io". ''Science'' 272:709–712, 1996.</ref>

The marked difference between Io's interior and those of its three outer counterparts has not gone unremarked. [[Uniformitarianism|uniformitarian]] thinkers suggest that Jupiter was at its hottest early in its initial accretion, and that lighter [[element]]s and [[compound]]s would not have been able to accrete as close to Jupiter as Io's orbit was. In this scenario, Jupiter is held to be the center of a "mini-solar system" with heavier elements and compounds accreting inward and lighter substances accreting outward.<ref name=solarviews/><ref name=Harmsworth>The concept of Jupiter as a proto-[[star]] that somehow failed to ignite is fairly widely held. This model states that Jupiter, composed as it is of [[hydrogen]] and [[helium]], would have ignited had it been sufficiently massive. But in that event, life on [[Earth]] could never have developed. See Harmsworth, Andrew, "[http://www.harmsy.freeuk.com/jupiter.html Entry for Jupiter]," ''Spacetech's Orrery: the Solar Sytem in Action'', last update July 2, 2007. Accessed February 18, 2008.</ref>

The marked difference between Io's interior and those of its three outer counterparts has not gone unremarked. [[Uniformitarianism|Uniformitarian]] thinkers suggest that Jupiter was at its hottest early in its initial accretion, and that lighter [[element]]s and [[compound]]s would not have been able to accrete as close to Jupiter as Io's orbit was. In this scenario, Jupiter is held to be the center of a "mini-solar system" with heavier elements and compounds accreting inward and lighter substances accreting outward.<ref name=solarviews/><ref name=Harmsworth>The concept of Jupiter as a proto-[[star]] that somehow failed to ignite is fairly widely held. This model states that Jupiter, composed as it is of [[hydrogen]] and [[helium]], would have ignited had it been sufficiently massive. But in that event, life on [[Earth]] could never have developed. See Harmsworth, Andrew, "[http://www.harmsy.freeuk.com/jupiter.html Entry for Jupiter]," ''Spacetech's Orrery: the Solar Sytem in Action'', last update July 2, 2007. Accessed February 18, 2008.</ref>

=== Volcanism ===

=== Volcanism ===