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Astronomy

Explosions in another world

Brazilian researcher explores volcanoes on Saturn and Jupiter moons

ESA/NASA/JPL/UNIVERSITY OF ARIZONATitan: fish-eye lens view taken by the Huygens space probe, at a distance of 5 kilometersESA/NASA/JPL/UNIVERSITY OF ARIZONA

Seen from a distance by untrained eyes, celestial bodies seem placid. But some are full of volcanoes, and only those who have witnessed the power of an eruption know what it feels like to feel the ground shaking and hear deafening explosions. It is possible to climb to the top of certain volcanoes, smell the sulfur from the burning lava and see it move slowly in the crater before it pours down the hillside. Only space travel is more exciting than that. At least, this is what Rosaly Lopes thinks. Rosaly, an astronomer, works at the Jet Propulsion Laboratory of Nasa, the American space agency. She brought together two things: studying volcanoes on earth and using this knowledge to explore, at a distance, similar formations on other planets. She is now listed in the Guinness Book of Records as the greatest discoverer of volcanoes (she has found 71 in Io, one of Jupiter’s moons). She is now helping to describe the ice-spitting volcanoes on Titan, Saturn’s largest moon, which is almost half the size of the Earth.

Titan’s volcanoes are being revealed thanks to the Cassini spacecraft, which has been orbiting Saturn since 2004. The building, control and planning of this mission is the responsibility of the Jet Propulsion Laboratory, which employs a staff of five thousand, mainly engineers. The science division where Rosaly works has some 500 researchers. “Every month or two, the Cassini passes close to Titan,” Rosaly tells us. Part of her function is to plan these passages and to work with the engineers that steer the spacecraft, making small changes in its orbit to adjust the observation angle and to determine which of the 12 instruments will collect data on Saturn’s moon.

Images of the first four years of the mission clearly indicate recent volcanic activity on Titan, according to two articles published this year in Geophysical Research Letters. The main basis for interpretation is what we know about how volcanoes on the earth function. Data such as the volcano’s shape, whether or not it is explosive, how the magma rises to the surface and what its eruptions are like help one to understand the images of the new volcanoes found in other parts of the Solar System. However, the Titan volcanoes have one striking difference, a phenomenon known as cryovolcanism. What pours out of the fractures in the ice’s surface is not melted rock, but frozen water, probably mixed with ammonia or methane and with the consistency of a puree. “Pure water would be unable to go through the layer of ice, as ice floats on water,” Rosaly explains. The mixture would lower the density of the liquid as soon as it reached the surface.

Nasa/jpl/usgsLiquid methane on Saturn’s moon: in lakes revealed by Cassini…Nasa/jpl/usgs

For the time being, researchers are yet to see active volcanoes on Saturn’s moon. What they have seen, however, with the aid of a spectrometer, was a change in brilliance that looks like volcanic flux. It may seem subtle, but for Rosaly this is a strong indication corroborating the radar images taken by Cassine when it first went past Titan, in October 2004. In 2007, the researcher described these images as cryovolcanic features in the journal Icarus. Titan has dunes shaped by wind and a methane cycle that is similar to the Earth’s water cycle. Its geologically complex surface is being constantly eroded  by rains, lakes and rivers of liquid methane, which reveals a complex interaction between the atmosphere and the surface.

Previous space explorations showed that Io (Jupiter’s third largest moon, out of 63 of them, and slightly larger than our Moon) has very different geology. From images obtained between 1996 and 2001 by the spectrometer of the spacecraft Galileo, Rosaly and her team described the volcanic activity of this moon in several articles, published in scientific periodicals such as Science in 2000 and Icarus in 2004, among others. However, there are still doubts as to the chemical composition of the lava out there. Galileo and telescopes on Earth show that the temperature of the material that comes out of the Io volcanoes may be higher than 1,300 degrees Celsius, hotter than Earth’s molten basalt. If this is correct, these volcanoes would be of a sort that was also found on Earth billions of years ago,” interprets the astronomer. Still, this measurement was taken at just one point and therefore many researchers do not regard it as reliable. The challenge is not small: lava cools down fast and the temperature is measured sporadically and at a great distance by devices that are complex to calibrate. This calibration needs to be reviewed in order to validate controversial observations.

