Volcanism has played a major part in shaping not only planet Earth, but other places in our universe. Though other planets show signs of volcanic eruptions, most seemed to have erupted in the distant past and are inactive now. Both Mars and Venus have volcanoes much larger than any on Earth, and they have erupted huge amounts of lava onto their surfaces in the past.
The Earth's Moon has no large volcanoes. However, vast plains of basaltic lavas cover much of the lunar surface. The earliest astronomers thought, wrongly, that these 'Plains were seas of lunar water'. Thus, they were called "mare " (pronounced "mahr-ay"). Mare means "sea" in Latin. In addition, other volcanic features also occur within the lunar mare. The most important are sinuous rilles , dark mantling deposits, and small volcanic domes and cones . Most of these features are fairly small, however. They form only a tiny fraction of the lunar volcanic record.
Mars has many distinctively volcanic features, including the largest volcano in the solar system, Olympus Mons, which towers 16 miles high over the Martian landscape.
Mars has an enormous bulge on one side of the planet, where the molten lava rising up to the volcanoes from inside the planet has pushed the solid crust 6 kilometres above the surrounding land.
Mars has the largest shield volcanoes in the solar system. It also has a wide range of other volcanic features. These include large volcanic cones, unusual patera structures, mare-like volcanic plains, and a number of other smaller features. However, volcanic features are not common. There are less than 20 named volcanoes on Mars, and only 5 of these are giant shields. Also, volcanism occurs mostly within three regions. Even the mare-like plains cluster near these regions. The main cluster of volcanoes and lavas is in Tharsis. A much smaller cluster of three volcanoes lies in Elysium. Lastly, a few paterae are near the Hellas impact basin.
Venus has more volcanoes than any other planet in the solar system. It has many young volcanoes. Over 1600 major volcanoes or volcanic features are known, and there are many, many more smaller volcanoes. (No one has yet counted them all, but the total number may be over 100,000 or even over 1,000,000). These volcanoes come in a variety of forms. Most are either Large Shields or Smaller Shield volcanoes, but there are also many Complex Features, several Unusual Constructs, and a few Large Flow Features. None is known to be active at present, but our data is very limited. Thus, while most of these volcanoes are probably long dead, a few may still be active.
Some researchers have 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, the innermost large moon of Jupiter, is about the same size and density as Earth's Moon. Io is the most volcanically active body known in the Solar System. Eruptions are so common and so large that the entire surface can be buried under 100 meters of material every 1 million years (it takes submarine volcanoes about 80 million years to resurface about two-thirds of the Earth). Impact craters, which are common on many planets and moons, are absent on Io because of the frequent volcanic eruptions bury them.
Io is about the same size as our own Moon, actually has more erupting volcanoes than the Earth. This is because it orbits very close to Jupiter, and is constantly being pulled around by the gravity of Jupiter and the Sun. This keeps the rocks beneath the surface hot enough to be molten lava, and it keeps bursting out through vents in the surface.
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.
This is a high-resolution image of part of Prometheus, an active volcano on Jupiter's volcanic moon Io. In earlier, lower resolution images, it appeared that all the dark material at Prometheus comprised a single, long lava flow. The new image shows for the first time that the northeastern end of this dark feature is actually a lava-filled caldera 28 kilometers (17 miles) long and 14 kilometers (9 mile s) wide. The underground source of the Prometheus lava is probably beneath this newly discovered caldera. Galileo scientists are intrigued also by the snowfield containing hummocks, seen to the east of the Prometheus caldera.
November 5, 1999 - NASA
New images from Galileo reveal unexpected details of the Prometheus volcano on Io including a caldera and lava flowing through fields of sulfur dioxide snow.
A volcanic crater several times larger than one found at Hawaii's Kilauea volcano has been photographed on Jupiter's moon Io during a close flyby performed by NASA's Galileo spacecraft.
The sharp images of Prometheus released today come from two of Galileo's onboard instruments -- the camera, and the near- infrared mapping spectrometer which observes in wavelengths not visible to the naked eye. The images were taken during the close flyby of Io by Galileo on October 10, 1999, and are part of a large batch of data currently being transmitted to Earth.
"We've been having a feast looking at the material from Io," said Dr. Rosaly Lopes-Gautier NASA's Jet Propulsion Laboratory, Pasadena, CA. "We have been waiting for such high-resolution images of Io for more than 10 years." Scientists will present an assortment of new images and describe their latest discoveries at a press briefing scheduled for November 19 at NASA Headquarters, Washington, DC.
