An article accepted for publication in “The Planetary Science Journal” reports a study on Io, one of Jupiter’s satellites, which specifically concerns its volcanoes. A team of researchers led by astronomer Imke de Pater of the University of Berkeley, USA, used the ALMA radio telescope to examine Io’s atmosphere as it enters and leaves Jupiter’s shadow, a phenomenon called an eclipse. That’s because during an eclipse it receives no sunlight, temperatures drop to the point that only the sulfur dioxide emitted by volcanoes is warm enough not to solidify. The conclusion is that between 30% and 40% of Io’s atmosphere is generated by volcanic activity. The researchers also found that some volcanoes emit not sulfur compounds but potassium chloride.
Io is the innermost of Jupiter’s great moons and one of the largest moons in the solar system. Its characteristics are heavily influenced by its proximity to the gas giant planet, which generates considerable tidal warming. The consequence is a strong geological activity that occurs mainly in the form of volcanism. There are now over 400 active volcanoes identified on Io and the gases they emit are above all sulfur compounds such as sulfur dioxide and sulfur monoxide. They contribute to the atmosphere existing on this moon, which is very thin but still an atmosphere, which can be studied to better understand the processes taking place.
Under the conditions existing on Io, sulfur compounds can be solid, but when those ices are exposed to direct sunlight they can sublimate and turn into gas. This makes it difficult to understand how much of those gases have that origin and how much is emitted by active volcanoes. To get an answer, Imke de Pater’s team examined Io using the ALMA (Atacama Large Millimeter/submillimeter Array) radio telescope, inaugurated in March 2013. ALMA is mainly used to observe very distant objects and was used in this case because it can detect the emissions of the various compounds in the atmosphere of an astronomically close object such as Io.
The researchers conducted the observations of Io entering and exiting Jupiter’s shadow cone. Between the two events, Io is in eclipse and receives no direct sunlight that can sublimate the sulfur compounds and the ones in their gaseous state condense and fall on the surface. This means that the only emissions present in this moon’s atmosphere are those generated by volcanoes. The measurements also indicated the presence of potassium chloride, which is interesting because it means that the magma of the various volcanoes has a different composition. The overall result is that between 30% and 40% of Io’s atmosphere is produced by its volcanoes.
The image (ALMA (ESO/NAOJ/NRAO), I. de Pater et al.; NRAO/AUI NSF, S. Dagnello; NASA/JPL/Space Science Institute) shows a composition of Io at radio frequencies detected by the ALMA radio telescope and at optical frequencies detected by NASA’s Voyager 1 and Galileo space probes. The planet Jupiter is shown in the background in an image captured by the Cassini space probe.
Io is interesting from a geological point of view for the number of active volcanoes, but the researchers intend to continue their studies by focusing on the atmosphere as well. They will need even higher resolution images, and this will require longer observations with the ALMA radio telescope. It will take a long time, but the researchers are hoping to uncover the details of the processes taking place on this very active moon.
