This full-disk image of Jupiter's satellite Io was made from several frames taken by Voyager 1 on March 4, 1979, as the spacecraft neared the satellite. Io is about 862,000 kilometers (500,000 miles) away here. A variety of features can be seen in the photo that appear linked to the intense volcanic activity on Io: the circular, donut-shaped feature in the center has been identified with a known erupting volcano; other, similar features can be seen across the face of the satellite. Io's volcanic activity appears to be of at least two general kinds -- explosive eruptions that spew material into the sky as much as 250 kilometers (160 miles) altitude; and lava that flows from vents across the surface. Io is the first body in the solar system (beyond Earth) where active volcanism has been observed.

PIA 00023

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