Storms raging on the sun for the last month have so badly disrupted radio communications in space that the signal rate from the Pioneer 11 spacecraft approaching the planet Saturn today was cut in half.
"Streams of electrons from the sun are causing bursts of high noise that drown out as much as 25 percent of our data," Pioneer Project Manger Charles F. Hall said today at the National Aeronautics Space Administration's Ames Research Center where Pioneer is directed, almost a billion miles from Saturn.
"This is completely unacceptable, which is why we're lowering our bit rate from 1,024 to 512 bits [of information] per second."
Lowering the transmission rate allows engineers to filter out the radio noise generated by the solar storms but it also means scientists on earth will get half measurements and half pictures of Saturn and its brilliant rings when Pioneer 11 makes it historic pass-by of the planet on Saturday.
"It will not effect the resolution of our pictures but it will mean the pictures will be a little smaller," Dr. Thomas Gehrels of the University of Arizona explained. "We may be getting a little less than the full planetary disc will all its rings in each picture."
The sun goes through 11-year cycles during which storms flare up and decline. The sun is rapidly approaching its period of maximum activity, in which the frequency and force of the storms ncrease.
A large flare burst on the surface of the sun a month ago. It was followed by two more in the last two weeks, their output of protons and electrons increasing dramatically in the last 24 hours. The shock wave created in space by this sudden tidal wave of solar particles was enough to raise the noise level in space to 10 times normal.
The situation will continue for days, Dr. John Simpson of the University of Chicago said, "It's like being locked up inside a magnetic bottle, where you have to take certain precautions."
Meanwhile, as it neared Saturn, Pioneer 11 was making its first significant discoveries about the giant ringed planet. Sometime in the early afternoon the 570-pound spacecraft flew into a detectable magnetosphere, proving that Saturn was surrounded by a strong and sizable magnetic field.
"We now know that Saturn has a finite, intrinsic magnetic field," Pioneer Project Scientist John A. Wolfe said today. "From what we see so far, it looks as if it's roughly equivalent in strength to the earth's magnetic field."
Since Saturn is so much bigger than the earth this means the planet's magnetic field is also larger than the earth's. Scientists estimated that Saturn has a magnetic field 700 to 1,000 times the size of the earth's magnetic field.
Finding that Saturn possesses a magnetic field means the planet has a fluid interior, which is carrying energy to the surface.Since the planet is spinning so fast -- it makes a complete revolution in 10 hours -- the energy carried out of the interior is generating its own magnetism as if it were a dynamo.
Saturn's strong magnetic field means the planet possesses belts of trapped radition, probably more than the earth but less than the giant planet Jupiter. Saturn's magnetic field also means the planet is generating its own heat, either through a process of cooling off or contracting since the beginning of time. Tidal heat may also be created in its atmosphere by the pull of the four giant rings and 10 known moons that are circling Saturn.
At 10:44 a.m. EDT, on Saturday, Pioneer 11 will pass under the outermost of the planet's four rings, spend the next two hours flying below the rings and then soar out from behind the planet and above the rings.
It will be an hour and 26 minutes before flight directors on earth know whether the Pioneer survived its passage of the rings; that is how long it takes for for the spacecraft's radio signal to reach the earth.
At the speed Pioneer 11 was transmitting information to earth, there were 5.5 million pieces of Pioneer information in space at any given second today. Each piece of information was separated by 182 miles of space.