# Gases/Gaseous objects/Io

"The camera on Cassini captured images of eclipsed Io in several colors ranging from the near-ultraviolet to the near-infrared. A black-and-white movie clip of 48 clear-filter frames spanning two hours during the eclipse was released on February 5 (PIA02882). Here, two colors have been added to show the type of evidence used by imaging scientists in determining the source of Io's auroral glows. The color pictures were taken at lower resolution -- 120 kilometers (75 miles) per pixel rather than 60 kilometers(37 miles) per pixel -- and less frequently than the clear-filter images. White dots near the equator are volcanoes, some of which are much brighter than the faint atmospheric glows. The brightest of them is the volcano Pele."
"Emissions of light (at wavelengths of 595 to 645 nanometers) likely arise from a tenuous atmosphere of oxygen. These glows would appear red to the eye and are consequently colored red in the movie. Emissions in near-ultraviolet wavelengths (between 300 and 380 nanometers), corresponding wavelength to the bright blue visible glows one would expect from sulfur dioxide. They have been colored blue in the movie. The blue glows are restricted to areas deep down in the atmosphere near the surface of Io, while the red glows are much more extensive, reaching heights of up to 900 kilometers (560 miles). This would be expected if the blue glows are indeed produced by sulfur dioxide, since sulfur dioxide molecules are heavier than oxygen atoms, so are more closely bound to the surface by gravity. The prominent blue and red regions near the equator of Io dance across the moon with the changing orientation of Jupiter's magnetic field, illustrating the relationship between Io's auroras and the electric currents that excite them."

## Greens

At right is an "eerie view of Jupiter's moon Io in eclipse ... acquired by NASA's Galileo spacecraft while the moon was in Jupiter's shadow. Gases above the satellite's surface produced a ghostly glow that could be seen at visible wavelengths (red, green, and violet). The vivid colors, caused by collisions between Io's atmospheric gases and energetic charged particles trapped in Jupiter's magnetic field, had not previously been observed. The green and red emissions are probably produced by mechanisms similar to those in Earth's polar regions that produce the aurora, or northern and southern lights. Bright blue glows mark the sites of dense plumes of volcanic vapor, and may be places where Io is electrically connected to Jupiter."
"North is to the top of the picture, and Jupiter is towards the right. The resolution is 13.5 kilometers (8 miles) per picture element. The images were taken on May 31, 1998 at a range of 1.3 million kilometers (800,000 miles) by Galileo's onboard solid state imaging camera system during the spacecraft's 15th orbit of Jupiter."

## Volcanic gases

Water vapour is consistently the most common volcanic gas, normally comprising more than 60% of total emissions. Carbon dioxide typically accounts for 10 to 40% of emissions.
Volcanoes located at convergent plate boundaries emit more water vapor and chlorine, higher H$_2$O/H$_2$, H$_2$O/CO$_2$, CO$_2$/He and N$_2$/He ratios than volcanoes at geologic hot spots or divergent plate boundaries per the addition of seawater into magmas formed at subduction zones.
In volcanoes with an open path to the surface, e.g. Stromboli in Italy, bubbles may reach the surface and as they pop small explosions occur, where the gas can flow rapidly through the continuous permeable network towards the surface, which explains activity at Santiaguito, Santa Maria volcano, Guatemala and Soufrière Hills Volcano, Montserrat.
Volcanic gases were directly responsible for approximately 3% of all volcano-related deaths of humans between 1900 and 1986.
The greenhouse gas, carbon dioxide, is emitted from volcanoes, accounting for nearly 1% of the annual global total.
Some volcanic gases including sulfur dioxide, hydrogen chloride, hydrogen sulfide and hydrogen fluoride react with other atmospheric particles to form aerosols.

## Hypotheses

* The volcanoes of Io originate from the current flowing through Io.