For scientists studying the Voyager 2 data from Uranus, the only thing that hasn't surprised them is the extent to which they have been surprised. They knew so little about Uranus in advance that they expected almost anything Voyager found to be a revelation. Nevertheless, they still weren't prepared for what the hardy spacecraft is sending back, as project scientist Edward C. Stone explains at every press conference at the Jet Propulsion Laboratory in Pasadena, Calif.
``We certainly didn't expect to find a dark polar stratosphere [on Uranus's night side] that was warmer than the sunlit side,'' he says. He says scientists also are baffled by winds on the planet, the circulation of which reflects a temperature distribution quite different from what they would expect to be produced with the sun shining down almost directly on the polar region.
Referring to estimates of the makeup of Uranus's Epsilon ring -- the outermost ring -- Dr. Stone remarks that he doesn't ``know of anyone that suggested we would find rings which were mainly meter-size and larger particles, when at Saturn all the rings were mainly centimeter and smaller size [particles].''
``It's just an indication that the Uranian system with the satellites is just totally different than anything else we've seen,'' he observes.
Scientists looking at Voyager's pictures of those satellites constantly refer back to what they saw at Jupiter and Saturn and shake their heads. Moon expert Laurence A. Soderblom of the United States Geological Survey said that the five major previously-known satellites are a collection of bodies quite unlike anything he has seen before.
He noted that the moon Miranda -- with its deep valleys, flowing fluids, craters, and other geological formations -- looks as though ``you took all the bizarre features in the solar system and put them on one object.''
The other moons, too, are puzzling. Most of them appear to be extremely active geological. But one of them -- Umbrial -- is very dark, old, and inactive. ``Why,'' Dr. Soderblom asked rhetorically. ``It's a good question,'' he said. ``We don't know why.''
Scientists studying the so-called ultraviolet (UV) electroglow, which had been detected by the International Ultraviolet Explorer satellite long before Voyager reached the planet, also ask ``why?'' A. Lyle Broadfoot of the University of Arizona likened the process, which solar UV stimulates, to speaking over a public address system.
He noted that he puts very little sound energy into the microphone. But, using energy from the local power station, the public address system fills the auditorium with audio energy.
He said that the process that takes weak solar UV and then emits much stronger UV as the electroglow is what is unknown. ``We do not know where the powerhouse is [on Uranus],'' he said, ``There is some process coupled to some mechanism in the atmosphere which generates this excess energy.''
Meteorologists, likewise, are puzzling over the possible nature of the unknown atmospheric mechanism that refrigerates the Uranian atmosphere at intermediate levels in the sunlit polar regions.
Some such mechanism must be at work for the winds deduced from cloud motion blow in the same direction as the planet rotates. This implies a temperature distribution which, like that on Earth, is warmer toward the planet's equator than at the pole. Yet, with the sun shining more strongly on the Uranian polar region, meteorologists would expect the temperature distribution to be the other way around.
Voyager will continue to study the Uranian system through February and scientists will continue to scramble to comprehend the information it sends back. Data ``are literally coming in like a firehose,'' Soderblom observed.
``Every day it just gets better,'' said an enthusiastic Edward Stone.