A volcano similar to Hawaii's Kilauea has been photographed on Jupiter's moon Io by the Nasa space probe Galileo.
The active crater, known as Prometheus, is several times larger than its terrestrial counterpart but has many physical similarities, exciting earth scientists who have been waiting for a high-resolution image of Io's surface for many years.
The new images taken by the Nasa spacecraft's camera and near-infrared mapping spectrometer show the northeastern end of the volcano consists of a lava filled caldera some 28km long.
It is thought this is the vent where the molten rock rises to the surface. It is then transported westwards through lava tubes for about 100km before breaking out onto the surface.
Here the lava interacts with snow and forms a plume up to 100km tall. Laszlo Keszthelyi, a Galileo research associate at the University of Arizona, Tucson, said: "Both volcanoes are long-lived eruptions, with flows that apparently travel through lava tubes and produce plumes
when they interact with cooler materials."
Kilauea has a small lava lake about 100m across from which lava is transported 10km in lava tubes into the Pacific Ocean.
There, large steam plumes are generated by the interaction of the lava and the ocean.
The Prometheus data were gathered on October 10, and much of it is still being transmitted to Earth. Another Io fly-by is planned for November 25.
These swoops are risky, because of the intense radiation from Jupiter's radiation belts, and they have been scheduled for the final portion of Galileo's mission.