![]() “Now we understand, as we did not before Cassini, that (surprisingly) the processes are the same as on Earth. Some processes must be steadily changing Titan’s surface to get rid of the craters. “We’d expect to see more – look at Earth’s moon,” Wall said. Titan doesn’t have nearly the number of craters that scientists thought - maybe just a few dozen. Until the Cassini flyby of July 22, 2006, that is. But with a dense haze preventing a closer look it has not been possible to confirm their presence. The existence of oceans or lakes of liquid methane on Saturn's moon Titan was predicted more than 20 years ago. “It’s a whole lot more earthlike than we expected,” Wall said. The radar instrument helped scientists create the first global topographic map of Titan. Each Titan flyby was a little different from the next, which allowed radar to see different areas of Titan. Each time the radar got a close look at Titan, it recorded what it saw as it flew by, producing one strip of mapping coverage. However, Cassini reached Saturn orbit in 2004 and performed more than 100 flybys of Titan. “Before Cassini, using Earth-based radio telescopes, just about all you would see was one bright spot, and you couldn’t see much else because of the atmosphere,” Wall said. “It’s actually called the ‘Titan Radar Mapper.’” Wall estimates that 90 to 95 percent of radar’s work since arriving at Saturn was on Titan. “Titan was radar’s reason for going, for being on the spacecraft,” Wall said. Radar data was used to create black and white images in which rough surfaces appear bright and smooth surfaces appear dark. By measuring exactly how long it took the radio waves to travel from the spacecraft to a surface (and dividing by the speed of light), radar determined the heights and depths of the veiled world’s surface features. Instead of visible light, Cassini’s radar emitted radio wavelengths, which bounce off hard surfaces. “A radar is like a flash camera,” Wall said. Steve Wall has been helping to design instruments for NASA missions since the mid-1970s and is a scientist at NASA’s Jet Propulsion Laboratory - as well as acting team leader for the radar instrument. ![]() Radio waves, however, can travel through thick atmospheres, which is why a car radio receives a signal whether it’s sunny, foggy, raining or snowing. When the Cassini mission was originally planned, scientists understood that Titan’s haze would hide its surface from most instruments. ![]()
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