Photographs taken today of Saturn's huge moon Titan revealed a peachtinted globe whose color is believed to be the result of methane smog in the clouds of its dense atmosphere.
Five pictures of Titan taken by the Pioneer 11 spacecraft from a distance of 220,000 miles showed that the largest moon in the solar system possesses an atmosphere so thick that it totally obscures the surface from Pioneer's view. The photographs showed clouds striped in red, orange and pink, giving the moon the appearance of a celestial peach.
"We're looking at something that's chemically very interesting," said Dr. James Pollack of the National Aeronautics and Space Administration's Ames Research Center, where the flight of Pioneer is directed. "The colors we are seeing we think are the photochemical disassociation of the clouds, meaning smog."
The clouds over Titan are believed to be so dense that its atmosphere could be even thicker than Earth's. At the very least, the atmosphere of Titan is denser than that of Mars and could even be thick enough to support some primeval form of life although it is almost one billion miles from the sun.
Measurements taken today of Titan by Pioneer's ultraviolet and infrared instruments will shed more light on how thick and how warm the moon's atmoshpere really is, but these measurements will not be available until later this week.
Scientists know the atmoshpere of Titan is thick with methane, ethane, acetylene and some hydrogen. They also believe there is nitrogen in its atom atmoshere, the result of photochemical breakup of ammonia near its surface.
"We think Titan has an atmosphere that is a lot like the atmosphere of the primitive Earth," Dr. Donald Hinten of the University of Arizona said. "The thickness of its clouds makes it almost like a miniature Venus, meaning that, as cold as it is, Titan could retain some heat to make it warmer than it should be." This would be similar to the "greenhouse" effect on Venus that traps the sun's heat in its atmosphere.
Measurements from Earth show that Titan's clouds are as cold as 310 degrees Fahrenheit below zero, but scientists are convinced that the smog in its stratosphere keeps its surface at least twice as warm as the upper part of its clouds. There is even some chance that the surface temperature of Titan is just below zero, suggesting to some scientists that primitive life forms could exist on or near the surface.
Pictures taken today of the peach-like moon showed bands of pink at the north pole, where scientists believe there is a polar cap of frozen methane. They believe this methane glacier is continually releasing vapor into the atmosphere, and that the vapor is then broken down by the ultraviolet light of the sun. The methane polar cap is believed to be as thick as 500 feet.
Measurements taken today by Pioneer of Saturn's brilliant rings showed that their temperatures are no more than 150 degrees Fahrenheit above absolute zero (minus 451 degrees Fahrenheit), regardless of whether they were in the sun or not. The planet Saturn itself was a little warmer than expected, with a global temperature of about 270 degrees below zero Fahrenheit.
This means that the planet is generating its own heat from contraction and from the separating out of atmospheric gases like hydrogen and helium which produces the heat of friction in the atmosphere, according to Dr. Andrew Ingersoll of the California Institute of Technology.