Page 22 - Curriculum Visions Dynamic Book

 An enormous volcanic explosion can be seen silhouetted against dark space over Io’s bright limb.
The brightness of the plume
has been increased by the computer, since it is normally extremely
faint; but the relative colour of
the plume (greenish-white) has been preserved.
The picture shows solid material being thrown up to an altitude
of about 160 km. To do this, the material must leave the volcanic vent at nearly 200 km/hr. The vent is about 300 km in diametre.
Io’s volcanoes
There appears to be no water on the surface of Io. The yellowish-white colour is most likely frozen sulfur dioxide. The surface also has volcanic vents and lava flows. The lava flowing from these distant volcanoes is very hot—
at least 2,000°C.
The volcano that was active at the time of the Voyager flyby has been named Prometheus. It can be seen on the full disk, page 20 (slightly right of centre).
The activity on Io is all the more intriguing since Io is too small to have a source of internal heat. It has been suggested that the energy comes from the combined gravitational pull of Jupiter and the other major moons, which pull and push at Io like a ball being first squeezed and then let go. Scientists call this a tidal effect; it is so powerful that it can produce intense internal heating within Io.
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