Whenever the moon crosses path with Earth and the sun, partially blocking the latter, we are usually in for a rare and spectacular treat. On Jupiter's moons, however, the effects of an eclipse can be quite frigid.
During eclipses, Jupiter casts a shadow on its volcanically active moon Io, resulting in an unprecedented kind of changes in the natural satellite's atmosphere.
Evidence taken by scientists from the Southwest Research Institute (SwRI) through the Gemini North telescope in Hawaii reveal that Io's atmosphere freezes and collapses whenever it is shaded by the gas giant.
The impact lasts for hours before the atmosphere goes back to normal.
Effects Of An Eclipse
The thin atmosphere on Io consists mainly of sulfur dioxide gas emitted from volcanoes.
So when Jupiter imposes its large shadow on the natural satellite, the thin atmosphere collapses as the sulfur dioxide gas freezes on the surface.
According to researchers, the atmosphere on Io begins to deflate when the temperatures plummet from -235 degrees Fahrenheit (-148.3 degrees Celsius) in sunlight to -270 degrees Fahrenheit (-168 degrees Celsius) during the eclipse.
During full eclipse, Io's atmosphere effectively collapses as most of the sulfur dioxide settles as frost on the surface.
But as soon as the Jupiter moon moves out of eclipse and returns in the sunlight, the affected atmosphere reforms and redevelops through a process called sublimation — the conversion of ice directly into gas.
This incredible Jupiter-Io eclipse typically lasts 2 hours of every Io day, which is equivalent to 1.7 Earth days.
SwRI scientist John Spencer says the findings confirm that the volcanic moon's atmosphere is in a constant state of collapse and repair. It suggests that a huge fraction of the atmosphere is supported by sublimation of sulfur dioxide ice.
Although the hyperactive volcanoes on Io are the main source of sulfur dioxide, sunlight affects the atmospheric pressure and controls the temperature of ice on the moon's surface.
"We've long suspected this," says Spencer. "But can finally watch it happen."
Breakthrough Findings
Constantine Tsang, lead author and senior research scientist at SwRI, says the research is the first to observe the Jupiter-Io eclipse directly.
In fact, prior to the study, no direct observation of the Jupiter moon's atmosphere has been made because it is difficult to glimpse in the darkness of the gas giant's shadow.
The research was possible thanks to TEXES or Texas Echelon Cross Echelle Spectrograph, which measured the atmosphere through heat radiation and not sunlight, as well as the Gemini telescope.
Details of the study are published in the Journal of Geophysical Research.
