Io is the most geologically active celestial body in the solar system. It has over 400 active volcanoes. Such activity is due to periodic heating of the satellite’s interior due to tidal gravitational effects from Jupiter and its other satellites – Europa and Ganymede. In some volcanoes, ejections are so strong that they rise to a height of up to 500 kilometers and are visible from Earth, but only through powerful telescopes.
Image Source: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM
Unlike most moons in the outer solar system, which are mostly water ice, Io is made mostly of silicon surrounding a molten core of iron and sulfur. Constantly active volcanoes give Io’s surface its unique features. Volcanic ash and lava flows constantly change the surface and paint it in various shades of yellow, white, red, black and green. Volcanic ejecta create Io’s thin, uneven atmosphere and leave traces in Jupiter’s magnetosphere, including a huge glowing plasma torus, a donut-shaped cloud that surrounds the moon.
Last year, Dr. Jeff Morgenthaler, who studies Io’s volcanic activity, found signs of a different type of eruption, either larger or longer. “This is a breathtaking observation., said Ashley Davies, NASA planetary and volcanologist. — This shows that Io is certainly one of the most volatile celestial bodies in the solar system, so it’s impossible to predict what it will look like when you point your telescope at it once more.”.
NASA’s Juno space probe, which has been in orbit around Jupiter since 2016 and is due to fly just 300 km from Io this December, might be of great help in further studying Io.
Because Io is far from the Sun and has a very thin atmosphere, its surface temperature averages around -93°C and is covered in a frosty layer of sulfur compounds. The products of volcanic eruptions, which come in many forms and intensities, can reach temperatures up to 1370 °C. When superheated lava comes into contact with sulphurous ice, explosive eruptions from cracks in the surface occur, and lava fountains are thrown into space for almost a kilometer.
Starting in 2017, Dr. Morgenthaler took a new approach, focusing on studying the plasma torus around Io at the I/O Observatory (IoIO) at the Planetary Science Institute in Arizona. While infrared telescopes show volcanic eruptions on Io, the study of the plasma torus around the moon provides insight into the chemical composition of erupted gases.
For several years, Morgenthaler tracked volcanic activity using IoIO and noted moments of increased concentration or color change of gases in the plasma torus. These changes correlate with volcanic eruptions, the intensity of which can be measured by the levels of sodium emitted from Io. But from September to December 2022, following a major volcanic eruption, he noticed that the torus contains much less sulfur dioxide than the size of the eruption would suggest. Thor was not as bright as expected.
This might mean that the chemical composition of the eruption was different from the others, that is, there was a release of substances with a different chemical composition. Studying the anomaly might reveal in more detail the different types of volcanoes on Io, as well as interactions between the plasma torus and other massive moons of Jupiter. However, to put it all together, much more data will need to be collected, including from other powerful telescopes on Earth such as the James Webb Space Telescope and from spacecraft such as NASA’s Juno probe.
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