In less than a month, we will stop getting any new science from Saturn. Cassini will take its final bow on September 15 as it plunges into the giant ringed planet. This might seem like a rather over-the-top finale, but it is necessary. Cassini is a contaminant risk for Saturn’s system and therefore must be destroyed.
The Cassini mission signed its own death warrant when it discovered salty oceans under the ice of Saturn’s moon Enceladus, and complex chemistry on its moon Titan. This is because Cassini has not been properly sterilized, so it's possible that bacteria from Earth hitched a ride to the outer Solar System when the probe was launched in 1997. While the deep-space conditions of the last 20 years might have been fatal for the bacteria, we cannot take the risk of them finding their way to cozy Enceladus.
The spacecraft is also running out of fuel, so a decision had to be made. NASA, the European Space Agency, and the Italian Space Agency developed the mission together and together decided that the best course of action was to destroy the probe this September.
A tragic ending doesn't have to stop the science, however. The researchers carefully thought out how not to waste a single second. This last chapter, called The Grand Finale, will have Cassini go where no other probe has gone before. It will conduct 22 daring orbits between Saturn and its rings. The last five of these orbits will be extremely close, taking the spacecraft just over 1,600 kilometers (1,000 miles) above the surface of the planet.
On September 11, the probe will use a gravitational push from Titan, Saturn’s largest moon, to get into a lower orbit. Just four days later, Cassini will have its last fateful encounter with the Lord of the Rings.
"This planned conclusion for Cassini's journey was far and away the preferred choice for the mission's scientists," Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory (JPL), stated in April. "Cassini will make some of its most extraordinary observations at the end of its long life."
She's not wrong. Cassini has taken some spectacular pictures of both the rings and clouds of Saturn. This is also just the beginning of the data analysis, as planetary scientists will be pouring on the data for a long time.
In its 13 years around Saturn, the mission has studied the system like never before. It had a probe attached to itself, named Huygens, that was dropped on Titan, Saturn’s largest moon. Titan has a thick atmosphere, as well as lakes and seas made of liquid methane. Titan and Earth are the only objects in the Solar System with large liquid bodies on their surface.
Lately, Enceladus has grabbed a lot of interest, and with good reason. A few months ago, it was announced that hydrothermal activities occur at the bottom of its ocean. Suddenly, this icy moon jumped to frontrunner of where life may exist outside of Earth, confirming that the team made undeniably the correct call to visit this region of the Solar System.
Hydrothermal vents indicate important chemical reactions, which might mean life. While it might turn out that the conditions are actually not suitable for life at all, that would be a gamble not worth taking.
"Cassini's own discoveries were its demise," said Earl Maize, an engineer at NASA's JPL who manages the Cassini mission, at the Grand Finale announcement conference last April. “It has essentially rewritten the books on Saturn. But it’s just a chapter, the book is not complete.”
Listing Cassini’s successes will take a long time, which tells us just how revolutionary this mission has been. Cassini will be used as a benchmark for all future planetary exploration missions.
The clock is now ticking for the spacecraft. It will soon plunge into Saturn and we can be certain that it will go down in a blaze of glory.
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