Io’s Where to Go When the Volcano Blows

Seething Io
Credit: Southwest Research Insititute

While NASA’s Juno spacecraft is just getting settled in for its stay in orbit around the solar system’s largest planet, a new study based on information from ground based instruments sheds light on how Jupiter’s gravity and shadow affect one of its moons.

Perhaps one of the most tortured bodies in the solar system, Io’s interior is constantly being kneaded by tidal heating as a result of the gravitational tug of war between the forces imposed by the massive world below as well as its other moons.

The result is a moon wracked by constant volcanic eruptions as vast plumes of sulfur dioxide (SO₂) are sent skyward. As a result, Io’s thin atmosphere is kept in fresh supply. What happens next is the subject of the study, which comes from the Southwest Research Institute in Boulder, Co.

From the SWRI Press Release:

“Data showed that Io’s atmosphere begins to “deflate” when the temperatures drop from -235 degrees Fahrenheit in sunlight to -270 degrees Fahrenheit during eclipse. Eclipse occurs 2 hours of every Io day (1.7 Earth days). In full eclipse, the atmosphere effectively collapses as most of the SO₂ gas settles as frost on the moon’s surface. The atmosphere redevelops as the surface warms once the moon returns to full sunlight.

“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,” said John Spencer, an SwRI scientist who also participated in the study. “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.”

Prior to the study, no direct observations of Io’s atmosphere in eclipse had been possible because Io’s atmosphere is difficult to observe in the darkness of Jupiter’s shadow. This breakthrough was possible because TEXES measures the atmosphere using heat radiation, not sunlight, and the giant Gemini telescope can sense the faint heat signature of Io’s collapsing atmosphere.”

Comment: It is interesting to note, as the release later points out, that the observations leading to the new findings were recorded over the span of just two nights in November 2013, as Earth based instruments were trained on the small world some 420 million miles away. Amazing what science can be performed in the relative blink of an eye, even when it is focused on something so far away.

And to think, Jimmy Buffet couldn’t find a way to work Io into what has to be the music world’s best known song about about a volcano, even though it rhymes with the tag line. Perhaps it is because SO2 ice makes for lousy margaritas.