Press Release
Johns Hopkins Applied Physics Lab Researchers Discover Massive Gas Cloud Around Jupiter
Image of Jupiter’s space environment, or magnetosphere, taken with the innovative energetic neutral atom (ENA) imaging technique by the Magnetospheric Imaging Instrument on NASA’s Cassini spacecraft as it flew past Jupiter in early 2001 at a distance of about 6 million miles (10 million kilometers) from the planet. The field-of-view represented by the image is 30 degrees on the horizontal axis and 36 degrees on the vertical axis. The color is coded according the number of ENA counts observed within each 1.4-by-1.9 degree pixel over a 15-hour observing period, with red representing the highest number of counts and light blue representing the background counts.
The central object represents ENA emissions from Jupiter itself, a consequence of the impingement of energetic ions from Jupiter’s magnetosphere onto the upper atmosphere. The two outer objects represent ENA emissions from a massive donut-shaped gas cloud — or torus — that shares an orbit with Jupiter’s moon Europa, at a distance from Jupiter of more than 400,000 miles (more than 650,000 kilometers).
The near-Europa emissions are “dot like” because the torus is viewed edge-on. The image is brightest where the imager’s line-of-sight passes through the greatest volume of the gas torus.
Credit: NASA/Jet Propulsion Laboratory/Johns Hopkins University Applied Physics Laboratory.
Using a sensitive new imaging instrument on NASA’s Cassini spacecraft, researchers at The Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., have discovered a large and surprisingly dense gas cloud sharing an orbit with Jupiter’s icy moon Europa.
Stretching millions of miles around Jupiter, the donut-shaped cloud, known as a “torus,” is believed to result from the uncommonly severe bombardment of ion radiation that Jupiter sends toward Europa. That radiation damages Europa’s surface, kicking up and pulling apart water-ice molecules and dispersing them along Europa’s orbit into a neutral-gas torus with a mass of about 60,000 tons.
The cloud’s mass indicates that the intense radiation Europa faces has more severe consequences than scientists thought, says Dr. Barry Mauk, head of the APL research team whose findings appear in the Feb. 27 issue of the journal Nature. The mass also shows that Europa, in an orbit some 416,000 miles (671,000 kilometers) from Jupiter, wields considerable influence on the magnetic configuration around the giant planet.
“Surprisingly, Europa’s gas cloud compares to that generated by the volcanically active satellite Io,” says Mauk. “But where Io’s volcanoes are constantly spewing materials — mostly sulfur and oxygen — Europa is a comparatively quiet moon, and the gas we see is a direct consequence of its icy surface being bombarded so intensely.
“By acting as both a source and a sink of charged radiation particles, the dense gas torus gives Europa much greater influence than was previously thought on the structure of, and energy flow within, Jupiter’s huge space environment, its magnetosphere,” he says.
The Applied Physics Lab team studied images of Jupiter taken in late 2000 and early 2001 with the APL-developed Ion and Neutral Camera on Cassini, now in route to Saturn. Mauk says this is the first substantial discovery made at an extraterrestrial planet using an innovative technique known as energetic neutral atom (ENA) imaging.
“Planetary magnetospheres glow with energetic neutral atoms, much like a red-hot piece of iron glows with photons of light, and such neutral-atom glows can be remotely imaged,” Mauk says. “To this point, no instrument has imaged that activity beyond Earth’s magnetosphere. ENA imaging makes visible the three-dimensional structure of planetary space environments, which, until recently, were invisible to remote imaging techniques.”
Research team members at APL and co-authors on the Nature paper, “Energetic neutral atoms from a trans-Europa gas torus at Jupiter,” include Dr. Donald Mitchell, Dr. Stamatios Krimigis, Dr. Edmond Roelof and Dr. Christopher Paranicas. Krimigis, head of the Space Department at APL, is principal investigator for Cassini’s Magnetospheric Imaging Instrument, which includes the Ion and Neutral Camera.
Cut-away schematic of Jupiter’s space environment showing magnetically trapped radiation ions (in red), the neutral gas torus of the volcanic moon Io (green) and the newly discovered neutral gas torus of the moon Europa (blue). The white lines represent magnetic field lines. Energetic neutral atoms (ENAs) are emitted from the Europa torus regions because of the interaction between the trapped ions and the neutral gases.
The Cassini Magnetospheric Imaging Instrument imaged those ENAs during flyby of Jupiter in early 2001. ENAs also come from Jupiter when radiation ions impinge onto Jupiter’s upper atmosphere.
Credit: NASA/Jet Propulsion Lab/Johns Hopkins University Applied Physics Laboratory
The APL-built Magnetospheric Imaging Instrument is one of 12 science instruments on the main spacecraft and one of six instruments designed to investigate the space environments around Saturn and its moons. Cassini will begin orbiting Saturn on July 1, 2004, and release its piggybacked Huygens probe about six months later for descent through the thick atmosphere of the moon Titan. Cassini-Huygens is a cooperative mission of NASA, the European Space Agency and the Italian Space Agency. NASA’s Jet Propulsion Laboratory, Pasadena, Calif., manages the mission for NASA’s Office of Space Science, Washington, D.C.
For more information on Cassini, visit http://saturn.jpl.nasa.gov. For more information on the Magnetospheric Imaging Instrument and its science mission, visit http://sd-www.jhuapl.edu/CASSINI/.