Prometheus is the "Old Faithful" of Io's many volcanoes. It has been active during every observation over the past 20 years by NASA's Voyager and Galileo spacecraft and the Hubble Space Telescope. The new spectrometer images show two distinct hot spots at Prometheus -- a large one to the west and a fainter, cooler one to the east. The images reveal numerous lava flows near the western hot spot and enable scientists to identify a crater, or caldera, 28 kilometers (17 miles) long and 14 kilometers (9 miles) wide near the hot spot to the east.
Previously, it was thought that the 50 to 100 kilometer- (30 to 60 mile-) tall plume observed at Prometheus formed where the lava erupts onto the surface. Now, however, it now appears that the plume forms at the far end of the lava flows. The caldera and eastern hot spot are thought to be associated with the vent where the molten rock rises to the surface. It appears that after the lava reaches the surface, it is transported westward through lava tubes for about 100 kilometers (60 miles) before breaking out onto the surface again. Here, numerous lava flows wander across a plain covered with sulfur dioxide-rich snow. The plume is created by the interaction of the hot lava with the snow.
This plume feature is just one of several similarities between Prometheus and Hawaii's Kilauea. Volcanologists say that Prometheus has been erupting for more than 20 years and Kilauea has been erupting for more than 16 years. The current vent at Kilauea consists of a small lava lake about 100 meters (330 feet) across that produces a relatively small thermal hot spot. From this vent, lava is transported 10 kilometers (6 miles) in lava tubes to the Pacific Ocean where large steam plumes are generated by the interaction between the hot lava and the ocean. Galileo scientists believe the plume seen on the western end of Prometheus is similar to this Hawaiian steam plume, except the Ionian plume is composed largely of sulfur dioxide and rises much higher because of Io's low atmospheric density and gravity.
Another Io flyby, this time at an altitude of 300 kilometers (186 miles), is planned for November 25 at 8:40 p.m. Pacific Time (11:40 p.m. Eastern Time). (Times given are in Earth-received time -- or the time when the signal of the event is received on Earth.) The Io flybys are challenging and risky, because Io lies in an area of intense radiation from Jupiter's radiation belts, and that radiation can harm spacecraft components. Because of the risk, the flybys were scheduled for the final portion of Galileo's extended mission.
October 11, 1999 - BBC Online
At 0600 GMT on Monday, the Galileo spacecraft swept within a few hundred kilometres of Io, the innermost moon of Jupiter. It was its closest ever approach to this strange volcanic moon.
Galileo remained in contact with ground controllers at Nasa's Jet Propulsion Laboratory in California and appears to be making its science observations. If all goes as planned, it will return data to Earth over the coming weeks.
Io is one of the wonders of the Solar System - a world like no other. About the same size as our Moon, it is covered in vast orange and yellow deposits of sulphur that give the world a unique appearance.
The sulphur is billowed hundreds of kilometres up into the sky by at least a dozen active volcanoes, making Io the most volcanically-active world in the Solar System.
As well as the active vents scattered over its surface, there are extensive frozen plains, mountain ranges and volcanic rings the size of England.
Io's activity comes from a gravitational tug-of-war with mighty Jupiter.
Jupiter's gravity raises tides in Io that are trying to drive the world further away from the giant planet. But Io is locked in place by the gravity of Jupiter's three other main moons.
The result is a massive input of energy into the world that becomes heat inside it providing the volcanic energy.
In 1979, the Voyager spaceprobe that flew through the system detected these alien volcanoes. More recently, the Hubble Space Telescope has been able to observe plumes above them.
It is the first time that Galileo has flown so close to Io. Until now the closest images taken of the volcanic moon were from a distance of 129,000 km (80,000 miles).
When Galileo passes within 600 km (380 miles), objects as small as 12 metres (40 feet) will be visible.
A second Io flyby is planned for 25 November as the finale to Galileo's two-year, extended mission orbiting Jupiter.
Galileo reached Jupiter in December 1995, entering orbit and dropping a probe into the Jovian atmosphere. It completed its main mission in December 1997 and then began its current extended mission.
Engineers hope that it will go on, if it survives the intense radiation field around Io. Its fuel will run out towards the end of next year but before that it will be moved into a wide circular orbit around Jupiter where its sensors could continue working for many years.
ALPHABETICAL INDEX OF ALL FILES
