LONGITUDINAL DISTRIBUTION OF ACTIVE PATERAE ON IO

Io is the most volcanically active planetary body in the solar system. Some of the most significant morphological features on Io associated with active volcanism are the paterae, which often contain large amounts of dark material on their basin floors indicating active volcanism. Around 400 of these paterae, with an average diameter of 41 km, pockmark the surface of Io (Radebaugh, 2001). They comprise about 2.5% of the entire surface area (Williams, 2008) making them significant in terms of global loss of heat. Black deposits are interpreted to be young silicate lava (Williams, 2002) that has not yet been covered by white SO2 frosts, and red deposits may be elemental sulfur emplaced as pyroclastic deposits. Thus, the age of activity can be determined on the basis of color. By color classifying these paterae based on amount of black deposits within their margins, we can discern where the active regions are now, and distinguish them from regions that have been in the recent past.

Of the paterae classified thus far, 30% show signs of active volcanism. Thirty-nine paterae have floors with >50% black material and 70 have <50% black material. Two hundred forty seven have no black deposits within their margins. The greatest numbers of all paterae are located between 330˚ and 0˚ longitude and between 210˚ and 180˚ longitude. The number of active paterae varies directly with the number of inactive paterae. Those paterae with any activity are dominantly found at the regions centered on 330˚ and 135˚ longitude. The number of active paterae varies in concert with the total number of paterae found in that longitudinal region. This implies that the number of active paterae is related to tidal flexing just as the total number is. Finally, preliminary analyses indicate that the total number of paterae is similar in both the sub- and anti- jovian hemispheres of the moon, but there are more active paterae on the anti-jovian hemisphere by ~37%.