From Gemini: “Gemini Tracks Collapse of Io’s Atmosphere During Frigid Eclipses”


Gemini Observatory
Gemini Observatory

August 1, 2016
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Artist’s concept of the atmospheric collapse of Jupiter’s volcanic moon Io, which is eclipsed by Jupiter for two hours of each day (1.7 Earth days). The resulting temperature drop freezes sulfur dioxide gas, causing the atmosphere to “deflate,” as seen in the shadowed area on the left. Credits: SwRI/Andrew Blanchard.

Gemini observations show that the thin atmosphere of Jupiter’s moon Io undergoes dramatic changes during frequent eclipses with the giant planet. The following press release, issued by the Southwest Research Institute, explains how the dramatic changes in temperature cause the moon’s atmosphere to collapse.

SwRI Space Scientists Observe Io’s Atmospheric Collapse During Eclipse

A Southwest Research Institute-led team has documented atmospheric changes on Io, Jupiter’s volcanically active satellite, as the giant planet casts its shadow over the moon’s surface during daily eclipses.

A study led by SwRI’s Constantine Tsang concluded that Io’s thin atmosphere, which consists primarily of sulfur dioxide (SO2) gas emitted from volcanoes, collapses as the SO2 freezes onto the surface as ice when Io is shaded by Jupiter. When the moon moves out of eclipse and ice warms, the atmosphere reforms through sublimation, where ice converts directly to gas.

“This research is the first time scientists have observed this phenomenon directly, improving our understanding of this geologically active moon,” said Tsang, a senior research scientist in SwRI’s Space Science and Engineering Division.

The findings were published in a study titled The Collapse of Io’s Primary Atmosphere in Jupiter Eclipse in the Journal of Geophysical Research. The team used the eight-meter Gemini North telescope in Hawai’i with the Texas Echelon Cross Echelle Spectrograph (TEXES) for this research.

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.

Tsang and Spencer’s observations occurred over two nights in November 2013, when Io was more than 420 million miles from Earth. On both occasions, Io was observed moving in and out of Jupiter’s shadow, for a period about 40 minutes before and after eclipse.

Io is the most volcanically active object in the solar system. Tidal heating, the result of Io’s gravitational interaction with Jupiter, drives the moon’s volcanic activity. Io’s volcanoes emit umbrella-like plumes of SO2 gas extending up to 300 miles above the moon’s surface and produce extensive basaltic lava fields that can flow for hundreds of miles.

This study is also timely given that NASA’s Juno spacecraft entered Jupiter orbit on July 4th. “Io spews out gases that eventually fill the Jupiter system, ultimately seeding some of the auroral features seen at Jupiter’s poles,” Tsang said. “Understanding how these emissions from Io are controlled will help paint a better picture of the Jupiter system.”

For more information, contact Robert Crowe, (210) 522-4630, Communications Department, Southwest Research Institute, PO Drawer 28510, San Antonio, TX 78228-0510.

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Gemini North
Gemini North, Hawai’i

Gemini South
Gemini South, Chile

Gemini’s mission is to advance our knowledge of the Universe by providing the international Gemini Community with forefront access to the entire sky.

The Gemini Observatory is an international collaboration with two identical 8-meter telescopes. The Frederick C. Gillett Gemini Telescope is located on Mauna Kea, Hawai’i (Gemini North) and the other telescope on Cerro Pachón in central Chile (Gemini South); together the twin telescopes provide full coverage over both hemispheres of the sky. The telescopes incorporate technologies that allow large, relatively thin mirrors, under active control, to collect and focus both visible and infrared radiation from space.

The Gemini Observatory provides the astronomical communities in six partner countries with state-of-the-art astronomical facilities that allocate observing time in proportion to each country’s contribution. In addition to financial support, each country also contributes significant scientific and technical resources. The national research agencies that form the Gemini partnership include: the US National Science Foundation (NSF), the Canadian National Research Council (NRC), the Chilean Comisión Nacional de Investigación Cientifica y Tecnológica (CONICYT), the Australian Research Council (ARC), the Argentinean Ministerio de Ciencia, Tecnología e Innovación Productiva, and the Brazilian Ministério da Ciência, Tecnologia e Inovação. The observatory is managed by the Association of Universities for Research in Astronomy, Inc. (AURA) under a cooperative agreement with the NSF. The NSF also serves as the executive agency for the international partnership.