Hot Times on Io

This high-resolution image of Jupiter’s moon Io was snapped last November 6 by the Galileo spacecraft, and it has given astronomers their best look at the most volcanically active object in the solar system since the Voyager flyby in 1979. The two small spots in the image’s lower left are volcanic calderas, collapsed depressions usually associated with hot spots. The calderas are dark because they are probably still filled with hot lava that has boiled away lighter-colored sulfur dioxide frost. In the upper left is an outpouring of lava some 250 miles long. Such massive lava flows are also known to have occurred in Earth’s past, but they have never been observed. Some researchers have proposed that these lava floods caused global extinctions on Earth and that they affect climate change, says planetary geologist Alfred McEwen of the University of Arizona, head of the Io observation team. So rather than waiting around for another 100,000 years for one to occur on Earth, we can observe Io, where they are happening today.