On April 26, after almost 13 years in orbit around Saturn, Cassini began its “Grand finale,” a series of 22 thread-the-needle orbits that pass inside Saturn’s rings.
“The results so far are showing that the planetary magnetic field at Saturn is very different from the planetary magnetic field generated at other planets,” says Michele Dougherty, a professor of space physics at Imperial College in London.
The earliest hint that something was unusual about Saturn’s magnetic field came from the very first probe to fly by Saturn, Pioneer 11, in 1979. Not everyone agrees that Saturn’s uncannily aligned poles are a fundamental problem for dynamo theory. In 1980, Stevenson proposed that, deep within Saturn, the magnetic field does have a tilt, but that the tilt is “Screened out” closer to the top of the atmosphere. No one knows exactly what would happen on Saturn if that planet’s dynamo-generated magnetic field were to vanish.
If Saturn’s dynamo is dying, its magnetic field will not shut off all at once.