Voyager Detects ‘Bizarre’ Magnetic Field : Uranus Data Reveals Strange Inner ‘Glow’
Uranus is emerging as a strange planet that glows from within in a phenomenon that scientists are calling “electroglow,” and it has a bizarre magnetic field that helps keep its narrow rings extraordinarily well defined, scientists reported Saturday at the Jet Propulsion Laboratory.
The new findings have been combed from the flood of data sent back to Earth from the Voyager 2 spacecraft, which is more than 1.8 billion miles from Earth and is now headed toward yet another challenge, the planet Neptune. It is due there in 1989.
The first close-up images of the Uranian moons and rings were released Saturday, and scientists announced that a 10th ring and a 15th moon had been discovered. The cameras aboard Voyager are not concentrating on the planet itself because of the dense gaseous atmosphere that enshrouds Uranus, the farthest object from Earth ever visited by a spacecraft.
By far the most spectacular photographs from the mission should be released today. Raw data transmitted back from Voyager Saturday, which will have to be “computer enhanced” to show details, revealed the Uranian moon Miranda to be a heavily cratered satellite with many curious geological features. Voyager passed within about 18,000 miles of Miranda, its closest encounter with any object in the Uranian system.
Unenhanced images that came in Saturday showed one huge region of Miranda that appears as if it had been swept with a giant broom. Another photo shows enormous geometric patterns that both excited and baffled scientists who were viewing the images as they came in.
“It’s just bizarre,” said one.
It will take several days for scientists to better interpret the data that will continue to pour in over the next few days, but in an effort to satisfy public curiosity about the mission, they are making an attempt at instant analysis.
They find some of the information easy to interpret. For example, Uranus, like all the other planets in the solar system with the exception of Earth, was found to be devoid of life. But it was found to be a dynamic environment governed by powerful electromagnetic forces.
Voyager has discovered another tiny Uranian moon, bringing the total number of known satellites to 15, including the five major moons whose existence was known long before the Voyager mission began in 1977. Voyager also discovered that one of the moons, Oberon, has a mountain that may be as tall as any in North America.
Lesson in History
What caused a mountain of that size, and what it may mean about the system’s history, remain largely a matter of conjecture. Laurence A. Soderblom of the U.S. Geological Survey, deputy leader of Voyager’s imaging team, said it was most likely created when a meteor struck the moon in the distant past.
Soderblom was more fascinated with a dark substance that appears to have coated the floor of large impact craters on the moon Oberon.
“It looks like it was deposited considerably after the craters were formed,” Soderblom said. He said it was “thought to be produced by fluids that extruded onto the floors of the craters” and later froze.
That would indicate that dynamic processes, possibly volcanic, took part in the formation of the moons, a conclusion that is also supported by evidence of large-scale faulting on some of the moons.
The moons Titania and Ariel were found to have spectacular faulting from some sort of geological activity.
Source of Surprise
That has surprised scientists because it had been thought that only satellites much larger than those found at Uranus would be likely to have internal, dynamic forces.
“We thought we had it all figured out,” said Harold Masursky of the U.S. Geological Survey, a member of the imaging team.
The discovery of the “electroglow” came while scientists were studying ultraviolet emissions from Uranus’ polar regions in search of some sort of auroral activity like the Earth’s “northern lights.” That activity on Earth is caused by “electrons coming in and causing air molecules in the atmosphere to glow,” said Voyager chief scientist Ed Stone, and scientists had expected to find similar activity at Uranus.
“We did not see that,” said Lyle Broadfoot of the University of Arizona, possibly because the magnetic field at Uranus is not quite strong enough.
Colliding Electrons
Instead, they saw a glow caused by electrons colliding with hydrogen molecules in the atmosphere of Uranus. Thus, in a sense the planet shines through its own power system, although one would have to be above the Earth’s atmosphere to see the ultraviolet glow.
Voyager scientists also found further evidence of the peculiar magnetic field generated by some sort of “electromagnetic fluid being stirred” inside Uranus by the planet’s rotation. That is the same way the Earth’s magnetic field is generated.
The magnetic field at Uranus is about 15% weaker than Earth’s, but it plays a powerful role in the dynamics of the Uranian system.
Norman F. Ness of the Goddard Space Flight Center in Greenbelt, Md., principal investigator on the magnetic field experiment, said the peculiar characteristics of the Uranian magnetic field probably account for the fact that the narrow rings around Uranus are surprisingly well defined, but dull. The 10th Uranian ring, discovered Friday but not announced until Saturday, was described as very faint.
Noting that all the rings are “not as bright as we had expected,” Brad Smith, chief of the imaging team, suggested that “there may be some form of sweeping mechanism that is getting rid of very fine materials.”
Reason for Brightness
He said that a higher percentage of small particles in the rings’ composition would reflect more light, causing the rings to appear brighter.
Scientists working on the project said smaller particles are more likely to carry an electrical charge, and that would cause them to interact with the magnetic field that constantly sweeps through the system. Thus the magnetic field probably pulls small particles out and away from the rings, leaving them less reflective while at the same time sharpening their edges.
The Uranian magnetic field, scientists have learned in the last couple of days, is quite different from anything found at any of the other planets in the solar system. Its greatest claim to individuality lies in the fact that the axis of the magnetic field is at an angle of 55 degrees from the axis of the planet’s rotation. That means that as the planet rotates--probably at a rate of about once every 16 hours--the magnetic field wobbles through an enormous gyration, much the same as a child’s top that is nearing the end of its spin.
Scientists are not quite sure yet just what impact that has on the complex Uranian system.
They will continue collecting Voyager data through the end of February, and many of the images and much of the data collected during Voyager’s closest encounter with the planet are still being processed at the Jet Propulsion Laboratory.
“The encounter is just beginning for most of the investigators,” said chief scientist Stone.
