Wobbling of a Saturn moon hints at what lies beneath

October 16, 2014

Using instruments aboard the Cassini spacecraft to measure the wobbles of Mimas, the closest of Saturn's regular moons, a Cornell University astronomer publishing in Science, Oct. 17, has inferred that this small moon's icy surface cloaks either a rugby ball-shaped rocky core or a sloshing sub-surface ocean.

"After carefully examining Mimas, we found it librates – that is, it subtly wobbles – around the moon's polar axis," Radwan Tajeddine, Cornell research associate in astronomy and lead author of the article. "In physical terms, the back-and-forth wobble should produce about 3 kilometers of displacement. Instead we observed an unexpected 6 kilometers of surface displacement," he said.

"We're very excited about this measurement because it may indicate much about the satellite's insides. Nature is essentially allowing us to do the same thing that a child does when she shakes a wrapped gift in hopes of figuring out what's hidden inside," Tajeddine said.

The astronomy team used a technique called stereo-photogrammetry to interpret images taken by the Cassini Imaging Science Subsystem to measure the libration. In this technique, astronomers employ Cassini photographs of Mimas taken at different times and from various vantage points to build precise 3-D computer models of the locations of hundreds of surface reference points. From these, the researchers determined the moon's shape and were able to notice that the satellite didn't rotate smoothly but rocked back and forth a bit as well.

The amount of the to-and-fro motion indicates that Mimas' interior is not uniform. These wobbles can be produced if the moon contains a weirdly shaped, rocky core or if a sub-surface ocean exists beneath its icy shell.

Mimas is about 400 kilometers in diameter, and its possible internal global ocean is located under an icy crust ranging in thickness between 25 and 30 kilometers. The moon itself is thought to have been formed either by the slow agglomeration of ring particles (a gradual buildup of matter) or direct growth within the primordial planetary gas nebula. The odd-shaped core would favor gravitational flattening by nearby Saturn, Tajeddine said. The 's relatively smooth and roughly spherical icy surface covers up whatever is underneath.

Explore further: Image: Crescent Mimas

More information: Science. DOI: 10.1126/science.1255299

Related Stories

Image: Crescent Mimas

September 16, 2014

A thin sliver of Mimas is illuminated, the long shadows showing off its many craters, indicators of the moon's violent history.

Cassini Set to Do Retinal Scan of Saturnian Eyeball

February 12, 2010

(PhysOrg.com) -- On Feb. 13, 2010, NASA's Cassini spacecraft will make its closest examination yet of Mimas, an eyeball-shaped moon of Saturn that has also been likened to the Death Star of "Star Wars." The spacecraft will ...

Image: Two moons passing in the night

August 1, 2013

(Phys.org) —The Saturn moons Mimas and Pandora remind us of how different they are when they appear together, as in this image taken by NASA's Cassini spacecraft. Pandora's small size means that it lacks sufficient gravity ...

Cassini returns images of battered Saturn Moon

March 12, 2013

(Phys.org) —Following its last close flyby of Saturn's moon Rhea, NASA's Cassini spacecraft captured these raw, unprocessed images of the battered icy moon. They show an ancient, cratered surface bearing the scars of collisions ...

Space image: Dione flyby

January 24, 2012

Saturn's moon Mimas peeks out from behind the night side of the larger moon Dione in this Cassini image captured during the spacecraft's Dec. 12, 2011, flyby of Dione.

Recommended for you

NASA telescope studies quirky comet 45P

November 22, 2017

When comet 45P zipped past Earth early in 2017, researchers observing from NASA's Infrared Telescope Facility, or IRTF, in Hawai'i gave the long-time trekker a thorough astronomical checkup. The results help fill in crucial ...

Uncovering the origins of galaxies' halos

November 21, 2017

Using the Subaru Telescope atop Maunakea, researchers have identified 11 dwarf galaxies and two star-containing halos in the outer region of a large spiral galaxy 25 million light-years away from Earth. The findings, published ...

Cassini image mosaic: A farewell to Saturn

November 21, 2017

In a fitting farewell to the planet that had been its home for over 13 years, the Cassini spacecraft took one last, lingering look at Saturn and its splendid rings during the final leg of its journey and snapped a series ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

cantdrive85
1 / 5 (2) Oct 17, 2014
Wobbling of a Saturn moon hints at what lies beneath


Then again, the Death Star may be affected by other forces and phenomena than just gravity. Such as that which Hyperion "telegraphed" to Cassini.
http://phys.org/n...cle.html

And the Death Star?
https://www.googl...imgdii=_

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.