The most volcanically active object ever observed in the solar system is Io. Its massive and sustained eruptions, extensive lava flows, and huge lava lakes are more substantial than any on Earth and have led researchers to wonder: Has Io always been that way? The question is hard to answer because its surface is constantly changing. In just a million years—which is short by geological standards—Io’s entire surface has been repaved by volcanic deposits, destroying craters and other evidence of geologic history over its 4.5-billion-year existence.
Now Katherine de Kleer of Caltech and colleagues have developed a way to study Io’s volcanic history by tracking its sulfur. With new isotope evidence and geochemical modeling, they found that Io’s volcanism was likely even more pronounced in the past and may have been present over the moon’s entire history.
The researchers observed sulfur gases in Io’s atmosphere with the Atacama Large Millimeter/Submillimeter...
