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| color=Yellow
| color=Yellow
| albedo=0.63<ref name=ssdphys/>
| albedo=0.63<ref name=ssdphys/>
| mfd=0.013 G<ref name=Kevelson>M. G. Kivelson, K. K. Khurana, R. J. Walker, C. T. Russell,
J. A. Linker, D. J. Southwood, C. Polanskey. "[http://www.igpp.ucla.edu/galileo/doc/sci273/text.htm A Magnetic Signature at Io: Initial Report from the Galileo Magnetometer]." Galileo Magnetometer Team Site, October 27, 2000. Accessed May 12, 2008.</ref>
| pmdm=7.86 * 10<sup>19</sup> N-m/T<ref name=calc/><ref name=Kevelson/>
| cmdm=2.10 * 10<sup>22</sup> N-m/T<ref name=calc/>
| mdt=1098.14 a<ref name=calc/>
| mhl=761.17 a<ref name=calc/>
}}'''Io''' is the innermost of the [[Galilean moons]] of [[Jupiter]]. It is the most [[volcano| volcanically]] active object in the [[solar system]] and the most dense of all [[planet]]ary satellites. Io was named for an Argive princess and priestess of [[Hera]] who became a fairly prominent mistress of [[Zeus]], after much suffering. That name, assigned quite by accident in the seventeenth century, might be quite apt today in view of Io's volcanic activity and the likely reason for it.
}}'''Io''' is the innermost of the [[Galilean moons]] of [[Jupiter]]. It is the most [[volcano| volcanically]] active object in the [[solar system]] and the most dense of all [[planet]]ary satellites. Io was named for an Argive princess and priestess of [[Hera]] who became a fairly prominent mistress of [[Zeus]], after much suffering. That name, assigned quite by accident in the seventeenth century, might be quite apt today in view of Io's volcanic activity and the likely reason for it.
=== Interior ===
=== Interior ===
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>
Further evidence that Io has an iron core comes from magnetometric measurements taken by Galileo. The magnetic flux density at Io's equator is about 13 milligauss<ref name=Kevelson/>. This corresponds to a magnetic dipole moment of 7.86 * 10<sup>19</sup> N-m/T. Considering Io's mass, Io likely had a magnetic dipole moment ''at creation'' of 2.1 * 10<sup>22</sup> N-m/T, according to [[Russell Humphreys]]' model for the creation of celestial magnetic fields.<ref name=Humphreys>Humphreys, D. R. "[http://www.creationresearch.org/crsq/articles/21/21_3/21_3.html The Creation of Planetary Magnetic Fields]." ''[[Creation Research Society Quarterly]]'' 21(3), December 1984. Accessed April 29, 2008.</ref> This in turn suggests a decay time of 1098 Julian years and a half-life of 761 Julian years. The corresponding decay time and half-life of the magnetic field of [[Ganymede]] agrees with this to within four significant digits, and suggests that both satellites have comparable core radii and conductivities.
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>