Distribution of Io's volcanoes: Possible influence on spin axis

[1] We examine the potential effect of volcano distribution on the orientation of Io's spin axis. Volcanoes dominate Io's surface and the massive outpourings documented in short intervals could cause instability in Io's rotation and a corresponding reorientation of its spin axis. Currently, the volcanoes and mountains exhibit a complementary distribution, with the maximum principal axis for the set of 351 volcanoes close to the position of the rotation axis. In addition, a delicate balance results from the near equivalence of the magnitudes of the maximum and intermediate eigenvalues. Assuming an otherwise homogeneous body, a changing mass distribution on its surface could control the location of the spin axis. In our models, changing the location of as few as three volcanoes is sufficient to cause dramatic shifts of the principal axis positions, and hence the spin axis orientation. This result, although somewhat diminished, still prevails even when a strong influence of Io's tidal bulge is included in the model.