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The spacecraft that showed us amazing things

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Cassini gazes across the icy rings of Saturn toward the icy moon Tethys, whose night side is illuminated by Saturnshine, or sunlight reflected by the planet. (Courtesy NASA)


Ten days ago, the Cassini mission to Saturn ended. NASA had commanded it to plunge in a death dive into the planet’s thick atmosphere. Streaking toward Saturn at 75,000 miles an hour, Cassini’s thrusters struggled to keep the spacecraft’s antenna pointed at Earth, trying to transmit as much data as it could. When it finally exhausted all its fuel, it looked away. The transmissions stopped. A minute later, the spacecraft broke apart and was completely vaporized. Its atoms are now and forever part of the planet it had orbited and studied for 13 years.

Cassini made amazing discoveries about the distant gas giant, its rings and many moons. Its discoveries revolutionized our thinking about life in the solar system. It was also a shining example of what we can accomplish when countries work together instead of going it alone.

The Cassini mission was a collaboration of three space agencies: NASA, the European Space Agency and the Italian Space Agency. Nineteen countries contributed hardware to the spacecraft. No single country could have funded, built and run such a complex mission alone. Because of the international cooperation, Cassini was able to show us spectacular things.

Cassini gazes across the icy rings of Saturn toward the icy moon Tethys, whose night side is illuminated by Saturnshine, or sunlight reflected by the planet. (Courtesy NASA)

Cassini’s cameras captured an enormous vortex at Saturn’s north pole, big enough to fit four Earths inside, a hurricane shaped by swirling jet stream winds into a nearly perfect hexagon, with six abnormally straight sides.

Then, there are Saturn’s rings, the flattest structures known — more than 60,000 miles wide, but only tens of yards thick in places. They’re composed of an enormous number of individual ice particles, ranging from marbles to chunks as big as a house, that jostle for position within a ring as they orbit like stock cars at Daytona.

Before Cassini, we thought Saturn’s moon Enceladus was a cold, dead world. The moon is only 300 miles wide, one-seventh the size of the Moon, and covered in ice. But Cassini photographed hundreds of geysers shooting out ice particles from cracks in the icy crust. As one scientist said, the moon appears to be “hurling its guts into space at a colossal rate.”

Cassini discovered that the core of Enceladus is hot, heated by constant pushing and pulling from Saturn’s gravity as it orbits the planet. A vast global ocean of salty water — about the same salinity as Earth’s oceans — lies under the moon’s icy surface. Hydrothermal vents on the ocean floor release heat and chemical compounds — including some building blocks of life on Earth — from the moon’s core into its ocean.

Clouds on Saturn take on the appearance of strokes from a cosmic brush thanks to the wavy way that fluids interact in Saturn’s atmosphere. (Courtesy NASA)

Enceladus has all the elements needed for life as we know it: liquid water, heat and simple organic chemicals. It may be the best place to look for life outside of Earth.

Titan, Saturn’s largest moon, on the other hand, may be the best place to look for life as we don’t know it. Titan is the only body in the solar system other than Earth that has a thick atmosphere, although it has no oxygen. Before Cassini, we knew little about Titan’s surface. Now, we know it is eerily Earthlike, with mountains, deserts and large dunes sculpted by wind. But instead of bedrock, Titan’s mountains and surface are made out of rock-hard water ice. Freezing-cold Titan has river channels carved by liquid methane and liquid ethane — essentially liquid natural gas — not water. Lakes of these liquid compounds dot the northern hemisphere. Indeed, Titan is the only place, other than Earth, that has stable liquids on its surface.

It’s tantalizing to wonder if some kind of truly alien microbial life could possibly have developed in Titan’s liquid methane lakes.

Cassini team members Scott Eddington, left, and Nora Alonge embrace on Sept. 15 in Jet Propulsion Lab auditorium in Pasadena, Calif, after telemetry ended as Cassini burned up in Saturn’s atmosphere. (Brian van der Brug/Los Angeles Times/TNS)

Unfortunately, it will be a generation before we can return to Saturn to find out.

As Cassini’s thruster fuel began to run out, mission managers decided they couldn’t risk an out-of-control spacecraft crashing into Enceladus or Titan. They worried that there could be hitchhiking Earth microbes that somehow survived the craft’s decades in space. To keep the moons’ environments free from Cassini’s microbial contamination, the managers decided to send the spacecraft plunging into Saturn while they could still control it.

We learned so much from Cassini, both in terms of groundbreaking science and international collaboration. RIP Cassini.

Sally Stephens is an animal, park and neighborhood activist who lives in the West of Twin Peaks area.

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