Io’s surface, shown in Figure 11.5 and the opening photograph
for Chapter 10, displays a wide variety of colors—
pale shades of red, yellow, orange, and brown. Mixtures of
sulfur, sulfur dioxide frost, and sulfurous salts of sodium
and potassium on the moon’s surface are the likely cause
of the colors. Bright patches may be fi elds of sulfur dioxide snow. You may well wonder how snow can fall from
Io’s nearly nonexistent atmosphere. According to current
understanding, liquid sulfur dioxide must fl ow beneath
Io’s surface, held at high pressure by the weight of overlying
material. Like water from an artesian spring, this pressurized
sulfur dioxide can be pushed out though fractures
in the crust, producing sprays of sulfur dioxide snow crystals
that travel for up to hundreds of kilometers before settling
back to the moon’s surface. (To see a similar process
in action, just operate a carbon dioxide fi re extinguisher.
These fi re extinguishers contain liquid carbon dioxide at
high pressure that immediately turns to “dry ice” snow as
it leaves the nozzle.)
Io’s surface, shown in Figure 11.5 and the opening photographfor Chapter 10, displays a wide variety of colors—pale shades of red, yellow, orange, and brown. Mixtures ofsulfur, sulfur dioxide frost, and sulfurous salts of sodiumand potassium on the moon’s surface are the likely causeof the colors. Bright patches may be fi elds of sulfur dioxide snow. You may well wonder how snow can fall fromIo’s nearly nonexistent atmosphere. According to currentunderstanding, liquid sulfur dioxide must fl ow beneathIo’s surface, held at high pressure by the weight of overlyingmaterial. Like water from an artesian spring, this pressurizedsulfur dioxide can be pushed out though fracturesin the crust, producing sprays of sulfur dioxide snow crystalsthat travel for up to hundreds of kilometers before settlingback to the moon’s surface. (To see a similar processin action, just operate a carbon dioxide fi re extinguisher.These fi re extinguishers contain liquid carbon dioxide athigh pressure that immediately turns to “dry ice” snow asit leaves the nozzle.)
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