The Cassini spacecraft made its deepest dip ever into the atmosphere of Titan, Saturn’s largest moon, at 8:28 PM Eastern time on 20 June. The data it collected will help determine whether the moon has its own magnetic field.

“For Titan scientists, this is one of the most anticipated flybys of the whole mission,” wrote space physicist Cesar Bertucci of the Institute of Astronomy and Space Physics in Buenos Aires, Argentina in a blog post. That’s saying something, as Cassini has already orbited Saturn for six years and may last seven more.

The flyby took Cassini within 547 miles of Titan’s surface, about two and a half times the altitude of the International Space Station. Although this distance shaved only 43 miles off the next nearest approach, the flyby was the first to take the spacecraft below Titan’s ionosphere, a layer of charged particles in the upper atmosphere. The ionosphere shielded the spacecraft from Saturn’s much larger magnetic field, allowing scientists the first hints of whether Titan has a magnetic field of its own.

Earlier measurements by the Voyager spacecraft and an earlier Cassini flyby at 590 miles showed that Titan’s magnetic field is weak at best, and certainly no match for Saturn’s. But that doesn’t mean it’s not there, Bertucci said. “We’d like to know what the internal field might be, no matter how small.”

Measuring the field will provide insight into the moon’s internal structure. In planets like Saturn or Earth, long-lived magnetic fields are driven by currents in a metallic, liquid core. These currents arise as the planet rotates. With its thick atmosphere of nitrogen and methane and its liquid hydrocarbon lakes, Titan resembles the early Earth more than any other body in the solar system, making the moon an ideal natural laboratory for studying the origins of life. If Cassini picks up a magnetic field, it might mean that Titan, like Earth, has a liquid core.

But it might not. There are two other explanations for a magnetic Titan, Bertucci wrote. Like Mars, Titan may once have had a liquid core that has since frozen, leaving behind residual magnetism in the crust. Or, if a conducting layer like an ocean lies on or below the crust, part of the surface could have temporarily picked up some of Saturn’s magnetism before Cassini got there.

The data should finish its downlink to Earth by the end of today, and a preliminary report on all the measurements from the flyby should be available by the end of the week, Bertucci told Wired.


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