Jupiter’s Moon Io ‘Collapses’ During Eclipse

Scientists have documented for the first time the atmospheric "collapse" in Jupiter's moon Io during an eclipse.

Astronomers from the Southwest Research Institute (SwRI) in Boulder, Colorado have observed that the thin atmosphere on Io, Jupiter's volcanic moon, becomes frozen when the moon is shaded by the giant planet during daily eclipses.

"This research is the first time scientists have observed this phenomenon directly, improving our understanding of this geologically active moon," Constantine Tsang, senior research scientist in SwRI's Space Science and Engineering Division and study author, said in a press release.

Io's atmosphere consists primarily of sulfur dioxide (SO2) gas emitted by volcanoes. When Jupiter casts its shadow on the moon during an eclipse, the SO2 freezes on the surface as ice. According to the data, the atmosphere "deflates" when temperatures drop from -235 degrees Fahrenheit in sunlight to -270 degrees Fahrenheit during an eclipse.

Io remains in the dark for about 2 hours of each day, which is about 1.7 Earth days. But when the moon moves out of the eclipse, the ice warms and converts directly to gas.

"This confirms that Io's atmosphere is in a constant state of collapse and repair, and shows that a large fraction of the atmosphere is supported by sublimation of SO₂ ice," John Spencer from SwRI and co-author of the study, said in a statement.

"Though Io's hyperactive volcanoes are the ultimate source of the SO₂, sunlight controls the atmospheric pressure on a daily basis by controlling the temperature of the ice on the surface. We've long suspected this, but can finally watch it happen."

Io is the most volcanically active body in the solar system. Its volcanic activity is caused by tidal heating, which is a result of Jupiter's gravitational pull. Io's volcanoes spew large quantities of SO2 gas that can rise up to 300 miles above the moon's surface.

According to the astronomers, there had been no direct observations of Io's atmosphere prior to the study, as it was difficult to observe the moon in the darkness of Jupiter's shadow.

But scientists were able to make observations using the large Gemini North telescope, which could sense the faint heat signature of Io's collapsing atmosphere, and the Texas Echelon Cross Echelle Spectrograph (TEXES), which enabled the astronomers to measure the heat radiation from the moon.

The scientists made their observations of Io over two nights in November 2013, when Io was more than 420 million miles from Earth.