| 03.18.2018

Rings, moons and the age of the universe – UI researcher measures mass of Saturn”s brightest ring

University of Idaho physics professor Matthew Hedman and others from NASA”s Cassini mission have discovered how to weigh Saturn”s rings – no giant scale necessary.

“What we did was literally weigh the rings, in the sense that we were figuring out their mass by measuring the gravitational interactions between the rings,” Hedman said.

Hedman said to do this, he and his colleagues measured the spiral waves caused by different gravitational pulls.

He said Saturn has many moons, and   while Saturn”s rings might only make three orbits around the planet, the moons might make four or five.   Due to this, the particles in the rings are pushed and pulled, and their orbits are distorted.

“As it distorts the orbits of the particle, they start pulling and pushing against each other, creating what are called spiral waves,” said Hedman. “Just like sound waves in air, these propagate through the rings.”

These waves function much like sound waves behave in the air. He said just like sound waves depend on the density of air and things like that, these spiral waves depend on the mass of the rings.

What made this mission unique was that Hedman was able to find some of these waves that no one had been able to detect before. He said there are three main parts of Saturn”s rings – the A ring, B ring and C ring.

Hedman said he and his colleagues were measuring spiral waves originating from the B-ring, Saturn”s brightest ring.

To do this, Hedman said they used a type of observation called an occultation.

“An occultation is when you watch a star as it goes behind the rings, so the rings block some of the starlight – basically, the more ring there is, the more light gets blocked,” Hedman said.

“You watch the star go behind the ring, and if its brightness varies you get a measure of how much material there is in the ring.”

He said the nice thing about using occultation is that the resolution is set by how big the star is, so they can obtain high-resolution data from this method. This is useful for studies like this because the wavelengths they”re measuring are kilometers long, and very difficult to ascertain through imaging.

Hedman said UI researcher measures mass of Saturn”s brightest ring here are many significant things about this research. First and foremost, he said it gives scientists more basic numbers about how things behave. Yet, it is just as important in determining factors in the age and creation of the universe.

“Knowing how much stuff is in the rings is important for trying to understand where they came from,” Hedman said.

It was originally assumed that because the B-ring was more opaque, there was more stuff in it, he said. However, Hedman said he and his colleagues found this might not be true. They found the mass of the rings to be much lower than what was expected.

Hedman said he couldn”t be more excited for the year 2017, the end of the Cassini mission. At that time, it will go from flying outside the rings to doing 20 orbits between the rings and the planet.

“The way the spacecraft moves as it passes through the rings will depend very much on the planet and the ring”s gravity field,” he said. “That gives you a completely independent way to measure the mass of the rings.”

Carly Scott can be reached at arg-news@uidaho.edu

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