Johns Hopkins Gazette: August 19, 1996

On Astronomy:
Hopkins Astronomer
To Do A Double-Take
On Jupiter

Double vision:
Stereoscopic observations
will provide clues
to plasma torus.

Emil Venere
News and Information

Astronomers taking advantage of a rare opportunity are using an Earth-orbiting telescope in tandem with the Galileo spacecraft to observe an enigmatic doughnut of gas that encircles Jupiter.

The stereo observations permit astronomers to see the huge formation from two angles simultaneously, which should enable them to learn more about the processes behind its puzzling shape.

Hopkins astronomer Doyle Hall is leading a team of researchers observing Jupiter with an ultraviolet telescope called the Extreme Ultraviolet Explorer. The satellite is in a low-Earth orbit, from where it sees the Jovian system face-on. At the same time, Galileo is getting a side view of Jupiter.

Astronomers are enjoying their first-ever dual-perspective observations of the huge torus of gas, which extends farther than the orbit of Io, one of Jupiter's largest moons. Called the Io plasma torus, it's a sea of electrons and positively charged atoms, or ions, caught up in Jupiter's magnetosphere.

Galileo began orbiting Jupiter in December 1995.

When Hall learned that the spacecraft would be observing the torus with an ultraviolet spectrograph, he asked NASA to let him use EUVE to view the planet at the same time.

"It's very exciting. To think that we are controlling a little object of metal that's now orbiting around Jupiter," said Hall, an associate research scientist in the Department of Physics and Astronomy. "That's kind of amazing.

"And secondly, the fact that we have such good control that we can time, down to minutes or seconds, the actions of a spacecraft orbiting Jupiter and a spacecraft orbiting the Earth."

The observations must be precisely coordinated so that astronomers are viewing the torus at the same time with both spacecraft. Because telescopes in space are ideal for ultraviolet astronomy, the potential scientific payoff is significant, Hall said.

Extreme ultraviolet light is invisible to earthbound astronomers; the wavelengths are too small to be seen with the human eye, and they are absorbed by the Earth's atmosphere. But certain objects are best seen in the ultraviolet, including very hot formations.

For example, when the Jovian system is observed in extreme ultraviolet light the super-hot torus shows up brighter than Jupiter itself.

Astronomers made a series of observations in June and will conduct similar observations in August.

Hall said the dual observations will help astronomers understand more about the torus, Io's atmosphere and processes on the moon's surface, as well as Jupiter's unusual magnetosphere-- the magnetic lines of flux that surround a planet.

"We are still struggling to understand all the details of Jupiter's magnetosphere," Hall said.

Scientists believe that sulfur dioxide spewing from volcanoes on Io eventually makes its way into space, where the molecules become ionized--they lose electrons from exposure to radiation and solar winds. The negatively charged electrons and positively charged sulfur and oxygen atoms then get trapped inside Jupiter's titanic magnetic field, feeding into the doughnut of gas.

"The specific processes that transport Io's volcanic gases and condensates from this tiny moon into Jupiter's magnetosphere to form the Io plasma torus are a subject of great debate in the planetary community," Hall said. "One goal of the coordinated observations is to gain a better understanding of this complicated mechanism."

Go back to Previous Page

Go to Gazette Homepage