During its two-and-a-half-hour descent through Titan's atmosphere, the probe was expected to send more than a thousand images and details about the lunar atmosphere's structure, composition, and winds.
"We should get a pretty thorough understanding of both the chemistry of the atmosphere and also what's going on at different altitudes of the atmosphere," Johnson said before the probe's arrival at Titan.
The atmosphere of Titan extends ten times farther away from the surface than the Earth's atmosphere does. Titan's atmosphere is composed of nitrogen, methane, and other organic compounds. Scientists believe the chemistry there is similar to that of Earth's before life evolved on our planet.
Data gleaned from the cameras and gas analyzers aboard Huygens may provide clues about the origin of life on Earth.
"It's like looking back in time, to a certain extent," Johnson said. "Imagine taking this chemical melting pot common in the Earth's atmosphere [billions of years ago] and putting it in cold storage, and you get Titan today."
The probe was expected to land just south of Titan's equator. But scientists were not sure what it would land in or on: ice, a sea of methane, or something else.
"Will Huygens splash or splat?" Bruce Betts, director of projects at the Planetary Society in Pasadena, said before the landing. "As an example of how we continue to understand Titan, there continues to be uncertainty as to how much of its surface is solid and how much is liquid."
After landing, the probe was expected to have no more than two hours to relay images about Titan's surface before Cassini drifted over the horizon, severing communications forever.
Titan's atmosphere is so thick that it has been impossible for scientists to determine what the surface of this moon looks like. Recent images of Titan taken by cameras aboard Cassini have only added to the mystery.
Showing light and dark patches, the images lack any sign of impact craters, suggesting that geologic activity or weathering has erased them.
"We can't really interpret what we're seeing," Johnson said.
It is highly unlikely that life exists on Titan. With a surface temperature of minus 180 degrees Celsius (minus 292 degrees Fahrenheit) and barely illuminated by the distant sun, Titan is not believed to have the warmth or light essential for life.
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