Savage Earth: Other Planets

Olympus Mons on Mars.




		Volcanoes on Other Planets by Kathy Svitil

	Just as it has on Earth, volcanism has played a powerful role in shaping other worlds in our solar system. "Venus, for example, is covered with volcanoes, and many of them are clearly geologically very young," says Alfred McEwen, a planetary scientist at the University of Arizona. Planetary probes have never picked up a clear sign of volcanic activity there, but, back in 1978, astronomers on Earth spotted a strange brightening in the planet's northern hemisphere. Many thought it might be an eruption. That same year, the Pioneer spacecraft detected high levels of sulfur dioxide, a volcanic gas. The Magellan spacecraft (1989-1994) detected hundreds of volcanoes on the surface of Venus. Although it is likely that Venus is currently volcanically active, no conclusive evidence of present-day eruptions has yet been observed. Mars also has many distinctively volcanic features, including the largest volcano in the solar system, Olympus Mons, which towers 16 miles high over the Martian landscape. "If volcanism had occurred up until the last 1% of geologic time, it is very unlikely to have stopped," McEwen says. "We just haven't observed anything that is a smoking gun on either Mars or Venus."

Volcanoes also shaped Mercury. There, however, the activity appears to have stopped operating early in the planet's history, billions of years ago. On our moon, too, volcanism operated early and then shut off sometime around 3 billion years ago.

On Jupiter's moon Europa, which has a fractured outer surface of ice (under which may lie an ocean), volcanism may still be operating, although probes have yet to detect the tell-tale signs of a volcanic eruption. "Although it is pure speculation, there could be silicate volcanism transmitted through the water," McEwen says. Another possibility, McEwen says, is ice volcanism. "A plume of water vapor or a water flow in the surface is considered a volcanic fluid if it is heated and warmed up by the internal heat of the moon," McEwen says. Some researchers have also suggested that the same sort of ice volcanism may be present on Saturn's moon, Enceladus. Another moon of Saturn's, Titan, may also be volcanic (which would explain the satellite's dense atmosphere), as may be Neptune's moon, Triton.

Io, one of Jupiter's moons.

Planetary scientists have no doubt that Jupiter's moon Io is volcanically active. In fact, the satellite -- which is about the size of our own moon -- is the most volcanically active body in the solar system. Recent images obtained by NASA's Galileo spacecraft have revealed about 100 active volcanic centers, each comprised of many calderas (large volcanic depressions in the ground), says McEwen, who heads the Galileo Io imaging team. As many as 500 volcanic centers may have been active in the last 100 years.

Io's calderas (craters) are remarkably hot. "Our temperature measurements indicate hotter temperatures than any active volcanism on Earth," McEwen says. "It implies that the magma is magnesium-rich -- comparable to the mantle composition of the Earth. This is what happened on Earth during the Archean era, 2.5 billion years ago, when the Earth was hotter. That's interesting, because it suggests that we might learn something about ancient volcanoes on Earth by studying Io today."


	Article: Mountains of Fire \| Sidebar One: Volcanoes of North America \| Sidebar Two: Montserrat \| Sidebar Three: Other Planets \| ANIMATION Hell's Crust: Our Everchanging Planet \| The Restless Planet: Earthquakes Out of the Inferno: Volcanoes \| Waves of Destruction: Tsunamis

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