ALMA Detects Volcanic Gases in Atmosphere of Io

Using data from the Atacama Large Millimeter/Submillimeter Array (ALMA), astronomers from India have detected acetone, disulfur monoxide, and carbon monoxide in the atmosphere of Jupiter’s moon Io.

This global view of Io was obtained in January 1999 by NASA’s Galileo spacecraft. Image credit: NASA / JPL / University of Arizona.

Io is the innermost of the four Galilean moons of Jupiter and the fourth-largest moon in our Solar System.

Aside from Earth, it is the only known place in the Solar System with volcanoes erupting hot lava like that on our planet.

Io has more than 400 active volcanoes, which are caused by tidal heating, the result of gravitational forces from Jupiter and other Jovian moons.

The moon’s yellow-white-orange-red coloration is produced by sulfur dioxide-frost on its surface, elemental sulfur and a variety of sulfur allotropes.

Io has a think atmosphere that can teach us about the exotic moon’s volcanic activity and provide us a window into its interior.

“The thin atmosphere of Io primarily consists of various volatile substances like sulfur dioxide (SO2), sulfur monoxide (SO), sodium chloride (NaCl), and the low amount of water,” Arijit Manna from Midnapore City College and Dr. Sabyasachi Pal from the Indian Centre for Space Physics explained in their paper.

“The volcanic species on Io are mainly formed by the combination of specific sublimation of volcanic frost layer and outgassing.”

In the study, the astronomers analyzed the high-resolution interferometric data gathered by ALMA.

They identified the emission lines of acetone (CH3COCH3) and disulfur monoxide (S2O) and an absorptional line of carbon monoxide (CO).

“The formation mechanism of acetone in the volcanic atmosphere of Io is completely unknown but the spectroscopic detection implies that a big amount of methane compounds may exist,” the researchers wrote.

“The carbon monoxide gas is formed with the photolysis of acetone; disulfur monoxide is formed by the decomposition of sulfur monoxide by the disproportionation method.”

“The volatile acetone and carbon monoxide are probably rising in the brightness of the Loki hot spot,” they noted.

“Disulfur monoxide is primarily responsible for the red feature observed in Io’s volcanoes.”

“The detected species in the volcanic atmosphere using ALMA calls for more comprehensive studies of their rotational lines and requires a re-examination of whether they co-exist in the same atmospheric position, and then to get more specific densities to predict the chemical formation process,” they concluded.

The team’s paper was published March 31, 2021 on the preprint server.


Arijit Manna & Sabyasachi Pal. 2021. ALMA detection of acetone, disulfur monoxide, and carbon monoxide in the Jupiter volcanic moon Io. arXiv: 2103.17018

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