Atmospheric Isotopes Reveal 4.5 Billion Years Of Volcanism On Io

Sulfur and chlorine isotopes in the atmosphere of Jupiter’s moon Io indicate that it has been volcanically active for the entire 4.57 billion-year history of the Solar System, according to a new study. The findings offer new insights into the moon’s history.

Io is the most volcanically active body in the Solar System. This extreme level of volcanic activity is the result of tidal heating from friction generated within the moon’s interior as it is pulled between Jupiter and its neighboring moons of Europa and Ganymede. However, how long Io has hosted such extensive volcanism isn’t fully understood.

Due to the moon’s current level of volcanic activity, the surface of Io is constantly being reworked, leaving a geological record of only the most recent million years of its history. Stable isotopic measurements of volatile elements in Io’s atmosphere could provide information on the history of volcanism on Io.

Katherine de Kleer and colleagues used the Atacama Large Millimeter/submillimeter Array (ALMA) to observe the gasses in Io’s tenuous atmosphere and determine the stable isotopic radios of sulfer- and chlorine-bearing molecules. de Kleer et al. found that both elements are highly enriched in heavy isotopes compared to average Solar System values due to the loss of lighter isotopes from the upper atmosphere as material is continuously recycled between Io’s interior and atmosphere. The findings indicate that Io has lost 94% to 99% of the sulfur that undergoes this outgassing and recycling process. According to the authors, this would require Io to have had its current level of volcanic activity for its entire lifetime.

Observed distributions of molecular emission lines from Io. Each panel shows an image extracted from the ALMA data cube for (A to H) the leading hemisphere and (I to P) the trailing hemisphere. For each species (labeled above each panel) we show the strongest detected line, on different intensity scales (color bars). Figures S1 and S2 show equivalent images for all measured lines. The dotted white circles indicate the size and location of Io, and the arrows indicate the north pole, sub-jovian and anti-jovian directions as labeled. The white ellipses in the lower left corners indicate the size, shape and orientation of the reconstructed ALMA beam (the spatial resolution). For NaCl and KCl, we interpret the discrete locations of gas emissions as plumes. Specific plumes are numbered in panels E and M; our identifications of the associated surface features are listed in table S4. All panels are on the same angular scale as Panel A, shown as RA and Dec offsets from the center of Io (Δ RA and Δ Dec, respectively).

Isotopic evidence of long-lived volcanism on Io, Science (open access)

Astrobiology