Mar 31 1981
From The Space Library
NASA Headquarters held a press briefing on scientific results of Voyager 1's Saturn encounter in 1980. On hand were, project scientists Dr. Edward C. Stone, California Institute of Technology (CalTech); imaging-team leader Dr. Bradford Smith, University of Arizona; and project manager E.K. Davis, JPL. Initial results included discovery of a ring system vastly more complex than imagined and a thick nitrogen atmosphere around Titan, Saturn's major moon.
Voyager 1 took 17,500 photographs of Saturn and its satellites between August 22 and December 15, 1980. The closest approach was November 12-126,000 kilometers (78,000 miles) from Saturn's cloud tops. From the spacecraft, as from Earth, the atmosphere of Saturn looked grossly similar to Jupiter's, with alternating light and dark zones, circulating storm regions, and other distinguishable cloud markings.
Unlike Jupiter, however, Saturn's markings were blurred by thick haze above the visible cloud tops; the haze layer at Jupiter was not as optically dense as Saturn's. Wind speeds were substantially higher than on Jupiter and did not appear closely tied to belt-zone boundaries. Highest winds, blowing eastward at the equator, were four times stronger than on Jupiter; velocity decreased to near-zero at about 40° latitude north and south.
Saturn's atmosphere consisted mostly of hydrogen, helium accounting for only 11% of atmospheric mass above the clouds compared to 19% at Jupiter. The difference was consistent with separation by gravity of helium and hydrogen in Saturn's interior and could explain the excess energy radiated by Saturn over that received from the Sun.
Voyager 1 found that the A, B, and C rings visible from Earth consisted of hundreds of small ringlets, a few of them elliptical; the classical gaps also contained ringlets. Intertwining ("braiding") of the rings was not explainable, although it might stem from electrostatic charging of their dust-sized particles. Voyager 1 discovered three new satellites, photographed the D and E rings, and confirmed the existence (2.8 Saturn radii from planet center) of a new ring postulated on the basis of Pioneer 11 findings.
The flyby observed all of Saturn's known satellites except Phoebe: Mimas, Enceladus, Tethys, Dione, and Rhea, all appeared roughly spherical and composed mainly of water ice. Titan was the most interesting from an Earth viewpoint because of its atmosphere, similar to what would have evolved on Earth had it formed at Titan's distance from the Sun. Previously considered the largest satellite in the solar system, Titan was found to be slightly smaller than the largest satellite of Jupiter (Ganymede). Both are larger than the planet Mercury. Titan's atmosphere consisted mostly of nitrogen, the main constituent of Earth's atmosphere; pressure near the surface was 60% greater than Earth's. The surface was not visible in photographs from Voyager 1 because of the haze layer, though the southern hemisphere was slightly brighter than the northern, possibly a seasonal effect. Titan's density seemed about twice that of water ice, indicating that it, like Ganymede, was made of equal amounts of rock and ice.
Voyager 1 was now headed out of the solar system, and its platform instruments were turned off December 19. Most fields-and-particles instruments on Voyager 1 were still monitoring the solar wind and its changes with distance and time; exact location of the heliopause (outer edge of the solar wind) was unknown, but might be reached around 1990, Voyager 2 would reach Saturn in August 1981 and proceed on a trajectory to Uranus. (NASA Releases 81-41, 81-44)
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