Mysterious Rings on Jupiter’s Volcanic Moon Io

Mysterious Rings on Jupiter's Volcanic Moon Io

Mysterious Rings on Jupiter’s Volcanic Moon Io

As the most volcanic object in the solar system, Jupiter’s moon Io attracts a lot of attention. NASA’s Juno spacecraft arrived at the Jovian system on May 7, 2016, and has been focusing more on Io in recent months.

While Io’s internal mechanics are complex, Juno’s images and data are beginning to provide a more complete picture of this strange moon’s volcanic activity. Io’s extreme volcanic activity is attributed to tidal heating caused by Jupiter’s powerful gravity. Some of the moon’s volcanoes spew plumes of sulfur and sulfur dioxide as high as 500 km (300 miles) from its surface. Sulfur in the lava flows colors Io’s surface in different shades of yellow, red, white, green, and black. Some of these lava flows stretch up to 500 km (300 miles) along the surface, enticing scientists to study the moon more thoroughly.

One of Juno’s instruments, JIRAM (Jovian Infrared Auroral Mapper), was designed to map Jupiter’s auroras. However, with Juno’s orbit gradually approaching Io, JIRAM is providing high-quality images and data from the volcanic moon. A team of scientists has presented new insights about Io’s volcanic activity in a study titled “Hot Ring on Io Observed by Juno/JIRAM,” led by Alessandro Mura of the National Institute of Astrophysics and the Institute of Space Astrophysics and Planetary Sciences in Rome, Italy.

“We started close flybys of Io in December 2023 and February 2024,” said Scott Bolton, senior research scientist at Juno, Southwest Research Institute in San Antonio. “The observations show fascinating new information about Io’s volcanic processes. Combining these new results with Juno’s long-term campaign to monitor and map the volcanoes of the north and south poles, which have never been seen before, JIRAM has proven to be one of the most valuable tools to learn how this tortured world works.”

Io has many features called “paterae,” which are complex craters with irregular or scalloped edges. These wide and shallow craters may hold lava lakes. Earlier observations from NASA’s Galileo spacecraft were inconclusive, but new images from Juno and JIRAM offer much higher resolutions.

In 2023, Juno reached within 13,000 km (8,100 miles) of Io’s surface, allowing JIRAM to capture more details. These images show more details of the paterae, and the features suggest that many of the craters have active lava lakes. “This new Juno/JIRAM data suggests that hot rings around paterae are a common phenomenon, indicating active lava lakes,” the authors write.

Infrared images of Chors Patera, a lava lake on Io, show that the white ring is the hottest part of the patera, with temperatures between 232 and 732 degrees Celsius, where lava from the moon’s interior is exposed. The red/green inside the ring could be a thick crust of molten material at -43 degrees Celsius, while outside the patera, the temperature is about -143 degrees Celsius.

“With the high spatial resolution of JIRAM’s thermal images and Juno’s close flybys, we discovered that Io’s surface is covered with lava lakes contained in caldera-like features,” said lead author Alessandro Mura. “In the area of Io’s surface where we have the most complete data, we estimate that about 3% of it is covered by one of these lava lakes.”

There remain questions about the nature of Io’s volcanic activity and what happens underground. These new images will help provide answers.

The lava lakes have a thin ring of exposed lava. There are no lava flows beyond or within the rim, indicating a balance between magma erupting into the lake and magma returning underground. “We now understand that the most frequent type of volcanic activity on Io is a huge lava lake where magma goes up and down,” Mura said. “The lava crust is forced to hit the walls of the lake, forming a typical lava ring found in lava lakes in Hawaii. The wall’s height is probably a few hundred meters, which explains why magma is generally not observed spilling out of the patera and moving across the moon’s surface.”

The researchers proposed two different geological models to describe the lava lakes of Io’s paterae: the “central upwelling model” and the “piston model.”

The central upwelling model explains that the adiabatic crust radiates through the convection process of the lake, then sinks at the edges, exposing lava. The problem with this model is the uniformity of the magma crust, as JIRAM’s image shows uniform heat throughout the magma crust.

The piston model describes a simple up-and-down movement across the lake surface that causes the destruction of the lava lake’s crust against the patera wall. This model also has problems, as vertical motion must be in progress at all sites, but no depth changes in the patera have been reported.

Activity at the edge where lava is hottest may hold the final answer. “Observation of activity at the lake boundary raises the question of whether any thermal or mechanical erosion is taking place between the surface of the lake and the wall of the patera,” the authors said. While the patera can grow larger over time, it only grows a few hundred meters each year, and no changes were observed during the visits of Voyager, Galileo, and Juno.

The Juno spacecraft may provide a deeper understanding of Io’s volcanic activity. Closer flybys have already been completed, and the data will be available in the future.

“Once the last Juno data is obtained, it will be useful to examine visible images of inactive paterae for signs of activity in previous lava lakes,” the authors concluded.

Source: Mysterious Rings on Jupiter’s Volcanic Moon Io

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Mysterious Rings on Jupiter’s Volcanic Moon Io

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