Nevertheless, the Galileo mission enabled us to explore the surroundings of Jupiter a fair amount. Using infrared images to measure the heat of the lava of Io’s volcanoes from 1996 to 2001, Rosaly discovered the 71 volcanoes that gave her the world record. “In some Io volcanoes, the lava flow melts the frozen sulfur dioxide on the surface,” she describes. The flow then carves up the ground until it meets deeper sulfur dioxide, creating a vertical cloud of smoke and particles known as a volcanic plume. “The lava advances and the plume advances with it, something we have never seen on Earth,” she tells us. Because of the strong volcanic activity that coats Io with molten rock, its surface is relatively young, as evidenced by a lack of the craters that are produced by the impact of asteroids and meteors.

Comparing terrestrial and extraterrestrial volcanoes is an important resource for developing an understanding of the planets. Far more than an adventure in which the researchers face nature’s most powerful forces, volcanologists look inside the valves that release the heat from within the middle of a planet or of a satellite, thus obtaining important information about their evolution. The Moon’s dark shadows, for instance, are veritable oceans of lava that were formed over three billion years ago. By now the Moon has cooled down enough to have no volcanic activity. Astronomers have also found volcanoes in Enceladus (another Saturn moon) and they suspect that they also exist on Venus. Because of the similarities between the volcanic activity of different planets, Io has helped us understand the properties of the Earth’s volcanoes and to reconstruct the history of this planet.

Nasa/jpl/Michael Carroll… and falling in the shape of a storm in the Hotei Arcus, an area with strong volcanic activityNasa/jpl/Michael Carroll

From spectacular volcanic eruptions to the exploration of other planets, what drives Rosaly is adventure and discovery. Hence the award she won this year from the Wings WorldQuest organization, which “celebrates and supports extraordinary women explorers and promotes scientific exploration, education and conservation to inspire future generations,” a principle that is aligned with the career of the Brazilian researcher. Being very nearsighted, she realized, as a child, that she could not become an astronaut. But instead of abandoning her dream, she chose to adjust it. She left Brazil at 18 to study astronomy in England, because she saw no opportunities here to explore other planets. “Today, the situation has changed a lot, but astrophysics research is far more advanced in Brazil than planetary astronomy,” she tells us.

As part of her doctorate at London University, she compared the volcanoes of Earth and Mars and was enchanted by the spectacle of the eruptions. This thesis gave rise to the book Turismo de aventura em vulcões [Adventure tourism in volcanoes], published in Brazil last year by the Oficina de Textos publishing house. In this work, Rosaly gives a lesson on volcanoes, informs us about them and encourages adventurous individuals to travel to see a volcano in action.

In Brazil, she collaborates with the educational project of Marcos Lune, from the Agreste Technological Center in Bezerros, in inner-state Pernambuco. Last year, he opened an experimental rocket launch base, named after the Brazilian researcher from NASA. She attended the event, talked about her work and still delivers teleconference talks. At the Center, high school pupils learn the basics of engineering, propulsion and geology. The center has been closed since the beginning of this year because it is being transferred to the town of Salgueiro, in a more isolated area. Rosaly hopes to further increase the enthusiasm of these youths, by showing that it is possible to graduate from a Brazilian government school and get to NASA, as she did.

Scientific articles
WALL, S. D. et al. Cassini RADAR images at Hotei Arcus and western Xanadu, Titan: evidence for geologically recent cryovolcanic activity. Geophysical Research Letters. v. 36, L04203. 2009.
NELSON, R. M. et al. Photometric changes on Saturn’s Titan: evidence for active cryovolcanism. Geophysical Research Letters. v. 36, L04202. 2009.
LOPES-GAUTIER, R. et al. A close-up look at Io from Galileo’s near-infrared mapping spectrometerScience. v. 288, p. 1.201-1.204. May 2009.

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