A New View of the Most Explosive Moon in the Solar System


Each year Dr. Morgenthaler has monitored volcanic activity through IoIO, he has noticed some kind of increased concentration, or brightening, of gases in the plasma torus. These changes correlate with volcanic outbursts, the intensities of which can be measured by the levels of sodium emitted from the moon. But, in September through December 2022, after a large volcanic outburst, he noticed that the torus contained much less sulfur dioxide than the size of the eruption would suggest. The torus wasn’t as bright as it should have been.

This could mean that the eruption had a different chemical composition from the others, or that different kinds of minerals had been disturbed. It would be like Mount St. Helens, a steep stratovolcano that can erupt explosively, sending dirt, rock and sodium into the atmosphere, erupting on Earth, rather than Mauna Loa, a gently-sloped shield volcano that erupts with liquid lava flows. Or it could mean that the torus was rapidly diffusing in response to the intense eruption.

More than anything, Dr. Morgenthaler said, it is a call for more research.

“I’m just raising the flag, and saying, ‘This has happened,’” Dr. Morgenthaler said after announcing the observation this month.

Studying the anomaly might draw out, in better detail, the different kinds of volcanoes on Io, as well as the interactions between the plasma torus and other massive moons around Jupiter. However, much more data will have to be gathered to put all the pieces together, including from other powerful telescopes on Earth, like the James Webb Space Telescope as well as from the Juno space probe.

For the moment, to study gases from Io, Dr. Morgenthaler said that his method, which is cheap and could be adapted by small research organizations and even some backyard astronomers, is often underutilized. But his work may open the door for similar and widespread research that could provide data to help understand the Jovian system.

Dr. Davies said that this kind of piecemeal research is integral to understanding Io. “You can think of it like looking at different parts of an elephant,” he said.

The fact that Dr. Morgenthaler’s most recent observation was made with largely accessible instruments opens the possibility of more studies, similar and different, in kind. “The more monitoring we can get, the better it will be,” said Dr. Davies.