Scitech | Cosmic oversights and migrant moons

Colossal new ring around Saturn sheds light on planetary origins

How did we miss it? A giant ring measuring around six million kilometres in width is no small oversight, especially when it’s surrounding a celestial body whose iconic planetary hula hoops are its defining trademark. Saturn is always associated with its beautiful bands, which have an unmatched prominence in our solar system.

The planet’s main rings are positioned relatively close to each other, and what was thought to be the outermost ring, the E ring, orbits at a distance of about 240,000 kilometres from Saturn. This new ring lies about 13 million kilometres from Saturn, 50 times more distant than the E ring, and is tilted 27 degrees so that it lies on a different plane from the rest of Saturn’s rings.

It turns out, however, that this ring behaves in peculiar ways, so it has strategically kept itself hidden from our view up until October of this year. In fact, if we were to try and see it again now, we wouldn’t be able to.

NASA’s Spitzer Space Telescope, launched in 2003, was the instrument used to catch the first glimpse of the ring. Picking up on the infrared light radiating from the dust and snowflake particles, the telescope was able to take a picture of the ring under very specific circumstances.

Olivia Jensen, a professor in McGill’s Department of Earth and Planetary Sciences, sheds some light on the recent development.

“The infrared telescope requires that the instrument you’re measuring with is colder than what you’re trying to detect,” Jensen said.

When the rings are “warmed” by sunlight, up to the toasty temperature of about negative 200 degrees Celsius, they reflect infrared radiation, which is picked up by the detectors on board the Spitzer as a brownish coloured light.

“This [ring] wasn’t seen earlier simply because it is so cold,” said Jensen. “The Spitzer telescope couldn’t see it again now – you actually couldn’t make the same measurement again.”

Scientists also discovered that the giant ring follows the same orbit as Phoebe, Saturn’s most distant moon. Tilted 27 degrees from the main ring plane, Phoebe orbits Saturn from over 12.9-million kilometres away and travels in a direction that is counter to the planet’s, which suggests that Phoebe is actually a migrant moon.

Unlike our own moon, which was formed by being “splashed” off the surface of our earth, Phoebe is almost certainly a body from another part of the outer solar system, which has been captured by Saturn’s gravitational force. And the ring itself is also made out of migrant material.

“Phoebe might be the source of this ring,” said Jensen. “The theory is that material is being driven off Phoebe’s surface because it’s hitting things like little micrometeorites, some as small as a grain of sand.”

These small collisions result in dust being knocked off the surface of the moon, and because Phoebe is a tiny moon, the dust is escaping from its weak gravitational field and getting trapped in Phoebe’s orbital path, distributing itself into a ring over time.

This explanation of the ring’s formation may explain why Iapetus, another of Saturn’s moons, has a uniquely two-toned appearance. Iapetus orbits in such a way that it is always travelling with the same side facing forward, the leading edge covered in blackness. Saturn’s gravity is most likely causing the new ring’s articles to fall into the moon’s path, covering Iapetus’s face in black dust.

While the discovery of this new ring clears up some of the mysteries associated with Saturn, it still leaves a lot of questions unanswered, as Saturn keeps its mysteries shrouded around itself like its innermost D ring.

But is this discovery really so earth shattering? Jensen thinks not.

“The last really big story in the press about the solar system was the discovery of Pluto in the thirties,” she said. “And now we’ve downgraded Pluto from even being called a planet!”

These new “developments” in our solar system, including this enormous dust band surrounding Saturn, don’t match up to that large discovery of a tiny planet. Although the cultural model of having nine planets has changed, it’s still just a social construction.

As Jensen put it, “It’s strange that astronomy should be at all political, but it was a political decision to downgrade Pluto from a planet to dwarf planet.”

As technology continues to improve, it will produce instruments more capable of competently measuring space and our solar system. While there are surely infinite discoveries waiting in an infinitely-sized universe, we will continue to form each of these advances in our understanding just like Phoebe formed this colossal new ring: one grain at a time.


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