Modern-day Galileos ponder Saturn’s magnetosphere
|Top: Raul Baragiola
Middle: A graphic showing the solar winds’ effects on Saturn.
Bottom: An ion mass spectrometer that Baragiola helped design for the Cassini space craft.
By Charlotte Crystal
Nearly four hundred years ago, Galileo Galilei trained the world’s first telescope on the night sky and was startled to discover the rings of Saturn. But it’s only been in recent decades that scientists have been able to seek detailed answers to many related questions.
From 1979 to 1981, NASA launched three spacecraft – Pioneer 11, Voyager 1 and Voyager 2 – to gather information about our sixth planet, its 34 moons and its seven beguiling rings. Most recently, in 1997, NASA sent aloft Cassini.
Cassini is a spacecraft programmed to gather data on Saturn — its atmosphere, rings, satellites and the surrounding magnetic field, known as the magnetosphere. Cassini reached Saturn in July 2004. In December, it dropped a Huygens probe to the surface of Titan, Saturn’s largest moon. Since then, the probe has been transmitting data back to Earth.
Two researchers in U.Va.’s School of Engineering and Applied Science have been deeply involved in the research into Saturn’s magnetosphere — Raul Baragiola, professor of engineering physics and materials science, and Robert E. Johnson, professor of materials science and engineering. Baragiola and Johnson are among a group of scientists who co-wrote an article titled “Composition and Dynamics of Plasma in Saturn’s Magnetosphere,” which was published in the leading, peer-reviewed journal Science last February.
The magnetosphere, a region of magnetic and electric fields, interacts with ions and energy that penetrate its space.
“We can’t see Earth’s magnetosphere but we know it exists because it creates the aurora borealis and radio static when proton particles from the sun hit it,” Baragiola said.
Other planets — though not all planets – in our solar system have magnetic fields. Mars doesn’t have one. Mercury has a weak one. Jupiter has the strongest one. Saturn’s magnetic field is weaker than Jupiter’s, but stronger than Earth’s.
“Exploring places with stronger fields and trying to understand what’s going on is a way to test our theories about Earth,” Baragiola said.
The team of scientists, led by D. T. Young of the Southwest Research Institute of San Antonio, Texas, found Saturn’s magnetosphere to be composed primarily of atoms derived from water molecules. The scientists identified four distinct regions of the magnetosphere, which are characterized by different properties and different combinations of atoms. Their findings point to the possible existence of a layer of oxygen [O2], similar to that found in the atmospheres of Saturn’s moons, Europa and Ganymede.
A greater understanding of the magnetosphere, beyond contributing to basic science and researchers’ understanding of the universe, is of particular interest to the telecommunications industry, and to the scientists and engineers involved in preparing for the next generation of space flight, Baragiola said.
Johnson contributed to the theoretical work and computer modeling, while Baragiola and his research team in the Laboratory for Atomic and Surface Physics contributed to the design of Cassini’s ion mass spectrometer and now analyze the data it sends back. If results come in that don’t fit existing theories, his team conducts lab experiments, trying to figure out what conditions might explain them.
“We reproduce the conditions on Saturn’s moons, such as hitting frozen ammonia with protons to see if the ammonia molecules remain stable or decompose,” Baragiola said. “Even though ammonia and water have been studied for ages at high temperatures, they haven’t been studied to the same extent at extremely low temperatures.”
Using liquid helium, Baragiola’s lab can reproduce the extremely cold environment on Saturn, its rings and its moons by taking experiments down to -270 degrees Celsius or -454 degrees Fahrenheit, close to absolute zero,
So far, the Cassini instruments have discovered the presence of oxygen around the rings of Saturn. They’ve also found hydrogen and oxygen atoms and water molecules in Saturn’s magnetosphere. And they’ve registered nitrogen ions on Titan.
Powered by a plutonium generator, Cassini should generate another five years or so of data, Baragiola said. Until the data stream ends, he and his team of modern-day Galileos will be in the lab, trying to understand what they see.