Cassini Seeks Clearer View of a Saturn Moon
Space scientists hope to get their first close-up view of one of the solar system’s most confounding objects today as the Cassini spacecraft passes within 745 miles of Saturn’s smoggy moon Titan.
Using an array of infrared and radar imaging instruments, Cassini will attempt to peer through methane clouds to glimpse a landscape that has always been shrouded from Earth-based observers.
Scientists have speculated that within Titan’s orange haze, gasoline-type substances may fall like rain on a frozen landscape of rock-hard ice and hydrocarbon pools resembling a toxic chocolate sundae.
“Cassini will see Titan as it has never been seen before,” said Charles Elachi, director of NASA’s Jet Propulsion Laboratory in Pasadena. “We expect the onboard instruments will pierce the moon’s dense atmosphere and reveal a whole new world.”
The craft also could function as a time machine, opening a window on Earth’s early history. As the only other body in the solar system with a nitrogen atmosphere, Titan’s surface chemistry is thought to be similar to Earth’s billions of years ago, said Toby Owen, a Cassini scientist from the University of Hawaii.
Titan is too cold -- at minus 290 degrees Fahrenheit -- for life to develop. As a result, it is more like a frozen popsicle than the pre-biotic soup of early Earth.
The bus-sized Cassini spacecraft was launched in 1997. Because of its large size, there was no rocket capable of sending it directly to Saturn, more than 900 million miles from Earth. Instead, the craft swung past Venus, Earth and Jupiter, using the planets’ gravity to slingshot itself into the neighborhood of Saturn and its 33 moons, 15 of which have been discovered since Cassini blasted off.
Titan, Saturn’s largest moon and the second-largest moon in the solar system after Jupiter’s Ganymede, is a primary objective of the $3.2-billion Cassini mission. It is the only moon in the solar system that has so far been found to have an atmosphere of any kind.
That atmosphere is so dense that it has long kept Titan’s secrets hidden from prying eyes on Earth. “It has a thick smog layer that makes the problems in the L.A. Basin seem trivial,” Owen said.
Cassini passed about 200,000 miles from Titan in July. Images revealed tantalizing bright shapes winking through the haze. But it was impossible to tell whether they were lakes, ice sheets or something else. The current fly-by should yield images as much as a hundred times sharper, resolving objects the size of a football field.
“We’ll be able to see very small geological features,” said Robert H. Brown, who leads Cassini’s Visual and Infrared Mapping Spectrometer team at the University of Arizona.
Cassini also is equipped with cameras, a composite infrared spectrometer and radar. Another instrument will sample Titan’s upper atmosphere, which extends hundreds of miles above the surface. So far, Earth-based telescopes have detected 19 different chemicals in Titan’s atmosphere.
This fly-by -- the first of 45 close approaches to Titan planned during the four-year mission -- also will pave the way for an even closer encounter in January. That’s when Cassini’s Huygens probe is scheduled to land on the surface of the moon.
The hubcap-shaped, 9-foot-diameter probe contains imagers and equipment to sample the wind and the surface. The probe was designed by the European Space Agency, a partner in the mission with JPL and the Italian Space Agency.
Scientists said Monday that Cassini had been performing perfectly so far. Entering the atmosphere of another world could raise unforeseen dangers, however.
“This is not the same white-knuckle situation we had during Saturn orbit insertion, but there are some things we can’t control,” said Earl Maize, Cassini’s deputy project manager at JPL.
One worrisome possibility is that rainy weather on Earth could disrupt the spacecraft’s signal. Cassini will have only one opportunity to send its data to Earth before the material is overwritten. It takes 74 minutes for data traveling at light speed to reach Earth from Cassini.
