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PSI’s Julie Rathbun Continues Investigation of Volcano on Jupiter’s Moon Io

loki eruption schedule

Above, each point on the figure is from a single night of observing. It gives the total brightness of the Loki volcano. . The square wave in the background is a fit to the recent eruptions. We’d expected Loki to get bright at around the time that square wave goes up (around September/October 2019). As you can see, the line goes up, but the data points stay low, so it shows that Loki did not erupt when expected. 


Last year, PSI’s Julie Rathbun predicted that the next eruption of the Solar System’s most powerful volcano Loki, found on Jupiter’s moon Io, would occur in the Fall of 2019. Starting with an observing run in mid-September, she anxiously hoped for the telltale increase in Loki’s brightness that would mean an eruption. But she saw a dim Loki on September 11 and 27, and again on October 13 and 29. That was the last observing run of the year because Jupiter is now too close to the Sun to make observations. 

She expected an eruption based on the recent eruption schedule. When measuring Loki’s total brightness, sometimes it is pretty dim, indicating it is not erupting, and sometimes it is bright, indicating a current eruption. Since 2013, Loki eruptions have begun approximately every 475 days. 

The lack of Loki erupting on schedule suggests that either Loki’s periodicity has changed, perhaps lengthening, or that it has again entered a phase without periodicity. Either way, Loki misbehaving is not surprising. In 2002, after Rathbun published a paper on Loki’s first 540-day periodicity, Loki stopped erupting periodically. The eruptions started back up again around 2013 and continued through 2019. We might again be in a phase without periodic eruptions. Or Loki may have erupted after the last observation of 2019. We will know more when observations start up again in February.

Jan. 19, 2020
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