Cassini Ends its Mission by Intentionally Crashing into Saturn’s Atmosphere

 
 

Cassini enabled us to explore parts of our solar system in ways never before imagined. Christine Coffey explores the amazing spacecraft’s legacy.

 

Despite being arguably one of mankind’s most successful space missions and a flagship for future international collaboration between NASA and its European counterparts, the general public were largely unaware of the progress of the Cassini-Huygens mission. That is until they discovered that NASA were going to intentionally crash it into Saturn last month. Nothing draws a crowd quite like the impending write-off of a $3.27 billion space probe.

On October 15th 1997, the Cassini-Huygens mission launched with a rocket launcher from the Cape Canaveral Air Force Station, Florida. It was the start of a mission that would last 19 years, 11 months, and 15 days. NASA and the European Space Agency entered this joint venture with modest objectives compared to the return of information received from the probes. They wanted to gather more information about Saturn’s many moons, profile the planet’s complex gravity field, and more specifically the mysterious rings that were first observed by Galileo in 1610.

“The mission revealed gigantic hurricanes on the planet itself, the largest of which is located at Saturn’s North Pole.”

The spacecraft initially used Venus and Jupiter’s gravity fields to slingshot itself into the outer Solar System, before eventually arriving in Saturn’s orbit on July 1st 2004. The spacecraft comprised of two main components, Cassini, the American orbiter, and Huygens, the European landing probe. On Christmas Day in 2004 the Huygens landing pod was detached from the Cassini orbiter to enter the atmosphere of Titan, Saturn’s largest moon. This moon is bigger than the planet Mercury and its size dwarves Pluto, which was still considered a planet when this project started.

Titan is a very cold ‘Earth-like’ moon, with average temperatures of -179.5oC. Huygens completed the farthest landing away from Earth and simultaneously the first landing in deep space. The landing probe collected data from Titan which was previously unobtainable because of the density of its atmosphere, which appears orange when viewed from space. We now have a clearer image of the moon itself, with its liquid methane lakes and ethane clouds that combine with nitrogen to create the moon’s organic smog. Titan’s methane cycle is rather similar to our water cycle here on earth. Today, Huygens boldly squats where no landing probe has ever squatted before and patiently waits to be retrieved. As of yet, no retrieval mission is planned.

“Its total distance covered came to an astounding 7.9 billion km.”

The Cassini orbiter went on to do a lot of travelling after its split with Huygens. Its total distance covered came to an astounding 7.9 billion km. A total of 294 orbits of Saturn were completed and much was discovered about the rings of Saturn in particular. The rings themselves are composed of rocks ranging in size from as small as fine dust to as big as mountains. The ring system itself is over four Earth diameters wide, but very thin, kept in place due to the gravitational pull of a large number of moons. The mission revealed gigantic hurricanes on the planet itself, the largest of which is located at Saturn’s North Pole. This storm is over twice the size of earth, has an eye approximately 2000 km wide and bizarrely, is almost a perfect hexagon in shape.

“Six new moons were discovered and the birth of a new moon was witnessed.”

Although Titan was the main focus in terms of Saturn’s moons, the people working on the project greatly underestimated the extent of information they would collect about the planet’s moons. In particular, the moon Enceladus was the surprise of the mission. Cassini reported geysers firing water and strong evidence of an ocean under its surface. This means there could be potential microbial life on both Titan and Enceladus. The moon Pan deserves a mention too, as Cassini imaging revealed similarities in shape to ravioli or a really large walnut. Six new moons were discovered and the birth of a moon was witnessed.

“In Cassini’s last manoeuvre, the orbiter had one more encounter with the moon Titan which changed its trajectory and set it hurtling towards Saturn, a manoeuvre which has been named the ‘Goodbye Kiss.’”

With little fuel left and a reluctance to leave Cassini in orbit in case it should crash with Titan or Enceladus, contaminating them with microbes from earth, an executive decision was made to terminate the mission by crashing the orbiter into Saturn’s atmosphere. NASA sent the orbiter into close proximity with Saturn’s rings, much closer than it had been sent before. In Cassini’s last manoeuvre, the orbiter had one more encounter with the moon Titan which changed its trajectory and sent it hurtling towards Saturn, a manoeuvre which has been named the ‘Goodbye Kiss.’

On September 15th 2017 Cassini crashed into Saturn’s atmosphere, igniting and breaking apart in a poetic end to a mission that encapsulated the ideals of space travel perfectly. As Linda Spilker, a member of the Cassini-Huygens team said, “We take comfort knowing that every time we look up at Saturn in the night sky, part of Cassini will be there, too.”

 

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