An article published in the “Journal of Geophysical Research” describes a research funded by NASA on the atmosphere of Io, one of the “Galilean” moons of Jupiter. A group of scientists led by Constantine Tsang of the Southwest Research Institute detected the changes taking place in the atmosphere of Io, noting how it collapses when it enters Jupiter’s shadow and the temperature drops.
Io is a unique moon due to the presence of more than 300 active volcanoes which make it the most geologically active celestial body of the entire solar system. This intense volcanic activity is caused by the gravitational forces acting on Io by Jupiter but also by the other Galilean moons. The result is a friction that generates a significant volcanic activity that produces an atmosphere, albeit thin, composed mainly of sulfur dioxide.
The volcanoes emit plumes of sulfur dioxide in gaseous form which may extend up to 480 kilometers (300 miles) above the surface of Io thanks to its reduced gravity in addition to basaltic lava that can flow for hundreds of kilometers. Sunlight isn’t very strong at that distance but is enough to maintain the atmosphere of Io in a gaseous state. However, when this moon enters Jupiter’s shadow the temperature drops to -148° Celsius to -168° Celsius (from -235° Fahrenheit to -270° Fahrenheit).
The observations in those conditions of darkness are difficult but the authors of this research did it. The key to this research consists of observations of the thermal radiation emitted by the atmosphere of Io and not the reflected sunlight. To accomplish this, the researchers used the Gemini North telescope in Hawaii and the TEXES (Texas Echelon Cross Echelle Spectrograph) instrument.
Every 1.7 days, Io enters Jupiter’s shadow and the subsequent eclipse lasts about two hours. During this period the temperature on the surface drops and the moment of total eclipse the atmosphere collapses into ice dropping on it. When Io is again hit by sunlight the temperature on its surface rises back up enough to cause the frozen sulfur dioxide’s sublimation restoring the gaseous atmosphere.
Scientists suspected the existence of this phenomenon but only it’s been possible to detect it directly. Now the continuous changes in the atmosphere of Io were confirmed with the observation of the correlation between the presence of sunlight on the surface and the state of the sulfur dioxide. This substance is produced by volcanoes but its temperature is determined by its exposure to sunlight.
A bit of sulfur dioxide emitted by Io’s volcanoes escape this moon’s gravity spreading in the Jovian system and contributing to some characteristics of the auroras visible at the planet’s poles. NASA’s Juno spacecraft reached the orbit of Jupiter on July 4 so this research will be useful to better understand what happens on Io but also for the Juno mission to study the planet.
