Io: A new view of the solar system’s most explosive moon – 01/29/2023 – Science

Io, the third largest of Jupiter’s moons, is caught in an explosive, pressurized dance.

Orbiting close to Ganymede and Europa, two of the other largest Jovian moons, and the planet itself, Io’s mineral makeup is constantly pulled and pushed by gravity, creating frictional heat deep within the moon. This makes it extremely volcanically active—hundreds of volcanoes and extensive networks of lava flows dot Io’s surface.

“It’s being squeezed like an exercise ball,” said Jeff Morgenthaler, an astrophysicist at the Planetary Science Institute.

Despite a slew of spacecraft in recent decades — including the Voyager 1 and Galileo missions — as well as constant observation of Earth, there are long-standing mysteries about the type of volcanic activity on Io and how the moon’s fiery energy interacts with Jupiter and other nearby bodies.

Last year, Morgenthaler, who studies the gases Io emits and the cloud created by gases around Jupiter, noticed signs that a different kind of eruption was taking place — more powerful or more persistent.

“It’s an exciting observation,” said Ashley Davies, a planetary scientist and volcanologist at NASA’s Jet Propulsion Laboratory, who was not involved in Morgenthaler’s study. “It’s showing that Io is certainly one of the most energetic bodies in the solar system, and we have no idea what it will look like when we point the telescope at it.”

The observation could help guide future study of Io, including preparations for NASA’s Juno space probe, which has been orbiting Jupiter since 2016 and is scheduled to fly within a few hundred kilometers of the Jovian moon in December.

As Io is far from the Sun and has a very thin atmosphere, its surface averages around minus 130 °C and is coated with an icy layer of sulfuric substances. The volcanic eruptions there, which come in many different forms and intensities, can reach temperatures of nearly 1,400°C.

When superheat meets supercold, molecules like sulfur dioxide and sodium can be hurled into space. Some of the most explosive eruptions come from fissures in the surface and hurl fountains of lava half a mile into space. The charged molecules create what’s known as a “plasma torus” in Io’s wake: a tire-shaped cloud of ionized gas that collects in Jupiter’s magnetic field.

It is possible to look directly at Io’s volcanic hot spots with infrared telescopes. However, since 2017, Morgenthaler has taken a different approach, focusing on the moon’s plasma torus via the Io Input/Output (IoIO) observatory at the Institute of Planetary Sciences in Arizona. Instead of using infrared light, Morgenthaler uses IoIO to block Jupiter’s light and measure the gas around it.

Davies said that while infrared telescopes can tell us where volcanoes are erupting on Io and how powerful they might be, studying the plasma torus can tell us when an eruption is chemically rich — signaling that it might be more powerful, more persistent. or more peculiar. An eruption could push more ionized gas into the torus. Another could send too much neutral gas. “It doesn’t always happen, and it’s an interesting link,” Davies said.

In each year that Morgenthaler monitored volcanic activity using IoIO, he noticed some sort of increase in the concentration, or greater brightness, of gases in the plasma torus. These changes correlate with volcanic explosions, the intensity of which can be measured by the levels of sodium emitted by the moon. But from September to December 2022, after a massive volcanic explosion, he noticed that the torus contained far less sulfur dioxide than the size of the eruption would suggest. The torus was not as bright as it should have been.

This could mean that the eruption had a different chemical composition than the others, or that different types of minerals were disturbed. It would be like Washington State’s Mount St Helena, a steep stratovolcano that can erupt explosively, sending earth, rock and sodium into the atmosphere, rather than Hawaii’s Mauna Loa, a shield volcano. slope that erupts with liquid lava flows. Or it could mean that the torus was rapidly spreading in response to the intense eruption.

It’s primarily a call for more research, Morgenthaler said. “I’m just waving the flag and saying, ‘This happened,'” Morgenthaler said after announcing the observation this month.

Studying the anomaly could reveal, in more detail, the different types of volcanoes on Io, as well as interactions between the plasma torus and other large moons around Jupiter. However, much more data will have to be collected to link all the pieces together, including from other powerful telescopes on Earth, such as the James Webb Space Telescope, and also from the Juno space probe.

For now, for studying Io’s gases, Morgenthaler said his method, which is inexpensive and can be adapted by small research organizations and even some amateur astronomers, is often underused. But her work could open the door to similar, broader research that could provide data to help understand the Jovian system.

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

The fact that Morgenthaler’s most recent observation was made with widely available instruments opens up the possibility of further studies, both similar and different. “The more monitoring we can get the better,” Davies said.

^{Translated by Luiz Roberto M. Gonçalves}