Cassini's quest: What a lonely probe is teaching us about Saturn

About 750 million miles away from home, one of NASA's oldest spacecrafts is nearing its end. The Cassini probe has been orbiting Saturn for nearly 13 years, and over the next four months, it's been programmed to pull off a series of increasingly risky maneuvers before it plummets into the planet's atmosphere, meeting its fiery doom on September 15.

Up until last month, Cassini had been observing Saturn from a safe distance. But as the spacecraft runs out fuel and the end of the mission nears, NASA's used the gravity of Saturn's moon Titan to push Cassini into a risky orbit that takes it between the planet and its rings. Risky, because on each of 22 orbits around the planet, Cassini will shift closer and closer to either the rings or Saturn's atmosphere. The closer it gets to the rings, the higher the chance that it could be damaged by debris. The closer it gets to the atmosphere, the greater the possibility that the friction in the air will cause it to rotate and push it off course.

On Monday, Cassini completed number four of the 22 trips trips that it'll take. This week, the focus was on the rings. The spacecraft measured Saturn's gravitational field to help scientists determine their mass. It scooped up dust from the rings, which could help scientists figure out how old they are. It also shot a radio signal back to Earth, through the rings, because scientists can use the interference to determine their size and density.

In the coming months, the probe will gather information about the planet's atmosphere and its chemistry, its gravity field, rotation rate and the size of its central core.  The probe will also help scientists learn more about the rings, their age and makeup and about some of Saturn's moons.

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The journey of the Cassini spacecraft is a long one. Launched in 1997, it had to slingshot around Venus, Earth and Jupiter to get to Saturn, seven years later. And the information that it's provided scientists has led to some incredible discoveries. In particular, new data on Enceladus and Titan, two of the planet's moons.

Titan's full of surprises in that some of its characteristics mirror Earth's. The landscape, for instance, has oceans and sand dunes. Its atmosphere is nitrogen-rich, like Earth's. And it's got smog, kind of like Los Angeles (though Titan's is the byproduct of natural processes).

Enceladus on the other hand is a big ball of ice, but only on the surface. Nineteen to 25 miles below that, there’s a salty liquid ocean with organic compounds, and possibly, hydrothermal vents. And what’s around hydrothermal vents here on earth? Life forms that’ve evolved to live in extreme conditions. The possibility of hydrothermal vents on Enceladus prompted scientists like Cassini Project Scientist Linda Spilker to push for a new mission to the moon.

Over the next four months, I'll be watching and talking about Cassini's descent to its doom and the new information that it gathers along the way. I'm going to dive into the history of the spacecraft, the discoveries that it's helped make and about the people behind the mission, some of whom are still at Pasadena's Jet Propulsion Laboratory.

I'm just starting my new role as KPCC's science reporter. Let me know what you think about Cassini or if you want me to look into anything else science-related.  Reach me on Twitter.