Voyager 2 Beams Back Surprises as It Hurtles Toward Uranus

The spacecraft Voyager 2 is sending back a few surprises as it hurtles toward a Jan. 24 encounter with the planet Uranus, scientists reported Tuesday.

Lead scientists on the project, who briefed reporters across the country via a closed-circuit television hookup from Washington, said the craft is still far away from the huge planet, but they said some clues are emerging.

Computer-enhanced photos from the spacecraft still show Uranus as a fuzzy, blue ball, although the most recent picture, taken last week, shows one of nine rings known to rim the planet’s equator. The planet appears blue because of the methane--natural gas--in its atmosphere.

Uranus is “the most remote object yet to be visited by a spacecraft,” said project scientist Edward Stone of the Jet Propulsion Laboratory near Pasadena. When the craft draws closer to the mysterious Uranian system, “the opportunity for discovery and surprises will be great.”

Voyager is to fly about 50,000 miles over the clouds that engulf the planet at 10 a.m. on Jan. 24, after passing within 18,000 miles of one of its known five moons, Miranda. The Miranda encounter will be the closest that Voyager will get to the Uranian system.

After it was launched in August, 1977, Voyager passed by the planets Jupiter and Saturn, sending back spectacular photographs of those bodies and their moons, and then began the long journey toward Uranus and possibly Neptune. As Burton I. Edelson, head of space science for the National Aeronautics and Space Administration, put it Tuesday, the craft is now passing through the “chill, wintry countryside” of the solar system.

Preliminary data from the spacecraft indicates that Uranus, the seventh planet from the sun, has a far weaker magnetic field than anticipated, but its atmosphere may contain 40% more helium than scientists had expected.

“If there is that much, it would have major implications for the interior of the planet,” said JPL’s Edward Stone, chief scientist on the project.

The higher percentage of helium would suggest that hydrogen must have been subtracted from the atmosphere and “dissolved in the oceans below,” leaving the atmosphere richer in helium, Stone said.

One of the most promising leads so far stems from what the Voyager has not found--receivers aboard the craft have been unable to detect any sort of radio waves emitted by the planet. That would indicate that the planet has no magnetic field, according to Michael Kaiser, a member of Voyager’s radio astronomy team.

Kaiser said the craft picked up radio emissions from Jupiter “literally on launch day.” But, although Voyager is much closer to Uranus now than it was to Jupiter then, “We have seen no signals whatsoever (from Uranus),” he said.

Since a planet needs an internal energy source to create a magnetic field, it seems likely then that the interior of Uranus is cold. By contrast, radioactive decay in the Earth releases heat, in effect turning the planet into a dynamo, thus creating a magnetic field.

The evidence so far suggests that Uranus “has no clear-cut energy source to drive a dynamo,” Kaiser said.

These findings are preliminary and are subject to revision during the weeks ahead as more and more data is supplied by the spacecraft.