Io is the most volcanically active body in the Solar System.
It is the innermost of the Galilean satellites of Jupiter
So-called, because they were first discovered by Galileo using the newly-developed telescope in 1610.
The USGS acknowledged the existence of nine active volcanoes on Io during the Voyager spacecraft fly-bys in 1979.
This is probably a gross underestimate, several hundred is a more likely figure.
Io is approximately the size of the Earth's Moon, a volcanically dead object.
The pervasive continuing volcanism on Io is attributed to the gravitational pull of Jupiter
which is opposed by those of the outer Galilean satellites giving rise to extreme tides in the body of Io.
A weak gravitational field and insignificant atmosphere give rise to volcanic plumes extending
nearly 300 km above the surface of Io.
The young age of the surface of the entire body is attested by the absence of impact craters.
The stamp below was issued by Ghana in 1990 as part of a minisheet of nine.
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