Discovery of Volcanic Activity on Io. A Historical Review

TL;DR

This paper recounts the historic discovery of volcanic activity on Io by Voyager 1, highlighting the process of image analysis and scientific observation that confirmed Io's active volcanism beyond Earth.

Contribution

It provides a detailed historical account of the first identification of volcanic plumes on Io through Voyager 1 imagery, emphasizing the discovery process and scientific context.

Findings

First evidence of active volcanism on Io identified in Voyager images

Volcanic plumes observed off the limb of Io four days after Voyager encounter

Image processing techniques confirmed volcanic activity

Abstract

In the 2 March 1979 issue of Science 203 S. J. Peale, P. Cassen and R. T. Reynolds published their paper "Melting of Io by tidal dissipation" indicating "the dissipation of tidal energy in Jupiter's moon Io is likely to have melted a major fraction of the mass." The conclusion of their paper was that "consequences of a largely molten interior may be evident in pictures of Io's surface returned by Voyager 1." Just three days after that, the Voyager 1 spacecraft would pass within 0.3 Jupiter radii of Io. The Jet Propulsion Laboratory navigation team's orbit estimation program as well as the team members themselves performed flawlessly. In regards to the optical navigation component image extraction of satellite centers in Voyager pictures taken for optical navigation at Jupiter rms post fit residuals were less than 0.25 pixels. The cognizant engineer of the Optical Navigation Image Processing System was astronomer Linda Morabito. Four days after the Voyager 1 encounter with Jupiter, after preforming image processing on a picture of Io taken by the spacecraft the day before, something anomalous emerged off the limb of Io. This historical review written by the discoverer recounts her minute-by-minute quest to identify what was a volcanic plume, the first evidence of active volcanism seen beyond Earth. Many ingredients of the account reflect historic themes in the process of scientific discovery.