Cassini spacecraft reveals 'secrets' of universe
By Amanda Jermyn



Wouldn’t it be great if we could watch the evolution of the universe unfold in real time? Now, thanks to the intrepid spacecraft Cassini, we might just get our chance to witness one small part of that evolution.

Cassini, a joint venture of NASA and the European and Italian Space Agencies, began orbiting the planet Saturn in July of 2004, treating us to stunning images of the gas giant, its moons and iconic rings ever since. Now images taken with Cassini’s narrow angle camera reveal what appears to be something never witnessed before: a new moon in the process of formation.

Dubbed Peggy, the object itself, about half a mile wide, is too small to be seen in the images viewed so far, yet its existence is inferred from the disturbances it creates.
According to Carl Murray, a planetary scientist at Queen Mary, University of London, the discovery was accidental. While examining images taken by Cassini in April 2013, Murray noticed disturbances at the edge of the A ring, the outermost of Saturn’s three main rings. One of these is an arc about 20% brighter than its surroundings, 750 miles long and 6 miles wide. Unusual protuberances were also noted in the usually smooth edge of the ring.

In a study published in the July 1st issue of the journal Icarus, Murray, the lead author, and colleagues speculate that the small icy object is a new moon forming within the ring and is in the process of migrating out of it. They attribute the observed disturbances to the new moon’s gravitational effects on the ring particles.

As most of Saturn’s 62 known moons and the particles that make up its rings are composed primarily of water ice, it is thought that the moons are formed from ring particles brought together by gravity. And since it has been observed that Saturn’s moons are generally larger the farther away they are from the planet, researchers propose that the moons gradually move away from the planet, merging with other moons on the way, resulting in the ones formed earliest being the largest and farthest out.

It is believed that in the distant past Saturn had a much more massive ring system, which spawned larger moons, such as Titan and Enceladus, but the process of moon formation has gradually been depleting the ring system, and the rings may now be reaching the point where they can no longer sustain moon formation. Detecting the new moon before it migrated beyond the edge of the A ring was a stroke of luck because beyond this point its gravitational effect would have been too weak to cause visible changes in the rings. Migrating beyond Saturn’s rings, the new moon is not expected to grow any larger. The dearth of particles for it to attract in this region will curb its growth, and it is possible it may break into smaller pieces and not survive.

Observing this process helps us understand more than just moon formation on Saturn, providing insights into how the Earth and other planets in our solar system may have formed and migrated away from the sun.

With the Cassini mission extended until 2017, its imaging instruments may yet unveil many more of Saturn’s mysteries for us here on Earth.

Join the Springfield Stars Club on Tuesday, September 23rd at 7:30pm at the Springfield Science Museum for a talk by Richard Sanderson entitled “A Retrospective of Summer Astronomy Events.” Sanderson is curator of physical science at the Springfield Science Museum and manages the museum’s Seymour Planetarium and Observatory. He is also an astronomy writer and co-author of the 2006 book, “Illustrated Timeline of the Universe.” Sanderson is a past president of the Springfield Stars Club and its current treasurer. Refreshments will be served, and the public is welcome. The meeting is free of charge for members, with a suggested donation of $2 per non-member.

Also, on Friday, October 3rd, the Stars Club and the Springfield Science Museum will host “Stars over Springfield,” an astronomy adventure for the whole family. Richard Sanderson will speak on “Eclipses.” A fee of $3 for adults and $2 for children under 18 will be charged.