TJO Newsletter Summer 2017

CANNONBALL! CASSINI’S FINAL DIVE By Mallory Thorp

After twenty years of exploring the solar system, So, what happens when you’re out of gas in the outer Cassini plans to go out with a bang. When NASA, the solar system? Without enough fuel, Cassini will lose the ability European Space Agency (ESA), and the Italian Space Agency to make fine adjustments to its course.1 We could leave Cassini (ASI) collaborated on a joint mission to send a man-made adrift in space, but such action is more harmful than it seems. object to Saturn, they had no intention of bringing it home. It The expired spacecraft could land on one of the moons of took Cassini seven years after its launch in 1997 to reach the Saturn, particularly Titan or Enceladus. Conditions on both Saturn system, and it doesn’t have the capacity to make the moons indicate possibly habitable environments. A crash same journey home.1 In fact, Cassini is running out of fuel. landing from Cassini would at least contaminate these environments before proper studies could be made, and at The Cassini orbiter was paired with the Huygens worst harm the early stages of life that could exist there.1 Probe for launch, the probe hitching a ride to Titan (one of the moons of Saturn) with the Saturn bound spacecraft. Cassini Naturally, the only solution then is to plunge Cassini itself has 12 instruments: some that see in wavelengths into the atmosphere of Saturn while we still have control of the invisible to the human eye, and others that can sense the tiniest spacecraft. But Cassini will not go down without a final show dust particles or even magnetic fields.2 Using these devices, worthy of its legacy. Cassini set out to collect as much information about Saturn as possible, as well as sending some excellent pictures back home. But these instruments, and the thrusters and reaction wheels that direct Cassini, need fuel to run.2 And the fuel gauge on this spacecraft is quickly pointing towards empty.

Figure 2: Image of Saturn and its rings taken by the Cassini Solstice Mission on February 3, 2017. Credit: NASA/JPL- Caltech/Space Science Institute

Cassini originally had two broad goals: to drop the Figure 1: Cassini-Huygens spacecraft, undergoing testing Huygens probe into Titan’s atmosphere, and to explore the before launch. Credit: NASA/JPL-Caltech/Space Science Saturn system for four years. Cassini completed this mission in Institute

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2008, having discovered new moons in the Saturn system such miles within the innermost ring.4 Along its dive, Cassini took as Methone, Pallene, and Polydeuces.2 The spacecraft numerous photos of the atmosphere (See Figure 3) . completed an extended mission called the “Cassini Equinox Cassini performed another successful dive on May 2, Mission” in 2010, further investigating the icy jets of and will continue to dive between the rings over the next few Enceladus and the methane lakes of Titan.2 Cassini has recently months. With the success of the first dive, Cassini is now finished its second extension (the “Cassini Solstice Mission”), sending in a constant stream of raw images of the planet with collecting fabulous images of Saturn like that shown above. each dive.5 On May 28, Cassini sent back some of the newest, After thirteen years of groundbreaking discoveries, and closest, pictures of the rings of Saturn (See Figure 4). Cassini is going to make the most of its final dive into Saturn. Beginning on April 26, 2017, Cassini performed its first of twenty-two dives between the atmosphere and the rings.4 Cassini will continue to orbit around Saturn, passing between the rings every week or so. On September 15, 2017, Cassini will perform one final dive as it falls into the atmosphere of Saturn and will be lost forever.4 Over the mission lifetime, NASA scientists will use data collected by Cassini to better understand the ringed planet. They will analyze the planet’s gravity and magnetic fields, study the material that makes up the rings of Saturn, sample ring particles that are funneled into the atmosphere by the magnetic fields, and collect up close pictures of the rings and atmosphere.1

That first dive was a nerve-racking day. Cassini Project Manager, Earl Maize, summarized NASA scientists’ concerns: “No spacecraft has ever been this close to Saturn before. We could only rely on predictions based on our experience with Saturn’s other rings, of what we thought this gap between the rings and Saturn would be like.”4 With the spacecraft traveling at 77,000 mph, even small particle collisions could be harmful to Cassini’s more sensitive equipment. To avoid any damage, Cassini was oriented such that its dish antenna would serve as a shield throughout the dive. As a consequence, Cassini would lose contact with Earth during this time.

At 11:56 p.m. (PDT) on April 26, 2017, 20 hours after Cassini went radio silent, Earth received a signal from the Figure 3: Raw images of Saturn taken during Cassini's first spacecraft.4 The dive was a complete success! Cassini dive. Top: Pole of Saturn. Bottom: Atmosphere of Saturn. approached the cloud top of Saturn within 1900 miles, just 200 Credit: NASA/JPL-Caltech/Space Science Institute

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SOURCES CITED

1 "Cassini: Mission to Saturn: Overview." NASA. Ed. Phillips Davis. NASA, 27 Apr. 2017. Web. 31 May 2017.

2 Dunbar, Brian. "JPL - Cassini-Huygens." NASA. NASA, 28 July 2008. Web. 04 June 2017.

3 Contributor, Elizabeth Howell Space.com. "Cassini-Huygens: Exploring Saturn's System." Space.com. Purch, 24 May 2016. Web. 05 June 2017.

4 "NASA Spacecraft Dives Between Saturn and Its Rings." NASA. Ed. Phillips Davis. NASA, 27 Apr. 2017. Web. 31 May 2017.

5 "Cassini: Mission to Saturn: Raw Images." NASA. Ed. Phillips Davis. NASA, 07 Nov. 2016. Web. 31 May 2017. Figure 4: Raw close-up image of rings, taken May 28, 2017. Credit: NASA/JPL-Caltech/Space Science Institute 6"2017 Saturn Tour Highlights." NASA. Ed. Phillips Davis. NASA, 24 Mar. 2017. Web. 31 May 2017. In the next couple of weeks, we can look forward to more stunning pictures of the ringed planet. Even on its final dive, Cassini will continue to send information to Earth about Follow @CassiniSaturn to get updates from Cassini’s “Grand the chemical composition of Saturn.6 Eventually, Cassini will Finale” Mission lose contact with Earth one last time. Friction with the atmosphere will set the spacecraft on fire and Cassini will burn up, more like a shooting star than a cannonball, as it plunges within the planet and disintegrates.6 During its final dive, Cassini will collect information about Saturn's atmosphere until contact is permanently lost.1

So do not weep for Cassini. The “Grand Finale” mission offers unprecedented opportunity to study the solar system’s second largest planet. Cassini program Scientist Curt Niebur put it perfectly: “The journey ahead is going to be a truly thrilling ride.”5

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