A silver-and-black Voyager spacecraft swept under the majestic rings of Saturn tonight after discovering that one of the rings has braids.
"It defies the laws of orbital mechanics as I understand them but two components of the fifth ring out are braided," said Dr. Bradford Smith of the University of Arizona, one of the scientists gathered at the Jet Propulsion Laboratory here to study photographs being transmitted from the spacecraft. "If the distribution of these braids is uniform around the entire ring then there are as many as 1,000 braids in the ring."
Not only is the fifth ring in braids, Smith said, but the 500-mile-long braids appear to have kinks in them. Smith said that as bizarre as the braids are the kinks are even more bizarre.
"If you look closely, you see abrupt bends in the braids, as if somebody took the surface and bent it," Smith said. "I don't even pretend to understand what this means."
Finding the braided ring was the highlight of a day that climaxed the 1.3-billion-mile flight of Voyager to Saturn. It is a journey that began more than three years ago at Cape Canaveral, took the spacecraft by Jupiter two years ago and, Congress willing, will take it across the orbit of Uranus in five years, Neptune in 10 years, distant Pluto in 14 years and then on out of the solar system.
As it sped under the rings at 50,000 miles an hour, Voyager sent back photographs that dazzled the mind and eye. Boyager's count of Saturn's rings has risen each day as the spacecraft neared the planet and today it rose again. The number of rings in sight of the spacecraft's cameras came to more than 300, a far cry from the six rings known to exist before Voyager's arrival at Saturn.
"I counted two dozen new ringlets in the Cassini division [the gap between the two brightest rings named for the Italian astronomer who found it] and stopped counting," Smith said. "By the time we get our best pictures of the rings, we may have as many as a thousand distinct rings."
Before soaring under the rings this afternoon, Voyager flew by the moon of Saturn called Titan and turned its instruments back at it to take a measure of its atmosphere, the only sizable atmosphere of any moon in the solar system. What it found was every bit as surprising as the 300 rings.
"Our first look at the data suggests we are not looking at a thin atmosphere," Voyager Project scientist Edward C. Stone said. "The atmosphere we see on Titan might be as dense as the atmosphere we have here on earth.
It will take at least another day for scientists to calculate how thick Titan's atmosphere is, what it's made of and how warm it is, but it was clear today that Titan's atmosphere is more complicated and a lot warmer than scientists expected.
"A conventional body one billion miles from the sun should be no warmer than 90 degrees above absolute zero," Dr. Garry Hunt of the University of London said. "We're seeing something much warmer than that, so that I can only infer there is a weak greenhouse effect on Titan like the strong one we find on Venus that traps the heat it gets from the sun."
So flawless was Voyager's flight by Titan that it missed its aiming point -- 2,500 miles from the moon's south pole -- by no more than 12 miles. Said Dr. Charles Kohlhase of the Jet Propulsion Laboratory: "That's like shooting a billiard ball at a pocket 2,000 miles away and making the shot."
One after another, Voyager's pictures streaming back to earth today showed why astronomers are so spellbound by the rings of Saturn. Giant beams of sunlight passed through the gaps in the rings, distant stars shone through the thinnest rings and several times one of the larger of Saturn's 15 moons would appear hovering beyond the outermost ring.
Closeup pictures of the moon named Mimas made it look like a woman's breast. The scientific explanation for its appearance was that there was a huge crater on the moon whose uplifted central peak had been carved in the moon's icy exterior forever by an ancient meteorite. Still another closeup picture of the moon Tethys revealed a trench 50 miles wide and almost a mile deep that had been left there by a deep-seated tremor millions of years ago.
"The features on these moons look frozen in time," said Dr. Laurence Soderblom of the U.S. Geological Survey. "That's because of their icy crusts. Ice at these temperatures [87 degrees above absolute zero] behaves just like rock."
The spacecraft had its closest encounter with Saturn at 6:45 p.m. Washington time, flying near its south pole 77,000 miles from the surface of the planet. Saturn above appeared streaked with golds, browns and yellows. White-and-tan clouds thousands of miles across swelled along inside the streaks, making the planet look like Jupiter.
As beautiful as the pictures were today, scientists said the photographs to be taken on Thursday as the spacecraft looks back at the planet in shadow might be even more spectacular. The sections of the rings darked by shadow on the inbound flight will show up in sunlight on the outbound leg. The glare that hides some of the structure in the rings will disappear as the spacecraft flies away from the planet, revealing details not seen on the inbound leg.
As the spacecraft flies away from the planet, it will also have its closest encounters with some of Saturn's largest moons.
Photographs taken today of the moon Rhea showed it glowing blue and white in an icy kind of brilliance that made it look like an enormous sapphire. wOne feature on the moon looked for all the world like a white crescent smile.
"The colors on these moons are very subtle," Soderblom said. "We won't know what to make of them until we see them up really close on Thursday."
Voyager's flight past Titan was so close early in the day that the moon's gravity gave the spacecraft an additional kick that put it slightly off course when it came out beyond the rings to photograph Rhea and the moons Dione, Tethys and Mimas. The spacecraft late tonight was 1,000 miles farther from Dione than flight directors wanted it to be.
"This is not a disaster by any means," the laboratory's Kohlhase said tonight. "We're still well within the path we wanted to be originally."
The pictures of Dione sent back by Voyager seemed to confirm what Kohlhase said. Brilliant images of this small moon showed Y-shaped patterns carved into the icy surface that suggested some ancient internal heating had cracked the surface.