Help Shape the Future of Space Exploration

Join The Planetary Society Now Join Now!

Join our eNewsletter for updates & action alerts

   Please leave this field empty
Blogs

See other posts from December 2009

Headshot of Emily Lakdawalla

Planetary Society Advent Calendar for December 16: Mimas

Posted by Emily Lakdawalla

2009/12/16 03:28 CST

Topics:

Mimas is the anti-Enceladus. At 397 kilometers in diameter it is not all that much smaller than 512-kilometer Enceladus, the next biggish moon out. But its ancient, cratered surface tells you that nothing particularly exciting has happened there over the past few billion years, unlike on geyser-rich Enceladus. When people post a picture of Mimas, they usually post one that includes a view of its gigantic crater, Herschel, and make a comment about how much it looks like the Death Star. So, to be different, I'm posting a view of Mimas that almost doesn't include Herschel. The crater is there -- it's taking a bite out of the terminator at left.

Mimas in natural color

NASA / JPL / SSI / color composite by Gordan Ugarkovic

Mimas in natural color
Cassini took the images for this color view of Mimas on June 28, 2007. The heavily cratered little world is more elliptical than spherical. Its largest crater, Herschel, is the bite out of the terminator at left.
This photo is actually in color, believe it or not; Mimas is very, very gray. Mimas is also not a sphere -- it's squashed around the middle, a result of its relatively fast rotation coupled with its relatively low gravity and its relatively close position to Saturn, which excites a pretty big tidal bulge. All in all, Mimas' surface tells you a great deal about the forces active within the Saturn system that act from the outside to control the shapes and surfaces of Saturn's moons.

Mimas sits on the boundary between round moons and lumpy "rocks." It has just enough self-gravity to be round -- or mostly so; the impactor that made Herschel came along relatively late in Mimas' formation, when the moon was pretty cold. The next smaller moons at Saturn are Hyperion, Janus, and Phoebe, all of which are very lumpy indeed. I think it's interesting how the roundness of these icy worlds depends in part on the timing of large impacts. Large impacts were undoubtedly part of the story of formation of these things, but early in their history they would have had enough primordial heat for their interiors to be relatively squishy (even if not liquid). As they aged, cooled, and hardened, impact scars were better and better preserved. I wonder if Mimas is rounder than Hyperion because it's closer to Saturn, experienced more tidal heating, and had some earlier lumpiness erased? Each one of these moons has its own, unique story to tell.


Each day in December I'm posting a new global shot of a solar system body, processed by an amateur. Go to the blog homepage to open the most recent door in the planetary advent calendar!

 

Or read more blog entries about:

Comments:

Leave a Comment:

You must be logged in to submit a comment. Log in now.
Facebook Twitter Email RSS AddThis

Blog Search

JOIN THE
PLANETARY SOCIETY

Our Curiosity Knows No Bounds!

Become a member of The Planetary Society and together we will create the future of space exploration.

Join Us

Featured Images

Phobos-Grunt imaged in orbit

Scanning electron microscope images of two pieces of Surveyor 3
A conceptual Mars outpost making rocket propellants from the local environment
Pete Conrad at the Surveyor 3 spacecraft, with the Apollo 12 Lunar Module in the background
More Images

Fly to an Asteroid!

Travel to Bennu on the OSIRIS-REx spacecraft!

Send your name

Join the New Millennium Committee

Let’s invent the future together!

Become a Member

Connect With Us

Facebook! Twitter! Google+ and more…
Continue the conversation with our online community!