A balloon built by France and the Soviet Union and tracked from Earth by the United States has become the first to measure wind speeds on another planet. It was dropped by spacecraft into the cloud-shrouded atmosphere of Venus on Monday and broadcast until yesterday morning.
Winds in the middle atmosphere of Venus carried the balloon, 10 feet in diameter, one fourth of the way around the planet at speeds up to 124 miles (200 kilometers) an hour.
"The batteries built to power our radio were designed to last precisely 46 hours and that is precisely what they did," Dr. Jacques Blamont of the French National Space Agency said by telephone from California's Jet Propulsion Laboratory, where the balloon was tracked. "Everybody involved in this international experiment is overjoyed with the results."
The interplanetary weather balloon was dropped from the Soviet spacecraft Vega 1 into the Venusian atmosphere -- 67 million miles from Earth -- and was inflated with helium at 10 p.m. EDT Monday.
Its radio signal was picked up by a U.S. antenna near Canberra, Australia, then relayed in turn to U.S. antennas in Madrid and in Goldstone, Calif.
"The balloon traversed about half of the nightside of the planet," Blamont said. "We received excellent data the entire time the balloon's radio was transmitting. Everything worked exceedingly well."
The balloon carried a gondola of instruments to study wind speed, turbulence and cloud-mixing. Scientists believe that turbulence and "wave motions" in the planet's dense acid clouds are the key drivers of the busiest "weather machine" among the four planets in the inner solar system -- Mercury, Venus, Earth and Mars.
The middle regions of the seething planet's atmosphere were chosen because they are believed to be cooler than winds near the surface and less violent than winds in the upper atmosphere.
To survive at the top of the clouds of Venus, a balloon would have to measure at least 50 feet across, too large even in an uninflated state to be carried by an unmanned spacecraft from Earth.
A second Vega spacecraft is to reach Venus today and a second balloon released.
Vega 1 is now on its way to a March 1986 rendezvous with Halley's Comet, where it will be joined by the second Soviet Vega spacecraft. In an unusual display of cooperation, the three huge U.S. antennas will help navigate the two Vegas to their rendezvous.