Cassini science team members await final loss of signal from the Cassini spacecraft, indicating it's destruction in Saturn's atmosphere. Cassini revealed new details about the unusual surface of the moon Titan, which is dotted with liquid methane lakes, rivers and oceans.
The twin Voyagers swung by Saturn in the 1970s and '80s, giving scientists a rough outline of the planet and its moons.
31 am, Paris time, the space probe will penetrate into the higher spheres of Saturn, before starting a precipitous drop.
Contact was lost with the Cassini spacecraft a minute after it reached an altitude of about 1,500 kilometres above the planets estimated cloud tops. Because of the density of the atmosphere this close to Saturn, the spacecraft used the MR-103H thrusters to maintain stability under conditions similar to those encountered during many of Cassini's close flybys of Saturn's moon, Titan, which has its own dense atmosphere.
But its current route, mortal as it may be, was too tempting.
Scientists and engineers altered the orbit of the spacecraft to run into Saturn, where it would safely burn up in its atmosphere.
Plenty of scientific analysis has already occurred since Cassini arrived at Saturn in 2004.
Spacecraft navigators predict the trajectory with astounding precision. During April, NASA added Cassini to the ever-descending series. It's spent the past 13 years studying the planet, its rings, and moons in unprecedented detail.
Some 4,000 scientific papers have been based on data from the mission, said Mathew Owens, professor of space physics at the University of Reading.
Saturn's rings cut across Titan's luminous crescent and the smaller moon Enceladus, June 2006. Jupiter's moon Europa is another example. Perhaps most importantly, it illuminated processes and forces that shaped the early days of the solar system-forces that have made our planet what it is.
In short, Cassini not only fulfilled its mission, it exceeded expectations. More than 175 refereed journal articles and book chapters have been published by MIMI team lead authors, said MIMI Deputy Principal Investigator Chris Paranicas, with hundreds of others that use MIMI data and include MIMI team co-authors.
Scientists believe Titan's "pre-biotic" environment could also support life, but not necessarily as we know it.
But Cassini still made the most of its final descent.
The spacecraft is in the process of emptying its onboard solid-state recorder of all science data, prior to reconfiguring for a near-real-time data relay during the final plunge, NASA said.
"It turns out that Titan has got big lakes, sand dunes and rivers which, from space, look pretty much like rivers on Earth".
"Cassini's finale tonight will certainly be a bittersweet moment, but I don't think of it like the death of a friend", Mr Nagle said.
NASA experts chose to carry out a controlled completion of the mission, to avoid collision of the device with the months of Saturn, which is potentially life.
Linda Spilker, Cassini's project scientist, said, "I'm feeling a mixture of sadness and pride".
Clark isn't the only one who is feeling the bittersweetness of the project's end.
"From its launch in 1997 to the unique Grand Finale science of 2017, the Cassini-Huygens mission has racked up a remarkable list of achievements". The company's propulsion has facilitated the end of NASA's Magellan, Lunar Prospector, and Mercury MESSENGER missions, among others.